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All Springer/NP/PCP Air Gun Discussion General => "Bob and Lloyds Workshop" => Topic started by: rsterne on December 23, 2018, 05:31:03 PM

Title: Simplified Balanced Valve
Post by: rsterne on December 23, 2018, 05:31:03 PM
There is a lot of interest right now in balanced valves for PCPs.... Part of this is because of my recent article in HAM, where I describe a few of the types that have been tried.... https://hardairmagazine.com/ham-columns/balanced-valves-for-pcp-airguns-theyre-here-today/ (https://hardairmagazine.com/ham-columns/balanced-valves-for-pcp-airguns-theyre-here-today/) …. Reading that over will give you a pretty good idea about how they work to reduce the hammer strike required.... Some of these designs, or variations of them, are used commercially, which is why I haven't given any specific details.... However, one design, and perhaps the simplest one to build, I have never seen used commercially....

As you all know, it is my desire to share things publicly, to further the sport of airgunning…. In that spirit, I have drawn up the concept for the next valve I plan to build for my Hayabusa…. I hope to have it work properly from .224 through .357 cal, although it is sized for the .357.... This may be an ambitious project, but I wanted to publish the concept drawing from the beginning, so that you can all share in this project, be it a success or failure.... Here is the drawing....

(http://i378.photobucket.com/albums/oo221/rsterne/Parts%20for%20Sale/Simpified%20Balanced%20Valve_zpsvtnfnmnj.jpg) (http://s378.photobucket.com/user/rsterne/media/Parts%20for%20Sale/Simpified%20Balanced%20Valve_zpsvtnfnmnj.jpg.html)

The poppet is made from Delrin or PEEK, and is threaded internally with 5-40 threads.... The stem is a piece of 1/8" O1 Drill Rod, threaded 5-40 at the front (the threads secure the poppet to the stem in shear), and drilled lengthwise back into where the exhaust port is, with a small cross-drilled hole, to vent the forward balance chamber of the valve into the exhaust port of the valve.... This means that the balance chamber will start out at atmospheric pressure between shots.... when the valve lifts from the seat and the pressure in the transfer port rises, so will the pressure in the balance chamber.... and when the valve closes again, that pressure will fall back to atmospheric gradually as the pellet moves down the barrel and departs the muzzle.... Since the area of the balance chamber is half the area of the valve seat, it will only take 1/2 the force to crack open the valve, allowing it to open quickly with less hammer strike.... Once open, the rising pressure in the balance chamber will help to shut the valve quickly, and as it takes a short time for that pressure to bleed out through the vent in the stem, hopefully resist any second hammer strike which might cause valve bounce.... At least that is the idea....

Most likely I will drill the lengthwise hole in the stem with a 3/64" (0.047") drill, partly because using a smaller drill it would be so easy to break.... The metering of the airflow through the vent will be done by changing the size of the single cross-drilled hole in the exhaust port area.... Since that is easy to get at, I can start small, at 1/32" (0.032") and go larger if necessary.... I want the hole to be large enough to prevent the valve from "blowing open" on its own, which it can do if the pressure in the balance chamber rises too slowly.... When a balanced valve blows open (like the Cothran valve does), it is impossible to tune with hammer strike, as the valve either works or doesn't.... ie it has a definite "cycle" nearly independent of hammer strike.... I don't want that, I want to be able to tune the valve over a wide range of velocity using only hammer strike.... This will (hopefully) produce a valve that can be used either regulated, or produce a bell curve when used in an unregulated PCP....

For this valve I plan to use a 7/16" OD poppet, made from PEEK, with a 5/16" front section.... That means the front diameter is 71.4% of the rear, so the area is 51%, about as close as I can get to my 50% goal.... The valve throat will be 3/8", which when you subtract the area of the 1/8" stem will leave the throat area the same as a hole of 0.354" (nearly .357 caliber sized).... The exhaust port will be 21/64" (0.328"), which is the same area as the chamber in my .357 Hayabusa which has a 9/64" (0.141") bolt probe.... I will make sure the transfer port and barrel port are also the same area, to insure the maximum possible flow....

One of the advantages of this valve design is that it only needs one dynamic O-ring instead of two like the SS Valve, so less potential for leaks.... The SS Valve is prone to "stiction" problems when the guns sits for a while between shots, and I have a gut feeling that is because at rest the O-rings are loaded in opposite directions and tend to "wedge" inwards towards the center balance chamber.... The front O-ring in an SS Valve would therefore be wedged towards the seat, and opposite to the direction of travel of the poppet when firing.... When you fire the gun after it has been sitting, the front O-ring, which is already wedged into the back corner of the gland, gets pushed even tighter into that corner by the motion of the poppet.... That may be the cause of the low velocity first shots sometimes experienced.... In this design, at rest the O-ring is pushed into the front corner of the gland, and as soon as the poppet moves on firing, it moves back away from that corner into the center of the gland.... I hope that will avoid any "stiction" issue on the first shot after sitting.... Only time will tell....

Anyways, there is the idea for a simple balanced valve, with minimum parts, that is relatively easy to machine.... By putting this out in the public domain, I hope to encourage others with the skills and equipment to jump on the train and let's get these balanced valves out of the station, and roaring down the track, into the mainstream of PCP airgunning….

Bob
Title: Re: Simplified Balanced Valve
Post by: mann on December 23, 2018, 06:36:43 PM
You could fit a new poppet into the ss valve and plug the jet hole . And use only one oring on it like you have in the drawing
Title: Re: Simplified Balanced Valve
Post by: rsterne on December 23, 2018, 06:40:55 PM
Yes, that is quite possible.... You would have to make sure that the front jet hole was sealed 100%, as any leak there would escape out the barrel.... If the idea works as it should, that would be an easy retrofit, and prove if it is the front O-ring "wedging" that is causing the stiction.... You might need to increase the clearance between the rear portion of the poppet and the thimble to allow the HPA to pass through easily.... The poppets are vented differently, of course....

Bob
Title: Re: Simplified Balanced Valve
Post by: mann on December 23, 2018, 06:43:13 PM
The wedging like your saying would definitely cause stiction and this way might just get around that
Title: Re: Simplified Balanced Valve
Post by: rsterne on December 23, 2018, 06:45:46 PM
Yeah, I was trying to figure out the "stiction" problem, and that is what I came up with.... O-rings migrate under pressure to the corner where the air is trying to escape.... in this case the outer, low pressure corner of the gland.... That means forward on the rear O-ring and towards the rear on the front one on a SS Valve.... The movement of the poppet on firing would tend to increase that wedging effect on the front O-ring, possibly causing the stiction problem on the first shot, until it cycles and recenters in the gland for subsequent shots.... Once you are shooting, the pressure fluctuation in the center balance chamber, and the movement of the poppet on firing, would tend to keep both O-rings moving around in the glands.... until the next time you let the gun sit for a while.... Just my thoughts on the matter....   ;)

Bob
Title: Re: Simplified Balanced Valve
Post by: mann on December 23, 2018, 06:52:16 PM
If my trying of the python chamber doesn't work then I will make a different poppet and give this a try should be easy enough to do  . What size vent hole should one try was thinking I'd drill the vent hole threw the poppet and that way the drill rod wouldn't have to be drilled or threaded
Title: Re: Simplified Balanced Valve
Post by: rsterne on December 23, 2018, 06:57:49 PM
I would use either 1/32" or a #60 drill.... 0.032" to 0.040".... Make sure you don't hit the bottom of the O-ring groove with the vent hole, not a lot of room between that and the stem.... You might have to drill from both ends, with the inner end on an angle?....

Bob
Title: Re: Simplified Balanced Valve
Post by: mann on December 23, 2018, 07:12:11 PM
Ok thanks for idea Bob
Title: Re: Simplified Balanced Valve
Post by: Hobbyman2007 on December 23, 2018, 07:41:39 PM
I’m just about ready for my first attempt in a ballanced valve . Not entirely sure what design I’m going to use or which rifle to build it for . I have a Cothran valve equipped .257 rifle and to be honest I don’t shoot it often at all . Bob in your drawing you’re using 50% of the poppet area to reduce it to 50% of cracking force . What I’m mostly interested in is being able to tune a bell curve to a shot string . What is the biggest factor for tunability ? Is it the relationship between poppet and balance chamber or is it the size of the vent to atmosphere that has the biggest effect on being able to tune the valve . Unlike the Cothran valve I don’t want to use available pressure to adjust the velocity .
Title: Re: Simplified Balanced Valve
Post by: rsterne on December 23, 2018, 11:27:48 PM
I don't yet have 100% proof, but I think the thing that causes a balanced valve to cycle "on or off" is too small a vent between the balance chamber and the exhaust port.... What happens in that case (I think) is that the pressure in the balance chamber is too low, and once the poppet lifts off the seat, it opens like a sleeve valve.... That is exactly what happens if the balance chamber is just vented to atmosphere, instead of connected to the exhaust port.... The best SS Valve I have had, that was the easiest to tune, was one that had a 3/8" poppet with a 1/4" front chamber, and quite a large 0.040" vent.... However, it did require a heavier hammer weight than the light hammer that would work with a smaller vent....

I have found that a larger vent requires a heavier hammer strike, and a heavier hammer, but once you have that they seem to be more tunable.... If the vent is large and the hammer strike too light, the valve seems to want to slam shut quickly, before the poppet is open enough to release much air.... That makes sense to me, because the pressure in the balance chamber builds before the valve is open more than a few thou.... When you increase the hammer strike enough that the momentum gets the poppet open far enough, that slamming closed effect seems to be overcome.... and then the valve becomes more tunable....

As I said, I'm not 100% sure of this relationship yet, more testing is required.... That is one of the reasons I published this design, to get more versions built, by more guys, so that we can learn more about what makes balanced valve tick.... If my idea is correct, once the vent is large enough to prevent the valve from "blowing open" (cycling), and the hammer strike is great enough to push the poppet past the "slamming closed" point.... I have a gut feeling that an even larger vent won't make any difference.... and the valve will be as tunable as it can get with those proportions between small and large diameters.... Logic tells me that the bigger the valve, the bigger the vent also....

I wish I could give you a hard answer.... but at this stage all I can do is say "try it".... and don't be afraid to experiment.... With the idea of using the cross hole in the stem to vary the venting, with a set of carb jet drills you should be able to work up a size at a time until you get past the "blow open" stage.... and eventually find the size where larger makes no difference.... Again, my gut tells me that is where you want to be for maximum tuneability....

Bob
Title: Re: Simplified Balanced Valve
Post by: jackssmirkingrevenge on December 24, 2018, 07:15:51 AM
If I could suggest a small variation, by matching the diameter of the stem to the housing you will trap air that will act as a cushion, removing the need for the bumper:

(https://i.imgur.com/PG10u4y.png)
Title: Re: Simplified Balanced Valve
Post by: Hobbyman2007 on December 24, 2018, 09:19:11 AM
If I could suggest a small variation, by matching the diameter of the stem to the housing you will trap air that will act as a cushion, removing the need for the bumper:

(https://i.imgur.com/PG10u4y.png)

That would work if there wasn’t a vent to atmosphere. But then you’d basically have a cobra valve withought the air bleed.
Title: Re: Simplified Balanced Valve
Post by: jackssmirkingrevenge on December 24, 2018, 09:39:20 AM
That would work if there wasn’t a vent to atmosphere. But then you’d basically have a cobra valve withought the air bleed.

Perhaps you misinterpreted my suggestion, I'm talking about air trapped in the stepped portion as indicated in green:

(https://i.imgur.com/Nza44hJ.png)
Title: Re: Simplified Balanced Valve
Post by: shorty on December 24, 2018, 10:12:20 AM
Here's my latest design that I having been toying around with.

Floating valve stem with oring bumper.
Hollow poppet

The idea is that the floating valve stem pushing against the hollow poppet creates a high pressure within the  (I will call it the) "cobra" chamber when fired and when the floating stem comes off the hollow poppet, the back pressure from the pellet/barrel aides in closing.

I have been working on the left design for more available air flow and smaller "cobra" chamber.

Title: Re: Simplified Balanced Valve
Post by: Hobbyman2007 on December 24, 2018, 12:42:27 PM
That would work if there wasn’t a vent to atmosphere. But then you’d basically have a cobra valve withought the air bleed.

Perhaps you misinterpreted my suggestion, I'm talking about air trapped in the stepped portion as indicated in green:

(https://i.imgur.com/Nza44hJ.png)



Yep , thought you mean the where the end of the valve stem is .
Title: Re: Simplified Balanced Valve
Post by: rsterne on December 24, 2018, 12:55:23 PM
Jack, the O-ring bumper is not a necessary part of the design.... but it is easy to incorporate when building the valve.... The idea is to prevent the poppet from "crashing" into the thimble if during tuning you use too much hammer strike.... It is also a VERY good idea to make sure that the stem is short enough that even if the hammer drives it flush with the back of the valve the poppet does not strike and part of the thimble.... It would be easy to drive the stem through the poppet, even though it is threaded, otherwise....

I don't know how many balanced valves you have played with designing and building in PCPs, but they can do things that are quite unexpected, particularly during development, and destroy themselves in short order.... They can blow open with huge force if the vent is too small.... slam closed if it is too large (the Cothran will destroy the seat doing that)…. and machine-gun while emptying the reservoir if you get the wrong balance between the way the valve operates and the hammer strike.... All in all, development can be pretty exciting....  :o

The bumper was to hopefully avoid such destruction by providing a resilient cushion, but with a VERY high spring rate.... I don't think the small amount of air trapped as you indicate would be capable of doing that job.... and it would require precision machining of two concentric bores in the thimble and concentric surfaces on the two diameters of the poppet.... Even then, I don't know if it would trap enough air to be useful without an O-ring.... However, thanks for the suggestion....

Title: Re: Simplified Balanced Valve
Post by: jackssmirkingrevenge on December 24, 2018, 02:55:19 PM
I don't know how many balanced valves you have played with designing and building in PCPs, but they can do things that are quite unexpected, particularly during development, and destroy themselves in short order.... They can blow open with huge force if the vent is too small.... slam closed if it is too large (the Cothran will destroy the seat doing that)…. and machine-gun while emptying the reservoir if you get the wrong balance between the way the valve operates and the hammer strike.... All in all, development can be pretty exciting....  :o

Virtually none compared to your body of work, so I defer to your experience as far as hammer valves go.  You've seen the one for the Apache elsewhere and there's also my first which was made for a 1322:

(https://i.imgur.com/C2PDAtO.jpg)

"that looks about right" design ::) :

(https://i.imgur.com/xbxmUDJ.jpg)

Quote
The bumper was to hopefully avoid such destruction by providing a resilient cushion, but with a VERY high spring rate.... I don't think the small amount of air trapped as you indicate would be capable of doing that job.... and it would require precision machining of two concentric bores in the thimble and concentric surfaces on the two diameters of the poppet.... Even then, I don't know if it would trap enough air to be useful without an O-ring.... However, thanks for the suggestion....

My feeling is that a simple o-ring bumper would be destroyed in short order and I have some experience with this, trying to arrest pistons for exhaust valves.  I've found that a carefully made air brake works wonders and indeed it's commonly used in other applications like for example pneumatic nail guns:

(https://i.imgur.com/YD68pEk.png)

You can see that the "hammer" (#21) traps air when it interacts with the bumper at the end of its travel.

Once you have the valve stem supported at both ends I don't see why concentric bores would be difficult to achieve and also the bumper area does not need to be 100% airtight either so you have a slight margin of error on top of that.
Title: Re: Simplified Balanced Valve
Post by: rsterne on December 24, 2018, 03:37:44 PM
Nice work on the 1322 valve.... I have used O-ring bumpers in SS valves, and despite runaway hammer bounce, never found any damage to them.... Maybe they don't even touch, providing the hammer can't drive the stem far enough to force that?.... If so, just a cheap "peace of mind" kinda thing.... I did have one valve stem back out of the PEEK poppet (in which case the O-ring would have come into play), despite being a press fit and glued in with Loctite 638 on assembly.... I don't know if that was a momentum related shear failure during machine-gunning, or if the air pressure found its way around to the front of the stem, or both.... but even in that case, the bumper O-ring showed no sign of a problem.... My gut feel is that without it, the PEEK poppet would have suffered damage from the hammering it took.... but who knows....  ???

Bob
Title: Re: Simplified Balanced Valve
Post by: rsterne on December 24, 2018, 04:01:24 PM
Mark, you mentioned the idea of plugging the front vent in an SS Valve and using a new poppet to set it up like this new valve.... The only fly in that ointment is that in some of Travis' SS Valves he uses a large front end on the poppet.... This makes the hammer strike higher, but he says makes the valve more tuneable.... In this design, a larger front end will make the valve EASIER to open, the opposite to what it does in an SS Valve.... If they are too close to the same diameter, you may have such a light hammer strike the valve may be hard to tune.... Just something to keep in mind, it may or may not be an issue....

Bob
Title: Re: Simplified Balanced Valve
Post by: rsterne on December 24, 2018, 04:41:45 PM
Travis and I were discussing this valve elsewhere, and I just wanted to warn anyone trying this idea that they may not want to put in a lot of effort until the idea is proven one way or the other.... He stated:

Quote
It will have a very narrow tuning field and no I dont think it will be capable of a bell curve other than the first initial shot being slightly slower than the rest.

Remember, not all ideas succeed, as I stated in my OP.... I guess we'll see what happens.... I'm 8) with it either way, because we will learn more about what makes balanced valves tick.... and that's EXACTLY what this thread is all about....  ;)

Bob

Title: Re: Simplified Balanced Valve
Post by: mann on December 24, 2018, 06:17:13 PM
Well here is the new poppet for the ss valve just need to drill a bleed hole with out hitting oring channel and install the stem
Title: Re: Simplified Balanced Valve
Post by: mann on December 24, 2018, 06:19:16 PM
Yeah it should open easy with the size of the front of the poppet oh well give it a try any way
Title: Re: Simplified Balanced Valve
Post by: rsterne on December 24, 2018, 06:27:46 PM
What are the diameters?....

Bob
Title: Re: Simplified Balanced Valve
Post by: mann on December 24, 2018, 07:08:03 PM
.350 and .280 which probably won't work
Title: Re: Simplified Balanced Valve
Post by: mann on December 24, 2018, 07:11:04 PM
Broke the bit trying to drill a vent hole spun out another little quicker this time
Title: Re: Simplified Balanced Valve
Post by: mann on December 24, 2018, 07:36:20 PM
Cheap bits I have broke again making a poppet for the python and trying it I couldn't plug the holes on the original
Title: Re: Simplified Balanced Valve
Post by: oldpro on December 24, 2018, 08:17:12 PM
 I think with out a check valve in the stem your going to get extreme pressure changes and cause the poppet to open then slam shut and not have a slow bleed check valve from keeping it bouncing off the seat at high speed and re-opening multiple times like hammer bounce but internally till the tank pressure is low enough to stop the action.

Title: Re: Simplified Balanced Valve
Post by: oldpro on December 24, 2018, 08:19:45 PM
Well here is the new poppet for the ss valve just need to drill a bleed hole with out hitting oring channel and install the stem
Are you plugging the jet and trying to make a balanced valve or going Cobra?
Title: Re: Simplified Balanced Valve
Post by: rsterne on December 24, 2018, 08:32:02 PM
Mark, that is 80% of the diameter and 64% of the area.... It will probably work, but pretty easy to open....

Travis, he is starting from an SS Valve, plugging the front jet/vent.... and building a new poppet with a through vent as per the drawing on my first post in this thread.... Only one O-ring, on the small end, none on the back.... Basically converting an SS Valve to this experimental design....

Bob
Title: Re: Simplified Balanced Valve
Post by: mann on December 24, 2018, 08:32:51 PM
I was going to plug the end and try that but everything I touch today just doesn't work out
Title: Re: Simplified Balanced Valve
Post by: mann on December 24, 2018, 08:35:02 PM
I'll have to make another new poppet and get a better bit from hardware store the ones I got are breaking and it's just not going my way tonight
Title: Re: Simplified Balanced Valve
Post by: PakProtector on December 24, 2018, 08:59:17 PM
First, I hate the idea of drilling through the stem...that is a DEEP hole. I am tempted to rig a hot wire to cut a small leak path along the threads. Probably have to run the tap back in.

In the mean time, I have resigned myself to a pre-hunt dry fire when I install my SS valve. I will probably take it apart and lube it with Krytox in hopes of reducing this friction. nah, it is coming apart for a good lube job...:)

Anyway, on with development; I would like to see high power valves come open on a reasonable cocking effore, a short hammer throw, and deliver a tune-able curve to the shot string. Shorter, faster hammer falls are all good for accurate shooting. Something like a 10 lb/in spring and 5/8" hammer travel, with hopefully a 40 gram hammer....
cheers,
Douglas
Title: Re: Simplified Balanced Valve
Post by: oldpro on December 24, 2018, 09:52:04 PM
What’s holding the valve closed on the seat?
Title: Re: Simplified Balanced Valve
Post by: PCPhack on December 24, 2018, 10:04:06 PM
First, I hate the idea of drilling through the stem...that is a DEEP hole. I am tempted to rig a hot wire to cut a small leak path along the threads. Probably have to run the tap back in.

In the mean time, I have resigned myself to a pre-hunt dry fire when I install my SS valve. I will probably take it apart and lube it with Krytox in hopes of reducing this friction. nah, it is coming apart for a good lube job...:)

Anyway, on with development; I would like to see high power valves come open on a reasonable cocking effore, a short hammer throw, and deliver a tune-able curve to the shot string. Shorter, faster hammer falls are all good for accurate shooting. Something like a 10 lb/in spring and 5/8" hammer travel, with hopefully a 40 gram hammer....
cheers,
Douglas

Put a small jet on the front of your SS, krytox, and heavy hammer tune will get you a tune where you can skip the pre-hunt dry fire.

An alternate way is to use a regulator set to a high set point, with a plenum near the cc of FPE you want, give it extra hammer and just dump the plenum on every shot.

Both are tricks I have used in two cases to fix it.
Title: Re: Simplified Balanced Valve
Post by: rsterne on December 24, 2018, 10:10:25 PM
The hole in the stem is about 1" long.... I have already drilled a stem 3/4" just to find out what it's like, and there was no issue at all, using a 3/64" HSS drill.... drilling in a lathe, of course.... It only took a few minutes.... The reason I stopped was the wife called me for dinner and the flutes on the drill are only 3/4" long.... so to drill the rest of the way I will have to pull the drill out more often to clear the chips.... There is no reason not to drill the vent hole right along the side of the stem, providing it will miss the bottom of the O-ring.... Stop the stem short, and drill an angled hole from the C/L of the end of the poppet that clears the O-ring groove and meets the vent hole....

I think the "stiction" in an SS valve (and Travis agrees) is the front O-ring wedging back when the gun is stored, squeezing out the lube, and since the poppet travel is forwards, towards that O-ring, it forces it even harder into the corner.... The poppet travels in the direction of the arrow below.... This generates additional friction between the O-ring and the thimble, particularly after the valve sits under pressure....

(http://i378.photobucket.com/albums/oo221/rsterne/Parts%20for%20Sale/O-ring%20Wedging_zpsxxalcs6g.jpg) (http://s378.photobucket.com/user/rsterne/media/Parts%20for%20Sale/O-ring%20Wedging_zpsxxalcs6g.jpg.html)

All the other balanced valves I have seen (and the rear O-ring on the SS Valve) are driven away from the loaded corner on firing, so no wedging can occur that is different after sitting.... That is why the SS Valve is the only one reported with stiction, AFAIK....

I want to see the same thing you do, Douglas.... and for Big Bores getting rid of the huge cocking force is a necessity, IMO....

At 3000 psi the force on the large end of the poppet towards the seat is:  (0.437 x 0.437 x PI/4) x 3000 = 0.150 x 3000 = 450 lbs....
At the same pressure, the balancing force forward on the large end of the poppet is: (0.312 x 0.312 x PI/4) x 3000 = 0.076 x 3000 = 229 lbs....
Therefore the force holding the poppet closed is (450 - 229) = 221 lbs.... or 49% of what it would be for a conventional valve with a 7/16" poppet.... The spring only needs to be strong enough to overcome the friction on the O-ring, plus a couple of lbs. to seat the poppet for filling....

Bob
Title: Re: Simplified Balanced Valve
Post by: oldpro on December 24, 2018, 10:21:41 PM
Bob it’s not going to seal I’m afraid the oring around the poppet is going to create lift as you try and air it up forcing the poppet up the thimble that’s why Don built his the other way around and put a shelf around the base of the poppet to create more surface area. I can tell you from experience if you do get it to seal somehow it will be extremely unstable. I am only saying this because I’ve been down this road.
Title: Re: Simplified Balanced Valve
Post by: rsterne on December 24, 2018, 10:24:19 PM
I don't see it, but I guess I'll find out after Christmas.... Sometimes experience is the best teacher....  ;)

Bob
Title: Re: Simplified Balanced Valve
Post by: oldpro on December 24, 2018, 10:39:57 PM
I don't see it, but I guess I'll find out after Christmas.... Sometimes experience is the best teacher....  ;)

bob
I didn’t see it either and all the math said it should work I even built a fixture to test it and yep it has lifting force.
Title: Re: Simplified Balanced Valve
Post by: rsterne on December 24, 2018, 10:42:44 PM
Well, thanks for the warning, bud.... When it turns out to be an epic fail, you can say "I told you so"....  ;)

At least I won't be able to say you didn't warn me....  ;D

Bob

Title: Re: Simplified Balanced Valve
Post by: WyoMan on December 24, 2018, 11:45:37 PM
I’m sure you guys have considered this, but with that setup you might need a soft and flexible seal on the seat to get a 100% seal every time. The Cothran valve has a loose piston (can wobble and adjust to the perfect alignment) to seal the vented chamber. As such, the stem and seal are free to “find and seal" to the seat.
If the setup is fixed on both ends (three points counting the stem), you’ll need exceptional tolerance and finish control… just my opinion

Wyo
Title: Re: Simplified Balanced Valve
Post by: rsterne on December 24, 2018, 11:52:32 PM
Gary, although I showed the thimble fixed in that diagram, you are correct, it requires excellent alignment and concentricity between the two ends of the valve.... When I build my SS Valves I mount the thimble in an oversize hole in the perforated wheel at the front end of the valve.... The thimble, like Don's rod, is free to move a bit radially in any direction so that it can self-align with the poppet.... It works perfectly, and I will use the same arrangement on this valve.... I am just not "good enough" to get the fit required otherwise.... and I can see no downside in making it "self-aligning".... I have been able to get a good seal even with a PEEK poppet by this method on a SS Valve, which has 2 O-rings and requires careful machining of the poppet and thimble to get the two different diameters sliding nicely.... This valve only has a single O-ring, and only one bore that needs careful machining.... In reality, the thimble can "rock" a bit on the poppet and still seal....

Bob
Title: Re: Simplified Balanced Valve
Post by: tkerrigan on December 25, 2018, 12:04:36 AM
I can see right now that it will be a while before I try building one.  Sure would be nice to have some for my 6 DAQ pistols and 1 carbine, they are a bear to cock.  Good luck on the project.  Regards, Tom
Title: Re: Simplified Balanced Valve
Post by: rsterne on December 25, 2018, 12:05:54 AM
One more post and you hit 1000, Tom.... *grin*….

Bob
Title: Re: Simplified Balanced Valve
Post by: lloyd-ss on December 25, 2018, 04:31:12 PM
Bob, good work on presenting a less complicated balanced valve. Simplifying a design and maintaining its best characteristics can be difficult. And getting rid of O-rings, particularly ones that function as dynamic seals is always a help with reliability.

Stiction is always a problem with dynamic O-rings that are constantly pressurized. But certain design practices can help minimize the problem. Think of "good" regulators. The best (not necessarily airgun related) rely on diaphragms, not O-rings, but many good ones do use O-rings.
To reduce stiction with dynamic o-rings, design manuals, like the Parker bible, will suggest that the o-ring glands can be made deeper and narrower, along with harder duro o-rings. Also, the compression on the o-ring can be biased toward the static diameter of the o-ring, with the static diameter having maybe 10% compression, and the dynamic side having only 5%. But its a lot of trial and error. Polished finishes on the dynamic surfaces never hurt either. And most important, I think, is keeping the clearance between the hard parts as tight as possible, like just a few thou total ont he diameter.....unless it causes other problems, like binding.  And that does point out one final problem, making balanced valves requires more precision than conventional valves. Sigh.  :(

O-rings aren't really that great for dynamic seals, but they are certainly used a lot.

There was some mention of the difficulty of drilling holes in stems, and I agree, a major pain. When I can, I prefer to use hardened dowel pins for valve stems, but that's not always possible. Here's one way to avoid having to drill a hole thru the stem, by grinding a groove along the stem before pressing or threading the poppet into place. I use a thin cut-off wheel in a Dremel tool, along with plenty of water to stop burning. I've had good luck with the technique.  BTW, this poppet didn't work, as you can see by how high the o-ring sticks up out of the groove. That's exactly opposite to what I said earlier.

(http://i226.photobucket.com/albums/dd79/loyd500/Valves/grooved%20stem_zps5lhcay8l.jpg)


I hope your new design is successful. The devil will be in the details of getting the diameters and passages the right size.
Title: Re: Simplified Balanced Valve
Post by: PakProtector on December 25, 2018, 08:23:14 PM
Bob, I think I have a way to make things more difficult:

The air chamber ahead of the valve poppet should get a check valve to keep it pressurized longer as a bounce inhibitor. It just has to leak enough that by the time you can load another pellet, it is back to zero. The more of that ~3 second interval you use the better I think, so a 'leak' would not have to be very large at all. You will see the chamber fill with throat pressure at a rate decided by the 'jet' size and its volume, and it just has to come back to zero before you pull the trigger again.

And no, I have no idea how to execute the idea that won't have a ball bouncing around loose after the first shot...
cheers,
Douglas
Title: Re: Simplified Balanced Valve
Post by: rsterne on December 25, 2018, 10:17:55 PM
The whole idea here, Douglas is *KISS*….

Lloyd, thanks for the comments.... I have used the idea of a groove ground in the shaft, pretty hard to control the size (area) of it.... Any comment on the idea of the "wedging" action I mentioned in Reply #34 being in issue?....

Bob
Title: Re: Simplified Balanced Valve
Post by: shorty on December 25, 2018, 11:01:51 PM
There is a very elegant solution to drilling a long hole through the valve stem.

Hypo-tubing with a short piece of drill rod epoxied in or cold welded in. I am pretty sure you can harden the hypo-tubing a bit. Cheap on amazon and almost every size available along with different wall thickness's.

I used this method when working on the decompression poppet.
https://www.gatewaytoairguns.org/GTA/index.php?topic=109867.0 (https://www.gatewaytoairguns.org/GTA/index.php?topic=109867.0)
Title: Re: Simplified Balanced Valve
Post by: lloyd-ss on December 26, 2018, 12:28:45 AM
Bob,
Yes, I tend to agree with tendency of the o-ring to extrude into the gap between the piston and the tube, and then become worse when the direction of travel further pinches it. The methods I described will reduce it, but won't make it go away. Getting the o-ring onto the other side of the pressure/travel should be a good fix.
Title: Re: Simplified Balanced Valve
Post by: rsterne on December 26, 2018, 12:39:38 AM
Yeah, I think if the pressure is forcing it one way, and the travel on firing the other, it should push the O-ring back into the middle of the groove.... I think the problem with the SS Valve is that the two O-rings are loaded in opposite directions, so the front one, which is wedged into the rear corner, gets a double does of friction on the initial firing after sitting for a while....

Bob
Title: Re: Simplified Balanced Valve
Post by: Motorhead on December 26, 2018, 02:36:54 AM
Yeah, I think if the pressure is forcing it one way, and the travel on firing the other, it should push the O-ring back into the middle of the groove.... I think the problem with the SS Valve is that the two O-rings are loaded in opposite directions, so the front one, which is wedged into the rear corner, gets a double does of friction on the initial firing after sitting for a while....

Bob
Yup .. a Bi-directional Chinese finger trap effect.
Title: Re: Simplified Balanced Valve
Post by: lloyd-ss on December 26, 2018, 08:09:45 AM
Years ago at work, I met with a very experienced application engineer... a guru.... for a company called Seal Science. Just in passing he said that selection of the wrong seal material was the most common problem he ran into. Unfortunately, he retired before I had a chance to privately corner him about airgun o-ring applications. Talk about a missed opportunity! Darn!  :'(
Title: Re: Simplified Balanced Valve
Post by: Hobbyman2007 on December 26, 2018, 09:01:10 AM
I’ve gone through some of my textbooks from trade school and some litterature from Parker , both seem to recommend the use of backup rings for pneumatic applications . Mostly due to keeping lubricant for the oring . I’m wondering since in our use of dynamic orings this might be a good practice and eliminate some of the sticksion issues were seeing . I know it’s been brought up before ,just wondering if anyone’s tried it .
Title: Re: Simplified Balanced Valve
Post by: lloyd-ss on December 26, 2018, 10:23:52 AM
I’ve gone through some of my textbooks from trade school and some litterature from Parker , both seem to recommend the use of backup rings for pneumatic applications . Mostly due to keeping lubricant for the oring . I’m wondering since in our use of dynamic orings this might be a good practice and eliminate some of the sticksion issues were seeing . I know it’s been brought up before ,just wondering if anyone’s tried it .


Denis, Looks like you are thinking outside the box, and in the right direction.  We rely on O-rings because of their price, availability, selection, and compact size, and they are usually very forgiving and work well.  But this stiction issue is a real bugaboo. I've used back-up rings in static applications at very high pressures, in particular when hydraulic pressure testing air tubes. The backup rings were needed to keep the O-rings from failing before the tube. And they worked! But I've never used anything smaller than a size 111, and the back-up rings, if you use 2, double the width of the o-ring gland, so that can be a problem. Spring or o-ring loaded u-cup seals work well, but small sizes are limited, gland sizes are usually large, and cost can be pretty high. I put a spring loaded glass filled Teflon seal in an air pump I made and it worked great, but golly, it was $20!

Bob's approach of eliminating/minimizing the problem by design, is good. But finding alternate kinds of seals is a good idea too. I see that McMaster has the backup rings down to size 004, and they are really cheap. You might only need the back-up ring on one side, so the groove width problem might not be too bad.  Good idea Denis!
Title: Re: Simplified Balanced Valve
Post by: oldpro on December 26, 2018, 01:44:30 PM
I’m sure you guys have considered this, but with that setup you might need a soft and flexible seal on the seat to get a 100% seal every time. The Cothran valve has a loose piston (can wobble and adjust to the perfect alignment) to seal the vented chamber. As such, the stem and seal are free to “find and seal" to the seat.
If the setup is fixed on both ends (three points counting the stem), you’ll need exceptional tolerance and finish control… just my opinion

Wyo
The SS valve has a floating thimble to allow for alignment. I agree with what your saying
Title: Re: Simplified Balanced Valve
Post by: rkr on December 26, 2018, 03:45:01 PM
I’m sure you guys have considered this, but with that setup you might need a soft and flexible seal on the seat to get a 100% seal every time. The Cothran valve has a loose piston (can wobble and adjust to the perfect alignment) to seal the vented chamber. As such, the stem and seal are free to “find and seal" to the seat.
If the setup is fixed on both ends (three points counting the stem), you’ll need exceptional tolerance and finish control… just my opinion

Wyo
The SS valve has a floating thimble to allow for alignment. I agree with what your saying

Alternatively you could copy JBs self centering valve design to let the poppet float.
Title: Re: Simplified Balanced Valve
Post by: mann on December 26, 2018, 05:12:38 PM
I may have to change my SS valve so the center floats may be just remove the threads and put a snap ring in the end of the valve to hold it from popping out
Title: Re: Simplified Balanced Valve
Post by: rsterne on December 26, 2018, 06:28:35 PM
Quote
The SS valve has a floating thimble to allow for alignment.

I haven't seen one of your new SS Valves with the threaded in one-piece thimble.... I figured they were fixed.... How do you float the thimble in them?....

Bob
Title: Re: Simplified Balanced Valve
Post by: oldpro on December 26, 2018, 06:44:38 PM
Quote
The SS valve has a floating thimble to allow for alignment.

I haven't seen one of your new SS Valves with the threaded in one-piece thimble.... I figured they were fixed.... How do you float the thimble in them?....

Bob
The old ones are threaded the new ones have a circlip on each side anda wavy washer to take up the slack but allow movement 
Title: Re: Simplified Balanced Valve
Post by: rsterne on December 26, 2018, 06:54:33 PM
Ahhhhhhh, didn't know you went back to the circlip.... I had one of your first SS valves, and it had a circlip.... The perforated mounting wheels I make on my SS valves are held in place with a circlip, and in addition the center hole is oversize and I use a shouldered screw tightened into the thimble to provide lots of radial movement for alignment.... Seems to work great, and I will do the same in the new valve.... I got the poppet roughed out and the stem made, threaded, drilled and glued into the PEEK today.... I'll make the thimble next and then finish the diameter on the poppet while holding it with the stem.... The front end of the stem is drilled with a tiny center drill so I can center it on a live center when doing the final turning and O-ring groove....

Bob
Title: Re: Simplified Balanced Valve
Post by: Tack Driver 10 on December 27, 2018, 04:53:48 PM
Bob, great job on explaining how these balanced valves function.
I was in the middle of a valve experiment and decided to take a stab at one for a 13xx.

This one uses two springs, one for the check and the other for the stem.
Some pics of the prototype minus the springs.
Title: Re: Simplified Balanced Valve
Post by: rsterne on December 27, 2018, 05:06:54 PM
That's some very nice machining, Tack.... It looks like the O-ring section of the poppet is the same diameter as the seating end, however.... That means it is 100% balanced, to the only thing holding the poppet closed will be the valve spring.... I think you may find that problematic....

The main reason for making a balanced valve is to reduce the hammer strike required to open it.... I can't imagine that being a problem in a 13XX.... Mostly this technology is for Big Bores where the hammer strike can get to the point you can't even cock the gun....

Bob
Title: Re: Simplified Balanced Valve
Post by: rkr on December 28, 2018, 02:49:04 AM
That's some very nice machining, Tack.... It looks like the O-ring section of the poppet is the same diameter as the seating end, however.... That means it is 100% balanced, to the only thing holding the poppet closed will be the valve spring.... I think you may find that problematic....

The main reason for making a balanced valve is to reduce the hammer strike required to open it.... I can't imagine that being a problem in a 13XX.... Mostly this technology is for Big Bores where the hammer strike can get to the point you can't even cock the gun....

Bob

How about if he made another "o-ring" groove in the area of the poppet that's not inside the thimble? Without o-ring that would provide the force needed to push the poppet against the seat while making manufacturing process easier with a straight thimble. It would also be rather easy to adjust the sealing force with the groove depth, you could probably even decrease it with epoxy or something if needed. In addition it would allow us to use bigger diameter easier to get o-rings thus making it easier to drill the vent channel through the poppet for those having problems with stem drilling.

Edit: Thinking it a bit further that groove would also cause force against the low pressure inside the thimble, I guess that would cancel the closing force with valve already closed. However, it should still assist in closing the valve while it is open since thimble should have high pressure inside at that point. Another try it if it works scenario I guess.

Edit 2: there's also air flow to consider in closing the valve. If it wasn't for that we couldn't close a valve that doesn't have a valve spring. Perhaps we should consider leaving out the "expanded" area of the thimble so that we could use the expanded area of the poppet in closing the valve faster? Or is that in there to slow down the valve closing?

Title: Re: Simplified Balanced Valve
Post by: Tack Driver 10 on December 28, 2018, 11:36:21 AM
Thanks for the inputs.
I was hoping the spring pressure would seal the valve but only to a point.

I think I'll make the stem top .187" and the seat .220" with a total stem width of .270"
With the spring pressure it may work.

Title: Re: Simplified Balanced Valve
Post by: rsterne on December 28, 2018, 12:49:38 PM
Quote
there's also air flow to consider in closing the valve. If it wasn't for that we couldn't close a valve that doesn't have a valve spring

This is a commonly held misconception.... It is not the spring that closes the valve, but the air pressure pushing on the diameter of the stem, which has atmospheric pressure on the outside of the valve.... A 1/8" stem at 3000 psi has a closing force of (0.125 x 0.125 x PI/4) x 3000 = 37 lbs.... Most valve springs are in the 5-10 lb. range, and as you mention, valves with no spring close just fine.... There is virtually no airflow affecting a valve such as the SS valve because the front end of the poppet is shrouded inside the thimble.... The air doesn't "pile up" against the front of the poppet like it might do if all that was in front of the valve was a spring (or just the poppet, with no spring or thimble)….

"Sails" (a washer on the poppet OD) that just clear the inside of the valve body certainly can cause a valve to close faster, but IMO it is not so much from the "drag" of the air moving past them as it is from the pressure differential that causes across the sail…. There is, in addition, a pressure differential that shows up across the poppet just before it closes, when the airflow is at its fastest through the seat.... In fact, the flow probably chokes (which means a minimum 47% pressure drop) when the valve is within a few thou of the seat on closing, that force adding to the pressure of the air in the exhaust port pushing on the area of the stem.... Marco has shown that you can affect the closing rate of a poppet by changing the shape, so there is probably some force caused by the drag of the air moving across the poppet surface.... However, the main closing force for most of the shot cycle is the stem area times the HPA pressure....

Bob
Title: Re: Simplified Balanced Valve
Post by: mann on December 28, 2018, 08:29:50 PM
Made a new poppet the ss valve drilled a.040 vent hole in the poppet threaded the poppet stem and drilled it also took the threads off the thimble and got a snap ring installed a groove in the valve put the poppet into the valve with the thimble I have to cut the stem to length yet but I'm pleased other wise 
Title: Re: Simplified Balanced Valve
Post by: mann on December 28, 2018, 08:32:38 PM
Here is the valve assembled with the floating thinmble I still have to plug off the jet to
Title: Re: Simplified Balanced Valve
Post by: Tack Driver 10 on December 28, 2018, 10:04:53 PM
Made this version today.
.185" and .220".

Depending on how this works I think a .200" x .250" would be better.
I had to stretch a #003 o-ring to fit for this one.
A #004 would fit a .200" diameter nicely.
Title: Re: Simplified Balanced Valve
Post by: rsterne on December 28, 2018, 10:12:32 PM
Nice work, guys.... I wish you both much success with your valve builds....

Now that Christmas is over, I got back into the shop to start on the parts for my new simplified balanced valve for my Hayabusa Mk.II…. Yesterday I roughed out the poppet and stem and assembled them.... The stem is made from a piece of 1/8" O1 Drill Rod.... It is drilled from the front end with a 3/64" drill to a depth of 1.20", which is about 1/4" behind the seat of the poppet, and about in the middle of the valve exhaust port.... It took a while to drill that deep, because the flutes on the drill are only 3/4" long, so after that I could only drill about 0.015" at a time before clearing out the chips.... otherwise the drill would have broken off in the hole for sure.... The front 5/8" of the stem is threaded 5-40, the reason for that size is that you don't have to turn down the shaft, the nominal OD of the threads is 1/8" and the die just screws on.... The new Die Holder I made worked perfectly, and the threads are nice and straight.... The poppet was turned down oversize and then drilled through with a #38 drill, which is the tap size for 5-40 threads.... It was then counterbored from the back to 0.128" for a depth of 0.300", leaving a shoulder inside where the unthreaded portion of the stem will stop.... and then tapped from there to the front of the poppet.... I then coated the inside of the hole in the poppet and the threads with Loctite 638 (green) and assembled the poppet and after wiping off the excess (and making sure there was none inside the vent hole), I left it to dry overnight....

The next step was to make the thimble.... I used a piece of 1144 Stressproof steel that is 1/2" OD, turned the back end flat, centerdrilled it, and then drilled a 1/4" hole 1.25" deep, the front of which is the spring pocket.... I then used a 19/64" drill (1 size under 5/16") and drilled in for the front portion of the poppet to a depth of 3/4", then drilled out the back to 27/64", finishing it to a depth of 0.300" using a 7/16" mill for the pocket to miss the rear part of the poppet.... I then used a 5/16" 4-flute mill to finish the front bore to a depth of 0.830", enough that the finished poppet can go just below flush with the back edge of the thimble without either the front of the poppet hitting the front of the bore, or the spring going coil-bound.... Once the bumper, which is a 7 mm ID x 1.5 mm CS O-ring (10 mm OD), is installed on the poppet, it will stop it 0.050" before anything can come to a crashing halt and get damaged....

The next step was to finish machining the poppet.... I ground the stem off flush with the front end of the spring seat in the poppet and cleaned up the end of the vent hole with a tiny center drill.... With the stem of the poppet in the lathe chuck, and the front running on a live center in the tailstock, I finished the poppet to size and machined the O-ring groove for the 5 mm ID x 1.5 mm CS 70D O-ring (8 mm OD).... It's nice doing it this way as it ends up machined true to the stem.... The last thing on the poppet was to drill the cross vent hole in the stem on the exhaust port side of the seat.... I used a 1/32" drill for that.... I have a selection of small drills coming, as the next size up I have currently is 0.040".... I can go all the way to 0.047" to match the 3/64" hole in the stem if necessary.... That is about 2.3 times the area of the current 0.031" vent hole....

The last thing to do on the internals of the valve was to finish the thimble.... I finished the length to 1.90", the same length as the previous SS valve thimble I made, so that if this new valve doesn't work I can make SS internals to fit the valve body (which I still have to make)…. I then drilled the front end to a depth of 1/2" and tapped it 8-32.... I turned the OD of that portion to 0.290" OD so that it will have lots of clearance in the 5/16" milled shoulder I will machine in the perforated front mounting wheel.... The center hole in that wheel will be 3/16", which will be a loose fit on the 8-32 screw used to mount the thimble.... I turned off the last 1/8" of threads on the mounting screw, so that it can be tightened up against the bottom of the threaded hole without damaging the threads.... When it is tight there is 1/4" of space between the head and the end of the thimble, so that I can set the end play to just a few thou and yet have lots of radial play so that the thimble is self-aligning with the poppet.... The last machining on the thimble was to cut a 10 deg. taper joining the two ODs.... Here is what all the parts look like....

(http://i378.photobucket.com/albums/oo221/rsterne/Hayabusa%20PCP/Hayabusa%20Mk%20II%20New%20Valve%20Parts_zpsrcn09wtn.jpg) (http://s378.photobucket.com/user/rsterne/media/Hayabusa%20PCP/Hayabusa%20Mk%20II%20New%20Valve%20Parts_zpsrcn09wtn.jpg.html)

I know for a fact that the O-ring doesn't leak, at least at low pressures, and yet slides easily.... If I slide the poppet into the thimble without the spring in place (with the vent hole plugged), it compresses the air in the thimble and the poppet pops back out from that tiny bit of pressure.... With the bumper O-ring in place the poppet stops with about 1/32" showing behind the back of the thimble.... I will set the back of the thimble 1/4 from the seat of the valve and that will give me about 0.220" of lift before the bumper touches inside the thimble.... The stem of the valve, however, will only protrude 0.200" behind the back of the valve body, so the hammer cannot drive the poppet far enough to make it crash inside the thimble....

Next step is to make the valve body, and the perforated wheel that mounts the front of the thimble....

Bob
Title: Re: Simplified Balanced Valve
Post by: mann on December 28, 2018, 10:49:40 PM
Nice work mine is binding up some I believe my drill rod is tweeked some I also may need to make my oring groove a tad larger
Title: Re: Simplified Balanced Valve
Post by: mann on December 28, 2018, 10:53:54 PM
I followed your same design just used the original thimble out of the ss valve . Left the lower oring out drilled threw the center of the poppet and vented out the drill rod . I used 6-32 threads though I didn't have the stuff for 5-40 threads
Title: Re: Simplified Balanced Valve
Post by: PakProtector on December 29, 2018, 09:42:52 AM
Mann, my SS valve thimble also has the threads remaining. I think that they remain useful for keeping it more closely centered in the valve body.
cheers,
Douglas
Title: Re: Simplified Balanced Valve
Post by: rsterne on December 29, 2018, 12:09:34 PM
Douglas, I think the reason for machining off the threads and going to a snap ring was to allow the thimble to self-center with the poppet by giving it some play....

Bob
Title: Re: Simplified Balanced Valve
Post by: PakProtector on December 29, 2018, 01:24:28 PM
Absolutely Bob, but the body I have is snap-ring'd and the thimble is threaded...and there is a non-trivial amount of radial float as it is.
cheers,
Douglas
Title: Re: Simplified Balanced Valve
Post by: TPL on December 29, 2018, 02:47:12 PM
Quote
there's also air flow to consider in closing the valve. If it wasn't for that we couldn't close a valve that doesn't have a valve spring

This is a commonly held misconception.... It is not the spring that closes the valve, but the air pressure pushing on the diameter of the stem, which has atmospheric pressure on the outside of the valve....
If there is no pressure difference over valve assembly then there is no loss either. You really consider it possible?

Of course there is pressure difference due to valve stem too, no-one is arquing otherwise.
Title: Re: Simplified Balanced Valve
Post by: mann on December 29, 2018, 03:04:53 PM
Well I sealed up the jet shortened the valve stem and got the bind to go away threw it in my spare air tube and the valve sealed up almost all the way I got a leak at my gauge block I have to deal with so I can tell exactly how it is but it has sealed up better than my first attempt when I was trying the python chamber where all the air was coming out the transfer port . So I believe the simplified balanced valve will seal up all the way just may need to burnished the poppet more
Title: Re: Simplified Balanced Valve
Post by: mann on December 29, 2018, 03:06:25 PM
I left the body of my valve threaded just removed the threads on the thimble and added a snap ring so it can self center
Title: Re: Simplified Balanced Valve
Post by: mann on December 29, 2018, 03:53:14 PM
Almost got it sealed up all the way at about 1500 psi it opens pretty easy and should work fairly well alittle more burnishing and it should seal all the way
Title: Re: Simplified Balanced Valve
Post by: Tack Driver 10 on December 29, 2018, 05:54:36 PM
Finished the valve mods and put the Mod Mule gun together.

Backed the power adjuster all the way back out 3/4" and it still dumped all ten pumps.
Need to swap to a much lighter hammer/spring.

Will do some tests next week.

Very pleased , thanks all.



Title: Re: Simplified Balanced Valve
Post by: rsterne on December 29, 2018, 07:36:18 PM
Of course, Timo, there is some pressure difference across a poppet.... if you read the remainder of that response I stated that.... Can you quantify what it might be in the case of a SS valve, or this valve, when the thimble is larger than the poppet, and no air "piles up" against the front of the poppet?.... Can you quantify the drag of the air sliding across whatever area of the side of the poppet is left exposed to the friction of the air sliding across it before it turns the corner at the seat?.... I can do neither, but I'm always open to theory or evidence that can give us some idea of the magnitude of those forces in closing the poppet, and during what part of the cycle they apply....

There are four closing forces that are relatively easy to quantify, and they apply at different times during the shot cycle....

1. The force holding the poppet closed, most all of which disappears in the first few microseconds as the pressure between the valve seat and the pellet rises to (nearly) reservoir pressure.... Once that occurs, and before the pellet has a chance to move any significant distance, there is virtually no "flow" to cause frictional losses across the poppet or through the seat....

2. The spring force holding the valve closed, which increases slightly as the poppet lifts from the seat....

3. The force resulting from the pressure inside the exhaust port acting on the stem area.... which acts throughout most of the time the valve is open....

4. Just before the valve closes, when the airflow is at its fastest.... as the poppet approaches the seat, the area between the two becomes so small that due to the Bernoulli effect, the flow there chokes because it exceeds Mach 1 for the gas used at the pressure on the valve side of the seat.... Once the flow chokes, the pressure drop across the (ever narrowing) gap becomes at least 47% of the pressure inside the valve.... This pressure differential increases until the valve seats, when the force returns to step 1 (pressure differential rises to 100%).... This force does not suddenly "turn on" when the flow chokes, but the magnitude is small when the velocity through that gap is below about Mach 0.9 (using the applicable SoS)…. This chart will give you that, note that it varies with pressure....

(http://i378.photobucket.com/albums/oo221/rsterne/PCP%20Internal%20Ballistics/Speed%20of%20Sound%2020C%20with%20Helium_zps3zw5mksn.jpg) (http://s378.photobucket.com/user/rsterne/media/PCP%20Internal%20Ballistics/Speed%20of%20Sound%2020C%20with%20Helium_zps3zw5mksn.jpg.html)

Between steps 3 and 4, and depending on the size, flow velocity and direction, and gas density, there is an additional force trying to close the valve, due to "drag" or pressure difference across the poppet.... It is this force that (to me, at least) is difficult to quantify.... I did some experiments by measuring valve lift with three conditions.... no pellet, normal shot with pellet, and with the barrel port blocked off (as if the pellet had infinite mass, so basically no airflow)…. My conclusions for that particular PCP was that based on the very small increase in lift when there was no airflow, compared to the other two conditions with normal and maximum flow.... that the additional force trying to close the valve from airflow was roughly the same magnitude as the spring force.... in the test case about 10 lbs. at maximum.... The calculated force from the air pressure acting on the stem was 38 lbs.... My conclusion was (and it could be in error) that the pressure acting on the stem was the dominant closing force on the valve....

As always, I am ready to consider theory and evidence to the contrary....

Bob

Title: Re: Simplified Balanced Valve
Post by: rsterne on December 29, 2018, 07:40:22 PM
The fact that you guys are getting the valve to seal up gives me confidence that we are onto something here.... I got the valve body machined inside and out today, but I still have to drill and tap the holes for the mounting screws, machine the exhaust port and TP recess, the O-ring groove to seal it into the tube, and make the perforated front wheel that mounts the thimble.... way to go, mann and Tack....  8)

Bob
Title: Re: Simplified Balanced Valve
Post by: mann on December 29, 2018, 09:21:38 PM
I had a slight set back broke the stem flush off in the head I was able to remove it with a left handed bit I think the hole in the stem was too large I can't get it seal completely I was getting air out the exhaust hole not alot so after I burnished the poppet several times it wasn't getting any better thought maybe my oring groove and oring were leaking and broke the stem when maching a new groove redrilled the stem with a smaller hole and got a new oring on the stem only one that fits good is a viton so I'll see what happens had to make a new stem also that's what I get for being in a hurry
Title: Re: Simplified Balanced Valve
Post by: mann on December 29, 2018, 09:22:21 PM
Drilled cross hole by hand that was fun only did the one side
Title: Re: Simplified Balanced Valve
Post by: mann on December 29, 2018, 09:50:02 PM
Wow my new oring seals up and it opens really easy just have to get the poppet to seal all the way  maybe if I cut another groove up so the air has a place to get around in the thimble idk
Title: Re: Simplified Balanced Valve
Post by: mann on December 29, 2018, 09:51:28 PM
The viton oring seems to work on the poppet though so that's a plus
Title: Re: Simplified Balanced Valve
Post by: rsterne on December 29, 2018, 09:52:24 PM
Yes, you only need to drill one side of the stem.... I have a 0.047" hole down the stem and a 0.031" hole through one side in the exhaust port area....

Bob
Title: Re: Simplified Balanced Valve
Post by: mann on December 29, 2018, 10:45:08 PM
I can get it to seal by first pushing should air through the exhaust of the valvewhich tells me I need to drill a bigger hole threw the stem and poppet I'm at .040 any other ideas
Title: Re: Simplified Balanced Valve
Post by: rsterne on December 29, 2018, 11:00:28 PM
I presume you mean "shop" air, not "should" air ?.... as in you are adding backpressure to get it to seal?.... I think more likely you have an incomplete seal on the poppet.... I can't imagine the size of the vent would make any difference to sealing.... Tack got his to seal up OK....

Bob
Title: Re: Simplified Balanced Valve
Post by: mann on December 29, 2018, 11:13:21 PM
Yeah I had it sealed up but I just blew the threaded stem out the back of the valve when I tapped the valve open oops just needs some good burnishing
Title: Re: Simplified Balanced Valve
Post by: mann on December 29, 2018, 11:23:03 PM
This valve hates me I had trouble getting it sealed with the ss poppet must be something in the seat I used peek poppets in other valves and they have sealed up
Title: Re: Simplified Balanced Valve
Post by: rsterne on December 29, 2018, 11:27:20 PM
Quote
I just blew the threaded stem out the back of the valve when I tapped the valve open oops

 :o ??? >:( :-[

Cut out a small disc of 220 sandpaper, stick it on the poppet seat with double-sided tape, and the use the poppet to sand the seat in the valve body by pulling gently on the stem while chucked in a portable electric drill.... I follow that by burnishing with "Solvol Autosol", a very fine abrasive polish.... and then just the clean plastic poppet.... Clean carefully between each step, of course.... I also undercut my PEEK poppets by 1 deg. to force the sealing margin to the very outside edge....

Bob

Title: Re: Simplified Balanced Valve
Post by: oldpro on December 29, 2018, 11:28:04 PM
 If you guys get this to work Ill be shocked but Im certainly rooting for you!!! Go Team! I tried this over a year ago I have the valve at the shop Ill show you how I made it work and that was cutting off the lower section of the poppet and re sleaving the upper to 3/16ths I believe. Ill show pics on Monday of the thimble and poppet. It just wont work at the 80% ratio
Title: Re: Simplified Balanced Valve
Post by: rsterne on December 29, 2018, 11:31:02 PM
Mine is 71% ratio on the diameters (50% on the area)…. I guess we'll see in a few more days....

Bob
Title: Re: Simplified Balanced Valve
Post by: mann on December 30, 2018, 12:06:17 AM
I'll glue the stem back in sand the valve seat and I've been using real fine metal polish that I've used to get my other valves to seal the seat is really shiny it just not quite good enough yet so I'll have to sand and retry
Title: Re: Simplified Balanced Valve
Post by: mann on December 30, 2018, 12:07:53 AM
I cut 2 lines in the lower part of the poppet to help get air in the thimble it's slams shut faster now  to
Title: Re: Simplified Balanced Valve
Post by: rsterne on December 30, 2018, 12:22:49 AM
I noticed that.... I have a few thou gap between the large end of the poppet and the ID of the thimble.... a lot of area, compared to the size of the vent hole in the stem.... but I can do that if necessary....

Bob
Title: Re: Simplified Balanced Valve
Post by: mann on December 30, 2018, 05:19:43 PM
I did everything you suggested Bob I just can't get it to stay sealed up up completely all the time . It will be good at lower pressure hit it with the hammer and it starts leaking again . I also tried a heavier poppet spring and under cut the poppet
Title: Re: Simplified Balanced Valve
Post by: Motorhead on December 30, 2018, 05:41:36 PM
I did everything you suggested Bob I just can't get it to stay sealed up up completely all the time . It will be good at lower pressure hit it with the hammer and it starts leaking again . I also tried a heavier poppet spring and under cut the poppet

Suggest paying attention to travis and his past comments ..... someone with first hand experience generally offers sound advise.
Title: Re: Simplified Balanced Valve
Post by: mann on December 30, 2018, 06:06:00 PM
Thanks for the word of encouragement
Title: Re: Simplified Balanced Valve
Post by: rsterne on December 30, 2018, 06:09:14 PM
I guess Tack's success in his pumper was an anomaly....  ::) …. I'll find out for myself in a few days when I get a chance to finish mine....

Bob
Title: Re: Simplified Balanced Valve
Post by: PakProtector on December 30, 2018, 06:30:43 PM
If the poppet is not cut square to the stem, no amount of polishing the seat is going to help. Had some fun with an SS valve. Started its first charge and found it leaking out the exhaust. Got it to 1k psi, and as it hissed away at me, I gave the stem a small tap through a dowel. KA-POW! No more leak. Keep your fingers away from the exhaust port if ever doing this...:) It would likely take your hide CLEAN Off...

On Bob's idea, I would suggest starting with a lighter balance/smaller amount of help. Work up...while y'all are at it, just keep in mind stability margin and Q...it could be that some resistance is needed to remove energy from the system.
cheers,
Douglas
Title: Re: Simplified Balanced Valve
Post by: rsterne on December 30, 2018, 06:51:23 PM
I have no idea if this valve will have the same "sweet spot" in terms of balance that the SS valve has, I just guessed that it might.... The successful SS Valves I have made had the small end between 2/3 and 3/4 the diameter of the big end (ie 67-75%).... The valves I built where the small end was less than 2/3 the diameter of the big end were so easy to open, they were subject to machine-gunning if the hammer strike was fractionally too hard, and was able to bounce at all.... At 3/4, the valve was getting too hard to knock open, IMO, but remember I was comparing it to a conventional valve that required a 1/2 lb. hammer with 2" of stroke that took over 28 lbs. to cock.... I know that Travis settled on 80% for his SS Valves, and that is probably just fine for the limited power PCPs he is producing them for.... Even at 80% diameter, he is reducing the hammer strike required by 36%....

Travis stated that he did get a valve of this design to seal up and work with a 3/16" small end.... He didn't state the diameter of the big end, but I'm guessing it was 0.350", the same as his SS valves have always been.... That is a ratio in diameters of 54%, and the valve would require 73% of the opening force it would as a 0.350" conventional valve.... ie a 27% reduction.... Remember, this valve works "backwards" compared to the SS Valve for the assist provided by the small end.... larger means MORE assist, not less as in the SS valve.... If the small end in this valve is 80% of the diameter of the big end, the opening force will be reduced by 64%, ie the valve will only require 36% of the opening force of a conventional valve with the same seat diameter....

My drawing in the first post of this thread suggests that the area of the small end be 50% of the big end.... ie the diameter would be ~71%.... That is right in the middle of the range I found worked well in my SS Valves.... Both the valves built so far are at 80-84% diameter on the small end, one of them sealed up (actually the one at 84%), the other one didn't.... If my 71% ratio doesn't work (which should get rid of 50% of the force holding the valve closed), then I'll try a smaller one.... We know that Travis got it to work by going smaller.... How much smaller should be the only question remaining, IMO....

but I've certainly been wrong before, and will be again.... I can tell you one thing, though.... If this valve doesn't work, that fact alone won't be good enough for me.... I will need to understand WHY it won't....  ???

Bob
Title: Re: Simplified Balanced Valve
Post by: lloyd-ss on December 31, 2018, 12:42:49 PM
There are so many subtleties to the balanced valves that it is easy to end up chasing your tail trying to get a new design to work. I know, I've got a box of failures, and just a few winners. But when they work well, they work really well.

Doing the area and force calculations of the various piston and seat diameters, at various pressures, and open distances, is very important.
If the math says that it WON'T work, then it definitely won't work. If the math says that it WILL work, then there is a chance that it might work, but a VERY SMALL chance that it will work well.  Getting it to work well almost always requires a second or third iteration.
Title: Re: Simplified Balanced Valve
Post by: oldpro on December 31, 2018, 01:10:15 PM
As promised here are pics of the cut down thimbles. The original and smaller .187 version
Title: Re: Simplified Balanced Valve
Post by: rsterne on December 31, 2018, 01:33:29 PM
Travis, thanks for the photos.... You didn't state the diameter of the seat, but taking measurements on my screen, from the top photo enlarged....

Upper poppet.... rear = 13.5 mm.... front = 10.5 mm = 78%
Lower poppet.... rear = 13.5 mm.... front = 9.5 mm = 70%

That is assuming that the seat on the poppet is right around the very outer edge of the larger diameter.... and does not allow for the bore of the thimble being larger than the front of the poppet (for clearance).... If anything, the sealing diameter of the front part of the poppet would be a larger percentage of the sealing diameter of the rear portion than what I have measured from the photos.... My design is 71%, so I remain hopeful....

You might like to consider this.... To have the same 36% reduction in opening force as your SS valve, with it's 80% front section on the poppet.... a valve to this design would require only a 60% front section.... As I said, the effect of changing the diameters is reversed.... At 70.7%, both systems have the same effect... half the opening force is cancelled out by the balancing portion....

Bob
Title: Re: Simplified Balanced Valve
Post by: oldpro on December 31, 2018, 01:48:52 PM
.282x355 and .185x355 respectively same lower sections and valve internals.
Title: Re: Simplified Balanced Valve
Post by: rsterne on December 31, 2018, 01:51:01 PM
Travis, sorry, but those dimensions do not match the photos.... .185x.355 is only 52%.... Measure it yourself.... If the front portion of the lower popper in the upper photo is 0.185", the rear portion is about 0.265".... Also, since both poppets are in the same photo, the front portion of the upper poppet is only about 0.205"....

Bob
Title: Re: Simplified Balanced Valve
Post by: oldpro on December 31, 2018, 01:56:12 PM
 Bob your absolutely correct I gave some bad info the .187 was on the Prod version I measured it and its .240 on the Mrod version. SORRY!!! Was going from memory so that was mistake number 1 lol.
Title: Re: Simplified Balanced Valve
Post by: rsterne on December 31, 2018, 02:04:42 PM
I will assume that the stem is 0.125".... It measures 5 mm on my screen.... Based on that, the rear of the poppets, which both measure 13.5 mm would be (13.5 / 5 x 0.125") = 0.338".... The front of the poppets would then be....

(10.5 / 5 x 0.125") = 0.263" for the larger one.... 0.263" / 0338" = 78%

(9.5 / 5 x 0.125") = 0.238" for the smaller one.... 0.238" / 0.338" = 70%

Is it possible that the small front end is 1/4" in that photo, not 3/16" ????

*LOL*…. Looks like 0.240" is the correct answer.... I should have scaled everything from the stem in the first place....  ::)

Bob
Title: Re: Simplified Balanced Valve
Post by: oldpro on December 31, 2018, 02:07:01 PM
I started thinking back and if I recall correctly I did end up using a .187 to 350 ratio to be able to get any real tuning effect I have since moved all my equipment and data up to JSAR so I will when time is available go back and find the data from over a year ago and that alone won’t be easy. I have lost data that I had no use for that is now relevant so I will go look threw it ASAP and find the chrono data also.
Title: Re: Simplified Balanced Valve
Post by: oldpro on December 31, 2018, 02:13:09 PM
 I just remeasured the above SMALLER poppet its Metric 6mm x 9mm.
Title: Re: Simplified Balanced Valve
Post by: rsterne on December 31, 2018, 03:13:24 PM
The smaller poppet in the above photo is (13 mm / 25 mm) = 52% at the small end, compared to where the seat is on the big end....  :o

Doesn't really matter anyways, I'll get back into the shop in a day or two.... suffering from "Motelus Interuptus" right now....  ::)

Bob
Title: Re: Simplified Balanced Valve
Post by: lloyd-ss on December 31, 2018, 05:57:32 PM
I'll get back into the shop in a day or two.... suffering from "Motelus Interuptus" right now....  ::)

Bob

Darn guests. Can't they just pay their money and take care of themselves! Jeez!  ;)
Title: Re: Simplified Balanced Valve
Post by: rsterne on December 31, 2018, 06:22:52 PM
New Years guests have checked out, and we have a few days respite now.... however, that means it's time to do our "off-season" maintenance.... This week I will be spackling any dents in the walls and repainting them (fortunately we still have some of the original paint, and once dry it matches perfectly)…. There are a few other jobs we do annually, in order to keep up our "5-star" rating with Trip Advisor.... the only one in this area, I might add....  8)

https://www.tripadvisor.ca/Hotel_Review-g1169466-d1167372-Reviews-Mozey_On_Inn-Coalmont_British_Columbia.html (https://www.tripadvisor.ca/Hotel_Review-g1169466-d1167372-Reviews-Mozey_On_Inn-Coalmont_British_Columbia.html)

Hey, it's a shameless plug, but you only have another 2 years to come and visit us before we close permanently on Feb. 28. 2021.... (yayyyyyyyyyy, freedom dayyyyyyyyyy)….   ;D

Bob

Title: Re: Simplified Balanced Valve
Post by: Hobbyman2007 on December 31, 2018, 07:12:09 PM
New Years guests have checked out, and we have a few days respite now.... however, that means it's time to do our "off-season" maintenance.... This week I will be spackling any dents in the walls and repainting them (fortunately we still have some of the original paint, and once dry it matches perfectly)…. There are a few other jobs we do annually, in order to keep up our "5-star" rating with Trip Advisor.... the only one in this area, I might add....  8)

https://www.tripadvisor.ca/Hotel_Review-g1169466-d1167372-Reviews-Mozey_On_Inn-Coalmont_British_Columbia.html (https://www.tripadvisor.ca/Hotel_Review-g1169466-d1167372-Reviews-Mozey_On_Inn-Coalmont_British_Columbia.html)

Hey, it's a shameless plug, but you only have another 2 years to come and visit us before we close permanently on Feb. 28. 2021.... (yayyyyyyyyyy, freedom dayyyyyyyyyy)….   ;D

Bob

Bob,
I might just have to take you up on the offer for a stay at the Mosey. We had a local watering hole of the same name in North Bay years ago . Lots of fun to be had . I’d love to give your .257 mono a try .
Title: Re: Simplified Balanced Valve
Post by: rsterne on December 31, 2018, 07:15:15 PM
Yeah, we get the occasional phone call asking if we still have the peelers.... *LOL*…. guys looking for the pub in North Bay....  ::)

Bob
Title: Re: Simplified Balanced Valve
Post by: PakProtector on January 01, 2019, 10:32:13 AM
It looks like there are two tuning quantities you can mess with. One is the volume of the balance chamber, and the other is the holes feeding it. they're pretty closely related; so adding wee plastic blocks to fill it up or by removing, make it bigger you'll be able to adjust the time it takes to develop closing pressure as the chamber fills with HPA during the shot.

For the usual, close while pellet at barrel midpoint I think you will want some variation of Lloyd's spreadsheet...driven by the barrel pressure output. For sure, with test data, tuning up the spreadsheet and flow values ought to be possible.
cheers,
Douglas
Title: Re: Simplified Balanced Valve
Post by: rsterne on January 01, 2019, 12:58:11 PM
If the valve is not tunable with hammer strike, then we definitely need changes.... I am not willing to accept another Cothran style valve where you must change pressure to change velocity, the valve is either "cycling" or "not".... Don's valve does a great job of developing big FPE from minimal hammer strike, which was what it was made to do.... It works well in regulated PCPs, but you can think of it as having a set "dwell", regardless of hammer strike.... You hit it hard enough to open, it stays open for "X" time (eg. 1 mSec) and then closes.... If you are launching a light bullet you get high velocity and low efficiency.... The heavier the bullet, the less it has travelled down the barrel when the valve closes, and the higher the efficiency.... The lower the velocity, the higher the efficiency....

An SS Valve with a large front vent and a small hole through the poppet acts in a similar manner.... I think both valves are "blowing open" until the pressure inside the balancing chamber builds to the point of closing them.... If you make the vent through the poppet larger in an SS Valve, it wants to close more quickly.... More hammer strike "drives" it open more, instead of it just blowing open.... so you can control lift and dwell with hammer strike.... Installing a small front jet adds a "Cobra" component, turning the front chamber into an air spring, and reducing the dwell.... It's like adding a stronger valve spring, allowing you to tune over a broader range of pressure.... but requires more hammer strike to do that....

IMO, the main reason to make a balanced valve is to reduce the hammer strike, particularly in Big Bore PCPs, where getting a hard enough hammer hit can actually be the limiting factor to the FPE.... Generally, they tend to be unregulated, so to get more than 1 or 2 shots you have to be able to produce a bell-curve.... That requires a valve where you can change the dwell with hammer strike.... So that is my goal.... I want to do it in the simplest manner, with the least parts and seals, and the easiest machining.... and I expect a few setbacks along the way.... The "stiction" problem in SS Valves that creates low velocity on the first shot after the gun sits, is such a setback.... and one we need a design change (getting rid of the wedging of the front O-ring) to overcome, IMO....

The cool thing is, that once accomplished, you should be able to use the balanced valve concept in regulated PCPs, or in lower powered PCPs, to reduce the cocking force, hammer weight and stroke, lock time, etc.etc…. The bottom line on efficiency is where you close the valve in the pellet's travel down the bore, ie the dwell as compared to the pellets weight, and hence velocity.... While different valve designs can have an effect on that efficiency by having a "squarer" flow profile.... or by resisting hammer bounce.... I still think the biggest gains in efficiency are made by changing the basics of what you can call the "shot profile" (a plot of air pressure vs. pellet position in the barrel).... which ultimately results in lowering the residual muzzle pressure as a percentage of the firing pressure.... and hence the amount of energy lost on every shot....

Bob
Title: Re: Simplified Balanced Valve
Post by: Tack Driver 10 on January 01, 2019, 01:49:58 PM
My original valve worked initially but started leaking so I decided to use a wedging type valve stem instead of a stem that sits on top of the seat. This is similar to the check valve on the input of the valve on a pumper.  They seal with very little pressure.

Made a stem from Teflon that wedged into the seat. Worked great for a few cycles then blew the head off the end. Too thin at the glad with a .030" vent through a .100" gland. Thought about making one from Delrin but figured I'd skip that step for now.

Next made a stem from brass with a Teflon wedge insert and it is what I'm currently testing. It has a .210" thimble through a .280" throat and a .330" stem diameter. It uses a #004 70 duro poly o-ring. If this works then I may try a .210" x .250" version.

FWIW....The valve stems looks bent but it's my old camera that is distorting the image.
Title: Re: Simplified Balanced Valve
Post by: shorty on January 01, 2019, 02:34:29 PM
Bob,
This is just my opinion and thoughts on a few things. I hope it helps this valve design.

I have a feeling your simplified balanced valve will operate like a Cothran valve or worse just become a dump valve. Unless you make the balancing chamber so small it defeats the purpose of cracking easy.
I also have a feeling you will not get enough of pressure delta across the cross through hole in the valve stem into the balancing chamber during firing sequence due to size constraints.

In your description above about the SS valve, I think there is something else going on but similar to your description but different (just my opinion).

After reviewing one of Lloyds balanced valve designs with opening and closing forces ( very easy to understand, thanks Lloyd ), I decided to try and put things into a spread sheet with the diagram of the valve to help see and calculate just as much as I can to help myself understand what's going on. It may not be exact or perfect as I am no expert.

I couldn't calculate the delta through the valve port so I excluded it. And, I put a revision in on your simplified valve to control dwell. This should also work for the cothran valve.

I have a feeling this would work just as a simplified cobra valve without O-rings and thimble too.

Title: Re: Simplified Balanced Valve
Post by: PakProtector on January 01, 2019, 03:07:02 PM
I like the larger stem bearing for developing closing force. The tuning by orifice size to the balance chamber is still there. So far so good...IMO, an' all that.

Douglas
Title: Re: Simplified Balanced Valve
Post by: PikeP on January 01, 2019, 05:18:25 PM
One issue with balancing a poppet valve is the duration of the valve cycle having such a tiny window @ ~1ms, that you either get it perfectly right, or not at all.

Ideally you want the most air flow through the transfer plenum which causes the exhaust side of the poppet to see the highest pressure rise in this configuration resulting in a valve that wants to "blow open" much like a Cothran. I think combatting that with a pressure chamber is a very delicate balancing act between orifice sizes.

Maybe the solution to that is balancing some in the throat like shorty is suggesting, attack the problem at its roots.
Title: Re: Simplified Balanced Valve
Post by: shorty on January 01, 2019, 05:34:38 PM
Change yellow highlighted cells. Green are results. It may not be correct but sure gets you thinking.
Title: Re: Simplified Balanced Valve
Post by: shorty on January 01, 2019, 05:38:46 PM
Simple Cobra.
Title: Re: Simplified Balanced Valve
Post by: shorty on January 01, 2019, 05:46:51 PM
This is Lloyds example that gave me the idea.

I also did the step poppet (SS valve ) and Cothran but will not share unless they say go ahead.

To me,
This was an eye opener (even if it has errors). Just knowing the "real" specs on any of these valves and running a DOE in minitab could possible map these valves with the least amount of work.

I hope you guys don't mind me using your diagrams.
Title: Re: Simplified Balanced Valve
Post by: rsterne on January 01, 2019, 06:23:58 PM
Tim, please explain the term in the closing force equation (D-F)…. When the valve is open even slightly there is HPA surrounding the poppet on all sides, and "D" is only a hole in the valve body, it exerts no force on the poppet.... I think that term (which is the force pushing the poppet away from the seat, if I understand you correctly, hence the negative sign) should be (B-F)…. This means that the diameter of the stem F cancels out, and the equation (assuming no air passes through the vent E) becomes....

Closing force = (B-C) - (B-F) + (A-F) = B - C - B + F + A - F = A - C …. which works out to 90.49 lbs....

I realize that you have not included any pressure change in the balance chamber C, through vent E.... but during the time the valve is open, the pressure in C is rising from atmospheric to some value nearing 3000 psi.... If we assume that the pressure becomes 3000 psi, then the forces change completely.... There is no net force across the diameter of the balance chamber at C, so the force there is zero.... This means that the entire poppet, with the exception of where it is penetrated by the stem F, is surrounded by 3000 psi.... This results in a closing force on the poppet, using the same equation as above, but letting C = 0, of....

Closing force = (B-C) - (B-F) + (A-F) = B - C - B + F + A - F = A - C = 184.75 - 0 = 184.75 lbs....

If there is a partial pressure rise in the balance chamber C, then the closing force will be some value between 90.49 and 184.75 lbs.... If the pressure is 1500 psi, then C = 47.13 lbs, and the closing force = (184.75 - 47.13) = 137.62 lbs....

Forget the concept of a balanced valve for a minute, and examine the effect of a larger valve stem.... If you have a 1/8" stem, the closing force is only 36.82 lbs.... With a stem diameter of 0.280", you have increased that 5 times to 184.75 lbs.... That means you will need 5 times the hammer momentum to get the same dwell.... You have vastly increased the hammer strike required because you have increased the diameter of the stem.... The same thing happens with a balanced valve, a bigger stem means more hammer strike is required.... What possible reason can you have for wanting to increase the closing force of the valve?.... All that does is increase the hammer strike required.... The whole point of a balanced valve is to reduce the hammer strike, not increase it.... You need only to substitute an MRod poppet in a Disco, changing nothing else, to see the advantage of a smaller stem on hammer strike, because you are reducing the stem from 5/32" to 1/8"....

Bob
Title: Re: Simplified Balanced Valve
Post by: rsterne on January 01, 2019, 06:30:22 PM
Your post labelled "Simple Cobra" is a conventional valve.... and the same problem exists, the valve "throat" has nothing to do with the forces.... If you use the minus sign to represent forces "away" from the seat and the plus sign to represent forces "towards" the seat, you will find it much easier to understand what is going on.... JMO....

Bob
Title: Re: Simplified Balanced Valve
Post by: PikeP on January 01, 2019, 06:46:56 PM
I'll interject by saying I've tested bigger and smaller stems and have found in my tests that the majority of the hammer energy goes into cracking the valve opened as it has to overcome anywhere from 100 to 400 static lbs holding the valve closed. It takes more energy to overcome 100 to 400 lbs static lbs of force on the poppet while closed and creating lift opposed to rising pressure against the stem OD. Pressure equalization in the transfer plenum happens faster than full lift can be generated so the valve stem OD does help greatly in closing a valve, which requires more hammer energy to counter after valve is cracked off its seat...the question I have is will a poppet with just enough pressure on it to seal operate with less than conventional hammer energy when balancing at the stem opposed to variable pressure at the poppet.

It only makes sense that if the valve stem is an integral part of closing a poppet valve that one should consider an approach revolving around just that...that is if closing the valve is your issue...especially in a timely manner. Just my 2c...if one had all the answers we wouldnt be here asking questions.
Title: Re: Simplified Balanced Valve
Post by: shorty on January 01, 2019, 06:53:16 PM
"please explain the term in the closing force equation (D-F)…. When the valve is open even slightly there is HPA surrounding the poppet on all sides, and "D" is only a hole in the valve body, it exerts no force on the poppet...."

I thought as the poppet opens and allows pressure to enter between the exit port and the pellet that "that" area increases in pressure. Now there is pressure on both sides of the poppet (HPA side "high" and exit port to pellet side "lower"). I thought that's how the mechanism worked.

In the simple revisions, since the valve stem is "knotched ?" I would think that opening force would not be affected since it's not on the HPA side until the valve is opened (creating a lower cracking force and faster closing in a balance design and just creating a faster closing in a cobra design).

I know some of the math is wrong  ;D But, I want the same thing as you.

Is there any chance you can put together a spread sheet similar to mine to help and post it?

Title: Re: Simplified Balanced Valve
Post by: PikeP on January 01, 2019, 07:08:36 PM
Generating minimal lift ie cracking a conventional poppet valve takes quite a bit of energy, once that is achieved you enter your tuning range where adding tiny bits of preload to the hammer spring which slightly increases hammer energy starts to have great effects with said tiny adjustments. Therefore its without question the pressure holding the valve shut and creating minimal lift absorbs a lot of energy before the transfer plenum even comes close to equalizing or we would have very wide ranges of spring preload required for tuning.

Remove most the above via reduced reference of poppet to pressure and exchange that for valve stem pressure nearly equal and the valve should operate...but the question is how well..and can a balance there be achieved. Just my 2c on shorty's idea. I have no clue if it will not work as I have yet to put enough thought into it and pen on paper ie data models dont carry as much weight as does prototyping and tangible models.
Title: Re: Simplified Balanced Valve
Post by: PikeP on January 01, 2019, 07:25:26 PM
Example from my data.

.125" stem turned at 20 fpe. Reduced stem bore and installed new poppet and stem with od of .096". No hammer spring or weight change resulted in no change in fps whatsoever...boggled I tried a different tune..tuning at 60 fpe on the same configuration, the. 096" stem took approximately 20% less hammer energy to achieve 60 fpe... which meant my tuning range narrowed, yet the valve was no easier to open on the low end.. the 20 fpe tune was 685 fps with 20.06gr and the 60 was 900 with 33.95gr. Due to the narrower tuning range (cut in half) I experienced double the extreme spread...which resulted in me going back to a .125 stem.

That to me says the valve stem od is very important in valve closure in the latter half of valve operation, and negligible in the former.

Therefore IMO valves with too narrow or no tuning range need more closing force in the latter part of valve operation. Also too narrow of a tuning range results in higher extreme spreads and a wider one will result in lower the further from velocity plateau you are.
Title: Re: Simplified Balanced Valve
Post by: rsterne on January 01, 2019, 08:20:33 PM
Tim, you are correct, the diameter of the valve stem makes no difference to the cracking force of the valve.... However, that force is only applied during the brief time the poppet (seat) material is decompressing, and for a few microseconds after that, while the port volumes (between seat and pellet base) are rising to (nearly) reservoir pressure.... A Delrin poppet at 3000 psi may be compressed 0.010" and a PEEK poppet half that, so the hammer energy required, while significant, and worthwhile reducing by using a balanced valve, is only part of where the hammer energy is used up.... Most of the remainder goes into overcoming the force from the pressure in the exhaust port acting on the valve stem.... Increasing that force will slow the hammer more while the valve is opening, reducing the lift and dwell.... and the slam the poppet closed faster as well, further reducing the dwell.... I can assure you that increasing the area of the valve stem by a factor of 5 will drastically increase the hammer energy required to release a given amount of air from a valve....

Bob
Title: Re: Simplified Balanced Valve
Post by: shorty on January 01, 2019, 08:26:46 PM
Ohhh, The "input" numbers supplied in the spread sheet mean nothing. I only supplied the spread sheet so that if someone wants to change a few of the balancing and closing forces, they can do it to see what happens.

And in hopes, see and improve on it. Like you I hope. ;D

By all means,
None of those "input" numbers I put in are legit at all.
Title: Re: Simplified Balanced Valve
Post by: mann on January 01, 2019, 09:38:33 PM
I think if I were to use derlin I maybe able to get the valve to seal all the way  curious are you use peek or derlin Bob
Title: Re: Simplified Balanced Valve
Post by: rsterne on January 01, 2019, 10:38:36 PM
Mark, I am using PEEK.... I have been giving this valve a lot of thought (since I can't seem to get any shop time ATM)…. and just like the SS Valve, I think we want as large a vent as possible through the poppet, between the valve exhaust port and the balance chamber.... With a large vent in the SS Valve, the pressure rise in the balance chamber is very fast, and the valve transitions from a balanced valve while cracking to a conventional valve during the rest of its cycle.... This makes it more responsive to tuning with hammer strike, and avoids it "blowing open" to any significant degree.... Yes, it requires more hammer strike than with a tiny vent through the poppet.... but the tuneability increase is huge and well worth it....

BTW, none of my SS Valves use a restrictive front jet.... I use a 1/16" hole through the thimble mounting screw.... I want to control the dwell with hammer strike to the greatest degree possible, and combined with the large plenum I always run, that means the pressure on the front of the poppet will always be reservoir pressure....

Back to your original question, yes, since you have a large front section on the poppet, and therefore little sealing force available.... a Delrin poppet would be a good idea....  ;)

Bob
Title: Re: Simplified Balanced Valve
Post by: rsterne on January 01, 2019, 10:41:17 PM
Tim, IMO you can remove the small part of the stem diameter, F, from your spreadsheet.... It works in both directions all the time, and so cancels out.... In addition, where you were using the throat diameter, D, you should just use the poppet seat diameter B.... Once the poppet is open, B also cancels out, of course....

HTHs....

Bob
Title: Re: Simplified Balanced Valve
Post by: WyoMan on January 01, 2019, 10:50:51 PM
As an aside, but kind of on-theme with this topic is getting hard sealing surfaces to seal with the reduced contact pressure on the seal/seat.

I’ve had reasonable success by simply using enough mechanical force on the seal and seat, and then letting it sit (somewhere warm) for a day or so. No lapping/abrasion necessary as it will cold-form to the seat. It can also correct an alignment issue (i.e. stem not perfectly square to the seat).

This is a 13xx valve with a Delrin exhaust valve. I’m using the wooden spacer so I can apply mechanical force on the seal by screwing the valve halves together:
(https://i.imgur.com/7wWPglZ.jpg)
(https://i.imgur.com/G9elyoK.jpg)

This is the bottom of the Delrin seal after a day or so:
(https://i.imgur.com/oRsgKAu.jpg)

I can get them to seal in a 13xx which is pressurized from empty at about 150 psi per pump. The air-tight seal may be due to the squaring of the stem, or the pressing-in of the new sealing surface, or the increase in the seal contact-area (the sides of the groove)… or all of the above…. don’t really know but I got the idea from Don Cothran… it works for me.

Great stuff guys… this has been an informative thread. Thanks-

Wyo
Title: Re: Simplified Balanced Valve
Post by: mann on January 02, 2019, 12:34:42 AM
I will give derlin a try . As far as blowing open the valve seems to open easy but also slams shut fairly fast I suppose it could be blowing open to some degree . It doesn't stay open though I tried quite a few hammer strikes and it seems to want to shut. I will get a few different bits from the hardware store and open up the hole some more I'll go up to .050 also with a derlin poppet
Title: Re: Simplified Balanced Valve
Post by: rsterne on January 02, 2019, 01:12:08 AM
Mark, that is good news indeed.... I suspect that there will be some vent diameter above which you can no longer find a difference in the way the valve cycles.... Even my .457 cal Hayabusa functions fine (500 FPE! ) with just a 0.040" vent.... I know this is a different beast, but I would be surprised if you need to go past that diameter with your much smaller valve....

Bob
Title: Re: Simplified Balanced Valve
Post by: skorec on January 02, 2019, 04:05:35 AM
Wow
 I am just  thinking dummy way  haw to improve the SS balance valve and here is it already solved.

Bob , Probably shorter moving of valve popped  is compensating with larger area D  ? 
         I hope that  repairing our mistakes  at thinking may précising your  ideas.

Lloyds simplifying idea of vent hole insidev the stem  may decrease the price.   

Title: Re: Simplified Balanced Valve
Post by: Brian W Cook on January 02, 2019, 04:50:16 PM
Here is my version of a balanced valve i built almost 17 years ago.   If i was to build new version it would probably be a little prettier as i built the first one while working night shift .  It was a bit overkill for a .452 barrel that i mostly shot round balls out of .   I vented it through the stem to a relief cut up in the valve body .   I had a vent into the port on the first version but can’t remember what the differences were  if any .
Title: Re: Simplified Balanced Valve
Post by: rsterne on January 02, 2019, 05:19:08 PM
Thanks for that, Brian.... Unfortunately, I don't understand how it works....  :-[

Bob
Title: Re: Simplified Balanced Valve
Post by: shorty on January 02, 2019, 05:22:38 PM
Brian,
Tell us more about it.

Was it hard to seal? Did it have a declining shot string? How low of a pressure before it would just knock open and stay open?

All those kinds of questions.  :D :D ;D
Title: Re: Simplified Balanced Valve
Post by: Brian W Cook on January 02, 2019, 05:30:31 PM
Like most of the valves posted lately .
I finally found a file reducer for my pics .
Title: Re: Simplified Balanced Valve
Post by: lloyd-ss on January 02, 2019, 05:36:57 PM
Like most of the valves posted lately .
..........................
Your valve is from 17 years ago.  Just goes to show how hard it is to come up with an idea that REALLY is new. Nice work, Brian!
Lloyd
Title: Re: Simplified Balanced Valve
Post by: shorty on January 02, 2019, 05:37:48 PM
Brian,
That looks nearly exactly like the simplified valve Bob is proposing.

I know you said it was 17 years ago but, we all have to know how the valve performed. Most importantly, did it have a declining shot string and were you able to tune it for a large range of power with hammer strike.
Title: Re: Simplified Balanced Valve
Post by: rsterne on January 02, 2019, 06:53:59 PM
Yep, it looks very similar to the valve I just suggested in this thread.... It is not surprising that the idea has been tried before in PCPs.... just long before I got back into airguns.... Pretty much every kind of valve around was invented decades (if not centuries) ago....

I am also very interested in how it performed, and how you were able to tune the shot string.... although I realize that most Big Bore guys tune for maximum power on the first shot and live with the velocity declining after that.... Were you able to tune it for a bell-curve.... or did you even bother?.... I really appreciate you taking the time to share the photos.... and any other information you can remember....

Bob
Title: Re: Simplified Balanced Valve
Post by: oldpro on January 02, 2019, 06:58:27 PM
Like most of the valves posted lately .
I finally found a file reducer for my pics .
17 Years ago!!! Wow thats a shocker... Could you tell us the diameters of the two sections of the poppet (large end over seat and small end with Oring) Did it work ok and were you able to tune it at all via hammer strike? Also what is the stem diameter?
Title: Re: Simplified Balanced Valve
Post by: rsterne on January 02, 2019, 07:09:07 PM
I was curious about that as well, Travis.... but scaling from the photos tells us that the balance chamber is twice the stem diameter (28mm and 14mm on my screen).... and the seat (which is tapered) is roughly 1.2 - 1.4 times the diameter of the balance chamber (33-40mm depending on where on the taper it seals)….That would make the balance chamber diameter between 70-85% of the seat diameter....

Bob
Title: Re: Simplified Balanced Valve
Post by: oldpro on January 02, 2019, 07:09:58 PM
Here are some measurements from Dons valve and as you can see the ratios are about what I’m suggesting.
Title: Re: Simplified Balanced Valve
Post by: PakProtector on January 02, 2019, 07:26:10 PM
Thanks for the PIX there Travis...just gave me an idear on keeping the balance chamber pressurized to lower risk of hammer bounce. Put the stem port just inside the body's stem bearing when it is closed. Kick it open, and flow to the balance chamber can happen, once it is closed, it will bleed rather more slowly through the stem/body bearing clearance. Thanks!
cheers,
Douglas
Title: Re: Simplified Balanced Valve
Post by: rsterne on January 02, 2019, 07:30:51 PM
Douglas, the vent hole in the Cothran valve is inside the exhaust port when the valve is closed, not back inside the valve body guide hole.... at least from my recollection.... I'm sure Travis can confirm, one way or the other.... Don uses a "leaky check valve" arrangement inside the very large diameter (0.175") stem, to maintain pressure inside the balance chamber and help prevent hammer bounce....

http://www.cothranmachine.com/PowerHouse%20Valve%20from%20October%202013.pdf (http://www.cothranmachine.com/PowerHouse%20Valve%20from%20October%202013.pdf)

Looks like you can see the vent centered in the exhaust port with the valve closed in that photo.... Also note that the valve seat is much smaller than the OD of the flange on the poppet where Travis is measuring it.... you can see the indentation on the seat washer....

Bob
Title: Re: Simplified Balanced Valve
Post by: oldpro on January 02, 2019, 07:56:15 PM
We can look at it another way also there are two areas of the SS valve the small end and large end of the poppets the small being .285 and large .352 that gives us .03352 square inches of area holding the valve closed or roughly a rod with a diameter of .206
Title: Re: Simplified Balanced Valve
Post by: PakProtector on January 02, 2019, 07:57:53 PM
Absolutely Bob, I did see that as you described...:) but that is what I was staring at when I came up wid it...LOL

In any case, I am going to get me a sack of wee drill bits and some stem material and likely have a go.
cheers,
Douglas
Title: Re: Simplified Balanced Valve
Post by: Brian W Cook on January 02, 2019, 08:00:46 PM
The port on mine is around .550 tapering to .375 going up into the barrel . The piston is .375 .    It was a pain to getting it to seat filling from empty.   I have a really long string of shots recorded somewhere that ended in the last shot only going 150 fps .  Using .452 rb. I’ll track that down
Title: Re: Simplified Balanced Valve
Post by: mann on January 02, 2019, 08:15:06 PM
Drilling threw the peek was harder to do than the stem . By putting the vent back into the body you could control the rate it exhausts the pressure off
Title: Re: Simplified Balanced Valve
Post by: oldpro on January 02, 2019, 08:40:03 PM
The port on mine is around .550 tapering to .375 going up into the barrel . The piston is .375 .    It was a pain to getting it to seat filling from empty.   I have a really long string of shots recorded somewhere that ended in the last shot only going 150 fps .  Using .452 rb. I’ll track that down
Thank You Brian!
Title: Re: Simplified Balanced Valve
Post by: rsterne on January 02, 2019, 08:43:31 PM
You lost me, Travis.... The SS Valve has two areas pushing the poppet towards the seat (0.285" and 0.352" on your valve), plus one area pushing it away from the seat (0.375")…. When the valve is closed that gives the following....

( (0.285 x 0.285) + (0.352 x 0.352) - (0.374 x 0.375) ) x PI/4 = 0.0506 sq.in.... just a whisker bigger area than a 1/4" rod.... The cracking force is therefore reduced to 52% of what it a conventional valve with a 0.352" seat would take (area = 0.0973 sq.in)....

Brian, thanks for the dimensions.... Is it the seat that measures 0.550" at the sealing diameter, or is that the exhaust port diameter?.... Did you have a spring inside the balance chamber to aid in initial sealing?....

Bob
Title: Re: Simplified Balanced Valve
Post by: jackssmirkingrevenge on January 03, 2019, 09:47:46 AM
Your valve is from 17 years ago.  Just goes to show how hard it is to come up with an idea that REALLY is new.

I know that feeling, spent years trying to perfect a pop-off type valve for an automatic airgun only to find out it was patented in 1927 (https://patents.google.com/patent/US1743576?oq=air+machine+gun)...
Title: Re: Simplified Balanced Valve
Post by: Brian W Cook on January 03, 2019, 12:02:22 PM
I checked the valve out a bit . The poppet OD is .550 and the port is close to .500 .  I tapered that to the .375 going to the barrel . The return spring was 250 OD .030 wire. 
It is “sticky” as built .   
I used a less than slick bronze bushing for the piston to operate in because it was handy.
To do it again i would use reservoir tubing with a larger inside diameter to inhance the air flow around the valve and use a slick material for the cylinder.   
Title: Re: Simplified Balanced Valve
Post by: Brian W Cook on January 03, 2019, 12:33:53 PM
I dug my one and only shot string out of my tool box .   
This started out at 3000 psi using close to 21 ci of air . I think the 746 FPS first shot can be blamed on sticktion
Title: Re: Simplified Balanced Valve
Post by: rsterne on January 03, 2019, 01:11:14 PM
Thanks for the additional dimensions, Brian, I am trying to figure out what the sealing diameter of the poppet is.... Do you think it seals near the OD, the ID, or pretty much all the way across the seat (which would by deduction be 0.025" across)….

That shot string, other than the first shot, is continuously falling.... Did you attempt to tune for a bell curve by reducing the hammer strike, or is that basically tuned for maximum velocity on the first shot?....

One other thing.... looking at the first photo you posted, the vent hole appears to be about 1/3 the diameter of the 3/16" stem, ie about a 1/16" hole.... Does that sound right, and is that the diameter all the way through, or did you have a smaller "metering" section anywhere?....

Bob
Title: Re: Simplified Balanced Valve
Post by: Brian W Cook on January 03, 2019, 02:27:19 PM
Yep that was a .062 hole .  Was a bugger drilling that far in the O1 stem .   Using some measurements of the hammer i figured it weighed 175 grams and i was using a .625 od by .062 wire spring with maybe 1-1/4 of stoke.
The main reason i never shot it anymore was its reservoir is made out of 1.25 x 1” id 6061 tube.   
Measuring the valve it’s close to .530 seat diameter.   
Title: Re: Simplified Balanced Valve
Post by: rsterne on January 03, 2019, 02:42:17 PM
Again, thanks for the information.... It turns out that your 0.375" balance chamber is exactly half the area of the 0.530" valve seat.... Time for me to head to the shop and finish off my new valve, which has exactly the same proportions....

Bob
Title: Re: Simplified Balanced Valve
Post by: oldpro on January 03, 2019, 02:44:31 PM
I dug my one and only shot string out of my tool box .   
This started out at 3000 psi using close to 21 ci of air . I think the 746 FPS first shot can be blamed on sticktion
I hope its not stiction thats what were trying to work around. Brian you are ahead of your time were just catching up!
Title: Re: Simplified Balanced Valve
Post by: Brian W Cook on January 03, 2019, 03:02:56 PM
I guess the most obvious thing would have been the lack of hammer bounce . Those last 15 shots would be impossible for a conventional poppet valve .   
I wish all of this internet connectivity was available back in 1986 when i was taking machine shop classes at night with full intentions of building a airgun to kill a deer with .   
Title: Re: Simplified Balanced Valve
Post by: oldpro on January 03, 2019, 03:32:47 PM
I guess the most obvious thing would have been the lack of hammer bounce . Those last 15 shots would be impossible for a conventional poppet valve .   
I wish all of this internet connectivity was available back in 1986 when i was taking machine shop classes at night with full intentions of building a airgun to kill a deer with .
No doubt!!! The things we could have done.
Title: Re: Simplified Balanced Valve
Post by: PakProtector on January 03, 2019, 05:07:33 PM
No doubt!!! The things we could have done.

Like buying Ford stock at $1.25/share. Then I could just retire, build my machine shop and learn how to make the most of it...:)
cheers,
Douglas
Title: Re: Simplified Balanced Valve
Post by: rsterne on January 03, 2019, 10:25:39 PM
I finally got back into the shop today and finished the new valve.... Here is the front end, showing the perforated mounting wheel for the thimble....

(http://i378.photobucket.com/albums/oo221/rsterne/Hayabusa%20PCP/Hayabusa%20224%20New%20Valve_zpsvof6r32i.jpg) (http://s378.photobucket.com/user/rsterne/media/Hayabusa%20PCP/Hayabusa%20224%20New%20Valve_zpsvof6r32i.jpg.html)

The thimble is free to move radially about 0.020" where it fastens to the center of the wheel, so that it can self-align with the poppet.... The back end has a much larger port than the previous valve.... You can see the vent in the stem down inside the exhaust port....

(http://i378.photobucket.com/albums/oo221/rsterne/Hayabusa%20PCP/Hayabusa%20357%20New%20Valve_zps82u60mav.jpg) (http://s378.photobucket.com/user/rsterne/media/Hayabusa%20PCP/Hayabusa%20357%20New%20Valve_zps82u60mav.jpg.html)

The throat is 3/8", and the stem is 1/8", so the area is the equivalent of a hole measuring 0.354", or almost bore area for the .357 cal and larger than all the other calibers that can fit on my Hayabusa Mk.II…. The exhaust port is 0.328", and the transfer port for the .357 will be the same size.... For the smaller calibers I will match the transfer port to the caliber.... The OD of the transfer port has increased to 7/16", so I had to drill the hole in the main tube out to match that....

On first assembly I had a small leak, so I took the valve apart, ran a 1/2" end mill (by hand) up against the seat, undercut the PEEK poppet by 3 deg. so that it only touches around the outer edge, and then lapped it with Solvol Autosol, cleaned everything and then burnished the poppet against the seat.... It sealed up just fine.... I started at 500 psi, there were no issues getting it to seal, and I dropped the hammer down the tube a few times to get it to burp.... It still wasn't leaking, so I filled it to 1000 psi, then 1500, 2000, 2500 and finally 3000 psi, which is the MSWP of this PCP.... Each time I dropped the hammer down the tube to fire the valve, and as expected as the pressure increased it took more hammer strike to get the valve to "pop".... There was no tendency for the valve to burp at pressures over 1000 psi, just a nice clean pop, and if I launched the hammer a bit harder, a very loud "BANG".... I am delighted that the valve seals up fine, and look forward to getting the gun built up so that I can test further....

I will be building a new SSG for this gun, it never had one.... Once that is done I will be able to find out how tuneable the valve is.... I have my fingers crossed....

Bob
Title: Re: Simplified Balanced Valve
Post by: mann on January 03, 2019, 10:41:47 PM
Nice work Bob looking forward to hear about some testing
Title: Re: Simplified Balanced Valve
Post by: oldpro on January 03, 2019, 10:46:29 PM
 Fingers crossed I hope hope hope it works and has no stiction or tendency to blow open. I really want it to work big time.
Title: Re: Simplified Balanced Valve
Post by: Hobbyman2007 on January 03, 2019, 10:51:05 PM
Now you’re getting somewhere Bob. Can’t wait to see the results . I’m still trying to figure out how to make the thimble stationary in an Evanix valve housing . I’ll be sticking to close to 70% ratio to start and work my way from there , using Delrin until I prove it works .
Title: Re: Simplified Balanced Valve
Post by: triggertreat on January 03, 2019, 10:57:37 PM
Fingers crossed I hope hope hope it works and has no stiction or tendency to blow open. I really want it to work big time.


Best of luck my friend!  Many including myself are hoping you have major success here.
Title: Re: Simplified Balanced Valve
Post by: rsterne on January 03, 2019, 11:08:47 PM
No tendency to dump with a wide variety of "flung" hammer strikes.... more force = louder bark, and only one of them.... I actually have quite a few things to do before I can test, I have to mill out the receivers for the larger TP, make that new TP plus an SSG, and hope I guess right on the hammer weight and stroke....

Bob
Title: Re: Simplified Balanced Valve
Post by: oldpro on January 03, 2019, 11:11:38 PM
No tendency to dump with a wide variety of "flung" hammer strikes.... more force = louder bark, and only one of them.... I actually have quite a few things to do before I can test, I have to mill out the receivers for the larger TP, make that new TP plus an SSG, and hope I guess right on the hammer weight and stroke....

Bob
any chance you could test with a loaded hammer?
Title: Re: Simplified Balanced Valve
Post by: rsterne on January 03, 2019, 11:26:00 PM
I may be able to.... but my question would be why?.... An SSG or SSS with the hammer in free-flight is so much better for not bouncing, preloaded hammers have pretty much gone the way of the dodo, at least for me.... The exception is big bores where I couldn't get enough hammer strike and had to have preload.... Hopefully, the balanced valve will make that a thing of the past....

Bob
Title: Re: Simplified Balanced Valve
Post by: oldpro on January 03, 2019, 11:31:57 PM
I may be able to.... but my question would be why?.... An SSG or SSS with the hammer in free-flight is so much better for not bouncing, preloaded hammers have pretty much gone the way of the dodo, at least for me.... The exception is big bores where I couldn't get enough hammer strike and had to have preload.... Hopefully, the balanced valve will make that a thing of the past....

Bob
To see if a loaded hammer will cause Ill effects as this is what most people will do.
Title: Re: Simplified Balanced Valve
Post by: rsterne on January 04, 2019, 01:19:49 AM
If I can find a tune that is below the plateau and a spring that will allow some preload, I will try that.... Just preloading if you are already on the plateau will tell you nothing.... as that is exactly how you tune for hammer bounce with any valve.... First of all I want to see if I can get it to shoot properly, before trying to intentionally make it act up....

Bob
Title: Re: Simplified Balanced Valve
Post by: MJP on January 04, 2019, 04:09:11 AM
You guys have been busy.  :D
Not that I have been idle, just coming to a way different approach to this airgun deal but that is going to be another topic on a some other day.  ;)

The most problems in this type balanced valves is the machining all the parts consistent and on same rotational axis, so that no binding occures.
After that it's just finding the right proportions for balancing.
The more balanced it is the less bellcurve there will be.

I personally can't figure the use of a bellcurve other than hunting off tethered.
But why not just use a bottle gun and reg?
And for a bench gun why bother to make a valve with other characteristics than consistency and power?
Velocity can be tuned with a regulator.
Just my 2C

Marko
Title: Re: Simplified Balanced Valve
Post by: oldpro on January 04, 2019, 07:39:04 AM
You guys have been busy.  :D
Not that I have been idle, just coming to a way different approach to this airgun deal but that is going to be another topic on a some other day.  ;)

The most problems in this type balanced valves is the machining all the parts consistent and on same rotational axis, so that no binding occures.
After that it's just finding the right proportions for balancing.
The more balanced it is the less bellcurve there will be.

I personally can't figure the use of a bellcurve other than hunting off tethered.
But why not just use a bottle gun and reg?
And for a bench gun why bother to make a valve with other characteristics than consistency and power?
Velocity can be tuned with a regulator.
Just my 2C

Marko
Your correct Marco I’ve made 5 versions of this valve with different ratios and the further from non balanced it got the less stable and lower ability it got to tune it and I expected that the biggest issues are these. Is stiction going to happen and if it does the further from non balanced it gets the worse the effect will be the other problem is adjustablness unregulated as this will be where most people building big bores will need some type of adjustability and third and most important and a thing that happened to me when the ratio was over 70% I could bang the buttstock on the ground (not hard) and make the gun go off so if this works and doesn’t have these issues then I think it’s a good change. I suspect though threw my own testing to get any adjustment the ratio can’t be higher than 60% and to keep enough force to keep it closed safely well that’s also the same ratio. We will see I’m building my version today using those parameters
Title: Re: Simplified Balanced Valve
Post by: rsterne on January 04, 2019, 12:45:40 PM
An SSG should prevent you from being able to bang the gun around and make it go off, because you would have to hit it unbelievably hard to overcome the preload on the spring.... Having some preload on the spring, and the closer the valve is to balanced, the worse that would be, I would think.... A 60% ratio of diameters on this valve produces exactly the same amount of balancing (36% less hammer strike) as an 80% ratio of diameters on an SS Valve, so I can understand you being happy with that.... I'm just greedy because of the high powered guns, that are so hard to cock, that I am currently converting.... hence why I am looking toward that 50% reduction (70% diameter) on both types of valves....

Even with a Big Bore I like to have a small bell-curve, because I want to have 2-3 shots within a very narrow ES.... and it usually isn't possible to tether one while hunting.... If you only shoot at paper, then tethering is a no-brainer, regardless of caliber.... High power for a give caliber and regulation without a tether is generally not possible because you need to run high pressure (4500 psi bottles help there), and need a large plenum.... Again, you need a bell-curve when you run unregulated.... Most of my varmint rifles are tuned for a shallow bell-curve to give a few shots within a 1-2% ES off tether, which has the added advantage of putting your tethered tune just on the high pressure side of the peak velocity.... That makes the gun more efficient so you use less air.... Having said that, the rifles I shoot the most are regulated, but I still have a few unregulated PCPs that get a lot of use because they are so small and light by comparison to a bottle gun….

Bob
Title: Re: Simplified Balanced Valve
Post by: MJP on January 04, 2019, 03:46:22 PM
Well you have the luxury of hunting with airguns. I'll just grab Sako .222 or Valmet 412 shotgun if I go hunting.

Try adding a "sail" on the poppet and you can get some bellcurve on simple balanced valve.
It'll blow open but closes pretty fast with flow helping the closing.

Marko
Title: Re: Simplified Balanced Valve
Post by: rsterne on January 04, 2019, 11:11:01 PM
Not sure why I would want to add a "sail" and restrict the flow though a valve on a Big Bore.... when I am striving to get the most I can out of the design.... but I suppose that is an option if I can't get a bell-curve like I did with my last SS Valve.... Today's progress....

The valve is still holding air fine after 24 hours, so I guess I got the leak fixed.... I spent the day today making/modding the rest of the parts to assemble the .357 version of my Hayabusa Mk.II using this new valve.... The first thing to do was to modify the receiver to accept the new 7/16" OD transfer port, and then drill out the port in the receiver to 0.328" to match the exhaust port in the valve and make the new transfer port from a piece of Delrin rod.... I then milled out the barrel port, leaving it 0.280" wide but increasing the length to 0.380" and blending that into the diameter of the transfer port.... This insures that the barrel port is at least as large as the transfer and exhaust ports, and also the same area as the chamber minus the bolt probe.... The ports are now all 0.328", compared to the 0.281" they were previously....

I have two hammers for this version of the Hayabusa…. The .224/.257 hammer weighs 123 gr. including cocking handle, and had a stoke of 1.2".... The .284/.308/.357 hammer weighs 147 gr. including cocking handle, and had a stroke of 1.45".... The new valve is 0.10" further back in the tube, so I lose that much stroke, and I decided to try the smaller hammer, even though the valve is larger than the .357 valve I had before.... I am confident that the balanced valve will at least make up that much difference.... I had a look at all the hammer springs I have to choose from, and decided to use the original spring from the .357 for my initial testing.... It is a McMaster Carr spring that is 3" long, 0.36" OD, made from 0.051" wire and rated at 15 lbs/in.... although once I set it, the length decreased by 0.1" and the rate was only 14.1 lbs/in.... The .357 originally took about 23 lbs to cock with this spring, at the 1.45" cocking distance.... With the SSG, using this spring, I have set the preload at 0.30" (4.2 lbs), and with a small gap between the SSG and hammer, and the new 1.10" cocking distance, the maximum cocking force will drop to about 19 lbs.... I suspect this will still be more hammer strike than I need for the new balanced valve, but I have two 3" springs with lower spring rates, of 0.047" and 0.049" wire, to reduce the hammer strike further if required.... I also have some 3.5" springs, but the spring rates are similar, and I have enough cocking distance without reaching coil bind with the 3.0" springs, so unless I need to increase the cocking distance, I should be able to stay with the 3.0" springs.... Here is what the new SSG looks like....

(http://i378.photobucket.com/albums/oo221/rsterne/Hayabusa%20PCP/Hayabusa%20357%20New%20SSG_zpsm7lifdbl.jpg) (http://s378.photobucket.com/user/rsterne/media/Hayabusa%20PCP/Hayabusa%20357%20New%20SSG_zpsm7lifdbl.jpg.html)

If I end up needing a heavier hammer with more stroke, I can revert to the other one I have.... but for now I will use this one from the .224/.257 version....

(http://i378.photobucket.com/albums/oo221/rsterne/Hayabusa%20PCP/SSG%20with%20257%20Hammer%20and%20TP_zpsfxwjeytc.jpg) (http://s378.photobucket.com/user/rsterne/media/Hayabusa%20PCP/SSG%20with%20257%20Hammer%20and%20TP_zpsfxwjeytc.jpg.html)

You can see the new, larger transfer port in that photo as well.... This is as big as I can go with the current valve and bolt probe design, it is 92% of the caliber, at 0.328".... I put the .357 barrel into the receiver before dinner.... and tomorrow I hope to finish the assembly and test this new valve in the .357 Hayabusa….

Bob
Title: Re: Simplified Balanced Valve
Post by: rsterne on January 05, 2019, 05:14:10 PM
Before removing the trigger group and stock from my .457 Hayabusa Mk.III (those are shared between all the versions), I thought I would perform a test to see if "stiction" was an issue with the SS Valve I recently built and installed in it.... The gun has been sitting for weeks, and still had over 3200 psi sitting in it, but I topped it up to its usual 3600 psi fill and fired 4 shots through the Chrony…. They were 962, 973, 978 and 973 fps.... That means the first shot was less than 2% below the peak, so stiction is NOT an issue for that valve....

I then assembled the .357 Hayabusa Mk.II, using the new simplified balanced valve I have been working on.... The first shot was with the 0.051" spring with 4 turns of gap, and with a 131 gr. bullet it screamed across the Chrony at 955 fps.... That is more power than I have ever had before, which is attributable to the larger port, of course.... I backed out the gap a couple of turns at a time, and the velocity didn't drop until I was 12 turns out, at which point it tanked to 275 fps.... I then reduced the gap to zero, and the gun was only slightly louder than with 10 turns of gap, and absolutely NO sign of hammer bounce or machine-gunning.... So, the initial test was successful on every count but one.... the valve acts like a Cothran valve, either it cycles or it doesn't....

I took the SSG apart and installed the lightest spring I have of that size, made from only 0.047" wire, with a spring rate of only 11 lb/in.... The velocity was essentially unchanged (a few fps less), and it still showed no signs of adjustability.... With 10 turns of gap it was 950 fps, 940 fps at 11 turns, and 270 fps at 12 turns of gap.... I spun the adjuster back in to 4 turns of gap and fired a few 154 gr. bullets through the Chrony and they were 892-894 fps (273 FPE).... Did I mention that this valve is INCREDIBLY STABLE for velocity?....  ::)

So, I have drained the air from the reservoir, and will be pulling the valve and drilling the vent out to 0.040" to see if that makes any difference.... If not, then I will go all the way to 0.047", which is the size of the hole through the stem.... Bottom line at the moment is that I am quite pleased with the new valve, it does 90% of what I wanted.... I have increased the size of the valve throat from 0.328" to 0.375", and the poppet from 3/8" to 7/16".... The hammer weight has been reduced from 145 gr. to 122 gr. (and can obviously be much less) and the hammer stroke from 1.45" to 1.09" (much less with the large SSG gap)…. The cocking force has gone down from 23 lbs. to about 9 lbs.... The shot cycle sounds crisp, with no sign of hammer bounce.... The ONLY thing I have not achieved so far is tunablity…. We'll see if that can be achieved or not.... If not, at least I have still produced a simpler balanced valve that yields big power for low hammer strike....

Bob
Title: Re: Simplified Balanced Valve
Post by: PikeP on January 05, 2019, 07:23:58 PM
If tunability is an issue I would attempt a 5/32" to an 11/64th" valve stem...I promise it will help (keeping stem od at .125" in throat) close the valve for a tunable range without sacraficing too much of the reduced hammer energy requirements to operate the valve...jmo! It certainly wont go back up to unbalanced valve conditions...instead of sailing the poppet you do the stem where air flow is negligible and virtually nonexistent...
Title: Re: Simplified Balanced Valve
Post by: rsterne on January 05, 2019, 10:13:56 PM
Increasing the stem diameter would certainly add closing force to the valve.... However, unless you turn down the part in the throat, you would definitely lose airflow through the valve.... I'm not as confident as you are that increased closing force will make the valve all that more tuneable....

This valve is obviously "blowing open" like a Cothran valve does.... I tried increasing the vent diameter from 0.032" to 0.040" (a 56% increase in area, possibly double the flow because of friction affects)…. and it made NO difference to the way the valve operated.... Same velocity, same cliff, at the same SSG gap.... I then made an MDS hammer to replace the steel one.... I kept the same 1.09" stroke but the hammer with handle weighs 1/3 as much, 42 g. instead of 123 g.... The only way the gun would fire with the light 0.047" spring was with the SSG gap set to zero.... With just 1/2 turn of gap the velocity dropped to under 200 fps.... BTW, as Travis requested, I tried some preload with this setup, by turning the SSG in a couple of turns, to give 4 lbs. of preload.... The velocity remained the same as with zero gap, the bark was a little louder, and there was still no sign of hammer bounce....

I tried the original 0.051" spring with the light hammer and it would fire properly (955 fps) with 1 turn of gap, but at 2 turns of gap it was inconsistent in velocity, shots varying from 450-950 fps.... (I saw similar things with the Cothran valve when it was right on the edge of the cliff, the ES went through the roof.... So, for that matter did the original SS valve I got from Travis, which had only about 100 fps of adjustability and then a cliff).... Anyways, I can either use the light hammer and the heavy spring with 1 turn of gap on the SSG.... or the heavy hammer and the light spring with about 8-10 turns of gap.... With the light hammer and heavy spring set to 1 turn of gap I checked the pressure drop.... With the tiny tank fitted my total volume is only 6.6 CI (108 cc) way too small for proper performance at 265 FPE (0.4 cc per FPE)…. Filled to 3000 psi, the pressure drop was 498 psi (measured with a digital gauge) for a shot of 956 fps with the 131 gr. bullet (266 FPE)…. That works out to 1.17 FPE/CI.... pretty respectable for this much power with way too small a plenum.... The normal volume available for a shot is 28 CI, which means that I should only see a pressure drop of about 120 psi instead of 500, and with the average pressure increasing from 2750 to 2940 the FPE should increase nicely as well, hopefully with an increase in efficiency too....

Obviously, neither current hammer solution is the best.... The next time I have the valve apart I will drill the vent out to 0.047", even though I don't expect that to make any difference in the tunability.... The next step is to get the hammer weight somewhere in the middle, so that I can use the light spring (hopefully) but with about 4 turns (0.20") of gap before it falls off the cliff.... To do that, I  will make a brass or steel insert for the MDS hammer, drill it out and press in the insert.... I think about double the weight I am now, which is 2/3rds what I started with, should be about right, but that is really just a guess, so I will try and hit about 80-85 g.... With 3 springs to choose from, I should be able to get it about right....

So I have accomplished all the goals, except tunablity…. This valve would be a sweet setup tethered to an adjustable regulator.... Since this version of my Hayabusa will primarily be shot tethered, I will likely leave this valve in the gun until I can come up with something better.... The alternative would be to make an SS valve with the same proportions and try that.... Before I go that route, I think I will fit the .224 cal barrel and receiver to this gun and see what happens, and what changes I might have to make for that huge caliber change.... If that works out OK, then I will complete the conversion for the other 3 calibers, .257, 7mm and .308.... Lots of fun ahead....  ;)

Bob
Title: Re: Simplified Balanced Valve
Post by: PakProtector on January 06, 2019, 10:06:57 AM
Bob, I would suggest a more significant reduction in hammer mass. Long ago whilst engaging in such a discussion with you( around the time Scott had created the first nylon Marauder hammers), you had mentioned that lighter hammers make the curve peakier, and workable over a narrower pressure range. I have the SS valve in my Flex, and it is going to get a lighter hammer. I am having issues getting the increasing part of the curve with the otherwise stock components...

Or maybe I am just talking through my hat...LOL
cheers,
Douglas
Title: Re: Simplified Balanced Valve
Post by: shorty on January 06, 2019, 11:32:47 AM
It's post like these that encourage me to learn more and more ( or at least I think I learn ). Thank you Bob. It has also made me get off my a## and get into the garage to do some work ( another big plus)

The biggest eye opener to me is that we do not even know how a conventional valve creates a bell curve or self regulate (or atleast I didn't fully understand until this morning " I think").

It is my thought now that in a conventional valve, a bell curve or self regulating is due to the hammers loss of energy from cracking force as lift is the remaining energy of the hammer after it has made it's collision.

Using that thought process reducing the hammer weight still may not generate a tune-able balanced valve because so LITTLE energy is lost to the collision of hammer and valve stem narrowing the lift control. As we see in a cothran valve.

Something else needs to regulate the lift and closing force after a balanced valve has been cracked.

I really think a stepped valve stem can do this. Since it does not affect cracking force, it should give control over the remaining hammer energy to control the lift and close the valve quickly.
While making the valve stem, all I could think was it probably could have been alot easier to use a shoulder bolt and grind off the head.

Thanks again as this really did get me off the couch. Hopefully I can get this valve stem into my test jig this afternoon and test at low pressures.

 Ohh yea, I got a new phone to take beautiful pictures now ( thanks Santa ).
Title: Re: Simplified Balanced Valve
Post by: rsterne on January 06, 2019, 12:45:55 PM
Douglas, you may have missed that I tried an all MDS hammer which only weighs 42 gr. including the cocking handle.... However, one thing hit me in the middle of the night.... The new hammer is cylindrical, with no cutouts, and I may have a partial vacuum developing behind it on firing.... First order of business today is to vent the rear cap....

Tim, the bell-curve is developed by the valve being unable to open fully against high air pressure, and able to open more as the pressure drops.... The same "math" applies to a balanced valve, if you can build one that doesn't "blow open" by itself once cracked.... The SS valve does that, and also the separate piston balance valves (3 piece poppet design) built by Lloyd and AAA.... Balanced valves occupy a space in between spool valves, which once cracked stay open until the tank is empty, and a conventional valve.... As always, when developing something new or different (to me, as this has been done before), the devil is in the details....

I am absolutely DELIGHTED that this thread has managed to get some of you guys into the workshop and experimenting.... Too many people still hold their cards close to their chest when they have a success, and refuse to share it.... I can understand that if you are trying to make a living building airguns or parts for them.... but for the rest of us, if everyone did that, we would never be where we are today.... When I got back into airguns over a decade ago, I was appalled by the lack of good information, and how nobody wanted to share what they knew.... I made it my goal to change that.... These forums are a place to discuss your ideas and share them.... I'm glad that is finally spreading to balanced valves.... It's about time, IMO....

Bob
Title: Re: Simplified Balanced Valve
Post by: PakProtector on January 06, 2019, 03:49:12 PM
Hey Bob, I did indeed miss that light hammer you already tried.

The basic 'thing' for me is, 'it isn't working as expected'...so why?

The evidence you present so far says that the closing force is not what you expected; the valve comes consistently open for a full power shot with hammer energy varying by at least a third. It also seems to be unaffected by at least a 50% difference in momentum.

So we have an opening/closing profile v time that is of similar lift and duration nearly no matter the input. I don't think the shape is all that important now. With the balance chamber vented to throat pressure, the closing force should rise dramatically. You made it bigger by 50% and it appeared to close no faster.

So...at low energy the opening falls off a cliff and the lift profile shrinks dramatically in (likely) both lift and duration. What happens if the hammer gets even lighter, and the vent goes smaller instead of larger? It would seem to me that the low energy, low momentum hammer would kick open the valve for a short duration lift/close and the muzzle energy would be small. Increase it, and there is longer for throat pressure air to flow through a small hole and increase closing force...and with minimum momentum, the chance for the thing to close more closely tied to energy

I don't quite think abandoning the machinery time is ripe yet. I recall fondly the discussion across the PCP gate as you and Lloyd tied hammer energy and momentum to valve opening/closing. Looks more like a tuning operation...:)
cheers,
Douglas
Title: Re: Simplified Balanced Valve
Post by: MJP on January 06, 2019, 04:04:21 PM

I have told enough for those that can listen and understand basics that can build similar valves that I have made, I just don't make pictures and diameters available in open forum.

It's ticking me off that some of the manufacturers use forums as R&D and then make profit out of it, patenting someone's ideas!

Marko
Title: Re: Simplified Balanced Valve
Post by: PikeP on January 06, 2019, 04:11:12 PM
Shorty the primary force that creates a bell curve or tunable range is the area of valve stem. Once enough lift is created to get desired air gun velocities both sides of the poppet are fairly equal with pressure, that's why  balanced valves tend to stick open...you are unequalizing the pressure differential at valve open for reduced pressure on poppet during valve close...its the latter half of the valve event that determines if you have a tunable range or not...that being if the force against the stem is higher enough than the pressure differential at the poppet. It's very simple and such a small force but is required...that's why conventional valves operate so well and efficiently...its an elegant operation and simply removing the reference of some force against poppet is not going to yield desirable results without increasing closing force at the stem.
Title: Re: Simplified Balanced Valve
Post by: PikeP on January 06, 2019, 04:27:41 PM
Marko,

I would much rather have my ideas stolen and see man kind progress, than to keep secrets and see evolution impeded...
Title: Re: Simplified Balanced Valve
Post by: rsterne on January 06, 2019, 04:58:50 PM
First of all, let me address the hammer venting.... I did that and there was indeed some issue with the new lightweight MDS hammer, as I could use 2 turns more gap once I vented the space behind the hammer and still get stable "wide open" operation.... The original hammer had a waist and a groove between the side and the back, and there is a huge cocking slot in the side of the tube, so no problem.... However, the MDS hammer was cylindrical, and a good enough fit to get a partial vacuum developing behind it, partly because of the vastly faster lock time from the lower mass.... The partial vacuum acted on that lower mass as a brake as soon as it entered the "free flight" travel once the SSG was no longer pushing on it.... So, with the venting, I am within the range I want for SSG gap with the 0.051" wire spring.... However, I would like to use a lighter spring, so I have made and installed a 5/8" brass insert 1.5" long inside the MDS hammer.... It is drilled 3/8" for a depth of 1-1/4", just like the other hammers, so is interchangeable.... The total weight, including the cocking handle is 77 g.... so 1.8 times as heavy as the MDS only hammer, and only 63% of the weight of the original.... I have secured the insert with Loctite 638 (green) and it is curing at 120*F at this time, while I am refilling my SCBA tank....

(http://i378.photobucket.com/albums/oo221/rsterne/Hayabusa%20PCP/New%20Mk%20II%20Hammer_zpskkhbvoay.jpg) (http://s378.photobucket.com/user/rsterne/media/Hayabusa%20PCP/New%20Mk%20II%20Hammer_zpskkhbvoay.jpg.html)

Marco, you have stated before that you don't wish to have your ideas "stolen" and used for commercial purposes, and I respect that position.... However, IMO it hampers the development and advancement of PCPs, and that attitude from others involved in the sport when I first started was the reason that a decade ago I took the exact opposite approach.... I am trying to "lead by example", and thereby encourage the sharing of ideas openly and freely.... Have I had some ideas end up being used commercially?.... Absolutely, and for the most part with my permission and blessing, and no money in return.... Do I get upset when they are "stolen" and not acknowledged?.... You bet I do.... Does that stop me from sharing everything I can?.... Not on your life....

Quote
I would much rather have my ideas stolen and see man kind progress, than to keep secrets and see evolution impeded...

Mike, I agree 100% with that statement.... Forums, IMO are for the public sharing of information, in the desire to see progress....
Title: Re: Simplified Balanced Valve
Post by: Motorhead on January 06, 2019, 05:03:09 PM

I have told enough for those that can listen and understand basics that can build similar valves that I have made, I just don't make pictures and diameters available in open forum.

It's ticking me off that some of the manufacturers use forums as R&D and then make profit out of it, patenting someone's ideas!

Marko

Don't wish to share what you know or think you know ? ... SAY OFF PUBLIC FORUMS
Don't wish to enable others to think outside the box and become better system engineers ... DON'T CONTRIBUTE TO THOSE THREADS

If you have the funds, ability to come up with and PROVE a deign is worthy of a patent .... Good for you ! If you had friends helping along the way ... Good for them !

Just sayin ...
Title: Re: Simplified Balanced Valve
Post by: Hobbyman2007 on January 06, 2019, 05:26:21 PM
What’s stoping the valve stem from being the same diameter as the valve throat to transfer port . It can be tapered through the opening so that it doesn’t impede on the flow through the valve , yet act as a sail to close the valve faster . It would be fairly easy to bore out the front of the valve and add a sleeve to an already existing stem .
Title: Re: Simplified Balanced Valve
Post by: rsterne on January 06, 2019, 05:38:29 PM
Douglas, I think what is happening is that the balance chamber, which starts at atmospheric, and is brought up to pressure through the vent in the poppet, is not getting enough air, soon enough, to prevent the valve from "blowing open".... Here is how I think the cycle is working, broken down into 4 stages....

1. The poppet has about 1/2 the force holding it closed that a conventional poppet of the same diameter, at the same pressure, would have.... This is the result of 450 lbs. of force holding the poppet against the seat, counteracted by 229 lbs. of force on the O-ring on the small end of the poppet trying to open the valve....

2. Once struck by the hammer enough to lift it clear of the seat and (nearly) equalize the pressure on both sides of the poppet, the 450 lbs. of force towards the seat largely disappears.... At that instant, before any air (or enough air) enters the balance chamber through the vent, you still have the 229 lbs. of force opening the valve, and it blows open.... If at the time the force on the large end of the poppet reaches essentially zero the pressure inside the balance chamber is 1500 psi, then you have about 115 lbs. trying to open the valve.... The larger the vent, the quicker the pressure in the balance chamber builds, and the sooner the "blowing open" stage ends.... However, there is a limit to how fast the air can make that trip from the exhaust port to the balance chamber, and that is the average speed of the air molecules at the ambient temperature.... We can assume that is 1650 fps, so it would take 1/12/1650 = 0.00005 sec (.05 mSec) for the pressure to have a chance of equalizing through a 1" long vent.... This is about the same time it takes for the pressure in the exhaust port (between valve seat and pellet) to reach ambient pressure as it fills with air, but the times are additive (in series), so the pressure in the balance chamber will always lag the pressure in the exhaust port by roughly 0.05 mSec.… It is during that brief instant the valve is "blowing open".... IMO....

3. Once the pressure in the balance chamber (nearly) equalizes with the pressure in the exhaust port (roughly 0.1 mSec after the valve cracks), there is now essentially zero force on the HEAD of the poppet (other than a bit of friction along the sides of it, which are shrouded by the thimble)…. However, there is, and has been since stage 2, a closing force equal to the pressure in the exhaust port times the area of the stem.... In the case of my 1/8" stem at 3000 psi, that is 37 lbs, call it 40 lbs. with the spring.... That force is available to stop the hammer, reverse it's travel, and start closing the valve.... Yes, a larger stem diameter would overcome the "blowing open" force sooner in the cycle, which is a good thing.... but for all the rest of the cycle it will require more hammer momentum to deliver the dwell we need to provide the necessary airflow for the shot....

4. As the poppet approaches the seat, at some point the flow through the gap exceeds the local Speed of Sound, and the flow chokes.... This is accompanied by at least a 47% pressure drop (a property of choked flow) across the head of the poppet.... This adds a minimum of 212 lbs. of closing force to that provided by the stem, so we have at least 250 lbs. of closing force at the very end of the cycle.... As the gap narrows further, the pressure differential narrows further, until the poppet makes contact with the seat.... During this time, the flow through the vent reverses, and the pressure in the balance chamber drops, until the valve closes, the pellet leaves the barrel, and we return to stage 1, ready for the next shot....

This is not the "gospel according to Bob", but I think it explains what is happening in this valve.... and why I feel that a smaller vent could lengthen the "blow open" cycle (by slowing the airflow through friction), but a larger one, once it is "big enough" can't really shorten it, because of the finite speed of the air molecules expanding through the vent....

Bob
Title: Re: Simplified Balanced Valve
Post by: rsterne on January 06, 2019, 06:21:23 PM
Mike, you are spot on that it is the force on the valve stem that creates the primary closing force.... Denis, this is the reason we don't use a valve stem equal to the throat diameter, or even close to that size, in conventional valves.... The closing force would be so great, and remember it is applied virtually the instant the pellet starts to move (that 0.05 mSec. delay as the pressure in the exhaust port rise to nearly reservoir pressure), that for almost the entire valve cycle we would have hundreds of lbs. stopping the hammer instead of tens of lbs.... Using my valve as the example, to equal the throat, the stem diameter (where it pierces the back of the valve body) would be 3/8" in diameter.... At 3000 psi, the closing force would be 331 lbs. instead of about 40 lbs.... Imagine how quickly that would slow a 3 oz. hammer, reverse its travel, and slam the valve shut.... All you would get is a "pop".... Try it with a conventional valve, and you will see why we use SMALLER stems, rather than larger.... We do that to reduce the required hammer strike for a given lift and dwell (ie airflow through the valve)….

Mike, you state:

Quote
its the latter half of the valve event that determines if you have a tunable range or not

As a "general statement" on PCP valves, I disagree, and here is why....

When the air pressure is greater, the hammer loses more of it's energy to crack the valve.... Its RESIDUAL energy and momentum is therefore less.... It is the residual energy that creates valve lift, and the residual momentum that creates dwell.... With more of the initial hammer energy "robbed" by cracking the valve, the closing (stem) force closes the valve faster, and you get less lift and dwell (they are, after all, interrelated)…. so you release less air, but that air is of higher pressure.... a quick, hard "smack" applied to the pellet....

As the air pressure drops, it is easier for the hammer to crack the valve, so it has more residual energy and momentum.... It opens the valve further, for a longer period of time.... so you release a large volume of air, but at lower pressure.... a longer, slower "push", but producing the same velocity, creating our typical bell-curve.... No bell curve, no potential to tune with hammer strike....

Specifically to this valve, however, if the valve is "blowing open" it is removing hardly any energy from the hammer (just enough to crack the valve, and that is half what it took previously)…. after that, I think it may be likely that the hammer is bouncing off the back of the valve body, and doing nothing to create lift and dwell.... The valve opens fully, (in this case I have allowed it to have about 0.20" of travel) and then eventually the closing force of the stem overcomes the (decreasing) lift of the balance chamber, and the valve closes.... It may or may not be hitting the hammer during that process, I don't know.... If we double the closing (stem) force, yes you will shorten the dwell, and therefore the valve cycle time.... That closing force will "catch up" to the decay in the "blow open" force sooner in the cycle....

If we made the valve stem (where it penetrates the valve body) the same diameter as the balance piston (5/16") then at the instant the valve cracks, and before the pressure in the balance chamber rises (my stage 2 above), the force on the stem closing the valve would equal the force on the balance piston opening it.... the force across the large end of the poppet is essentially zero, so the valve doesn't "blow open".... OK, we solved that problem.... However, 0.05 mSec later, once the pressure in the exhaust port and in the balance chamber equalize, we now have 229 lbs. force trying to close the valve instead of about 40 lbs.... You got rid of the blowing open, and replaced it with an impossible job for the hammer to overcome.... Is there a happy medium out there somewhere?.... Maybe.... If so, then this thread will have accomplished its original goal.... by travelling in an unexpected direction.... Isn't collaboration and brainstorming great....  8)

Bob
Title: Re: Simplified Balanced Valve
Post by: Hobbyman2007 on January 06, 2019, 06:56:17 PM
Ok , so what if the stem was say 1/2 the throat diameter just like the poppet and ballanced chamber being half or close to . Could that not get the the end of the cycle to shorten and hence be able to tune it with hammer strike ?
Title: Re: Simplified Balanced Valve
Post by: rsterne on January 06, 2019, 07:43:47 PM
OK, guys.... here is what happens with THIS valve when you change the outer stem diameter.... The data points are for 1/8", 3/16", 1/4" and 5/16" (which equals the diameter of the small end of the poppet)…. I assumed a valve spring force of 3 lbs....

(http://i378.photobucket.com/albums/oo221/rsterne/Hayabusa%20PCP/Balanced%20Valve%20Stem%20Diameter_zpsh7rmguk8.jpg) (http://s378.photobucket.com/user/rsterne/media/Hayabusa%20PCP/Balanced%20Valve%20Stem%20Diameter_zpsh7rmguk8.jpg.html)

The red line is the closing force in lbs. due to 3000 psi acting on the diameter of the stem that penetrates the valve body.... Note that the diameter in the actual throat, which gets in the way of the airflow, doesn't matter to the force, but you have to keep it at 1/8" to not restrict that flow.... The closing force is 40 lbs. with a 1/8" stem, rising to 232 lbs. with a 5/16" stem.... The force is being applied once the pressure in the balance chamber reaches 3000 psi, which should in theory be the case for 90-95% of the valve cycle.... The hammer momentum must overcome this force to produce the necessary dwell to produce the shot....

The blue line is the percentage of 3000 psi that the balance chamber must fill to, for there to be no further "blowing open" force, ie the net force on the small end of the poppet and the stem is zero.... There is some force blowing open the poppet until that pressure reaches 83% (~ 2500 psi) with a 1/8" stem, but only 33% (~ 1000 psi) with a 1/4" stem.... With a stem that equals the front (small) poppet diameter of 5/16" there should, in theory, never be a force causing the valve to blow open....

Any bets what the optimum stem diameter might be.... assuming we're on the right track here?.... Guesses?....

Bob
Title: Re: Simplified Balanced Valve
Post by: shorty on January 06, 2019, 08:19:19 PM
Very interested to know those numbers.

My guess was what I made to allow the valve to operate at a minimum pressure of 1000 psi with out jack hammering.

Balance chamber .29"
Poppet head .4"
Balance stem .25
Main stem .175"
Throat .26"

Opening force at 1000psi around 60lbs and around 180 lbs at 3000lbs
Closing force at 1000 psi  around 60 lbs and around 180 lbs at 3000lbs

That would be my guess as that's what I already built. Hope it's right.
Title: Re: Simplified Balanced Valve
Post by: Hobbyman2007 on January 06, 2019, 08:30:15 PM
Sorry Bob , I’m still trying to wrap my head arround the graph. But if I were to take a stab at it .... x marks the spot at just under .225” .
Title: Re: Simplified Balanced Valve
Post by: rsterne on January 06, 2019, 08:32:14 PM
Why would you have the main stem (the part in the throat) so large, at 0.175".... Will not that severely restrict the flow with a throat of only 0.26"....  ???

Bob
Title: Re: Simplified Balanced Valve
Post by: rsterne on January 06, 2019, 08:33:41 PM
Denis, the fact that the two lines cross at that point really doesn't mean anything.... it is just a function of the axis values I chose....

Bob
Title: Re: Simplified Balanced Valve
Post by: shorty on January 06, 2019, 08:35:24 PM
It is the easiest way to refine the balancing. I left it big on purpose because it is easy to remove more material than making a new stem. The hole through it is .098" so I can pull it down from .175" to a smaller size if I got it wrong.

Title: Re: Simplified Balanced Valve
Post by: PikeP on January 06, 2019, 08:42:46 PM
Another thought on valve operation. Slightly rendunant but a different take. A lot of the hammer energy goes into the 150~ lbs of force holding the valve shut until enough lift has pressurized the transfer plenum, the tiny remaining hammer energy we can look at as our tune range which is majorly influenced by what closing force there is...generally as little as 20 to 30 lbs is plenty pressure differential to get the job done...if that differential is reduced or removed the tunable range follows.

I'd keep the stem od at. 125" or even .115" in the throat / transfer plenum. I haven't sat down and performed any calculations on the pressure differentials and ideal stem OD in its bore, but it shouldnt be too hard to do.
Title: Re: Simplified Balanced Valve
Post by: rsterne on January 06, 2019, 08:59:14 PM
I tried the MDS hammer with the brass core.... With the 0.051" wire spring the velocity was normal with 9 turns of gap and zero with 10 turns.... I replaced it with the 0.047" wire spring and that required 2 turns less gap.... 7 turns was full velocity, 8 turns wouldn't fire, or barely fire....

I then tried both bullets from a 3000 psi fill at various SSG gaps from zero to 7 turns.... At zero gap I suspect the hammer is bouncing off the back of the valve, because the velocity was slightly less and it used a few psi less air than at 2 turns of gap.... At 2 turns of gap the FPE/CI was 0.83 with the 131 gr. bullet and 0.99 with the 154 gr.... At 4 turns that increased to 0.96 and 1.08.... At 6 turns of gap, I got 1.13 FPE/CI with the 131 gr. and 1.37 with the 154 gr.... At the lightest hammer strike that would give full velocity (955 fps with the 131 gr. and 894 fps with the 154gr.), which was 7 turns of gap, I got 1.17 FPE/CI with the 131 gr. bullet and an astounding 1.44 FPE/CI with the 154 gr. bullet.... Bear in mind I am still using the tiny tank with a total air reservoir of only 6.6 CI (108 cc)…. The FPE should increase with the 22 CI bottle fitted, and the efficiency may climb even higher.... To say I am blown away with getting over 1.4 FPE/CI at over 270 FPE would be an understatement....  :o

Bob
Title: Re: Simplified Balanced Valve
Post by: PikeP on January 06, 2019, 08:59:37 PM
Running calculations on the poppet vent show incredibly low flow...has anyone sat down and ran theoretical flow numbers into various vent sizes at the operating pressue? Would seem to me you'd want the vent sized properly to achieve equal pressure in roughly .5 millisecond to 1 ms, no?
Title: Re: Simplified Balanced Valve
Post by: rsterne on January 06, 2019, 09:00:58 PM
Quote
I haven't sat down and performed any calculations on the pressure differentials and ideal stem OD in its bore, but it shouldnt be too hard to do.

You're a better man than I am, Gunga Din.... Go for it !!!!

Bob
Title: Re: Simplified Balanced Valve
Post by: PikeP on January 06, 2019, 09:01:17 PM
Valves operating very well it's got to be right on the edge of being tunable...I think. Good work.
Title: Re: Simplified Balanced Valve
Post by: PikeP on January 06, 2019, 09:13:03 PM
Running some quick theoretical napkin math I get a chamber size of .2~ cc filling up in 1~ ms at 3000 psi with a .04" vent...would be nice to nail down a sensible formula that made vent sizing easy...
Title: Re: Simplified Balanced Valve
Post by: PikeP on January 06, 2019, 09:39:49 PM
Another interesting note. 1.4 fpe/ci translates to roughly 28% of the total energy being transferred to the pellet in the form of KE, which I've found scales through all calibers when operating efficiently near plateau.
Title: Re: Simplified Balanced Valve
Post by: rsterne on January 06, 2019, 09:47:19 PM
The balance chamber in my valve is 5/16" diam. x 0.25" stroke, plus the spring well, which is 1/4" diameter and about 1/4" deep, minus the volume of the spring wire.... However, once the poppet has lifted 0.200", the remaining chamber is only 5/16" diameter x 0.050", plus the spring/well.... My vent is 0.047" for nearly all of it's length (roughly 1") and 0.040" for a length of about 0.037" (less than 1 diameter)….

Using Lloyd's Internal Ballistics Spreadsheet, for the shots at 7 turns of gap I get a dwell of about 2.5 mSec. for the 1.4 FPE/CI shot with the 154 gr. @ 272 FPE, and about 2.6 mSec. for the 1.17 FPE/CI shot with the 131 gr. @ 266 FPE.... For the shots at 2 turns of gap, which produce the same velocity but use more air, the dwell is about 3.3 mSec, but the overall efficiency of the shot (and therefore the valve cycle) is down.... I have no explanation for the mechanism whereby the valve could have longer dwell and would be less efficient while producing no more FPE, however.... It is normal for a heavier bullet to be more efficient in extracting FPE from a given amount of air, of course.... At 1 mSec. into the shot, the bullet has only moved about 2" down the barrel (and at 0.5 mSec. only about 1/2").... so your estimate of 0.5-1 mSec. for the venting time should be OK....

Question, Mike.... Do you think drilling out the cross vent to 0.047" (same as the vent through the stem) will help?.... I guess it can't hurt....  ::)
In addition, I do agree that with approaching 1.4 FPE/CI, we must be getting close to being tuneable.... I hope....  ::)

Bob
Title: Re: Simplified Balanced Valve
Post by: Gippeto on January 06, 2019, 10:10:44 PM

Don't wish to enable others to think outside the box and become better system engineers ... DON'T CONTRIBUTE TO THOSE THREADS

Just sayin ...

Entitled people make me....

(https://cultura.estadao.com.br/blogs/marcelo-rubens-paiva/wp-content/uploads/sites/111/2013/12/Picture-43.png)

Title: Re: Simplified Balanced Valve
Post by: rsterne on January 07, 2019, 12:37:59 AM
Tim, I checked the force required to open, and get the same numbers as you, 60 lbs. @ 1000 psi and 179 lbs. at 3000.... However, as I mentioned before, the stem diameter (the stepped down part in the throat) and the throat diameter itself have nothing to do with the opening or closing force.... The closing force is from the diameter of the part of the stem that penetrates the valve body.... I get 49 lbs. @ 1000 psi and 147 lbs. at 3000.... I am completely confused by your comment that changing the 0.175" diameter of the stem is the "easiest way to change the balancing".... Please explain?....

There is also, of course, the transition force that is the cause of the valve trying to blow open.... You have certainly used a large vent, which should help.... and the large closing force from the 0.25" OD of the stem may very well overtake any residual blow open force from the poppet.... providing it doesn't also overpower the ability of the hammer strike to create the necessary dwell.... Good Luck with your building and testing....

Bob
Title: Re: Simplified Balanced Valve
Post by: MJP on January 07, 2019, 01:16:05 AM

I have told enough for those that can listen and understand basics that can build similar valves that I have made, I just don't make pictures and diameters available in open forum.

It's ticking me off that some of the manufacturers use forums as R&D and then make profit out of it, patenting someone's ideas!

Marko

Don't wish to share what you know or think you know ? ... SAY OFF PUBLIC FORUMS
Don't wish to enable others to think outside the box and become better system engineers ... DON'T CONTRIBUTE TO THOSE THREADS

If you have the funds, ability to come up with and PROVE a deign is worthy of a patent .... Good for you ! If you had friends helping along the way ... Good for them !

Just sayin ...

And then you all are wondering why some people leave, and don't write anymore.
I hate stupid people, people with narrow minded way of thinking. I have shared my thoughts more than once, just to be told it's not how things work. Well not my problem anymore.
If you can't see beyond the box then it's better to look in the mirror and wonder why.

Marko
Title: Re: Simplified Balanced Valve
Post by: rsterne on January 07, 2019, 01:21:47 AM
Please, let's not derail a very useful thread where people are working to a common goal.... We may not have all the answers, but by cooperating we may find a few more.... If you aren't interested in that approach, you are more than welcome to work on your own, and leave us "stupid people" to muddle on....

Bob
Title: Re: Simplified Balanced Valve
Post by: Motorhead on January 07, 2019, 01:27:08 AM

I have told enough for those that can listen and understand basics that can build similar valves that I have made, I just don't make pictures and diameters available in open forum.

It's ticking me off that some of the manufacturers use forums as R&D and then make profit out of it, patenting someone's ideas!

Marko

Don't wish to share what you know or think you know ? ... SAY OFF PUBLIC FORUMS
Don't wish to enable others to think outside the box and become better system engineers ... DON'T CONTRIBUTE TO THOSE THREADS

If you have the funds, ability to come up with and PROVE a deign is worthy of a patent .... Good for you ! If you had friends helping along the way ... Good for them !

Just sayin ...

And then you all are wondering why some people leave, and don't write anymore.
I hate stupid people, people with narrow minded way of thinking. I have shared my thoughts more than once, just to be told it's not how things work. Well not my problem anymore.
If you can't see beyond the box then it's better to look in the mirror and wonder why.

Marko


So are you saying you KNOW IT ALL and we all should be blessed in your sharing being the final word on subject ???

I'm not trolling you ... it is a legitimate question based upon what you stated in "Quote" above.
Title: Re: Simplified Balanced Valve
Post by: rsterne on January 07, 2019, 01:28:42 AM
ENOUGH ALREADY !!!!

If necessary, I will lock this thread....

Bob
Title: Re: Simplified Balanced Valve
Post by: Motorhead on January 07, 2019, 02:15:46 AM
Not sure this is the place or correct thread to question some of the dynamics going on ... but here are some thoughts running threw my head.

We are reading about some ratios of diameters that allow crazy easy opening but sadly hang open unable to close fast enough to have a short dwell cycle.
That being based on what ever the weight of hammer is, it must be carried back as poppet is closing and where we seem to be universally fighting to control. * heavy poppet return spring or air springs etc ...

What would we get if you had a balanced valve set up for easy opening able to be struck with a light hammer or AKA: bobbin that bottomed out once poppets pushed in on a purposely elastic surface creating a newtons cradle rebound type strike ?  If we get the weight and mass off the poppet stem faster than the poppet cycling, the poppet is left to only carry it's own mass / weight to get closed.
Would this not be a possible miens to the goal of reducing dwell on a more balanced valve geometry ?

Hope this makes sense 
Title: Re: Simplified Balanced Valve
Post by: MJP on January 07, 2019, 02:24:38 AM
There is enough flow in pcp valve to $uck O-rings from "half gland" and yet still I have been told that it doesn't matter that much in closing the valve?

Martyring doesn't work so well as some might think.

It's really simple to try how much flow affect closing, make a really streamlined valve and see how much difference you'll get when adding a corner or two retaining the same valve area.
Studying fluid dynamics and dry flow can reveal interesting things.

And nature really knows how things should be done, just take a look at some of the birds flying or the fish swimming , wondering how the shape became like that.

Marko
Title: Re: Simplified Balanced Valve
Post by: PakProtector on January 07, 2019, 05:00:48 AM
hey-Hey!!!,
It could be that you can shrink the balance chamber volume with some solid packing( like a pill of delrin). should be able to get it a wee bit smaller, and enough reduced to see if that is going to help...

Douglas
Title: Re: Simplified Balanced Valve
Post by: rkr on January 07, 2019, 05:08:40 AM
There is enough flow in pcp valve to $uck O-rings from "half gland" and yet still I have been told that it doesn't matter that much in closing the valve?

Martyring doesn't work so well as some might think.

It's really simple to try how much flow affect closing, make a really streamlined valve and see how much difference you'll get when adding a corner or two retaining the same valve area.
Studying fluid dynamics and dry flow can reveal interesting things.

And nature really knows how things should be done, just take a look at some of the birds flying or the fish swimming , wondering how the shape became like that.

Marko

The flow will create low pressure area in front of the "sail" of the poppet so it should help in closing the valve. How much force that creates is IMO impossible to calculate but we could experiment with that phenomenon in order to get some educated guesses.
Title: Re: Simplified Balanced Valve
Post by: PikeP on January 07, 2019, 07:07:07 AM
Something like this might help? If interested let me know and I'll share the excel file. Would imagine once fully functional if its not already to be worth the sweat and tears.

The second pic shows what happens when you change vent size or use the suggested chamber volume.


The last pic is same as first but only changed chamber reduction from 70 to 60
Title: Re: Simplified Balanced Valve
Post by: PakProtector on January 07, 2019, 07:44:37 AM
On the ss valve, we have two areas that can force the valve shut. Small piston( which is always at tank pressure), and large-small which is at rest vented to the outside, and provides the reduction in seat pressure when closed. Given the results Bob has so far gotten, it *SEEMS* that the vented balancing chamber is not coming up to throat pressure when fired, and the valve knocks open. I'd count that as a vote for the large stem behind the throat, which when pressurized during firing can deliver a significant close force...

I wish I had some time to try building one...but at least one other is on the way. Looking forward to seeing the results.

Douglas
Title: Re: Simplified Balanced Valve
Post by: Brian W Cook on January 07, 2019, 12:28:22 PM
I had kinda forgotten about my old experiment until i had seen some post about Cothran valves and the balanced valves .  I had to go dig the reservoir tube out of a pile of airgun stuff and disassemble it to see what exactly i made .   Working nights for 20 years will make a guy forget stuff.     
I think on mine the airflow around the poppet does most of the closing action.   
Speaking of air , if you could magically put your hand in a tank of 3000 psi air what would it feel like viscosity wise ?
Title: Re: Simplified Balanced Valve
Post by: rsterne on January 07, 2019, 12:35:39 PM
Marco, thank you for the suggestion of streamlining the poppet to reduce the closing force on it.... Could you please explain how I can do that further when the front and sides of the poppet are already inside a streamlined thimble?.... Or, are you suggesting that I lose the lower part of the thimble in an attempt to have the flow help close the poppet faster?.... Some specific suggestions instead of broad generalizations or criticisms would be most welcome....

Douglas, I could perhaps extend the spring seat on the poppet into an internal guide (stuffing) to get rid of some volume....

Mike, I will need to study your spreadsheet further (there is a lot of information there)…. but it would seem that drilling out the front cross vent so that the whole vent is 0.047" (or larger) should help, no?.... I also don't understand the "percent chamber reduction" (70 or 60), is that the small end of the poppet divided by the large end (diameter ratio), and if not, what is it?....

Bob
Title: Re: Simplified Balanced Valve
Post by: MJP on January 07, 2019, 01:04:55 PM
It was meant as an example to try on a normal non balanced valve without any valvespring.
Just to demonstrate how much there is closing force just by in flow alone.

Brians valve is definitely aided by flow over the valve head directed by the slots.

Marko
Title: Re: Simplified Balanced Valve
Post by: rsterne on January 07, 2019, 01:07:13 PM
Brian, I don't know what 3000 psi air would "feel" like, but perhaps this representation (molecules not to scale, but spacing is) would be a good visual....

(http://i378.photobucket.com/albums/oo221/rsterne/Ballistics/Air%20Molecule%20Spacing_zps4xvo9y3v.jpg) (http://s378.photobucket.com/user/rsterne/media/Ballistics/Air%20Molecule%20Spacing_zps4xvo9y3v.jpg.html)

The point is that the molecules of nitrogen and oxygen are much closer together in compressed air.... the molecules themselves (which are incredibly tiny) don't compress, what happens is that you reduce the space between them.... In a liquid, they are touching but still free to move.... and in a solid they are in what amounts to a crystalline structure, each molecule is vibrating in place, but fixed relative to its neighbours.... The density and viscosity of air at 1 bar are: Density= 1.189 kg/m^3, Dynamic Viscosity= 18.23, Kinematic Viscosity= 15.33.... at 200 bar they are: Den= 232.02, Dyn.Vis= 23.99, Kin.Vis= 0.1029.... Sorry, but I don't know viscosity relates to "feel".... Compressed air at room temperature, above about 550 psi, is considered a "supercritical fluid"....  ::)

Bob
Title: Re: Simplified Balanced Valve
Post by: rsterne on January 07, 2019, 01:31:23 PM
Quote
It was meant as an example to try on a normal non balanced valve without any valvespring.
Just to demonstrate how much there is closing force just by in flow alone
.

OK, got it, thank you.... Can you give me some feel for how much difference the shape of the poppet makes?.... For instance, no spring, two poppets both the same diameter, one a cylindrical shape and the other streamlined (eg parabolic nose, or whatever you find best)…. With no other changes, are you talking a couple of turns on a preload adjuster?.... or "WOW, I have to change to a MUCH lighter spring" ?....

Bob
Title: Re: Simplified Balanced Valve
Post by: Brian W Cook on January 07, 2019, 01:43:33 PM
Was just throwing that question out there .  Sitting here at lunch i can wave my hand around and feel the slight resistance of the air .   Was wondering what 200 times that would be like .   Sometimes things that can’t be felt or seen are hard to imagine.   
Shortly after my piston valve stuff i figured out knocking a conventional.437 poppet open really wasn’t that hard and just went with that setup.   
If i were to revisit the piston valve it would be to get a .750 port to open for my 1” rifled barrel i whipped up a few years ago . 
Thanks for the technical data Bob !
Title: Re: Simplified Balanced Valve
Post by: MJP on January 07, 2019, 01:47:13 PM
It closer to the WOW than couple of turns.
In my 9mm pistol the streamlined would dump the tank vs stepped poppet pressure drop was around 50bar from 250bar.
On a same spring and hammer.
Cylinder is around 65cc

Marko
Title: Re: Simplified Balanced Valve
Post by: TPL on January 07, 2019, 01:55:05 PM
Sorry if we don't have a formula or graph to estimate the closing force by flow but it definately is there as we can consider it. What we have got so far is no - there is no meaning, it is common missunderstanding. Ok, that'll be it.

Where is our doctor of physics now? His calculations incuded temperature changes too?

PS: Is it that hard to test?
Title: Re: Simplified Balanced Valve
Post by: rsterne on January 07, 2019, 02:06:00 PM
OK, Mike, I printed out those screen shots of your spreadsheet so that I could study them.... In a nutshell, compared to the first one, where the chamber fill time was 0.96 mS, the other three options reduced it to 0.73-0.76 mS.… You only changed 1 thing at a time (thank heavens, or I would have gotten lost)…. One option was increasing the vent from 0.040 to 0.045", which moves the air faster, filling the balance chamber sooner.... Another option was reducing the height of the balance chamber from 0.20" to 0.15", with a corresponding reduction in the volume of air to move to fill the balance chamber, again filling it sooner.... The last option was to reduce the diameter of the front portion of the poppet from 0.28" (70%) to 0.24" (60%), which increases the force holding the poppet on the seat, and also the volume of the balance chamber, again filling it sooner.... (I noticed that you increased the hammer spring rate to knock open the now harder to open valve, completely appropriate)…. OK, so I got how those changes work.... However....

I am complete baffled by the cells labelled "Reduced lbs." and "Lbs Valve Closed".... I have no idea what they are.... Using your first photo, the poppet OD is 0.40" and the front of the poppet is 0.28" (70%)…. When the valve is closed, there is no stem force.... The force on the poppet towards the seat is:

(0.40^2 x PI/4 x 3000) - (0.28^2 x PI/4 x 3000) = 377 lbs - 185 lbs = 192 lbs.... I don't see that number anywhere.... This means, of course, that I don't understand the "xx% Equalized Force" cells either.... HELP !!!

Bob
Title: Re: Simplified Balanced Valve
Post by: rsterne on January 07, 2019, 02:11:37 PM
Marco, thanks for that, it gives me some idea of the magnitude of what you found....

Timo, please don't just throw fuel on the fire, either help or don't bother.... Generalized statements may work for you, because you understand, and have seen the results first hand.... However, without quantifying them, it is impossible for others to understand the importance of these effect.... If you have already done the tests, why would you not share the results, instead of saying "is it that hard to test" (in other words, do it yourself)?....

Bob
Title: Re: Simplified Balanced Valve
Post by: PakProtector on January 07, 2019, 02:21:15 PM
Viscosity of air at 300K:
1 Bar 184.5 N-s/m^2
100 bar 205 N-s/m^2
1000 Bar 545 N-s/m^2

Get air at 1 Bar up to 1300K and its viscosity is 496 N-s/m^2

Did not find a value for 200 Bar/300K yet, but I'd bet on something OTO 230-240 N-s/m^2.
cheers,
Douglas
Title: Re: Simplified Balanced Valve
Post by: TPL on January 07, 2019, 02:28:36 PM
Bob, unfortunately I cannot quantify it any better than "remarkable".

But if we can discuss about it as existing phenomena, we have come over some threasold now anyway.

Again, I am sorry for not saving all the measurements on scientific basis but am still quite sure myself.

Why would I need to be the one who is quantifying it? I'm just saying it is real.
Title: Re: Simplified Balanced Valve
Post by: oldpro on January 07, 2019, 02:35:59 PM
https://www.engineeringtoolbox.com/air-absolute-kinematic-viscosity-d_601.html (https://www.engineeringtoolbox.com/air-absolute-kinematic-viscosity-d_601.html)
Title: Re: Simplified Balanced Valve
Post by: rsterne on January 07, 2019, 03:00:56 PM
Mike, I have a spreadsheet also (compliments of Lloyd) that calculates the closing force on the poppet at various stages of the valve cycle.... The chart below is for my current valve (7/16" poppet with 5/16" balance chamber).... with three stem diameters, 1/8", 3/16 and 1/4".... A conventional valve of the same poppet diameter, but no balancing, is shown in black for comparison....

(http://i378.photobucket.com/albums/oo221/rsterne/Hayabusa%20PCP/Balanced%20Valve%20Closing%20Forces_zpsmgsysjit.jpg) (http://s378.photobucket.com/user/rsterne/media/Hayabusa%20PCP/Balanced%20Valve%20Closing%20Forces_zpsmgsysjit.jpg.html)

Numbers above the "zero" axis indicate a closing force.... while those below it indicate an opening force, trying to blow the valve open before the balance chamber fills with air.... The horizontal axis is the percent of 3000 psi in the balance chamber and is NOT the complete valve cycle.... Mike says that is about 1 mSec.... To get some feel for what the forces are over the entire valve cycle, you must extend the final value of each line, which is the closing force on the stem area that penetrates the valve body, over to the right for the entire length of the valve cycle, which is 2-3 times (or more) the time it takes for the balance chamber to fill to 3000 psi....

I hope this will allow all of you (as it did me) the opportunity to visualize the forces acting on the poppet, and why the current version is blowing open....

Bob
Title: Re: Simplified Balanced Valve
Post by: rsterne on January 07, 2019, 03:12:17 PM
Thanks for those graphs, Travis.... It appears that the Dynamic Viscosity varies little at room temperature below 500 bar.... However, nearly all the decease in Kinematic Viscosity occurs between 1 bar and 50 bar, and above that it changes little.... Dynamic Viscosity is the difficulty in "shearing" the liquid as something passes through it.... ie the resistance felt by the moving object.... That changes little for air below 500 bar.... Kinematic Viscosity is that value divided by the Density.... Since the Dynamic (shearing) viscosity doesn't change much, but the Density increases rapidly with pressure.... the Kinematic Viscosity drops rapidly as the pressure increases.... For our purposed, logic tells me that the Dynamic Viscosity would be what we would "feel".... and below 500 bar it doesn't vary that much.... It increases by about 1/3 at 3000 psi....

Bob
Title: Re: Simplified Balanced Valve
Post by: Brian W Cook on January 07, 2019, 04:12:56 PM
Looks like a pretty slow increase till it’s beyond 8 to 10000 psi .  That helped clear that up .  Thanks !
Title: Re: Simplified Balanced Valve
Post by: rsterne on January 07, 2019, 05:23:28 PM
Continuing on from Reply #237 above.... Here is a MODEL to help you visualize the closing forces on a valve throughout the shot cycle.... Please note this is NOT based on data, it is a representation ONLY....

(http://i378.photobucket.com/albums/oo221/rsterne/Hayabusa%20PCP/Balanced%20Valve%20Force%20vs%20Dwell_zpsqljpop7b.jpg) (http://s378.photobucket.com/user/rsterne/media/Hayabusa%20PCP/Balanced%20Valve%20Force%20vs%20Dwell_zpsqljpop7b.jpg.html)

For this chart I have made some broad assumptions.... I used 1 mSec. as the time it takes to equalize the pressure in the balance chamber (equivalent to the 100% of 3000 psi in the previous chart)…. I used a dwell of 3 mSec. as being typical for my gun and valve at the current performance level.... I assumed that the flow would choke 10% of that dwell before the valve closed, at 2.7 mSec.… At that point, therefore, the closing force across the big end of the poppet, and available to the stem, are 50% of the reservoir pressure, ie 1500 psi.... The slope between 2 mSec. and 2.7 mSec. is added drag from the poppet, and increasing pressure differential, as the flow accelerates to supersonic at the seat.... At 2.7 mSec. the flow will be less than half the full flow rate.... The slope between 2.7 mSec. and 3.0 mSec. is that brief time during which the flow is choked and the pressure differential across the poppet is again approaching 100% of reservoir pressure, and the valve is slamming shut....

The point of this is to help us (me included) to see what forces the hammer must overcome, and when.... Think about it this way.... The area between the force line and the zero axis (horizontal grey line), over the first half of the dwell (while the valve is opening) is the energy/momentum the hammer must provide.... The larger that area, the greater the hammer strike you need.... During the time the force line is below the axis, the valve is blowing open, and the hammer is doing nothing.... I tried to calculate that area over the 1.5 mSec. while the hammer is opening the valve (ie adding up only the positive values), and I got the following numbers.... in lbs.ms, how is that for a weird unit....  ::)

Conventional Valve = 105
1/4" Stem Balanced = 154
3/16" Stem Balanced = 85
1/8" Stem Balanced = 48

Providing I didn't fumble on the calculator keys, my balanced valve, but with a 1/4" stem, should require 47% MORE hammer strike than a conventional valve with a 1/8" stem.... so there is no point in trying that.... :o …. Changing from a 1/8" stem to a 3/16" stem will need roughly 78% more hammer strike required compared to the 1/8" stem it has right now.... but still be significantly less than a conventional valve of the same size.... If I calculate the value for my original valve (3/8" conventional poppet, 1/8" stem) I get a value of 93.... This compares to 48 for my current valve.... and indeed the hammer strike required is less than half what it used to be.... Increasing the stem to 3/16" may, however, not yield a significant reduction in the hammer strike required (85 vs. 93)…. I think 3/16" may be a bit big, certainly I don't want to try larger....  ???

To put in context what the flow is like at the various stages in the above chart, using Lloyd's Internal Ballistics Spreadsheet, in rough terms, at 1 mSec. the pellet has travelled about 2" and is going about 335 fps.... At 2 mSec. it is about 8" down the barrel, travelling about 615 fps.... When the valve closes at 3 mSec. the pellet would have moved about 16" and be going about 810 fps.... By the time it reaches the muzzle at 28", it has acquired the 956 fps MV recorded, and that takes just over 4 mSec. from the moment of firing.... Using the Bernoulli equation for a bullet velocity of 760 fps (@ 2.7 mSec.), and assuming the airflow is the same through the valve, the valve would choke when the poppet is about 0.040" from reaching the seat on closing.... That would be pretty close to how far it is still open at 2.7 mSec. so that was not a bad guess....  8)

Bob
Title: Re: Simplified Balanced Valve
Post by: PikeP on January 07, 2019, 06:07:23 PM
Some great info Bob. Curious how the 5/32 or 11/64 stem diameters I suggested would do?

Here is some added data to my spreadsheet also showing how the closing force is influenced at 25, 50, 75, and full pressure chamber equalization...this spreadsheet currently works out 4 ways to optimize valve closure, chamber volume, vent size, pressure reduction %, and stem size od.
Title: Re: Simplified Balanced Valve
Post by: mann on January 07, 2019, 06:15:56 PM
Wouldn't it make sense to to inceases the vent hole to .047 or make the chamber smaller like was said earlier to get the balance chamber filled faster .
Title: Re: Simplified Balanced Valve
Post by: PakProtector on January 07, 2019, 06:41:55 PM
well Bob, you could be working in cubits, stones and fortnight time scales...LOL

So, says I, do please take this model of yours and run it on the SS valve as a check of assumptions and model correlation.
cheers,
Douglas
Title: Re: Simplified Balanced Valve
Post by: mann on January 07, 2019, 07:24:55 PM
I'm going to make a new poppet and thimble and I'll use .250 and .375 with derlin . I'm going to shorten the thimble so it only contains the balance chamber and start out with a .040 vent hole and I'll up the vent hole if needed . I'll also use a 1/8 inch stem so I don't choke the exhaust to much since I'm only running a .200 exhaust port
Title: Re: Simplified Balanced Valve
Post by: PikeP on January 07, 2019, 07:40:15 PM
Added valve dwell and lift..pretty hard to calculate dwell on a balanced valve so I just used correction factors till it matched Bob's calculated valve dwell at his power level...although I think 3ms is a long valve duration and think its closer to 2 than 3 but that's JMO! As my calculations may be off somewhere.

**corrected closing factors ar various pressure  equalizations which reflect Bob's chart
Title: Re: Simplified Balanced Valve
Post by: oldpro on January 07, 2019, 07:47:42 PM
I'm going to make a new poppet and thimble and I'll use .250 and .375 with derlin . I'm going to shorten the thimble so it only contains the balance chamber and start out with a .040 vent hole and I'll up the vent hole if needed . I'll also use a 1/8 inch stem so I don't choke the exhaust to much since I'm only running a .200 exhaust port
Drop the small end to 210 and you will be able to tune it with hammer strike and no need for huge vent holes in the stem etc. It will require more hammer strike but will have a better ratio for tuning. Not my opinion or a guess its a fact as tested by myself.
Title: Re: Simplified Balanced Valve
Post by: mann on January 07, 2019, 07:51:49 PM
Thanks Travis
Title: Re: Simplified Balanced Valve
Post by: PakProtector on January 07, 2019, 08:28:51 PM
I'm going to make a new poppet and thimble and I'll use .250 and .375 with derlin . I'm going to shorten the thimble so it only contains the balance chamber and start out with a .040 vent hole and I'll up the vent hole if needed . I'll also use a 1/8 inch stem so I don't choke the exhaust to much since I'm only running a .200 exhaust port
Drop the small end to 210 and you will be able to tune it with hammer strike and no need for huge vent holes in the stem etc. It will require more hammer strike but will have a better ratio for tuning. Not my opinion or a guess its a fact as tested by myself.

To Mann and Travis, how big a throat?
cheers,
Douglas
Title: Re: Simplified Balanced Valve
Post by: PakProtector on January 07, 2019, 08:32:20 PM
Just to put down a possible solution, make the hole in the stem bigger( say 1.8mm for a 33% increase in its area), and a 4mm stem( cut down to .125" in the throat ) we get hopefully faster fill of the balance chamber, and some assist from the 4mm stem area. Now is O1 available in metric sizes....heh-heh-heh
cheers,
Douglas
Title: Re: Simplified Balanced Valve
Post by: mann on January 07, 2019, 08:36:28 PM
I'm not sure what size the throat in the ss valve is
Title: Re: Simplified Balanced Valve
Post by: rsterne on January 07, 2019, 08:38:59 PM
Mike, I still don't understand the "Reduced lbs." and "Lbs. Valve Closed" numbers, how did you get those?.... I get 192 lbs. for the force holding the 0.40" valve closed at 3000 psi with a 0.28" balance chamber.... 377 - 185 = 192....

Douglas, I have some 5/32" drill rod, and I can thread it 8-32 (a thou missing on the thread peaks from the minimum OD spec. of 2A class threads)…. I have a feeling that will work great, and could easily drill it to 1/16" or a bit larger.... It will still be slightly greater area in a 3/8" throat than my ports, which are 0.328".... works out to the equivalent of 0.341", even without slimming.... my guess is, no measurable loss in FPE.... 8)

Bob
Title: Re: Simplified Balanced Valve
Post by: shorty on January 07, 2019, 08:47:47 PM
I blew the dimensions opening up the valve to accept the new valve stem and then pulled too much of the valve stem to get it to fit. Rushing and not paying attention.

Keep up the great work and figure this out. I am out of the game until more material arrives.

Title: Re: Simplified Balanced Valve
Post by: PakProtector on January 07, 2019, 08:58:26 PM
I'm not sure what size the throat in the ss valve is

J drill goes in, so .273-ish IIRC. Mine is .290 now. I think it ought to be even bigger; when I get to machine a poppet from PEEK, it will grow again to .302. I have not quite a shortage in hammer energy; the Flex originally came outfitted with a standard valve with a .281 throat.
cheers,
Douglas
Title: Re: Simplified Balanced Valve
Post by: rsterne on January 07, 2019, 09:03:32 PM
Here is the previous model with the 1/4" stem replaced by one of 5/32" (blue line)….

(http://i378.photobucket.com/albums/oo221/rsterne/Hayabusa%20PCP/Balanced%20Valve%20Force2%20vs%20Dwell_zpsron8sgn8.jpg) (http://s378.photobucket.com/user/rsterne/media/Hayabusa%20PCP/Balanced%20Valve%20Force2%20vs%20Dwell_zpsron8sgn8.jpg.html)

The lbs.ms hammer value (up to the 1.5 mSec open position) is 64.... I am currently at 48 with the 1/8" stem, so a 33% increase in hammer strike required, and a 50% increase in the closing force from the stem + spring from 40 lbs. to 60 lbs.... The "blow open" force goes to zero at 74% of 3000 psi instead of 83%.... I think I like that, along with a 1/16" vent hole....

Mike, can you run those numbers, please?....

Bob

Title: Re: Simplified Balanced Valve
Post by: oldpro on January 07, 2019, 10:27:58 PM
I'm going to make a new poppet and thimble and I'll use .250 and .375 with derlin . I'm going to shorten the thimble so it only contains the balance chamber and start out with a .040 vent hole and I'll up the vent hole if needed . I'll also use a 1/8 inch stem so I don't choke the exhaust to much since I'm only running a .200 exhaust port
Drop the small end to 210 and you will be able to tune it with hammer strike and no need for huge vent holes in the stem etc. It will require more hammer strike but will have a better ratio for tuning. Not my opinion or a guess its a fact as tested by myself.

To Mann and Travis, how big a throat?
cheers,
Douglas
.280
Title: Re: Simplified Balanced Valve
Post by: PikeP on January 07, 2019, 11:02:25 PM
Here is what I get with a .0469 or 3/64 vent and a 5/32 or .1563" stem

2nd pic is with the 1/16th or .0625" vent and .1563 stem.

Last pic is my favorite with a 9/64th stem or .1406" with the .469" vent.

I think finding true dwell or as close as possible and aiming for full pressure equalization in half its time give or take would be optimal...although maybe it's closer to either 25 or 75%...but of course that's what we are here to learn. It could be fairly static and more favored towards throat pressure equalization and may require focusing on that figure over dwell.
Title: Re: Simplified Balanced Valve
Post by: rsterne on January 07, 2019, 11:19:18 PM
Mike, I still don't understand the "Reduced lbs." and "Lbs. Valve Closed" numbers, how did you get those?.... I get 192 lbs. for the force holding the 0.40" valve closed at 3000 psi with a 0.28" balance chamber.... 377 - 185 = 192....

Bob
Title: Re: Simplified Balanced Valve
Post by: PikeP on January 07, 2019, 11:28:44 PM
Mike, I still don't understand the "Reduced lbs." and "Lbs. Valve Closed" numbers, how did you get those?.... I get 192 lbs. for the force holding the 0.40" valve closed at 3000 psi with a 0.28" balance chamber.... 377 - 185 = 192....

Bob

My apologies, the reduced force calculation is correct at the 70%figure however the simple math of reducing 70% of .4 doesn't translate with pressure..need to correct that. Any idea how to approach quickly figuring what diameter equals 70% force of .4?

Also is your 70% ratio to the poppet od or pressure reduction?
Title: Re: Simplified Balanced Valve
Post by: rsterne on January 07, 2019, 11:31:54 PM
You used the diameter (70%), you need to use the area (49%)…. or just take the diameter of the balance portion (0.28") and calculate the area x pressure = 185 lbf…. Then subtract that to get the force holding the valve closed (377 - 185) = 192....

If you actually want a 70% reduction in force, then you need to use SQRT 70% = 0.8397 x 0.4" = 0.335" for the diameter of the balance portion.... I am using ~ 70% diameter (0.312" / 0.437") on my valve....

Bob
Title: Re: Simplified Balanced Valve
Post by: PikeP on January 07, 2019, 11:37:52 PM
Makes sense I'll update my sheet accordingly to that. I was going the other way with ratios
Title: Re: Simplified Balanced Valve
Post by: PikeP on January 07, 2019, 11:49:49 PM
Fixed...here is the updated sheet.
Title: Re: Simplified Balanced Valve
Post by: rsterne on January 07, 2019, 11:53:35 PM
I think we have determined that a 70% reduction in the force (ie 84% of the diameter) will not work.... In my SS valves (which work the other way, the smaller the front portion, the larger the reduction) I ended up using 2/3 - 3/4 the diameter.... Travis uses 80% of the diameter for the front portion.... With this design I think 1/2 the force (70% of the diameter) is the biggest you can go.... Travis is talking about using 56% of the diameter.... We don't know yet, but I think those may be the outer limits of the range.... That would mean for my valve, with a 7/16" poppet, the front end would be 1/4" - 5/16"....

Bob
Title: Re: Simplified Balanced Valve
Post by: rsterne on January 07, 2019, 11:58:12 PM
Those look right.... Can you please do my current valve, with a 1/8" stem and a 0.040" vent, 1" long, and increase the height of the balance chamber to 1/4", hammer travel to 1", hammer weight to 77 gr., hammer spring rate is 11 lb/in.... Then change the vent to 0.047".... Then the stem to 0.156".... Then the vent to 0.063".... Those 4 models should be all I need (I hope)….

Thanks....

Bob
Title: Re: Simplified Balanced Valve
Post by: PikeP on January 08, 2019, 12:04:31 AM
I think what we are ultimately trying to achieve is a hybrid valve that starts off balanced and quickly returns to conventional functions ideally around peak lift. Whatever parameters give that outcome will likely require hammer energy right in between that of a fully balanced and conventional valve. Hopefully these valves become standard use for big bores with tunable range and a healthy amount of reduced force to operate the valve. I think vent sizing, chamber volume, force reduction %, and valve stem od are all critical in getting this design perfected and operable across many calibers. Hopefully we can dial in a spreadsheet to represent at least what we're experiencing which may allow exploring more ways to skin this cat being there are 4 very favorable variables in action here.
Title: Re: Simplified Balanced Valve
Post by: rsterne on January 08, 2019, 12:08:05 AM
Quote
I think what we are ultimately trying to achieve is a hybrid valve that starts off balanced and quickly returns to conventional functions ideally around peak lift.

I agree 100% with that assessment.... My stated goal in the first post was a significant reduction in hammer strike, along with tunablity…. combined with minimum parts and easy to machine.... The devil is definitely in the details.... I also think that once the correct proportions are determined, the valve should be scalable....

Bob
Title: Re: Simplified Balanced Valve
Post by: PikeP on January 08, 2019, 12:11:15 AM
Here are the 4 models you requested Bob.

Added a 5th to fill some gap.
Title: Re: Simplified Balanced Valve
Post by: rsterne on January 08, 2019, 12:29:04 AM
That is brilliant, Mike.... Thanks so very much.... This is fun stuff, eh?....

I think it is pretty obvious what I need to do.... I need to first drill the vent in my existing stem to 0.047".... While I have it out, I may just be able to drill everything out to 0.052" (the next number drill larger than 3/64" is a #55) without breaking any drills.... I hope.... If the flow rate increases to 94 mg/ms, I should be down to about 0.93 mSec.… I won't complain if you want to add that model (1/8" stem)….  ::)

After that is tested, to see if it makes any difference....  ie shows any signs of being tunable.... then I need to make a new poppet with a 5/32" stem and 1/16" vent hole....  8) …. WOOHOO, this is exciting stuff !!!!!!!!!!!!!!!

Bob
Title: Re: Simplified Balanced Valve
Post by: PikeP on January 08, 2019, 12:37:20 AM
An important note and thought. The pressure chamber fill time calculation relies on throat being full pressure..would likely have to add a few micro seconds to that time for this event to fully occur..however I'm guessing its minimal but likely to raise the current figure by 15 to 20%...I could try to estimate that figure and add it into the calculation however with how marginal it is compared to fill times I may leave it out.

I think this also implies vent distance from seat is important...if your vent entered the throat during lift I'd imagine it be even better.
Title: Re: Simplified Balanced Valve
Post by: PikeP on January 08, 2019, 12:40:27 AM
You were correct in your assumptions with the
.052 vent and .125" stem.
Title: Re: Simplified Balanced Valve
Post by: rsterne on January 08, 2019, 12:41:51 AM
I don't think we need to refine things like that, that are not well understood.... The model will grow and improve with time.... These spreadsheets end up having a mind of their own, and a life of their own as well....  ::) …. I think you have a very workable model right now.... With a bit more experimenting to set the parameters, it will likely get to the point of predicting results.... which is the ultimate goal for any model....

Thanks, I'll see if I can drill the stem out to 0.052" without breaking the drill and ruining the poppet....  ;)

Bob
Title: Re: Simplified Balanced Valve
Post by: PikeP on January 08, 2019, 01:15:52 AM
Might I suggest after you drill the vent to .052", if it's not enough...try reducing the chamber height by .05" to achieve the following. Small incremental changes seem best as you really do seem to be close based on your current efficiency and power level

Also added medium hammer weight which is scaled equally to heavy and light which predicted what Bob is currently using.
Title: Re: Simplified Balanced Valve
Post by: rsterne on January 08, 2019, 01:21:51 AM
I may be able to reduce the cavity height with a filler block.... We haven't allowed for the spring cavity, which adds even more volume.... I am also considering using a stronger spring....

Bob
Title: Re: Simplified Balanced Valve
Post by: PikeP on January 08, 2019, 01:48:30 AM
Valve spring rate would harshly effect the first 25 or 50 percent of valve opening more than chamber sizing, vent sizing or even stem od sizing as it would be a mostly static force increasing slightly with lift and the other 3 variable through shot cycle. Just my 2c!
Title: Re: Simplified Balanced Valve
Post by: PikeP on January 08, 2019, 02:08:29 AM
Added spring volume by mass assuming density of music wire at 7.86 g/cm3...for builds that use a spring inside the pressure chamber. Also added separate calcs for spring chamber in case dimensions vary, but can be left at 0 if not.
 
I also added optimal fill time until more things are figured out where we may be able to automatically calculate that based on parameters, also added a flow efficiency correction factor.

I also subtracted half the valve lift from pressure chamber height to determine volume as it spends the majority of the time at 50% through the valve opening event.

Feel free to request any other additions.
Title: Re: Simplified Balanced Valve
Post by: MJP on January 08, 2019, 02:57:56 AM
No matter if you get one size working just right, the valve won't be scalable so easily.
And making the hole in the stem vs having a straight hole in the valve face alters the behavior.
All the time you are altering the time how the balancing chamber gets filled.
You are forgetting the flow in the equations, flow over a corner creating dead space for x amount of time.
Its just not all about pressure.

Something that works on a large scale wont work on smaller one, I'm not going in to measurements because I all ready have a headache from your nonsense fractional system.
It was nice to see couple of metric dimensions but rest of it was all chinese.

Oh forgot to mention that even the location of the hole on side the stem how far it is from the valve face has an affect.

Marko
Title: Re: Simplified Balanced Valve
Post by: PikeP on January 08, 2019, 03:04:44 AM
I apologize for the imperial units but it's what many in north America are raised up on and accustom to.

Bob started this thread with interest in understanding what makes balanced valves tick..or not tick. The point of the model is to help find optimal dimensions and other variables. If it helps push balanced valves more into main stream I'm all for it. Every variable you speak of can be accounted for and flow losses are already one of them, not to say all are currently accounted for but I dont think it will be necessary once some blue prints are laid out...the ratios may scale just fine provided all things are scaled equally..we will certainly find out in time.
Title: Re: Simplified Balanced Valve
Post by: MJP on January 08, 2019, 03:16:20 AM
No need to apologize, it's just my problem that you guys have not adopted to use metric system like it was planned decades ago.  ;D

But what comes to the scale, the simple version wont scale up without modifications. At least what I have tried didn't.

Douglas, you can get metric O1 from Europe.

Marko
Title: Re: Simplified Balanced Valve
Post by: PikeP on January 08, 2019, 03:34:58 AM
I agree Marko that the metric system is simpler and superior.

I think there is a scalable set of variables that will work where some key variables remain constant.

I ran a quick calculation and compressed air at 3000 psi should travel the 1.1 inches to the chamber in .06 ms...being that air is traveling roughly 17.52 RMS inches per ms at that
pressure...pretty intense. However I have now included it since it's a factor..also my flow coefficient is currently set at 95%. Could need lowering with such small orifaces but ultimately once dialed in would stay relatively equal for similar vent sizes.
Title: Re: Simplified Balanced Valve
Post by: PikeP on January 08, 2019, 07:25:48 AM
Some interesting math I did. To generate 270 fpe  @ 28% thermal efficiency you need to eject 3491 mg at 3000 psi. Bob's 1.17 fpe/ci shot was at at 23% thermal efficiency using roughly 18 ccs of air. Where as his 1.44 fpe/ci shot was at roughly 28% thermal efficiency and ~14 ccs...its pretty amazing when you can backwards calculate required air mass ejected for a desired energy level, it helps build a high powered rifle around that knowledge, to be able to not just set goals but more than likely meet them. I find sizing your port  to flow 10% higher than your intended fpes required air mass is best. Where a .33 port should flow 3882 mg/ms at its peak. Of course knowing a ports limitation is only a small part of the equation and only one of many questions answered out of the many that remain.
Title: Re: Simplified Balanced Valve
Post by: PakProtector on January 08, 2019, 12:53:52 PM
Getting the stem vent hole close to the poppet face gets a shorter path down the stem....so on a resistance per length affair, it is absolutely directionally correct. I am thinking about a vent hole diameter under the poppet face from what I recall of the benefits of exhaust port shape and usual modification.
cheers,
Douglas
Title: Re: Simplified Balanced Valve
Post by: rsterne on January 08, 2019, 01:27:11 PM
Glad to see lots of activity on this thread.... I have similar problems converting back and forth between Metric and Imperial measurement, as although we are "officially" on the Metric system in Canada, our proximity to the USA requires a complete and thorough knowledge of how to convert between them.... I admit, having been brought up and schooled using Imperial measure that it is my default system.... I often wonder today how many people even know how to work with fractions.... Or, with cursive writing now left out of the Curriculum in schools, how many of the kids today will even be able to sign their name to legal documents.... I can just see marriage licenses and land deeds with "X's" on them, co-signed by a witness with the words "His Mark" above and below, like was common 200 years ago.... *end rant*….  ;D ;D ;D
 
Back to the topic at hand.... Yes, there is a huge mass of air behind the bullet.... At 3000 psi, air weighs 60 gr. per CI.... The 28" barrel of my .357 cal, at 3000 psi, would contain (.357^2 X PI/4 x 28) x 60 = 168 gr. of air, more than the bullet I was launching.... Basically, there goes half your input energy, or more, right there.... Speaking of which, have any of you seen the claim of 2900 fps with a 144 gr. roundball launched from a Texan with the assistance of a vacuum drawn on the barrel....

https://www.youtube.com/watch?feature=share&v=GhpsG7rSQiQ (https://www.youtube.com/watch?feature=share&v=GhpsG7rSQiQ)

Nearly 2700 FPE of energy in the bullet, from a 3' barrel in .457 cal.... would require about 5500 psi input with NO losses, including no energy lost to the propelling air.... Yeah, I have my doubts....  ::)

Bob
Title: Re: Simplified Balanced Valve
Post by: rkr on January 08, 2019, 01:40:07 PM
Getting the stem vent hole close to the poppet face gets a shorter path down the stem....so on a resistance per length affair, it is absolutely directionally correct. I am thinking about a vent hole diameter under the poppet face from what I recall of the benefits of exhaust port shape and usual modification.
cheers,
Douglas

From flow point of view that is a low pressure area. On the other hand having entry hole in the poppet face gives air flow much less sharp turn than a tight 180 degrees turn to the inside of the valve shaft. Rounding up the entry hole in the poppet face could help.
Title: Re: Simplified Balanced Valve
Post by: Brian W Cook on January 08, 2019, 04:50:51 PM
In regards to the video the guy could have put a bit of distance between the aluminum foil and the chronograph.  His numbers were kind of inconsistent. 
Title: Re: Simplified Balanced Valve
Post by: MJP on January 08, 2019, 05:31:22 PM
That was completely bs the whole video, not showing what he put in the breech and shooting way to close to the chrony.
If making a video claming something so extraordinary then show what you are doing, and not just some part of it. Who knows he could be shooting plastic balls.
780fps gun don't get to be 2900fps gun with some vacuum, not even if loading it with hydrogen. And that would be incredible dangerous and stupid!

Marko
Title: Re: Simplified Balanced Valve
Post by: Hobbyman2007 on January 08, 2019, 05:33:53 PM
I’m having a hart time with the vent hole creating the issue of tunability. The Evanix airspeed is using a similar vent hole arrangement to cycle the action with a huge piston in comparison . If I was to guess the vent hole in it is .065” to .085” . I would be more inclined to have a closer look at flow past the poppet as MJP suggests . I’m going to be trying a valve with no vent to atmosphere and only a stiff return spring in the ballanced chamber  for testing .
Title: Re: Simplified Balanced Valve
Post by: oldpro on January 08, 2019, 08:12:28 PM
I’m having a hart time with the vent hole creating the issue of tunability. The Evanix airspeed is using a similar vent hole arrangement to cycle the action with a huge piston in comparison . If I was to guess the vent hole in it is .065” to .085” . I would be more inclined to have a closer look at flow past the poppet as MJP suggests . I’m going to be trying a valve with no vent to atmosphere and only a stiff return spring in the ballanced chamber  for testing .

 Prepare for the Big Bang I tried that and it didn’t go well.
Title: Re: Simplified Balanced Valve
Post by: rsterne on January 08, 2019, 08:32:15 PM
The Evanix doesn't need to cycle to 3000 psi in less than 1 mSec.… A small vent is fine if the time is available for it to build the pressure it needs.... JMO....

Bob
Title: Re: Simplified Balanced Valve
Post by: Hobbyman2007 on January 08, 2019, 08:34:14 PM
Tried the no vent valve today ( mainly because I can’t drill a small enough vent lol) what happened was basically a cobra valve . Before the thimble I would get 12 shots averaging at 900 fps from 220 to 160 bar within 4% Es . With the thimble installed the velocity started much slower at 800 up to 930 fps at 175 bar and would go back down to the mid 800’s at 140 bar . That happened over 24 shots . Right off the bat I know the ballanced / easier opening is not working . As I lost nearly 100 fps at the same fill pressure. I will try a bit of preload and see if this will get me back to the same power and improve the efficiency . No Big Bang Travis but no big gains either . This is not the best platform to test with to start as it’s a side lever and I really don’t need to reduce the cocking force . Worst comes to worst , I gain some efficiency with a non vented cobra chamber .
Title: Re: Simplified Balanced Valve
Post by: oldpro on January 08, 2019, 09:52:31 PM
Tried the no vent valve today ( mainly because I can’t drill a small enough vent lol) what happened was basically a cobra valve . Before the thimble I would get 12 shots averaging at 900 fps from 220 to 160 bar within 4% Es . With the thimble installed the velocity started much slower at 800 up to 930 fps at 175 bar and would go back down to the mid 800’s at 140 bar . That happened over 24 shots . Right off the bat I know the ballanced / easier opening is not working . As I lost nearly 100 fps at the same fill pressure. I will try a bit of preload and see if this will get me back to the same power and improve the efficiency . No Big Bang Travis but no big gains either . This is not the best platform to test with to start as it’s a side lever and I really don’t need to reduce the cocking force . Worst comes to worst , I gain some efficiency with a non vented cobra chamber .
sound like its not balanced and you have basically a standard valve. I would drill the vent hole and see if you start leaking air.
Title: Re: Simplified Balanced Valve
Post by: PikeP on January 08, 2019, 11:09:15 PM
Added quite a bit. Now calculating some pressure drop during the shot and using the average pressure for flow into chamber along with other calcs as itll better model what's going on during the shot cycle with the balanced valve. Here is the updated one of Bob's current valve.

Title: Re: Simplified Balanced Valve
Post by: rsterne on January 09, 2019, 02:33:27 AM
Looks good, Mike.... I don't know where you are getting your valve lift figure from.... but it seems very low to me.... Measurements of several PCPs show the actual lift to vary from about 1/8 the throat diameter when sipping air to 1/2 the diameter when the valve is open until the pellet leaves the muzzle.... With a shot such as we are getting here, I would guess the valve lift is about 1/4 the throat diameter, or about 0.094".... plus or minus a bit....

BTW, the hammer travel available is 1.09", but the SSG propels the hammer less than that depending on the gap setting.... With 7 turns of gap (the greatest I can use and still get maximum velocity, and the best efficiency) you would subtract (7 x 0.050") from 1.09", so the distance the hammer is being accelerated is only 0.74".... The hammer can only drive the poppet stem 0.20" before it hits the back of the valve body.... However, if the valve is blowing open (which I suspect), it could travel a bit further than that before the poppet bounces the O-ring bumper against the inside of the thimble.... maybe 0.23", I haven't measured it precisely.... When I am building valves, I always allow the stem to travel slightly more than 1/2 the throat diameter to enable the gun to reach maximum velocity (valve open until pellet exits the muzzle)…. and I have yet to fail to reach the plateau (maximum velocity) doing that....

Bob
Title: Re: Simplified Balanced Valve
Post by: PikeP on January 09, 2019, 03:45:30 AM
Good to know. Those little details add up. Is the hammer spring exactly 11 lb/in and under zero preload when uncocked? I added a few changes that raised the valve lift to .076", still not quite where you have it but getting there

Once developed if this spreadsheet helps build a balanced valve I'll certainly release it here.

I added ideal barrel length and approximate valve close for the intended energy output for efficient conditions, the estimation was based off Bob's current estimation himself at the valve closing at 16"~ down the barrel.

The optimal barrel length is surprisingly easy to calculate for a given energy level. I tested it with various calibers at different power levels and it scaled surprisingly well. For example a 65 fpe 25 cal at 2000 psi is recommended a 23" barrel where as a 500 fpe. 45 cal at 4000 psi only needs  the same 23" of barrel. This calculation is based entirely on intended fpe, pressure, plenum size, and caliber. It does not currently take into account port size which is assumed to be suited for the caliber. I also calculate the optimal port size for a provided intended fpe at the given pressure, caliber, plenum and barrel length.

Also added optimal plenum size at current pressure and set point based on current plenum volume. Values are based on keeping pressure drop between 7% and 10% which I can certainly widen to 7% to 14% comfortably.

Also scaled recommended hammer spring ratings to stem size where as before it was scaled only to force holding poppet shut. Surprisingly I estimate the .1563" stem only needing 11 to 12 lb spring with 78~ grams of hammer. Will be interesting to validate or refine that calculation although my tests up to this point seem in line.
Title: Re: Simplified Balanced Valve
Post by: rsterne on January 09, 2019, 01:08:52 PM
Hammer spring is 10.9 lb/in. and the preload is 0.31" when uncocked, but mounted on the SSG.... I didn't measure the valve lift on this gun, but I have on some others, using a lightweight indicator rod through the RVA with a siding O-ring.... Unfortunately, you can't do that with an SSG.... The 0.094" is just a guess, your 0.076" is likely in the ballpark....

Lloyd's Internal Ballistics Spreadsheet, and my personal experience, dictate MUCH longer barrel lengths than you are indicating.... By optimum, I mean the barrel that can produce maximum FPE in the projectile for a given air release by the valve.... The expansion of the air after the valve closes can add a LOT of velocity, while adding to the efficiency as well.... all without using 1 mg. more air.... Compare the Texan with its 34" barrel to the Texan SS or Carbine with their 23".... HUGE difference in velocity with the same bullets....

Bob

PS - Additionally, I think you will find that the larger the plenum the less pressure drop at the pellet during the shot.... I can't see any reason for there to be an "ideal" plenum volume (ie where the pressure and/or FPE and/or efficiency peak.... Bigger is better, IMO, providing you don't lose primary reservoir volume to achieve it.... It's just that the gains above 1 cc/FPE are minimal.... Actually, the higher the overall FPE/CI achieved, the smaller a plenum you can "get away with", without losing too much power or needing increased plenum pressure....

When I remove my "tiny tank" and replace it with the 500 cc bottle, the reservoir/plenum volume becomes 460 cc (instead of 108 cc)….

RBS
Title: Re: Simplified Balanced Valve
Post by: rsterne on January 09, 2019, 04:42:05 PM
I DID IT !!!!!!!!!!!!!!!!!!!!!!!!!!!!!

Adjustable, efficient, low hammer strike.... everything I wanted.... Details to follow....

Bob
Title: Re: Simplified Balanced Valve
Post by: rsterne on January 09, 2019, 05:00:42 PM
First of all, the changes I made, and final dimensions.... I pulled the valve and disassembled it and drilled the through vent out to 0.052 (#55 drill)…. that went really easy, no chance of breaking the drill.... I then drilled another cross vent closer to the seat of the poppet on the opposite side of the stem, and enlarged it to 1/16" and angled it about 30 deg. to ease the flow.... I left the previous 0.040" vent there, 0.1" further out.... The vent length from the large cross hole to the end is 1.0".... I turned the spring seat down a few thou to accept a spring made from heavier wire that was still 7/32" OD, but 0.028" wire and 1" long.... It has 5 lbs. of force when the valve is closed, and a spring rate of about 14 lb/in.... The travel depth available to the poppet is 0.250", but the O-ring bumper reduces the travel by 0.030" to 0.220".... However, the stem only protrudes from the back of the valve by 0.210", so the hammer cannot even drive the poppet far enough to hit the O-ring bumper.... The balance chamber is therefore 0.315" diameter (I measured it) and 0.250" long.... In addition there is a spring chamber 0.250" diameter and 0.40" long.... You can subtract from that volume the spring seat on the poppet of 0.160" diameter by 0.100" long, and the volume occupied by the spring, which weighs 0.72 g.... The poppet c/w O-rings weighs 4.32 g. so including 1/3 the weight of the spring, the poppet mass for calculations would be 4.56 g.... The gun was reassembled and tested for leaks, and had none....

Now to put all my results into a spreadsheet and produce some charts.... Stand By !!!

Bob
Title: Re: Simplified Balanced Valve
Post by: mann on January 09, 2019, 05:19:38 PM
Derlin finally made it so I'll try to make a new poppet tonight it will probably end up being .375 and .218 or what ever drill bit I have close to .210
Title: Re: Simplified Balanced Valve
Post by: tkerrigan on January 09, 2019, 06:22:44 PM
Good news Bob, I hope they end up being simple enough that I can make some, I have six DAQ pistols that are a bear to cock.  Thanks for the effort on this project, we really appreciate it.  Regards,Tom
Title: Re: Simplified Balanced Valve
Post by: oldpro on January 09, 2019, 06:24:38 PM
Bob here’s that simple balanced valve tune it was buried 50 pages deep into my tune sheets lol.

Created: 12/12/17 7:45 PM
Description: SS 2 .25 cal Mrod
Notes 1: 2700 tether poppet 250/352
Notes 2: 1/4 turns
Distance to Chrono(FT): 1.00
Ballistic Coefficient: 1.000
Bullet Weight(gr): 34.00
Temp: 59 °F
BP: 29.79 inHg
Altitude: 0.00
#          FPS   FT-LBS       PF
9     932      65.59    31.69   
8     561      23.76    19.07   
7     420      13.32    14.28   
6     446      15.02    15.16   
5     403      12.26    13.70   
4     336      8.52     11.42   
3     302      6.89     10.27   
2     283      6.05     9.62   
1     255      4.91     8.67   
Average: 437.6 FPS
SD: 208.3 FPS
Min: 255 FPS
Max: 932 FPS
Spread: 677 FPS
Shot/sec: 0.1
True MV: 438 FPS
Group Size (in): 0.00
Title: Re: Simplified Balanced Valve
Post by: rsterne on January 09, 2019, 06:27:49 PM
I can see why you gave up on it, Travis.... I'm glad I didn't....  ;)

With the changes detailed about, the valve is now adjustable, and incredibly efficient.... Here are the results, using the SSG with the 11 lb/in spring and 3.4 lbs preload, with the gun tethered at 3000 psi....

(http://i378.photobucket.com/albums/oo221/rsterne/Hayabusa%20PCP/Hayabusa%20Balanced%20Valve_zpsxh82dhnr.jpg) (http://s378.photobucket.com/user/rsterne/media/Hayabusa%20PCP/Hayabusa%20Balanced%20Valve_zpsxh82dhnr.jpg.html)

The valve is working about the same as an SS valve in terms of adjustability.... The hammer spring is perfect for the 131 gr. bullet, it is solidly on the plateau at over 950 fps with 2 turns of gap.... With the 154 gr. bullet it needs a slightly heavier spring or more preload to reach the plateau, which would be at about 890 fps.... However, since I never tune my guns to shoot on the plateau because it is quite inefficient, this SSG spring setup is just fine.... The cocking force is just 13 lbs. instead of the 23 lbs. with the smaller, conventional valve.... I tried a couple of short strings just to prove that I can get a bell curve, but bear in mind this is with the tiny tank fitted, and a total reservoir volume of only 108 cc....

(http://i378.photobucket.com/albums/oo221/rsterne/Hayabusa%20PCP/Hayabusa%20Balanced%20Strings_zpsipozoyow.jpg) (http://s378.photobucket.com/user/rsterne/media/Hayabusa%20PCP/Hayabusa%20Balanced%20Strings_zpsipozoyow.jpg.html)

With the 154 gr. bullet I had the SSG adjusted with 2 turns of gap, for about 3% below the plateau, and got a declining shot string, although the first 2 shots were within 15 fps (2% ES)…. With the 131 gr. bullet, I used 5 turns of gap on the SSG to produce a nice bell-curve at about 9% below the plateau.... The first three shots had an ES of only 8 fps, which is less than 1%.... Bear in mind that with the 500 cc tank fitted, the total air capacity is 460 cc, which will give over 4 times the shot count within the same ES....

I need to brag about the efficiency for a minute.... What I got for each of the 4 shots with the 131 gr. bullet is plotted on the dotted line above.... The first shot only used 284 psi from my 108 cc reservoir, or just 129 CI of air to produce 216 FPE, for 1.67 FPE/CI.... That is definitely off the scale compared to any other Big Bore PCP I have ever shot, or am aware of.... The average over those 4 shots was 1.53 FPE/CI....  :o

To say I am delighted with where I am would be a complete understatement.... It was difficult to get here, requiring several changes to the valve.... but it turns out that the large vent through the stem was the key.... We have to get a high enough flow rate through the vent to keep the valve from blowing open.... Once that is achieved, the valve is definitely tunable, and capable of producing a bell-curve.... I am just over the moon the way this worked out.... My thanks to all those who provided input along the way, and in particular to Mike, who by quantifying the fill time for the balance chamber led me in the right direction....  8)

Bob
Title: Re: Simplified Balanced Valve
Post by: PakProtector on January 09, 2019, 06:35:54 PM
Rock on Bob!!!!
cheers,
Douglas
Title: Re: Simplified Balanced Valve
Post by: shorty on January 09, 2019, 06:42:10 PM
Congratulations Bob. Efficiency is amazing.

Please list all your new specs on the valve.

Do you now think that a cothran valve can be tune-able with the slight modification to valve stem ?
Title: Re: Simplified Balanced Valve
Post by: oldpro on January 09, 2019, 06:42:54 PM
I can see why you gave up on it, Travis.... I'm glad I didn't....  ;)

With the changes detailed about, the valve is now adjustable, and incredibly efficient.... Here are the results, using the SSG with the 11 lb/in spring and 3.4 lbs preload, with the gun tethered at 3000 psi....

(http://i378.photobucket.com/albums/oo221/rsterne/Hayabusa%20PCP/Hayabusa%20Balanced%20Valve_zpsxh82dhnr.jpg) (http://s378.photobucket.com/user/rsterne/media/Hayabusa%20PCP/Hayabusa%20Balanced%20Valve_zpsxh82dhnr.jpg.html)

The valve is working about the same as an SS valve in terms of adjustability.... The hammer spring is perfect for the 131 gr. bullet, it is solidly on the plateau at over 950 fps with 2 turns of gap.... With the 154 gr. bullet it needs a slightly heavier spring or more preload to reach the plateau, which would be at about 890 fps.... However, since I never tune my guns to shoot on the plateau because it is quite inefficient, this SSG spring setup is just fine.... The cocking force is just 13 lbs. instead of the 23 lbs. with the smaller, conventional valve.... I tried a couple of short strings just to prove that I can get a bell curve, but bear in mind this is with the tiny tank fitted, and a total reservoir volume of only 108 cc....

(http://i378.photobucket.com/albums/oo221/rsterne/Hayabusa%20PCP/Hayabusa%20Balanced%20Strings_zpsipozoyow.jpg) (http://s378.photobucket.com/user/rsterne/media/Hayabusa%20PCP/Hayabusa%20Balanced%20Strings_zpsipozoyow.jpg.html)

With the 154 gr. bullet I had the SSG adjusted with 2 turns of gap, for about 3% below the plateau, and got a declining shot string, although the first 2 shots were within 15 fps (2% ES)…. With the 131 gr. bullet, I used 5 turns of gap on the SSG to produce a nice bell-curve at about 9% below the plateau.... The first three shots had an ES of only 8 fps, which is less than 1%.... Bear in mind that with the 500 cc tank fitted, the total air capacity is 460 cc, which will give over 4 times the shot count within the same ES....

I need to brag about the efficiency for a minute.... What I got for each of the 4 shots with the 131 gr. bullet is plotted on the dotted line above.... The first shot only used 284 psi from my 108 cc reservoir, or just 129 CI of air to produce 216 FPE, for 1.67 FPE/CI.... That is definitely off the scale compared to any other Big Bore PCP I have ever shot, or am aware of.... The average over those 4 shots was 1.53 FPE/CI....  :o

To say I am delighted with where I am would be a complete understatement.... It was difficult to get here, requiring several changes to the valve.... but it turns out that the large vent through the stem was the key.... We have to get a high enough flow rate through the vent to keep the valve from blowing open.... Once that is achieved, the valve is definitely tunable, and capable of producing a bell-curve.... I am just over the moon the way this worked out.... My thanks to all those who provided input along the way, and in particular to Mike, who by quantifying the fill time for the balance chamber led me in the right direction....  8)

Bob
I had the SS valve then so I had no need to work on this anymore BUT that said I see I was wrong. I have room in the poppet to add and additional vent hole and effectively double the vent area. I still have all the parts that's what I took the pic of for you in a previous post so let me find some valve bodies and see if I can get this to work.
Title: Re: Simplified Balanced Valve
Post by: PikeP on January 09, 2019, 07:46:13 PM
Bob I am thrilled. First let me say the ideal barrel length I calculate is more less the minimum length required to achieve said power and my calcs put a .45 cal 23" barrel shooting 250 gr at 4000 psi right there..although more length would nearly always be ideal. I changed the wording to Min opposed to ideal and I'll add one for ideal. The optimal plenum volume is simply within range to keep pressure drop down to 5% to 10% which I can make user adjustable.

I also adjusted the optimal fill time formula and now use the chamber ratio as a variant so it scales..


Here is your updated sheet from me...please tell me if I need to correct any inputs. It is a comparison of the .04 and .052 vent. Notice how close the 100% fill time is to your dwell with the .04 vent?  ;D

I just noticed I have valve lift marked as Ms when it's in inches. Silly but corrected
Title: Re: Simplified Balanced Valve
Post by: mann on January 09, 2019, 08:05:45 PM
Cool good job Bob . I got a derlin poppet made tonight it's at .250 and .375 with .040 vent hole need to make the thimble yet though
Title: Re: Simplified Balanced Valve
Post by: Hobbyman2007 on January 09, 2019, 08:50:18 PM
Very impressive . Thanks all for sharing . I must say in the last three years that I’ve been involved in the PCP world , all of the advancements were done here on the GTA . Best site ,best people period .
Title: Re: Simplified Balanced Valve
Post by: rsterne on January 09, 2019, 08:50:53 PM
Mike, that looks good.... The valve spring preload is actually 0.35" = 5 lbs.... If I use your chamber volume of 0.529 cc at 233 mg/cc, filled at 86 mg/ms I get 1.43 ms for the  fill time, not 1.50.... That is without factoring in the reduction in balance chamber volume due to poppet lift.... At 1/2 the dwell of 2.64 ms the lift you calculated is 0.085", which would reduce the chamber by (0.315^2 x PI/4) x 0.085 = 0.0066 CI = 0.109 cc.... That means at full lift the total balance chamber is only 0.42 cc, and the fill time would be quite a bit less, at about 1.14 ms.… At least I think that is correct....

If you assume a parabola for the lift to dwell curve, the lift at 1/4 of the dwell should be about 0.707 x 0.085" = 0.060".... get where I'm going with this?.... I think the fill times are overestimated because the poppet is displacing volume from the balance chamber as it opens....

Bob
Title: Re: Simplified Balanced Valve
Post by: PikeP on January 09, 2019, 08:58:23 PM
I am using a value of 1/2 valve lift to displace the volume during the shot cycle as that is likely its average displacement...I know it's not perfect but it's currently calculated that way. I could certainly include it all. Original volume no lift is .58 cc.

The fill time is calculating additional losses hence our minor difference from 1.43 to 1.5 ms...also calculates the distance in the valve stem - vent size / 2

Do you think the current 1/2 lift value represents average chamber volume or would 2/3rd or full lift be better? Chamber volume at full lift should be .475 cc
Title: Re: Simplified Balanced Valve
Post by: rsterne on January 09, 2019, 09:31:45 PM
Tim, all of the dimensions are in the right hand side of Mike's last spreadsheet in the reply above.... If there is something you can't find, just ask.... but no point me listing them all over again.... I have no idea if you can mod. a Cothran valve to not blow open, as they were designed to do that....  I can tell you that if you remove the metering rod in the stem you will destroy the soft poppet seal in a few shots....

Douglas, Travis, Mark and Denis.... Thanks for your comments and support.... It has been a long and frustrating process, but I learned a lot and the reward of getting it to work as desired is sweet indeed....

Mark, I would suggest you increase the vent to 3/64" (0.047") if possible.... Realistically I don't think you can go too big....

Bob
Title: Re: Simplified Balanced Valve
Post by: mann on January 09, 2019, 09:36:29 PM
Ok thanks Bob I think your right I don't think you can go to big . The chamber will just fill faster up to a point where it can't fill any faster
Title: Re: Simplified Balanced Valve
Post by: rsterne on January 09, 2019, 09:56:14 PM
Mike, let me work through the balance chamber volumes and see if I get the same results.... I'll work in CI and convert at the end....

Main chamber = (0.315^2 x PI/4) x 0.25" = 0.0195 CI
Spring chamber = (0.250^2 x PI/4) x 0.40" = 0.0196 CI
Vent = (0.052^2 x PI/4) x 1.0" = 0.0021 CI
Total of above = 0.0412 CI

Subtract the following volumes....

Spring volume = 0.0057 CI
Spring Seat = (0.160^2 x PI/4) x 0.10" = 0.0020 CI

Resulting volume when valve closed = 0.0412 - 0.0057 - 0.0020 = 0.0335 CI = 0.549 cc

When the chamber is filled, the valve is at very close to full lift of 0.085" (that occurs at 1.32 ms), so we need to deduct....

(0.315^2 x PI/4) x 0.085" = 0.0066 CI = 0.109 cc.... This reduces the total volume to 0.549 - 0.109 = 0.44 cc....

At the 50% fill point, I think we can assume the valve is open about 75% of the way, at the 25% point about 40% way.... and at 75% fill probably about 90% of full lift.... That means from the 0.549 cc we need to deduct about 0.044 cc at 25%, 0.082 cc at 50%, and 0.098 cc at 75%.... That's as close as I can estimate it.... This would make the volume of the balance chamber at each percentage the following....

25% = 0.505 cc
50% = 0.467 cc
75% = 0.451 cc
100% = 0.440 cc

From that you can get the mg of air needed and then the time to fill....

Bob
Title: Re: Simplified Balanced Valve
Post by: rsterne on January 09, 2019, 09:57:19 PM
Mark, I can tell you that squirting shop air through the vent at 0.052" is a HUGE amount more than at 0.040".... :o

You can drill the cross vent closer to the poppet seat, or drill a 2nd one (closer) on the other side, like I did....

Bob
Title: Re: Simplified Balanced Valve
Post by: mann on January 09, 2019, 10:09:10 PM
I'll up the size and drill another hole closer to the poppet head
Title: Re: Simplified Balanced Valve
Post by: lloyd-ss on January 09, 2019, 10:18:40 PM
Bob,
Very good results on this new simplified valve!  With the bigger vent thru the stem, you have the benefit of the easy opening balanced valve, but then it immediately backfills via the large vent, and becomes a conventional valve with conventional tunability.
Good news!
Lloyd
Title: Re: Simplified Balanced Valve
Post by: oldpro on January 09, 2019, 10:27:52 PM
 Bob Good job Buddy and it looks like I gave up to early originally but I had another valve in the works so I strayed from what looks to be a better solution. Excellent work and way to stick with it and get the desired results. I found the valve parts and put it together and will test  it again before the extra vent hole and after to compare results. If I come close to your efforts I will be very pleased so once again congrats.
Title: Re: Simplified Balanced Valve
Post by: PikeP on January 09, 2019, 10:28:57 PM
Updated my sheet to reflect that new volume reduction and those lift values. Here is another comparison of the .04 and .052 venting on your valve. Should look about right


Also added optimal vent sizing approximation. Can/will tweak that along the way.
Title: Re: Simplified Balanced Valve
Post by: oldpro on January 09, 2019, 10:42:24 PM
Updated my sheet to reflect that new volume reduction and those lift values. Here is another comparison of the .04 and .052 venting on your valve. Should look about right
Wheres the small end poppet in the mix? Am I not seeing it?
Title: Re: Simplified Balanced Valve
Post by: PikeP on January 09, 2019, 10:49:11 PM
I think that is the spring seat bob refers to in which case its volume reduction is under the new misc chamber volume entry cell. This sheet has grown quite large but once tested across multiple calibers and power levels we should have the simplified balance valve set in stone and public knowledge as not how to just build one but how they tick. Good times ahead.
Title: Re: Simplified Balanced Valve
Post by: oldpro on January 09, 2019, 11:05:04 PM
 So the big end on the seat is .437 and small balance piston .250 Correct?
Title: Re: Simplified Balanced Valve
Post by: PikeP on January 09, 2019, 11:24:14 PM
From what I gather the poppet on seat is
.437" OD and the balance chamber is .315" which equates to roughly 52% less force against the poppet while its seated. Balance chamber od should technically read ID which I just changed as to not cause confusion
Title: Re: Simplified Balanced Valve
Post by: mann on January 09, 2019, 11:25:15 PM
It says balance chamber od is .315  I don't see the dimension of the balance part of the poppet
Title: Re: Simplified Balanced Valve
Post by: PikeP on January 09, 2019, 11:36:45 PM
It says balance chamber od is .315  I don't see the dimension of the balance part of the poppet

The balance part is the entire ID of the chamber as you have to keep it sealed with oring on the poppet so the force is applied to that whole area.
Title: Re: Simplified Balanced Valve
Post by: mann on January 09, 2019, 11:53:50 PM
Yeah I figured it had to be close to .315 to get the seal
Title: Re: Simplified Balanced Valve
Post by: rsterne on January 10, 2019, 01:10:03 AM
Mark, I drilled the balance chamber in the poppet just under 5/16" and then finished it with a 5/16" end mill and then polished the bore with 220 and then 400 grit paper.... The finished ID was 0.315", which is 72% of the OD of the large end of the poppet.... I used a 5 x 8 mm O-ring (1.5 mm CS = 0.059")…. I turned the groove in the poppet 0.100" smaller than the 0.315" bore, so 0.215".... This gave a crush on the O-ring of 15%, and I used a 70D Buna-N O-ring, lubricated with Dow 55.... The small end of the poppet was turned to be a sliding fit inside the 0.315" bore, so about 0.312".... When you are calculating the area so you can get the correct force, you use the ID of the bore, which is the OD of the installed O-ring....

Mike, I noticed a couple of small errors.... The Hammer Gap is only 0.10", not 0.42".... The spring is preloaded 0.31" on the SSG, and then there is a gap of 0.10" (at 2 turns) between the end of the stopped guide and the inside of the hammer.... When the hammer first touches the SSG guide on cocking, it is 0.10" from the valve stem, and the spring at that point has a preload of 3.4 lbs.... In addition, the valve spring when the poppet is on the seat is compressed 0.35" and the load is 5 lbs.... In addition, I would estimate the Wasted Transfer Port volume at about 2 cc, including the chamber in the barrel....

Bob
Title: Re: Simplified Balanced Valve
Post by: rsterne on January 10, 2019, 01:13:53 AM
Travis, the small end is 5/16", big end 7/16".... nominal diameters....

bob
Title: Re: Simplified Balanced Valve
Post by: PikeP on January 10, 2019, 01:55:54 AM
Bob, iirc you had more gap earlier and less hammer pl, but I could be mistaken. I'll correct all those figures. What's your estimated valve dwell and lift with those figures based on Lloyd's info so I can try to match that data as closely as possible as I haven't formulated that part of the model particularly well. Itll certainly help keep all the other data more accurate.
Title: Re: Simplified Balanced Valve
Post by: MJP on January 10, 2019, 02:24:42 AM
Nice work Bob, achieving what you wanted in a valve.
The port can be too big for a given hammer, closes off too quick if you have bigger balancer piston.
All you get is a small pop and that's it.

Marko
Title: Re: Simplified Balanced Valve
Post by: rsterne on January 10, 2019, 12:58:19 PM
Mike, you are correct, I was running more gap earlier, because the valve was blowing open.... Now that it is better controlled, more hammer strike is required, and when you vary it, you get a velocity change (as it should be) instead of just a change in air use.... I tune regulated PCPs about 3-5% below the plateau (maximum) velocity to get decent efficiency.... 2 turns of gap is about 97% of maximum, and that is the 0.10" gap (the adjuster is 20 TPI)…. In order to get a bell-curve in an unregulated PCP, you need to be about 10% below the plateau, and somewhere between 7-9% will often give you a couple of equal shots.... 5 turns of gap is about 91% of maximum, and produced a decent bell-curve with the 131 gr. bullet.... Heavier bullets need a bit more hammer strike, of course, as you can see I can't quite max. out the 154 gr. with the 11 lb. hammer spring, even with zero gap on the SSG....

I set up Lloyd's spreadsheet for the new, higher efficiency with the 154 gr. bullet, and it says the dwell is likely about 2.2 mSec. with the valve closing when the bullet is about 9" from the breech.... Here is the output from his spreadsheet at these settings....

(http://i378.photobucket.com/albums/oo221/rsterne/Hayabusa%20PCP/Hayabusa%20357%20Lloyd3_zpsvjvpchdi.jpg) (http://s378.photobucket.com/user/rsterne/media/Hayabusa%20PCP/Hayabusa%20357%20Lloyd3_zpsvjvpchdi.jpg.html)

That is for the first shot in the string, of course, at 3000 psi.... SSG at 2 turns of gap.... 858 fps (252 FPE).... 1.46 FPE/CI (380 psi drop, 173 std. CI of air used)…. 13.7 cc of air at 3000 psi.... The lift would only be slightly less than before, but your current 0.085" is probably in the ballpark....

Bob
Title: Re: Simplified Balanced Valve
Post by: rsterne on January 10, 2019, 01:42:31 PM
Just to give everyone an idea of what I started with.... my .357 Hayabusa Mk.II had slightly smaller ports (0.281") and a bit smaller throat at 0.328" (1/8" stem) and a 3/8" poppet.... With the same 154 gr. bullet, the gun maxed out at 866 fps (257 FPE), at 0.74 FPE/CI.... basically using twice the air it does now per shot for the same velocity.... When tuned for a 6 shot bell-curve it averaged 824 fps at 1.13 FPE/CI.... It was using a 145 g. hammer with 1.45" of stroke, that took 23 lbs. to cock....

With the new balanced valve, it maxes out at about 890 fps (271 FPE) because of the larger ports.... With the new balanced valve I am now using a 77 gr. hammer and an SSG with a much lighter spring and just under 1" of stroke, and the cocking force is down to 13 lbs.... It can be tuned to the same velocity that it maxed out at before, using about half the air.... so the efficiency has roughly doubled.... and so far I have only been testing with my "tiny tank" and a total reservoir volume of 108 cc instead of 460 cc....  :o

I fully expect the maximum velocity and energy to increase when I fit the 22 CI bottle.... because the pressure drop during the shot will be a lot less.... I hate making predictions, but 300 FPE on 3000 psi is not out of the question, according to Lloyd's spreadsheet....  8)

Bob
Title: Re: Simplified Balanced Valve
Post by: Brian W Cook on January 10, 2019, 02:18:27 PM
 I dug out my oldest poppet i made with the piston on the end . At the time i wasn’t worried about how fast the high pressure air would get back to the “chamber”.
Hence the minimal exposure of the hole . 
Doing one now i would football shape the piston around the Oring to minimize any drag and probably use a square bottom Oring grove to allow a bit of movement.   
Title: Re: Simplified Balanced Valve
Post by: rsterne on January 10, 2019, 02:54:01 PM
Thanks for sharing that, Brian....

Mike, I have a question for you.... I have a smaller OD spring here that will fit in a 13/64" hole (0.203") instead of 1/4".... It weighs 0.71 g. (so almost the same)…. I would have to turn the spring seat down to 0.130" from 0.160" OD to fit inside it.... I am pretty sure I can use it with no other changes required.... That would make the spring cavity only 2/3rds the volume it is now.... Based on my previous calculations, I think that brings the total chamber volume down to 0.453 cc, less the 0.109 cc from the poppet lift, which would mean the chamber at 100% fill would only be 0.344 cc instead of 0.444 cc.... I think that brings the fill time down to 1.05 ms.… Could you check these figures and comment please?.... I think it may be worthwhile to stuff the front spring hole and try the smaller OD spring....

Bob
Title: Re: Simplified Balanced Valve
Post by: PikeP on January 10, 2019, 03:31:05 PM
Here is the current and modified spring chamber approximations as requested. I think I can scale required hammer spring energy to the fill times as now it's just final closing force and opening force. I think I'll need to determine the ideal timing first for our bell curve based on required dwell for  a particular arrangement.
Title: Re: Simplified Balanced Valve
Post by: oldpro on January 10, 2019, 04:26:27 PM
Here is the current and modified spring chamber approximations as requested. I think I can scale required hammer spring energy to the fill times as now it's just final closing force and opening force. I think I'll need to determine the ideal timing first for our bell curve based on required dwell for  a particular arrangement.
I wish I had this a few years ago!!! Awesome mike just awesome.
Title: Re: Simplified Balanced Valve
Post by: rsterne on January 10, 2019, 04:42:28 PM
Thanks, Mike.... I agree with Travis, awesome job.... How do you determine the "optimum fill times" at the various percentages ???

If I could suggest that you change the vertical scale on the right hand side to -200 to +100.... then the numbers would be on the lines, instead of drifting away from them....

Bob
Title: Re: Simplified Balanced Valve
Post by: oldpro on January 10, 2019, 04:52:57 PM
 Bob any noticeable stiction yet? Also do you think it will be stable with a loaded hammer?
Title: Re: Simplified Balanced Valve
Post by: rsterne on January 10, 2019, 05:15:56 PM
No stiction that I have noticed.... I fired the gun set up for 3000 psi down to less than 1000 psi with NO hammer bounce.... Also, a couple days ago, per your request, I preloaded the SSG against the hammer 2 turns, which was 5.6 lbs. of preload, and all it did was get louder.... Reply #184, with the smaller vent in place.... The only thing I haven't tried is preloaded and way less pressure, but I am confident preloading will not be an issue.... However, with the efficiency I am getting with this valve with an SSG, I may never find out....  ::)

Bob
Title: Re: Simplified Balanced Valve
Post by: oldpro on January 10, 2019, 05:19:04 PM
No stiction that I have noticed.... I fired the gun set up for 3000 psi down to less than 1000 psi with NO hammer bounce.... Also, a couple days ago, per your request, I preloaded the SSG against the hammer 2 turns, which was 5.6 lbs. of preload, and all it did was get louder.... Reply #184, with the smaller vent in place.... The only thing I haven't tried is preloaded and way less pressure, but I am confident preloading will not be an issue.... However, with the efficiency I am getting with this valve with an SSG, I may never find out....  ::)

Bob
I can test it tomorrow I did put the old valve back together and ran a string to verify my original string. I will add additional vent hole and see what happens tomorrow time permitting as were really busy getting ready for shot show. I didnt have any 34s like in original strings but same effect is noted.

Created: 01/10/19  1:06 PM
Description: test balanced valve
Notes 1: 25.4 Jsb
Notes 2:
Distance to Chrono(FT): 1.00
Ballistic Coefficient: 1.000
Bullet Weight(gr): 25.40
Temp: 59 °F
BP: 29.79 inHg
Altitude: 0.00
#          FPS   FT-LBS       PF
10    1001     56.52    25.43   
9     795      35.65    20.19   
8     634      22.67    16.10   
7     609      20.92    15.47   
6     485      13.27    12.32   
5     517      15.08    13.13   
4     446      11.22    11.33   
3     402      9.12     10.21   
2     434      10.62    11.02   
1     384      8.32     9.75   
Average: 570.7 FPS
SD: 196.8 FPS
Min: 384 FPS
Max: 1001 FPS
Spread: 617 FPS
Shot/sec: 0.1
True MV: 571 FPS
Group Size (in): 0.00
Title: Re: Simplified Balanced Valve
Post by: mann on January 10, 2019, 05:34:20 PM
Bob how do you keep the threads from causing inconsistency on your ssg do you only use a minimal amount of threads on them
Title: Re: Simplified Balanced Valve
Post by: PikeP on January 10, 2019, 06:41:21 PM
Bob right now I have optimum fill time set to a factor of dwell and balance ratio in Hope's this will scale well...of course that ratio can be modified provided fine tune it or throw in another variable. If I reduce dwell time to 1.2 seconds the recommended optimal fill time drops to .8 ms. If I take that same 33 gr hammer and put the balance ratio to 82% I go back up to 1.5ms optimal fill time...for example.

Here is the current formula in use.

Dwell * (reduced force % / 100) * correction factor

I also re did the above graphs to reflect minor changes as well as the scaling on chart Bob recommended. I get slightly less air ejection and use than what you're getting of course I'm just predicting it out of thin air so I will have to fine tune that as well as other things I'm sure.
Title: Re: Simplified Balanced Valve
Post by: PikeP on January 10, 2019, 07:35:39 PM
Here is some more data reflecting potential changes based on barrel length alone, port size alone, plenum size alone, and projectile weight alone. This may give a good look into what kind of energy is possible with each change for the configuration being built.

Also modified air usage...was using full 3000 psi opposed to average pressure for air mass ejected. And 1.45 instead of 1.46 fpe/ci
Title: Re: Simplified Balanced Valve
Post by: rsterne on January 10, 2019, 08:30:23 PM
After the gun sat overnight, I shot the pressure down using 68 gr. roundball, starting from 3000 psi.... It took 11 shots to get down to 270 psi.... The first shot was supersonic at 1160 fps, the 2nd shot was 1108, and it progressed down to 446 fps for the 11th shot, taken at only 315 psi.... There was NO sign of hammer bounce, regardless of how low the pressure got.... the gun just got quieter and quieter as the velocity dropped.... I then refilled it and cranked in 2 turns of preload on the SSG, so that there was 4.7 lbs. of preload against the stem.... I was finally able to get the valve to dump the tank down to about 300 psi in 1 shot by doing that.... Now, you would never tune the gun this way, because you are wayyyyyyyyyyy up on the plateau and the efficiency would be terrible.... but there you go, Travis, I forced it to machine-gun for you....  ::) …. I really doubt it would ever do this with any kind of a tune you would ever use, but if you insist on running lots of preload against the stem, you may be able to create a tank dump....  ;D

After draining the tank I pulled the valve out yet once more, because I had a smaller poppet spring I wanted to install, and then sleeve down the spring chamber to reduce the volume and speed up the pressure rise in the balance chamber.... I made a Teflon sleeve to fit inside the 1/4" bore of the 0.40" deep spring chamber, and drilled it out to 13/64".... This reduced the volume of the chamber from 0.55 cc to 0.45 cc, and I was curious what effect that would have on the tuning range.... I put the gun back together, and this is what I got....

(http://i378.photobucket.com/albums/oo221/rsterne/Hayabusa%20PCP/Hayabusa%20357%20New%20Valve2_zpsyty6gnro.jpg) (http://s378.photobucket.com/user/rsterne/media/Hayabusa%20PCP/Hayabusa%20357%20New%20Valve2_zpsyty6gnro.jpg.html)

NOTE: When calculating the efficiency, I forgot to include the air in the hose, gauge and valve.... I have estimated that at 12 cc, making the total 120 cc instead of 108.... This reduced the FPE/CI numbers to more realistic values, shown on the corrected graph above.... I still won't have the actual numbers until I install the 22 CI bottle....

The maximum velocity stayed the same at 955 fps, but the velocity dropped off faster as I increased the gap, as I expected it might.... Instead of a range of about 120 fps before the valve quit working, that range increased to 180 fps.... The velocity was still very stable when tuned below 800 fps, whereas with the larger spring chamber I couldn't even tune it that low.... Being able to tune it down that far allowed the efficiency to reach even higher than yesterday, I got to 1.57 FPE/CI at 864 fps (217 FPE)…. With my old conventional valve at the same power I was getting 1.13 FPE/CI, which I thought was pretty good at the time.... I'm now using 2/3rds of the air for the same power....  :o

Decreasing the balance chamber size by 20% certainly widened the tuning range.... However, it really only made about 1 turn difference in the SSG gap for the same velocity.... That means the valve is taking the same hammer strike to open, but with the pressure in the balance chamber rising faster, a bit more hammer strike is needed to get the same dwell.... It was definitely worth changing to the smaller poppet spring and making the chamber smaller.... Once again, it seems obvious (now) that you want the smallest balance chamber you can achieve, with the largest vent.... That definitely seems to be the key to getting this valve tuneable....

Bob
Title: Re: Simplified Balanced Valve
Post by: rsterne on January 10, 2019, 08:37:24 PM
Mark, I only thread the SSG rod enough for the nuts and where the bumper O-ring sit.... When the hammer is uncocked, the guide rod running through the adjusting bolt is mostly smooth (full OD)….

Mike, your spreadsheet is growing, just like Topsy….  ;D .... I will be interested in seeing what happens when you use the smaller spring chamber as I calculated in Reply #330.... This is the way I plan to leave the gun, for now.... The next experiment will be to fit the .224 cal barrel on this beast and see what happens....  :o ::) ;)

Bob
Title: Re: Simplified Balanced Valve
Post by: PikeP on January 10, 2019, 08:52:30 PM
Bob here is the updated chart with current config. I optimized the formula for fill time to reflect your success. Hopefully it trends..and as I suspected it seems to be about half the figure of dwell seems optimal...that seemed like the optimal timing to have closing force acting in your favor based on the parabolic lift profile over the dwell time of an efficient valve.
Title: Re: Simplified Balanced Valve
Post by: PikeP on January 10, 2019, 09:01:38 PM
Would be nice to have either the vent size be adjustable or the volume on the fly...I think matching either will be critical to large changes in power or caliber ie dwell requirements. A variable volume adjuster or vent throttle screw that were drilled into stem seem quite possible. Increasing or decreasing volume externally would be fun to integrate.
Title: Re: Simplified Balanced Valve
Post by: PikeP on January 10, 2019, 09:09:24 PM
Do you believe my theory now that closing the valve and obtaining a tuning range is determined in the latter half of the valve event. Former is opening and as I stated much earlier you wont require much more hammer energy when increasing closing force in the latter half of the valve event. Tried and true.
Title: Re: Simplified Balanced Valve
Post by: mann on January 10, 2019, 10:03:48 PM
I'll have to give your ssg a try I've only used one and it was a internal ssg where the hammer was also on the bolt the whole assembly would go forward and hit the poppet  instead of just the hammer
Title: Re: Simplified Balanced Valve
Post by: rsterne on January 10, 2019, 10:27:27 PM
Mike, your latest spreadsheet is great, and appears to have a lot of functionality that agrees with reality.... I'm not sure that it is the latter half of the cycle that governs the tuneability or not.... It could simply be that if the valve blows open faster than the hammer is travelling you don't get the tunability.... However it is a reasonable explanation I can accept without any evidence to argue against it....

OK, so here is a question for you.... If I change the barrel and transfer port only to .224 cal, and use a 41.3 gr. bullet.... what do you think will happen?.... The valve in theory can release enough air for a .357 cal barrel, but the rate at which it is released will be "throttled back" by the bore area.... It would be a fairer comparison if I had a bullet of the same SD.... The SD of the 131 gr. in .357 cal is 0.147.... In .224 cal that would be 51.6 gr. bullet.... Unfortunately, I don't have anything that weight.... Any guess what the 41.3 gr. bullet might do, and if I will have any tuning range?.... It has the same SD as a 105 gr. bullet in .357 cal....

Bob
Title: Re: Simplified Balanced Valve
Post by: mann on January 10, 2019, 11:20:34 PM
I think you'll have tunability choking it off by the transfer port it should cause greater pressure in the balance chamber probably shutting the poppet faster and will need more hammer strike for more dwell would be my thoughts on it
Title: Re: Simplified Balanced Valve
Post by: rsterne on January 10, 2019, 11:54:59 PM
I'm not so sure.... The pressure in the transfer port will basically be reservoir pressure.... The required dwell is related to the SD (weight) of the bullet, and you choose a bullet with the same SD, the dwell should be similar, the velocity should be similar, the valve should close with the bullet in about the same position down the barrel, and the volume of HPA used to fill the barrel to that point should be proportional to the bore area.... This will be VERY interesting.... I have never built a gun for a larger caliber and then just replaced the barrel with a much smaller one before.... The .224 is less than 40% of the bore area of the .357 cal....

One thing for sure.... If this gun works with the .224 cal with minimal changes, then all five calibers I have should work.... I also have barrels in .257 cal, 7 mm and .308 cal.... The .224 and .257 share receivers, as do the .308 and .357.... The 7 mm (which was built much later) is built quite differently, but the receiver also fits this lower assembly.... For sure I will learn something, no matter what happens....  8)

Bob
Title: Re: Simplified Balanced Valve
Post by: MJP on January 11, 2019, 12:55:43 AM
Well I think you'll need smaller vent hole for the smaller caliber, or more hammer strike.
But it will work, and you'll be amazed how little the "wasted volume" affects efficiency or power.

Marko
Title: Re: Simplified Balanced Valve
Post by: PikeP on January 11, 2019, 03:05:31 AM
Bob my guess is roughly 1k fps if you only change the caliber and pellet weight with same barrel length.  If you find we need more tuning range and it acts like the valve did with .04 vents on the .357 cal then we have plenty of room for improvement without sacraficing too much hammer strike. Maybe between 1/4 and 1/2 value of dwell for fill time is most optimal and will provide the widest range without requiring too much additional hammer energy. Just need to find the sweet spot if the current isnt.

We went from 0, to 120 to 180 fps of tuning range...I think it could be widened with a 50% or so increase which would make it much more forgiving when changing calibers. 300 to 400 fps would IMO be a fairly optimal tuning range to cover multiple calibers, power levels and projectile weights.

Attached are proposed changes that I feel are within reason that should yield nearly 30 to 50 percent more tuning range using 36% of valve dwell as a optimal fill time opposed to 50%...if we could find a really good valve spring..mcmaster's has a .18 od spring at .375" lenght, 9 lbs per inch, that will compress .255" down to .12"...I think this spring or similar is perfect for this application....   

.12" of compression distance seems like plenty of room to create lift. The ends of the spring need to be ground flat and slightly reduced which will increase this distance to .14"..tight tolerances yea but it's what we want and need imo!

However if tuning range increases with smaller calibers then that's great but I find that less likely.

I also made other minor changes to estimate fps output... I think you'll hit the 300 fpe with larger bottle no problem. 😉
Title: Re: Simplified Balanced Valve
Post by: PikeP on January 11, 2019, 04:34:51 AM
The few changes I'd like to make before releasing this sheet publically are optimal fill times(still testing), and approximating valve dwell and lift better(not sure where I stand on this). The rest of the sheet is basically dialed in 100% for all general purposes of building a balanced valve, or to build a pcp rifle based on desired energy output from a particular arrangement of pressure, caliber, barrel length, port size and projectile weight. No guess work just get to work.

 The hammer weight and spring rate approximations certainly make things easier but can use one modification and that is including hammer travel length or providing it via calculation...either output would be pretty sweet I just need to put time/energy into it.

The recommended minimum hammer gap setting is simply a bit over half your estimated valve lift, that is to provide adequate distance for the hammer to travel while the valve closes before striking again..I've found in my tests under this figure results in hammer bounce wasting air. YMMV.

I also added a desired tunable fpe range based on current data at 0, 100~, 200~, and hopefully 300~
Title: Re: Simplified Balanced Valve
Post by: rsterne on January 11, 2019, 02:32:55 PM
Mike, those look like interesting results.... If combined with a 5/32" stem and a 1/16" vent hole, 100% fill times of just over 0.5 ms should be possible, with a positive closing force at 50% fill.... ie within maybe 1/4 ms of valve strike?....

I have no idea how you are estimating your valve lift and dwell, but I would like to understand that better.... I agree that SSG gap needs to be some small value, and not zero.... Don't forget that valve lift is inversely proportional to gap in some way, less gap creates more lift and dwell.... Also, once the valve lift exceeds 1/4 the throat diameter, the flow RATE no longer increases with additional lift, because of curtain limiting (curtain area = throat area at L = D/4)…. However, increased hammer strike beyond that does increase the dwell, and hence the volume of air that flows through the valve, just not the flow rate.... Thinking about what happens to air use with an SSG, once the gap gets too small, the air use definitely increases.... There is probably some relationship between throat diameter and minimum gap.... So instead of using half my "estimated" valve lift, use half the maximum lift where the curtain effect takes over…. Since the flow rate limit occurs at throat D/4, something like throat D/8 for minimum gap?.... That would be about 1 turn on my gun, and you certainly don't want less SSG gap than that.... In a gun like a stock MRod or Disco, D/8 would be ~ 0.025", and you wouldn't want less than that....

We have some very common factors between your spreadsheet and my "rule of thumb" calculations.... I see that your maximum FPE is proportional to port diameter, something I have used for a long time, even though I didn't have the math to prove it.... Perhaps you do?.... Also, within practical limits, maximum FPE is proportional to barrel length, which is the distance the force acts through and easily provable via math.... The limit is when the bullet friction overcomes a good percentage of the force from the air.... Thinking about this, it all ties into my "lofty goal" calculation, which you have probably seen.... This applies to valve dwell > bullet departure from the muzzle, ie max. possible velocity....

FPE goal = (C x D x PI/4) x P x L / 24 …. where....
C = caliber (in)
D = smallest port diameter (in)
P = average pressure (psi)
L = barrel length (in)
24 = inches per foot (12) and the factor for "minimum typical losses" of 50% of input the input energy....

In case you didn't notice, for full bore-area ports, barrel volume in CI = (C^2 x PI/4 x L).... which means that FPE is proportional to barrel volume.... This means a .50 cal with a 1 ft. barrel has the same potential FPE as a .25 cal with a 4 ft. barrel....  8)

There is a "condition" for the above, however, so that the mass of the driving air and the bullet mass (and hence the overall internal efficiency) stay within a reasonable range.... The bullet weight should be about FPE/2, so that the velocity is about 950 fps.... Lighter bullets, at higher velocity, will have more difficulty achieving the 50%, because the internal efficiency of the PCP drops because more of the energy goes into the air.... Conversely, heavier bullets, at lower velocity, may exceed the 50%, because the air mass is proportionately less important.... as can be seen when bullet weight = FPE (velocity ~ 671 fps)…. The only person I have seen exceed the 50% level without using heavy bullets is Marco his short barreled .22 cal on a .45 cal chassis, running at about 4500 psi.... I have seen a few guys exceed 50% when shooting heavy bullets.... I have trouble getting past 45%.... and I think most "good" PCPs run about 25-30%.... A factor of 33% would, of course, make the divisor in the equation 36 instead of 24....

NOTE: Reading this over, I wonder if the bullet weight can be tied into barrel volume x air density.... ie the mass of the air in the barrel.... which is ultimately responsible for the FPE potential.... For my gun, at 3000 psi the barrel holds 169 gr. of air, so I am wondering what the % would be for a 169 gr. bullet at 950 fps = 339 FPE.... With full bore area ports, my lofty goal formula would predict 350 FPE.... WOW, that's pretty darn close....  :o

I agree that with the 22 CI bottle, and a total reservoir of 460 cc, I should be pushing 300 FPE with the .357 cal 154 gr. bullet at 3000 psi.... Lloyd's spreadsheet, in fact, predicts that, although with the higher average pressure in the latter part of the shot cycle I may need a bit more hammer spring to see that.... Fortunately, I have two stronger ones to choose from, 13 & 15 lb/in....

The true test of your spreadsheet is how it matches other valve designs, both balanced and conventional, IMO.... The "perfect" spreadsheet will work for everything, right?....

Bob
Title: Re: Simplified Balanced Valve
Post by: PikeP on January 11, 2019, 08:31:58 PM
Your numbers do add up for that config I get about .65ms fill time and with .1563 stem 3 lbs force at 75%  instead of -18 on the. 125 stem. I'd imagine it would vastly widen tune range but at the cost of a small chunk of hammer energy (probably 12 to 13 lb spring) where the last change i recommended should really put it where it needs to be...I think. But still good to have plenty of options if any issues arise.

I use a derivative of your formula Bob, it incorporates pellet mass, pressure drop via  pressure* plenum volume/(plenum volume+wasted volume+(total barrel volume / 2.2)), as well as port diameter/bore diameter. Currently no correction factors and it gives very reasonable results until the weight of air becomes much greater than that of the pellet, in which case a correction factor is needed as you're going to be accelerating more air than pellet ar a certain weight. I guess you can call the .2 a correction factor but I find it more honest than simply 2.

I think lift can be closely approximated by working backwards from fpe obtained and at
what equivalent port od would limit that fpe and then figuring 1/4th of that or very close to after considering the valve stem..I think it's a good approximation..

I think with a balanced valve, calculating lift and or dwell based entirely off hammer energy has got to be a tough approach unless you know exactly how your balanced valve is behaving...right now my dwell figure is a huge guess so if you have any tips feel free to share.

Title: Re: Simplified Balanced Valve
Post by: oldpro on January 11, 2019, 09:01:06 PM
 Ok My friend Ill be the first to admit I was Half wrong LOL.  I got it to work with great efficiency and adjust-ability thank you. It just took more venting into the thimble and decreasing the thimble volume as much as possible. Ill post numbers on monday right now i have to get back to shipping semi autos. I did have to adjust the ratio from 250x350 to 210/350 and add venting now it bell curves
Title: Re: Simplified Balanced Valve
Post by: PikeP on January 11, 2019, 09:07:23 PM
Ok My friend Ill be the first to admit I was Half wrong LOL.  I got it to work with great efficiency and adjust-ability thank you. It just took more venting into the thimble and decreasing the thimble volume as much as possible. Ill post numbers on monday right now i have to get back to shipping semi autos. Thanks Buddy

Gotta love when the math is telling you what's wrong right before your own eyes. Congrats on success.
Title: Re: Simplified Balanced Valve
Post by: oldpro on January 11, 2019, 09:11:08 PM
Ok My friend Ill be the first to admit I was Half wrong LOL.  I got it to work with great efficiency and adjust-ability thank you. It just took more venting into the thimble and decreasing the thimble volume as much as possible. Ill post numbers on monday right now i have to get back to shipping semi autos. Thanks Buddy

Gotta love when the math is telling you what's wrong right before your own eyes. Congrats on success.
Didnt have the math to work with back then it was all educated guessing and a lot of R&D
Title: Re: Simplified Balanced Valve
Post by: Motorhead on January 11, 2019, 09:14:25 PM
Ok My friend Ill be the first to admit I was Half wrong LOL.  I got it to work with great efficiency and adjust-ability thank you. It just took more venting into the thimble and decreasing the thimble volume as much as possible. Ill post numbers on monday right now i have to get back to shipping semi autos. Thanks Buddy

Gotta love when the math is telling you what's wrong right before your own eyes. Congrats on success.
Mike ,
Will be the first to admit the math and such is way over my head. Tho love to see another member here offer what appears to be a solid understanding of the subject and an ablity to present it where we dummies can somewhat understand it.
Also becoming aware in reading & coming to realizing your only 69 posts into your membership here on the GTA ...
I Congratulate you Sir on some most excellent contribution.
Title: Re: Simplified Balanced Valve
Post by: PikeP on January 11, 2019, 09:19:35 PM
Ok My friend Ill be the first to admit I was Half wrong LOL.  I got it to work with great efficiency and adjust-ability thank you. It just took more venting into the thimble and decreasing the thimble volume as much as possible. Ill post numbers on monday right now i have to get back to shipping semi autos. Thanks Buddy

Gotta love when the math is telling you what's wrong right before your own eyes. Congrats on success.
Didnt have the math to work with back then it was all educated guessing and a lot of R&D

I hear ya...that's when I had the light bulb in my head to run a quick fill rate calc on Bob's current valve and look where we are now, likely able to tune a balanced valve to within couple hundred fps of a desired tune range. In terms of air use compared to bell curve that would be an interesting chart as we are attempting to control air mass ejection which directly effects FPE output and not the other way around. For example I think the current air mass ejection range is roughly 9 to 16 ccs or 2000 to 3500 mg of air which is pretty amazing.
Title: Re: Simplified Balanced Valve
Post by: PikeP on January 11, 2019, 09:20:55 PM
Ok My friend Ill be the first to admit I was Half wrong LOL.  I got it to work with great efficiency and adjust-ability thank you. It just took more venting into the thimble and decreasing the thimble volume as much as possible. Ill post numbers on monday right now i have to get back to shipping semi autos. Thanks Buddy

Gotta love when the math is telling you what's wrong right before your own eyes. Congrats on success.
Mike ,
Will be the first to admit the math and such is way over my head. Tho love to see another member here offer what appears to be a solid understanding of the subject and an ablity to present it where we dummies can somewhat understand it.
Also becoming aware in reading & coming to realizing your only 69 posts into your membership here on the GTA ...
I Congratulate you Sir on some most excellent contribution.

Thanks, I hope many are able to benefit from these and future findings that bring balanced valves out of the dark ages and into modern big bores as a standard.
Title: Re: Simplified Balanced Valve
Post by: PikeP on January 11, 2019, 09:43:19 PM
Another thing with the .1563" stem. The average closing force from 50% to full is 11 and from 75% to full its 30...similar to a conventional with .125" for the latter quarter. Where as currently the valve is roughly -10 avg force from 50% to full and 12 from 75% to full. I like the thought of a .1563 stem as long as the 12 to 13 lb hammer spring requirment isn't bothersome.

Further calculations suggest around  12 to 13 lb of hammer energy required will be a fairly sweet spot for tunable range...dont ask me how I arrive at that it's just a cross connection I distinguished. I implemented hammer travel into my expected hammer weight and spring requirment and scaling from my non balanced valve to your balanced valve if we want it to act like a conventional valve is roughly 216 lbs of total force holding it close you'll want ~13 lb/in of spring. I think if we get the valve to behave in such a way that requires said 13 lbs we will find our ultimate sweet spot...that is for this balance ratio

Title: Re: Simplified Balanced Valve
Post by: rsterne on January 11, 2019, 10:24:35 PM
Douglas pointed out to me that the 9/64" stem you suggested earlier can be skimmed down a couple of thou and threaded 6-32, but the root diameter would still only allow me to use a one size larger drill for the vent, at 0.055".... Of course by going to 6-40 threads I could use a #53 or 1.5 mm drill (0.059")…. With the 5/32" stem, which will accept 8-32 threads (and leave a 0.001" flat on the thread peaks) I can easily drill to 1/16", or even up to a #50 drill (0.070").... If I ever feel the need to build another poppet, I will probably go all the way to 5/32"....One other advantage to the 5/32" stem is that I can turn the threads off to form the spring guide for a 3/16" OD spring.... It could even stick out the top of the poppet 1/4" for a longer guide, without hitting anything, and take up more volume.... Yes, the vent would be a bit longer, but I think getting rid of the volume is more (slightly) beneficial....

IMO the 13 lb. hammer spring (which is actually 12.4 lb/in) is not an issue, with the preload and cocking stroke we have now (max. 1.4" including the preload on the SSG and zero gap).... The conventional valve (which was only a 3/8" poppet instead of 7/16") used the 15 lb. spring (actually it is 14.1 lb/in), but 1.63" compression at full cock = 23 lbs.... That was difficult but manageable with the separate cocking handle I have on this hammer.... You would never manage it by pulling a bolt back.... Anything much over 15 lbs. of force a bolt is problematic, you need a side lever or separate cocking, IMO.... I am currently only at 13 lbs. max. force to cock the .357 with the balanced valve, and the least I had on the .224/.257 Hayabusa with the conventional valve was 21 lbs, and the .457 was nearly 30 lbs. (now under 19 lbs. with the SS Valve)... When I first installed the balanced valve in this gun I had the 14.1 lb. spring fitted with 0.30" preload, and even at full cocking stroke (no gap on the SSG), it was a breeze to cock compared to the conventional valve....

I think you have done a tremendous job on your spreadsheet.... Can you imagine what it will be like a year from now?....  :o ;D 8) ::)

Bob
Title: Re: Simplified Balanced Valve
Post by: PikeP on January 11, 2019, 10:56:52 PM
I think we could control a 80 to 86% balance ratio. The 86% ratio valve would only have 120 lbs against it  with your current poppet od when closed likely opening with with 9 lbs of spring on the 77 gr hammer and still a wide enough tune range... of course its optimistic but it's a healthy force against the poppet closed and with a .1563 stem you achieve avg positive closing force between 75% and 100% of 30 lbs and 60 lbs at 100% full. Something to ponder if you bother making a big change with the valve or another thimble and poppet.

I'll definitely tweak what's needed as more data is obtained

270+ fpe on just an average spring energy of 8 lbs or so is a pretty sweet deal compared to the old 15 lb average or so...nearly cut right in half.
Title: Re: Simplified Balanced Valve
Post by: tkerrigan on January 11, 2019, 11:13:53 PM
I think Mike should be rated higher than a shooter.  He's sure doing his part on this thread.  Regards, Tom
Title: Re: Simplified Balanced Valve
Post by: mann on January 11, 2019, 11:14:59 PM
Well I got it working chamber is .278 putting the oring on the .250 upper poppet under some compression lower poppet .375 drilled a .052 vent and put it closer to the poppet next I made the thimble out of peek .278 hole it is approxmently .690 length to the hole . I may have to make a longer stem it protrudes just under a 1/8 inch out the back of the valve. I put it in a tube and it sealed at under a 1000 psi tossed a hammer against it a few times and it isn't blowing open it was 40 some gram hammer . I will have to fill my air tanks and do some more testing tomorrow. This may just replace the Cobra valve in my 25 brod
Title: Re: Simplified Balanced Valve
Post by: rsterne on January 11, 2019, 11:39:13 PM
Mike, while an 11/32 - 3/8" small end might work, I won't be trying it.... Did you notice that Travis is going the other way, he's down at 60% now, and getting a bell-curve.... I have a feeling that just like in the SS valve, which works at 2/3-3/4 of the diameter (66-75% and Travis uses 80%)…. this valve likely has a similar "sweet spot".... 66% in the SS valve is like 75% in this one, and 75% in the SS valve is like 66% in this one.... The 80% Travis uses in his SS valve is like using 60% in this one.... Using 80% in this valve would be like running 60% in an SS valve.... I tried 62% in an SS valve, and all I got was runaway hammer bounce and terrible adjustability....

Mark, I don't understand, how can you run a 0.250" poppet in a 0.278" chamber?.... The O-ring should be extruding into that 0.014" gap (0.028" diametrical difference)…. Might be OK at 1000 psi, at 3000 I think you'll lose the O-ring....

Bob
Title: Re: Simplified Balanced Valve
Post by: mann on January 11, 2019, 11:55:10 PM
I just cut in the oring groove at a guess and in order to get it to fit into the chamber I had to go larger viton oring what I should have done is cut the oring deeper into the poppet . It probably will come off I can make a new thimble again right now I was happy to get everything to seal up and to get it to start working  . I don't really have correct tooling to cut in the orings just using small hss pointed bit on my little lathe
Title: Re: Simplified Balanced Valve
Post by: mann on January 12, 2019, 12:36:52 AM
I'm also still learning how to do some of these things on the lathe so it's a learning experience and gives me something to tinker with 
Title: Re: Simplified Balanced Valve
Post by: Motorhead on January 12, 2019, 12:56:00 AM
I'm also still learning how to do some of these things on the lathe so it's a learning experience and gives me something to tinker with 

Like using a butter knife to carve prime rib ..... yea that would be rather difficult.
Doable but not pretty.

Yea the tolerances there talking here requires good tooling and established technique .... Tho half the fun and learning comes from our mistakes & there is nothing wrong with that !
Title: Re: Simplified Balanced Valve
Post by: PikeP on January 12, 2019, 01:23:53 AM
I do think 120 to ~200 lbs force is a good spot for low hammer energy requirements which you certainly are right at so I dont blame you for being perfectly content with the 72% balance. I would be. I just cant help but think of how possible a 86% valve would do with some impeccable designing.

Look forward to seeing how the other calibers act with the current valve and if any more refinement is necessary in the valve which we are well prepared for.

Mark I agree with Bob and would heed his advice.

Thanks Tom. Just doing what anyone on my shoes that can do, should do. Still have work to do.
Title: Re: Simplified Balanced Valve
Post by: rsterne on January 12, 2019, 01:42:04 AM
I have the .224 and .257 barrels prepped (barrel ports remachined to match up to a 0.257" transfer port)…. and the transfer port recess in the .224/.257 receiver milled out to 7/16" OD with a 0.257" hole through to the barrel.... I re-polished the chambers in the barrels and need to clean them.... but have to repair my broken cleaning rod first.... I also have to make a tapered Delrin transfer port with one end at 0.328" and the other at 0.257"....

I found that I have some .224 cal "Bowman" cast bullets from an Arsenal mold I convinced them to make and put in their catalogue....

(http://arsenalmolds.com/image/cache/catalog/224%20Bob%20Sterne-500x500.JPG)

I completely forget I had this and cast some bullets last year but never shot them.... It is a 4-cavity mold with 2 cavities converted to HP by Eric at HollowPoint Mold Services.... The FN bullets are 47.6 gr. and the HPs are 45.6 gr.... This bullet is a scaled down Lyman 257420, so it should shoot great.... The weight is closer to what I need for this gun, so I'll be testing these first, after I size them to fit the chamber.... They are a bit lower SD (0.136) than the 131 gr. Lee RN bullets in .357 that I have been testing (0.147), so in an ideal world, should shoot a bit faster than those.... I guess we'll see soon.... maybe tomorrow, with a bit of luck....  8)

Bob
Title: Re: Simplified Balanced Valve
Post by: PikeP on January 12, 2019, 06:10:19 AM
Any thoughts on what a safe minimum holding force a balance valve should have provided it wont easily discharge itself and seal properly even if  poppet material needs to be softened to achieve it? I'm curious even just for testing purposes how light of a hammer we can use in a pcp and compare it to current hammer weights. I'm curious how quickly the poppet creates lift..and would an incredibly fast moving hammer prove itself to be vastly beneficial over traditional or moderate hammer weight...would be a test for another day/thread but the question pertains here and should set a realistic minimum for those interested and attempting builds.

I think the combo of the lightest possible hammer strike and a very well timed strong closing force like a .1563 stem will be a potentially winning combo although maybe the gains will be non existent or marginal in terms of potentially less air usage for equal power.

I sure wish I had a lathe and mill handy right now.
Title: Re: Simplified Balanced Valve
Post by: PikeP on January 12, 2019, 06:32:15 AM
Hmm..its so simple..calculate your minimum dwell for desired fps from a desired projectile weight..say that's as low as .7ms dwell..use THAT as your base factor instead of peak power dwell as that will simply come with more hammer strike...WHY didn't I think of that? Oh wait I just did 😉

I think minimum desired dwell * .75~ will be a great place to set our optimal fill time, based on Bob's results with the .04 vent being near that figure for peak, we use the same figure for minimum desired dwell...its actually so easy...it just makes sense. That would also make this valve scale up just fine with either changing hammer weight or added spring when changing caliber...that's not asking much...my brain needs a vacation, because it's currently BLOWN. I think 2 balanced valve configs could cover all.the calibers we commonly use...with ease. (Small and big bore)

That dwell factor should be a measure of pellet SD and barrel volume or length much like Bob mentioned earlier..I haven't formulated anything myself however it makes sense..or maybe just SD and velocity alone can approximate dwell... hmm..welp I'm on vacation. Get to work boys 😆


Heres a graph of my prediction for caliber changes for the .224 and .257 provided same ratio porting (92% of bore) and barrel length ect.

Ps. Bob I understand the .2 correction factor on the pressure drop modifier that I use in your modified formula. The longer the barrel the higher it must be and the shorter the barrel the less it must be...there is a golden ratio hence Marco surpassing that 50% mark with a short barrel..its acceleration related which I'm sure you can grasp rather easily.

Pss. What sounds cooler. Balanced valve or  pneumatically timed balanced valve
Title: Re: Simplified Balanced Valve
Post by: rsterne on January 12, 2019, 02:07:51 PM
Mike, it took me a minute to grasp what you were saying.... I know, of course, that lower velocity and energy means less dwell.... What I think you are saying is that the fill time of the balance chamber must reduce as the valve dwell reduces.... Otherwise, the valve is "blowing open" for too long a period of time.... That is what was happening with the original valve, the fill time was too great, so I could not dial the velocity down.... When I made the vent larger, I got a 120 fps tunable range.... When I reduced the spring chamber, that went up to 180 fps... This is because those lower velocities require a shorter valve dwell, and if the fill time is too large a percentage of that, then you cannot dial the velocity down that far.... I did this graph to help visualize the concept....

(http://i378.photobucket.com/albums/oo221/rsterne/Hayabusa%20PCP/Balanced%20Valve%20Dwell_zpsmtp0jwdm.jpg) (http://s378.photobucket.com/user/rsterne/media/Hayabusa%20PCP/Balanced%20Valve%20Dwell_zpsmtp0jwdm.jpg.html)

Lloyd's spreadsheet model isn't perfect for predicting the ACTUAL dwell, but it is good at comparing what the dwell must be doing in relationship to the velocity.... ie the trends.... The blue line above is based on the data for the 154 gr. bullet when using the 7/32" spring and the 0.052" vent.... I was done using a constant "efficiency" factor, and the two left hand data points are PROJECTED, whereas the points at 700 fps and above I could actually get the gun to shoot.... Remember it fell off the cliff below 700 fps.... You could also think of the blue line as the way a conventional valve reacts in terms of tunability and producing a bell-curve....

The orange line is based on the last set of data I took, using the 131 gr. bullet, with the 3/16" spring (and smaller chamber volume), still with the 0.052" vent.... What is happening to the curve toward the left end is the "roll over" in velocity we experience as we approach the cliff in balanced valves.... A small decrease in dwell produces a larger drop in velocity.... It seem clear to me that reducing the fill time of the chamber will move that to lower velocities.... so other than the slight increase in hammer strike required, that is a very good idea.... Keeping the balance chamber volume small, and using as large a vent as possible, seems to be the ticket for this valve design.... While we don't know for sure the ACTUAL dwells we are working with.... and hence can't determine with precision what percentage of that the chamber fill time must be.... we can relate the actual adjustable range of the valve with the calculated fill time of the balance chamber.... Your spreadsheet has given us that ability....

One other thought has occurred to me when looking at these curves.... If you restrict the airflow by using a smaller transfer port (or an adjustable one)…. you will move the entire curve downwards.... The peak velocity will drop, and the rest of the curve will as well.... This approach will work not only to decrease the velocity, but to allow you to shoot lighter bullets (or pellets) and still have a tuneable range and produce a bell-curve.... The combination of the two, plus using different pressures for different bullet weights, should produce a tuneable range and bell-curve with any projectile you care to use....

Bob

PS, I agree that part of Marco's success in exceeding the 50% mark is due to the short barrel and very high pressure.... The high pressure supplies a lot of acceleration early on.... and the short barrel limits the mass of air used to accelerate the bullet.... Keeping the mass of the air less than the mass of the bullet is key to raising the efficiency.... Perhaps we can work that into our calculations, particularly as it applies to my "lofty goal" formula.... You using a factor of 2.2 (instead of 2) for the divisor brings the expectations more into line with the 45% number that is a lot easier to hit (ie it lowers the goal, but makes the prediction easier to reach)….

RBS
Title: Re: Simplified Balanced Valve
Post by: mann on January 12, 2019, 03:49:18 PM
Well I made a new thimble out of aluminum and drilled the chamber with a 1/4 in bit and tried the poppet with out the oring it fit good tried with it and it didn't go . Cut the oring groove a tad deeper and it fit no problem and added the buffer oring the chamber end up being .684 long by .253 poppet is like .248 should work . I don't know about the volume my math isn't that good because of the spring and spring guide on the end of the poppet
Title: Re: Simplified Balanced Valve
Post by: MJP on January 12, 2019, 03:53:15 PM
The spring isn't actually needed, if you can fill it quick enough the first time.

Marko
Title: Re: Simplified Balanced Valve
Post by: PikeP on January 12, 2019, 04:34:47 PM
Yes that graph is perfect. So for example I think a target of .5 to .75 ms close times to be optimal and I think that time scales relatively well for any caliber ive thrown numbers at...having a slight ability to adjust that via choking as you mentioned or even a vent restrictor would be nice but not even necessary once you achieve .4ms~ 100% fill time.

You nailed the CF explanation. Need to find a way to tie it into barrel length because length should be the one variable that effects the accuracy of your formula most.
Title: Re: Simplified Balanced Valve
Post by: PikeP on January 12, 2019, 04:43:50 PM
I think .4 ms is good for small bore and big bore but big bore can be 50% greater to aid in reduced cocking, while sacraficing a small tuning range. I firmly believe the hammer has done the majority of its work in this time and pressure differential and pre full equalized chamber you have less required hammer energy to further increase or decrease lift ie: you're tuning range which is generally in the neighborhood of 50% additional average spring force.

Ie: optimally 2/3rd hammer energy goes into the first .4 to .6~ ms and you enter a tuning range...where the latter 1/3rd variance of hammer energy determines air mass ejection and ultimately pellet velocity. At least optimally...because 50% + or - avg spring force is optimal...imo

Here is a revision based on your chart Bob. 10 lb spring 106 gr hammer or current hammer 13 lb spring still. Really not bad..the spring used would be out of a pen or lighter..I've found them in this dimension on the sheet. Gotta love metering air flow down to 400 to 600 micro seconds, or 1/2000th of a second.
Title: Re: Simplified Balanced Valve
Post by: PikeP on January 12, 2019, 05:19:37 PM
More math that I think applies. You want your closing force to be roughly 15 to 20 percent of holding force, and you want this force through the majority of the shot cycle...that simple ratio will allow roughly 40% variance in average hammer energy resulting in a tuning range..I think...conventional valves are commonly 15 to 20 and Bob's right at 19% with his ratio...so keeping between 15% and 20% when determining balance ratio is probably ideal..

Alternatively a higher percent ratio can be used for larger chamber volumes or smaller vents that fill slower to achieve similar results. Not enough data to verify which method is potentially more efficient or easier to operate within its tunable range.
Title: Re: Simplified Balanced Valve
Post by: mann on January 12, 2019, 06:32:43 PM
Here is a shot string with a 45 gram hammer and 8 lb spring 2800 fill 215 cc air tube unregulated  no ssg
1.861
2.857
3.858
4.886
5.850
6.854
7.855
8.873
9.860
10.846
11.849
12.863
13.868
14.859
15.848
16.856
17.844
18.829       avg 856 fps
                           55   fpe
                          1.56 fpe/ cuin
Not to bad with out a ssg I might have to make one and see
Title: Re: Simplified Balanced Valve
Post by: oldpro on January 12, 2019, 06:46:10 PM
Here is a shot string with a 45 gram hammer and 8 lb spring 2800 fill 215 cc air tube unregulated  no ssg
1.861
2.857
3.858
4.886
5.850
6.854
7.855
8.873
9.860
10.846
11.849
12.863
13.868
14.859
15.848
16.856
17.844
18.829       avg 856 fps
                           55   fpe
                          1.56 fpe/ cuin
Not to bad with out a ssg I might have to make one and see
What is your poppet sizes and bleed hole size?
Title: Re: Simplified Balanced Valve
Post by: PikeP on January 12, 2019, 07:13:23 PM
Congrats mann...very happy to hear more success occurring. I think I've solved a lot of the issues with the closing force over closed force ratio. Before balancing Bob's valve was 10 percent. Which is off the charts meaning tons of hammer energy required for a less than ideal tune range...reducing the force to half doubled that number resulting in a much easier to operate valve..and with getting the chamber filled nearly asap the valve quickly returns to nominal operations of a pcp for the closing event..I think 20% cf ratio is really ideal..likely on full effect at the 25% to 33% of peak dwell mark...
Title: Re: Simplified Balanced Valve
Post by: mann on January 12, 2019, 07:17:30 PM
Poppet balance part is at .250 bottom is at .375  bleed hole is .052
Title: Re: Simplified Balanced Valve
Post by: mann on January 12, 2019, 07:20:25 PM
Ported to .200 all the way barrel transfer port and valve
Title: Re: Simplified Balanced Valve
Post by: PikeP on January 12, 2019, 07:34:17 PM
Here is a draft for small bore...set for wide tuning range pellet shooter. Anyone can feel free to use these or similar dimensions... this is a .25 cal up to 92% bore porting but would work for all small bore...although a .177 really doesn't need balancing even when full bore..and a .22 wouldnt benefit from this design much as the force reduction co.pared to a nominally built unbalanced one is only 15% or so compared to the 35% on the .25 cal.

If anyone has a recommended minimum closing force I can build a version based on that..this one is 100 lbs.

I certainly wont oppose any volunteers with a lathe and motivation to build me a thimble/poppet once a small bore version is set in stone. 😁
Title: Re: Simplified Balanced Valve
Post by: mann on January 12, 2019, 07:37:25 PM
The ssg is also helping now that I tried it I had a string at 64 fpe at 1.42 fpe /cuin with out much tuning at all really just tossed in Ssg and tried at that power level string is
1.925
2.944
3.944
4.941
5.927
6.931
7.921
8.916
9.915
10.914
11.903
12.896   
I'm going to change out the spring and try it at 55 fpe level which was first string I posted and see how much the ssg has helped
Title: Re: Simplified Balanced Valve
Post by: rsterne on January 12, 2019, 07:38:08 PM
OK, so first of all, I have an admission to make.... Although the plenum is 108 cc, I forgot to allow for the volume in the microbore hose, gauge and valve, which I now estimate at about 12 cc.... Therefore the volume dropping in pressure when I was calculating the efficiency was wrong, it is about 120 cc, which is the reason the numbers were higher than the should have been.... They are still very respectable, but that 1.74 FPE/CI I thought I had achieved is a much more believable 1.57 FPE/CI.... or thereabouts.... I won't have a final figure until I install the 22 CI bottle, of course, because that will increase the plenum from 108 cc to 460 cc.... I went back and replaced the graph in Reply #340 with a (more) correct version....  :-[

Anyways, on to todays exciting news.... First thing was I checked a "cold bore shot" of the .357 after storing over night at 3000 psi.... The gauge showed no indication of a pressure drop, and with a 131 gr. bullet the first shot was 914 fps.... I refilled it to 3000 psi and took another shot, and it was 927 fps.... That is only a 1.4% difference, and it is quite possible the gun may have lost 50 psi or less overnight.... So score another victory for the new valve.... stiction is non-existent....  8)

I cleaned the .224 and .257 cal. barrels, installed the .224 cal on the receiver, and made a tapered transfer port.... I used a milling cutter with a 7 deg. taper, and made a 7/16" OD port that is 0.328" ID on the bottom and 0.257" ID on the top.... I got the length right for a slight compression fit, and installed the .224 barrel and filled the gun to 3000 psi.... I still had the SSG gap set at 2 turns, loaded a 47.6 gr. bullet that was sized to 0.223", and took the first shot across the Chrony…. The resulting 1022 fps (110 FPE) put a pretty big grin on my face....  ;D …. That is more power than I have ever had before from the .224 cal.... The best I did previously was 106 FPE, but to be fair, that was with a 41.3 gr. swaged RWS bullet at 1077 fps.... Later in the day I tried one of those at this setting and it did (are you ready for this) exactly the same 1077 fps.... This pretty much shows that the gun is (and was) maxed out, because the most restrictive point in the porting system (the chamber where the 0.088" diameter bolt probe restricts the area to the equivalent of a 0.198" hole) hasn't changed.... More to come in a while....

Bob

Title: Re: Simplified Balanced Valve
Post by: PikeP on January 12, 2019, 07:38:58 PM
The ssg is also helping now that I tried it I had a string at 64 fpe at 1.42 fpe /cuin with out much tuning at all really just tossed in Ssg and tried at that power level string is
1.925
2.944
3.944
4.941
5.927
6.931
7.921
8.916
9.915
10.914
11.903
12.896   
I'm going to change out the spring and try it at 55 fpe level which was first string I posted and see how much the ssg has helped

Very impressed mann... congrats that's a bell curve at over 60 fpe with 8 lb spring and a light hammer...its working, quite well..
Title: Re: Simplified Balanced Valve
Post by: PikeP on January 12, 2019, 07:44:11 PM
Ughh bob I put 120 cc into your plenum volume...changed caliber, portsize and pellet weight. The current formula spit out this...off by 2 fps  ::)

Also not sure why others thought Bob would need more hammer strike going down in caliber..that's the opposite to how physics works.
Title: Re: Simplified Balanced Valve
Post by: rsterne on January 12, 2019, 07:48:48 PM
Mark and Mike.... nice progress.... I like the design for a .25 cal pellet valve, Mike.... Notice how close your 109 FPE prediction was for my gun in .224 cal?....  8)

Note the plenum volume remains at 108 cc, the additional 12 cc only affects the pressure reading once it equalizes after the shot, that air is NOT available within the very brief shot cycle....

Bob
Title: Re: Simplified Balanced Valve
Post by: PikeP on January 12, 2019, 07:54:36 PM
Mark and Mike.... nice progress.... I like the design for a .25 cal pellet valve, Mike.... Notice how close your 109 FPE prediction was for my gun in .224 cal?....  8)

Note the plenum volume remains at 108 cc, the additional 12 cc only affects the pressure reading once it equalizes after the shot, that air is NOT available within the very brief shot cycle....

Bob

Here is 108cc available. With 2.2 cf. The 109 was honestly with a 2.3 cf I was testing and forgot about, but feel 2.2 is where a 28 inch barrel belongs...roughly

2 fps off the other way 😂

Estimated within .195%...
Title: Re: Simplified Balanced Valve
Post by: PikeP on January 12, 2019, 08:36:20 PM
Think I found a way to formulate approximate dwell based on power levels...it requires metering air flow through a given port size and the required time to flow the avg air required for said energy...

I see a trend of achieving half the ports potential flow over the entire valve open event..although this may be closer to 45 percent which would add more valve duration.

If we assume 28% of energy making it to the pellet as a baseline then we can approximate the length of time your port at 45% to half its peak flow has to be open..

If my ports max flow is 980 mg a ms, and I pump 800 mg of air through it, that means my dwell time is approximately 800/(980/2)..
 1.63ms...or at 45% 1.85 ms...

It's probably not 100% accurate but a good approximation. Just like how I calculate lift..

Say Bob's valve moved 3725 mg a ms and his 250 fpe shot was roughly 3300 mg. That means 3300 / (3725/2) = 1.8ms or at 45% 1.96 ms...

Opinions Bob?

Here is what I got after completing the above formula for your 250 fpe shot.

Seems good enough for ball park to me.
Title: Re: Simplified Balanced Valve
Post by: rsterne on January 12, 2019, 08:45:51 PM
So here is the meat and potatoes of today's testing of the .224 cal Hayabusa Mk.II based on the .357 cal. version.... Remember, all I have done is replaced the upper, nothing in the lower tube has been touched, and the SSG gap settings are still the same as on the .357 version.... I was using a 47.6 gr. "Bowman" bullet, which is a scaled down version of the Lyman 257420, made by Arsenal, which is designed to be stable in the 14" twist TJ's barrel.... With 2 turns of gap on the SSG it shot at 1020 fps (110 FPE) and peaked at 1035 fps (113 FPE) at zero gap.... Here is a plot of velocity and efficiency vs. SSG gap.... I had a usable tuning range of about 140 fps with this (admittedly oversized) valve in the .224 cal....

(http://i378.photobucket.com/albums/oo221/rsterne/Hayabusa%20PCP/Hayabusa%20224%20New%20Valve_zps9g5whedg.jpg) (http://s378.photobucket.com/user/rsterne/media/Hayabusa%20PCP/Hayabusa%20224%20New%20Valve_zps9g5whedg.jpg.html)

I also tested some lighter bullets, just a few shots to see what velocity they reached.... At 2 turns of SSG gap, the bullet I used previously in this gun, the 41.3 gr. swaged RWS that is virtually identical to a .22LR bullet shot 1077 fps (106 FPE).... I have some of the NOE version of the Lyman 225107 which weigh 38.3 gr. and they shot at 1116 fps (106 FPE).... and were just supersonic at zero gap.... I also have some of the swaged NAA 30.6 gr. bullets which are similar to a .22 Short, and they went 1195 fps (97 FPE), still at 2 turns of gap on the SSG.... The two cast bullets I tested I sized to 0.223", the swaged were nominally 0.224" and I did not touch them.... Now that I have NOE sizing bushings in various sizes, I find that the 0.223" chambers a lot easier than the 0.224".... At 0.225" you nearly have to beat on the bolt handle to chamber bullets in this barrel....

The next step was to see what kind of shot strings I could get at various SSG gap settings.... Remember, I only have a 108 cc plenum (120 cc including the valve, gauge and hose), so these shot strings are only about 1/4 as many shots as they will be once I install the 22CI bottle.... Anyways, here is the results, all shots over 96% of the peak velocity are shown....

(http://i378.photobucket.com/albums/oo221/rsterne/Hayabusa%20PCP/Hayabusa%20224%20New%20Strings_zpsxhj6xe6d.jpg) (http://s378.photobucket.com/user/rsterne/media/Hayabusa%20PCP/Hayabusa%20224%20New%20Strings_zpsxhj6xe6d.jpg.html)

At zero gap I have a declining shot string.... With 2 turns of gap, the first 2 shots were within 1 fps, and the velocity then dropped 2.5% for the 3rd shot, and the 4th was down more than 4%.... At 5 turns of gap, I was starting to get a nice bell-curve, the first 4 shots were within a 15 fps ES (1.5%), so the gun is tuned right at the top of the bell curve.... The average over those 4 shots is 983 fps (102 FPE)…. At 7 turns of gap the first shot was about 6% below the peak, so it isn't shown, and the bell-curve starts at 2850 psi.... 7 shots later the 4 % ES ends, the average velocity is 924 fps (90 FPE), and the pressure is down to 1870 psi.... That is nearly a 1000 psi pressure range within a 4% ES, which is very good.... With the 22 CI bottle installed I should get about 4 times the shot count.... although that may be slightly less as I expect the FPE to increase because of the higher average pressure during the shot with 460 cc on tap instead of just 108 cc.... The string I didn't shoot, at 6 turns of gap, looks to be the one that will start right at 3000 psi and still be within a 4% ES.... I'm guessing it would have been 6 shots at about 950 fps average (96 FPE) at around 1.25 FPE/CI.... If that comes to fruition, that will be more than a 50% increase in shot count from my previous .224 cal version, with the conventional valve....

I couldn't be happier with the results.... I had hoped I could just swap calibers without any other change, but there were times I thought that was a pipe-dream.... It turns out it wasn't a dream at all, but a reality....  8)

Bob

PS.... Mike, now that you have a complete second set of data for the same valve in a MUCH smaller caliber, I suspect you will find that some things meet your expectations while others don't.... Chew on this for a while and see what you come up with.... BTW, the .224 cal barrel is 29" long, not 28" like the .357 and others.... I haven't run the data through Lloyd's spreadsheet, but "in theory" I think the dwell should be the same as on the .357 for each SSG gap setting.... At least I don't see why it should change, do you?....

RBS
Title: Re: Simplified Balanced Valve
Post by: PikeP on January 12, 2019, 08:51:31 PM
Dwell is entirely measurement of the duration it takes to flow x amount of air through an expanding and contracting orifice..it will change based on the demands you place on it, at peak operation going up in caliber requires more dwell because you have to flow more air and the port flow rate cant keep up with the demand for more air...its subtle but there. More so increasing barrel length and higher  pellet sd effects dwell because this allows the use of more air ejection..which adds more valve duration. This is why you need much heavier ammo and longer barrels when you increase caliber to achieve their optimal energy levels...ie more dwell to allow more air ejection




29" barrel...any other changes...like port size?


Title: Re: Simplified Balanced Valve
Post by: mann on January 12, 2019, 09:09:18 PM
My hammer and spring set up while on the ssg I can't get lower than the 930 area with out being a cliff if I go back to before with out the ssg I can remove more preload and get it down to the 55 fpe range with about 1.5 efficiency I'm going to give that a try in my brod tube and see what happens it regulated at 2100 
Title: Re: Simplified Balanced Valve
Post by: PikeP on January 12, 2019, 09:16:43 PM
My hammer and spring set up while on the ssg I can't get lower than the 930 area with out being a cliff if I go back to before with out the ssg I can remove more preload and get it down to the 55 fpe range with about 1.5 efficiency I'm going to give that a try in my brod tube and see what happens it regulated at 2100

You need to slightly decrease chamber volume to open up the tuning range...while you have it out I would try...keep up the good work. A lighter hammer or spring might work if your ssg is simply too heavy or over sprung
Title: Re: Simplified Balanced Valve
Post by: mann on January 12, 2019, 09:32:49 PM
Yeah I'll have to try a lighter hammer I'm going to give it a run in my brod and see how it goes
Title: Re: Simplified Balanced Valve
Post by: rsterne on January 12, 2019, 09:52:59 PM
I have had somebody ask what my "tiny tank" is.... Here it is on my 6mm Regulated PCP, with my digital gauge in place as well....

(http://i378.photobucket.com/albums/oo221/rsterne/6mm%20Sporter/Regulated%20for%20Testing_zpsozzbopsf.jpg) (http://s378.photobucket.com/user/rsterne/media/6mm%20Sporter/Regulated%20for%20Testing_zpsozzbopsf.jpg.html)

It is just a piece of 1" CRS drilled and tapped the same as the threads on a bottle (either 5/8"-18NF or 18mm x 1.5mm), plus a shoulder for the O-ring, with minimal internal volume (just a few ccs)…. I originally made them to use when testing and adjusting regulators, so that I didn't have to waste a bunch of air every time I took the reg. apart.... It turns out that replacing the bottle on a PCP with one has the same benefit when you are working on it.... You don't blow of hundreds of ccs of HPA every time you have to tear the gun apart to work on the valve.... You just remove the tank, and screw on its tiny replacement.... After your development is finished, you swap them back again....

Bob
Title: Re: Simplified Balanced Valve
Post by: rsterne on January 12, 2019, 10:08:19 PM
Mike, the valve is the same, but the transfer port tapers down from 0.328" to 0.257" (so I can use it for the .257 barrel, which fits the same receiver)…. Then the barrel port tapers from the round 0.257" hole to an oblong port measuring 0.180" x 0.270", which is the equivalent area to a hole of 0.230" (just over bore size)…. All my Hayabusas use a probed bolt (except the 7mm), the one on the .357, which is 0.140", brings the total annular area of the chamber down to the equivalent of the 0.328" transfer port.... In the .224 and .257 cal bolt, the probe is 0.088", so the equivalent annular area is the same as a hole of 0.206".... Therefore, that is the most restricted part of the porting system on the .224 cal.... Note the bullet I am testing with is 47.6 gr., not 46.7 gr. as per your Reply #393...

On the .257, the same thing applies, with the smallest point again being the chamber around the probe, and the equivalent hole is 0.241".... The .257 barrel, which I hope to test tomorrow, is 28" long....

Bob
Title: Re: Simplified Balanced Valve
Post by: mann on January 12, 2019, 10:23:48 PM
Well I got about 5 more shots with the Cobra valve but I was at 820 ish fps this valve was at 855 most of the time high of 865 es was under 20 until the last couple shots last shot of 67 was at 835. I was using the same spring but way less preload on 13 lb flat spring which was cocking super easy I'm pleased about the same amount of shots with more power I'll do some more tuning tomorrow and if I can hit 100 shots at 50 plus fpe and with es at 15 or less it would be great
Title: Re: Simplified Balanced Valve
Post by: mann on January 12, 2019, 10:41:35 PM
If I make the chamber smaller or shorter it will fill faster and close the valve faster? Also helping tuning range ?
Title: Re: Simplified Balanced Valve
Post by: rsterne on January 12, 2019, 11:06:22 PM
Mark, making the chamber smaller does not make the valve closer faster, per se.... It allows the chamber to fill faster, preventing it from blowing open as easily.... That requires a bit more hammer strike at the top end of the power range.... and extends the tuning range as well.... The closing is primarily from the diameter/area of the stem, and that has a major effect on the hammer strike required to maintain dwell.... Generally, more dwell equals more velocity and FPE....

It's the old story of finding the best compromise.... If we reduce the hammer strike too much, then we lose the ability to use that hammer strike to vary the velocity.... At the limit, we end up with a valve like I had when I started (or a Cothran valve)…. ON or OFF, and no tuneability.... It is becoming increasing more obvious that you can't make the chamber too small, or the vent too large, IMO.... although past some reasonable limits you may not gain, either.... Mike is trying to define those limits, so we know when to stop trying for "more"....

Bob
Title: Re: Simplified Balanced Valve
Post by: mann on January 12, 2019, 11:11:10 PM
Thanks for explaining Bob helps me understand better on how it works
Title: Re: Simplified Balanced Valve
Post by: PikeP on January 12, 2019, 11:34:34 PM
Nice testing rig Bob. I do similar when testing
 to reduce hpa volume to nearly nil.

I'm confident Bob's current version even if needing tweaked like I advised with the spring swap is basically full proof for high powered big bore. Next tests will be small bore version and then anyone else's variation such as .1563" stems or other balance ratios.
Title: Re: Simplified Balanced Valve
Post by: rsterne on January 12, 2019, 11:38:15 PM
Mike, is there any point to looking at the barrel length in CALIBERS instead of inches, and the effect that has on the efficiency, dwell, and FPE ?.... Naval guns, and artillery pieces, are measured in calibers.... The 16" guns on the Iowa class Battleships were called a 16"/50 because the barrel was 50 calibers long (66 ft. 8 in.)…. A 25" barrel on a .25 cal is 100 calibers long, and the same ratio on a .50 cal would be 50" long.... I looked at this a while back and discussed it with Lloyd, and we thought it had a bearing on the efficiency of the shot.... A length of 100 calibers is probably about as long as we really need, I think.... ???

Bob
Title: Re: Simplified Balanced Valve
Post by: MJP on January 13, 2019, 03:15:33 AM
You have now come to the point we where some years back, changing just the upper on a working lower.
All of the guns use the same valve, from .50 cal to .223

Now you found out for yourself that there is no disadvantage of the higher port volume, what you call wasted volume.

Nice work on the valve to get it bellcurve, something that I found no need for in my application.

Marko
Title: Re: Simplified Balanced Valve
Post by: PikeP on January 13, 2019, 04:18:01 AM
Bob I do think there is merit in your line of thinking with caliber length. So much on my mind I'll have to let that marinate for awhile.

After thinking about it..I think optimal dwell can be simply in the neighborhood of barrel length / bore diameter / 40...but the issue with using caliber lengths is very small barrels can take advantage of more dwell than really long ones..but it seems to scale sensibly even if 40 isn't the best constant. Between 30 and 40 seems reasonable. My current method of measuring dwell by metering air seems accurate for both low lift and full lift conditions regardless of the type of valve..which has a huge advantage to using newtonian mechanics to attempt to resolve it. The caliber length method is great for optimal dwell approximation but not low lift dwell / reduced power approximations unless we find some other scaling factor. Just my opinion. Dwell is the time it takes a dialating orifice to eject a specific mass of air and I dont think there's any better way to measure it than to run simulated computations for the dialating orifice down to the hundredth of an inch for every 100 micro seconds to build a real flow profile that determines lift within .001" and dwell within .01 MS. For now I use ejected mass / lifts average flow rate + time to create appreciable air flow at near .09 ms.

I ran some interesting throat/transfer plenum fill rate calcs..seems to be in the neighborhood of .25ms to get equal pressure into the transfer plenum due to choked flow...or .22 ms for a 1 cc .25 cal throat compared to .27ms for a 1.56 .357 throat. Which likely adds some micro seconds to our fill times in the pressure chamber, some of which are currently accounted for...but not all currently. For example the first .1 ms of lift has such choked flow that I'll likely add at least  75 to 100 micro seconds to the current fill times..I've come this far with precision might as well!
Title: Re: Simplified Balanced Valve
Post by: rsterne on January 13, 2019, 02:13:41 PM
The concept of "optimum dwell" concerns me a little, it depends on what you mean by optimum.... It is certainly valid for trying to optimize the balance between power and efficiency.... That is why for years I have been telling people that the valve should close before the pellet reaches halfway down the barrel.... which would be a divisor of 50 on a barrel length of 100 calibers (typical-ish for small bore airguns)…. Using Lloyd's spreadsheet, it appears that having the valve close when the pellet is 1/4-1/3 of the barrel length is more common.... and for very efficient PCPs (those approaching 2.0 FPE/CI) it is much sooner.... In fact the efficiency peaks for conventional valves at extremely short dwell.... Here is some data from a modded 2260 regulated at 1600 psi, varying only the hammer strike.... Yes, that was nearly 200 shots at about 620 fps on a 13 CI tank....  8)

(http://i378.photobucket.com/albums/oo221/rsterne/PCP%20Internal%20Ballistics/22XX%20PCP%206%20Efficiency_zpsusj3ubak.jpg) (http://s378.photobucket.com/user/rsterne/media/PCP%20Internal%20Ballistics/22XX%20PCP%206%20Efficiency_zpsusj3ubak.jpg.html)

According to Lloyd's spreadsheet, at the peak of the efficiency curve, which occurred at about 620 fps, the dwell was only about 0.4 mSec. and the valve was closing when the pellet was only about 2.2% of the way down the 24" barrel (or roughly about 1/2" from rest) and only going about 200 fps.... All the rest of the velocity was obtained through the expansion of that tiny sip of HPA....  :o …. At 800 fps, with efficiency 1.50 FPE/CI, the valve dwell would be about 0.9 mSec. (10% of barrel length) and at 900 fps, with efficiency 1.30 FPE/CI, the dwell would be about 1.25 mSec (19%)…. At 990 fps, with efficiency of 1.05 FPE/CI, the dwell is about 1.6 mSec., with the valve closing when the pellet was about 1/3 of the way down the barrel.... As you can see, I did not have enough hammer strike available to get to the plateau, but Lloyd's spreadsheet predicts the efficiency would be down to about 0.4 FPE/CI at that point (valve open until pellet departs the muzzle), and the dwell to do that would be over 3 mSec.… I have found with numerous PCPs that if the valve closes when the pellet is about halfway down the barrel, the efficiency is about 0.7-1.0 FPE/CI.... The efficiency is DEFINITELY related to the pellet position when the valve closes (ie the dwell)…. Once the pellet is halfway down the barrel, the efficiency tanks.... it takes a huge increase in the amount of air released to get the last few fps.... Many PCPs only lose about 3% of their velocity when the valve closes at 50% compared to what they can do with a "dump shot".... Conversely, a .25 cal MRod with internal regulator tuned for a "40/40" shot string (40 shots at 40 FPE) will have a dwell of less than 1 mSec. and the valve will be closing when the pellet has travelled less than 3" down its 20" barrel.... In PCPs, the efficiency (in FPE/CI) peaks when the valve closes before the pellet reaches 10% of the barrel length, for many guns probably less than 5%....

Bob

PS, don't fall into the trap of thinking there is choked flow at the beginning of the shot cycle, when the valve is opening.... The pellet is not moving, or barely so, and therefore the velocity of the column of air is near zero.... All that is happening is that the molecules of air are filling the "wasted" transfer port space, in the same manner they are filling the vent to the balance chamber.... The limiting factor, as I understand it, is the molecular speed of the air molecules.... With a 1" long transfer port (valve seat to pellet base) and 1650 fps (19,800 in/sec) as the "average" molecular speed, it only takes about 0.05 mSec. for the air to reach the pellet base.... The valve is physically open quite far by then.... lots of area and no real flow velocity, so no choking....

Adding this.... At 0.1 mSec. the valve is open about 20% of its total lift, let's say 0.016".... and the pellet has only moved about 1/32" and moving about 40 fps.... I don't see how there is any possibility of choked flow....

RBS
Title: Re: Simplified Balanced Valve
Post by: mann on January 13, 2019, 03:38:52 PM
I switched hammers from 45 grams to a peek 31 gram and I may give the tss a try also with a few different springs
Title: Re: Simplified Balanced Valve
Post by: PikeP on January 13, 2019, 04:09:37 PM
Optimal dwell can be found and I have a lot of theory behind the mystery of dwell but not enough time spent pondering it to feel worth sharing..but I sense there's a lot of mystery surrounding dwell for you as well...pretty difficult to quantify. If you load the hammer with less spring it moves slower..poppet should also move slower.. sufficient air pressure to base of pellet to begin its movement is slower..the pellet itself moves slower because slower pressure build up...you see where I am going with this...meanwhile the difference in lift may only be. 02"...care to do that math? Btw I'm not implying lower energy shots have longer dwell than high energy I'm implying the difference in dwell between the two is less than you think but still present..imo

At .1 ms I get 20 mg per micro second flow rate through my valve and 158 mg per microsecond flow at .2 ms...and my throat is 450 mg...tell me again how enough air makes it to the pellet in .05ms to begin its movement..10 out of 450 mg is 2 percent...I think .1 ms pellet movement is much more likely in your average pcp...that's 100 micro seconds..now if it's really half that at 50 micro seconds..color me impressed. Care to run the flow numbers at that time resolution to tell me the pressure at the pellet at .05ms?
Title: Re: Simplified Balanced Valve
Post by: mann on January 13, 2019, 04:12:24 PM
How can the spring be way easier to cock and give me almost a 100 fps over the other spring this flat 13 lb spring cocks so easy
Title: Re: Simplified Balanced Valve
Post by: mann on January 13, 2019, 04:20:35 PM
Ok I switched to the lighter hammer backed off the spring and got the same speed out of the valve it sounds quiter I think the heavier hammer was really smacking the rear of the valve . Set right now at about 850 fps with 34 gr mk 2  13 lb flat spring which cocks easier than a 10 lb spring I need to see how many shots I can get
Title: Re: Simplified Balanced Valve
Post by: PikeP on January 13, 2019, 04:34:29 PM
Air to the base of the pellet traveling 1650 fps at 19.8 inches per ms takes .076 ms alone to travel the 1.5" in my valve...that's at a equal pressure not the rising throat pressure..that also assumes air accelerates from 0 to 1650 in 0 microseconds..
Title: Re: Simplified Balanced Valve
Post by: PikeP on January 13, 2019, 05:09:46 PM
More in regards to my lift equivalent port theory...which may be wrong. If you change transfer port size, it doesn't matter how hard you hit the valve that transfer port will be one of the variables determining energy output and that's due to its flow rate..same applies to throat and lift...you hit a valve only so hard to create an opening either equal to or a % of your transfer port and you get the expected energy output. I'm all about K.I.SS and the above theory works out on paper and in my head...I'm certain it's as close as I can get without using an order of hundreds of combined formulations and simulations, or as Lloyd is doing with real world tests...but even his data will only be as good as the equipment and method.
Title: Re: Simplified Balanced Valve
Post by: mann on January 13, 2019, 05:23:10 PM
Changing the transfer port to smaller size can and does control fps and lower es I've used that exact way to control fps and es on my Marauder 22 with a Cobra valve . Took some trial and error but it worked well
Title: Re: Simplified Balanced Valve
Post by: PikeP on January 13, 2019, 05:36:50 PM
Here is a simple dwell and lift model I made. Note that the average flow is 430~ mg/ms which incidentally is half of the lifts equivalent port flow rate(870)..because the average port flow rate matches the average predicted lift and dwell... it all ties together really well..doesn't mean its correct but it's the best I've come up with..this is an estimated 56 fpe. 25 cal dwell and lift model. The air mass of 795 mg ejected and the 874 mg per ms flow rate of equal porting are the only known variables in this equation..


If your average flow rate numbers dont match predicted dwell and lift which present a beautiful graph like below something isn't right. Predicted dwell here is 1.82ms

The theory behind this dwell model carries the same principle that got the balanced valve tunable so if it's wrong I guess I got real lucky solving balanced valves.
Title: Re: Simplified Balanced Valve
Post by: rsterne on January 13, 2019, 05:50:19 PM
As I understand it, the air molecules are already moving at 1650 fps, so they don't have to accelerate.... Now granted, only about half of them are moving in a direction that would take them through the valve.... so maybe that 0.1 mS is a better number, I haven't a clue, which is why all this stuff is still a mystery, right?....

OK, so here is a bit more data for you to chew on.... I hooked my .224 cal gun up to a regulator at 1830 psi and shot the 30.6 gr. NAA bullets.... All the way from zero gap to 4 T, the velocity was 1016-1018 fps (no real variation, random over those 4 turns)…. At 8 T gap it was 1010 fps, plus or minus a few fps, and at 6T "in between", again +- a few fps.... So basically solidly on the plateau, out past the gap where the valve quit working at 3000 psi.... Now it gets interesting.... At 10T gap, the ES started to pick up, I got anywhere from 970-997 fps.... At 12T gap it was unusable, the velocities seemed to alternate between 770-775 fps and 845-860 fps, every other shot.... This is the typical unstable operation I have seen with the Cothran and SS valves when you are too close to the cliff.... and indeed at 13T gap there was no shot, and even at 12.5 T it wouldn't fire.... So basically the valve reverted to untunable at 1830 psi.... In addition, I tried shooting a string at 10T gap, and got two shots, 995 fps and then 944 fps, ending at 1370 psi.... It would NOT shoot a 3rd shot at the same gap....  :o

I was hoping I could just use less pressure in order to shoot a lighter bullet, but that did NOT work.... Possibly with a lighter hammer spring, so that the SSG gap was much smaller I may have been able to get it working.... but I could not just dial it down.... Any idea what the explanation is?....

Bob
Title: Re: Simplified Balanced Valve
Post by: rsterne on January 13, 2019, 06:01:08 PM
Nice model, and I get where you're going.... but I admit I have no basic understand of flow rates or the math behind it.... so you could be spot on, or dead wrong, and I wouldn't be able to input anything useful, one way or the other.... My understanding is that in a conventional valve, the lift to dwell curve was essentially a parabola, but if the lift exceeded 1/4 the throat diameter, the flow was clipped, like this.... In all the diagrams below, the mass of air flowed is roughly represented by the area under the curve.... (ie below the curtain limit)….

(http://i378.photobucket.com/albums/oo221/rsterne/PCP%20Internal%20Ballistics/ValveFlow1_zps5a9bbe8d.jpg) (http://s378.photobucket.com/user/rsterne/media/PCP%20Internal%20Ballistics/ValveFlow1_zps5a9bbe8d.jpg.html)

I further understood that the lift was proportional to the residual hammer energy, and the dwell was proportional to the residual hammer momentum.... residual being that which was left over after the valve cracked off the seat and the stem area x pressure was the primary (and relative constant) closing force.... Something like this happening if you change hammer mass M or velocity V.... Force F is closing force....

(http://i378.photobucket.com/albums/oo221/rsterne/Important/ValveLift6_zpsd0dc022d.jpg) (http://s378.photobucket.com/user/rsterne/media/Important/ValveLift6_zpsd0dc022d.jpg.html)

If those concepts are completely in error, then I will have to start at square one on my understanding of PCP Internal Ballistics.... Since I'm too old to go back to college, that isn't likely to happen.... so perhaps I should forget even trying to understand it at all....  ???

Bob
Title: Re: Simplified Balanced Valve
Post by: PikeP on January 13, 2019, 06:30:08 PM
Heres a 20 fpe model same rifle. Notice how the average flow rate is half of the lifts flow rate of 470~ ejected mg at 244 mg/ms...1ms dwell..

I think this model accurately represents lift and dwell times thanks to the added z axis of air mass ejection...you cant just model lift and dwell with x and y without the z making sense of it all. Just my 2c...if I didn't scale the graph the lift and flow rates would be overlapped perfectly...
Title: Re: Simplified Balanced Valve
Post by: rsterne on January 13, 2019, 06:47:44 PM
The one thing I get from those two diagrams is that the area under the lift curves (or the flow rate curves) is ROUGHLY proportional to the FPE.... At least that much I seem to understand.... I would love to see them both on the same graph, plotted to the same scale, with the same instant of valve opening.... What is the throat diameter, and where does the curtain limit (D/4) kick in?.... or does it?....

Bob
Title: Re: Simplified Balanced Valve
Post by: PakProtector on January 13, 2019, 07:06:54 PM
Bob, I have no idea...but we have some data already...:)

From the maximum velocity experiments, let's say that the pressure wave moves at something like 2300 fps. The valve has to be off its seat in order to fill in the volume behind the pellet( of what ever it may be, swaged spool, NAA or a heavy cast). I think the spread sheets can probably capture this adequately now.

Either way, the valve is acting like the first iteration where the balance chamber did not fill quickly enough.

Time for a game of Is/Is Not?

I see no reason to discard the Energy/Momentum relationship to lift and dwell. With earlier analysis, it should be possible to develop the lop-sided lift profile( due to the time at negative pressure against the hammer whilst the balance chamber comes up to pressure).

I suspect a solution will be to build the small bore valve with a bigger stem once y'all get a handle on what that closing force/opening curve is plotted.
cheers,
Douglas
Title: Re: Simplified Balanced Valve
Post by: mann on January 13, 2019, 07:17:35 PM
Bob I have same thing happened to me I was getting adjustability from bout 950 fps down to 850 ish if I back out the spring adjuster it will fire once or twice and fps would be around 800 then nothing would happen on the third shot I could turn the adjuster in a1/4 turn it was back to to 850 and would stay that way or only slightly go up until some preload on the hammer this is also regulated at 2100 psi it got a little better with a lighter hammer
Title: Re: Simplified Balanced Valve
Post by: PikeP on January 13, 2019, 07:31:12 PM
If you try to solve lift or dwell with newtonian mechanics you're in for a lot of error...you cannot predict the behavior of the valve for every microsecond of time and every thousandths inch of lift..it would require some serious computational strength and a large blend of harmonic, and very precise algorithms to which I'd say...good luck to you sir, for being so ambitious in trying to achieve such...throw in a different stem od,  closing force, balanced valve and the above just gets a whole lot more difficult...I bet air density shifts (large) would throw off such calculations...I highly doubt you're calculating the deflection of air at a specific density nor its potential momentum and kinetic energy based solely on its movement..
Title: Re: Simplified Balanced Valve
Post by: mann on January 13, 2019, 09:11:32 PM
I'm going to drop in a smaller transfer port see if that helps me
Title: Re: Simplified Balanced Valve
Post by: rsterne on January 13, 2019, 09:33:26 PM
HI Mike....

Before you showed up, and gave us the benefit of your extensive knowledge of flow dynamics, Newtonian Mechanics was all we had to use.... For me, it's still all I can understand, but that's OK, I'll leave the heavy lifting to those smarter and better educated than me.... In the meantime, you should know that while I do not have a extensive database of ACTUAL lift measurements, I do have a few, done with a simple mechanism like this....

(http://i378.photobucket.com/albums/oo221/rsterne/22%20cal%20Disco%20Double/Lift%20Rod%20and%20SSG_zpsj3e24ohf.jpg) (http://s378.photobucket.com/user/rsterne/media/22%20cal%20Disco%20Double/Lift%20Rod%20and%20SSG_zpsj3e24ohf.jpg.html)

The lower item is an SSG, the upper one is a device for measuring lift directly.... It consists of a very light aluminum tube, with a small screw in the end to act as a spring seat.... It slides through the rear velocity (preload) adjuster, and on the outer end is a small O-ring that is a slide fit.... The screw is captured between the end of the spring and the hammer, so the tube travels with the hammer.... You simply slide the O-ring up against the end of the adjusting bolt before you fire the gun, and as the tube travels forward with the hammer, the O-ring is pushed back, and the resulting gap between it and the adjusting bolt is how far the valve opened.... In case there was a bit of drag in the system, I can fire the gun a second time to confirm the gap.... If the gap is large enough, I measure it with calipers.... If it is too small for that, I use feeler gauges, starting small, and adding/substituting more until they just fill the gap.... I wear a pair of magnifiers so that I don't accidently slide the O-ring while measuring.... It may be crude, but it works extremely well, and the sliding assembly is a small fraction of the weight of the hammer, so I don't think it causes any glaring error in the lift measurement.... I'll dig up some measurements taken with this device, and you can see what the lift is actually doing....

Bob
Title: Re: Simplified Balanced Valve
Post by: rsterne on January 13, 2019, 09:50:43 PM
Here is a recent set of measurements I made on a Cothran valve in my .35 cal Disco Double.... First the relationship between velocity and preload for 3 bullet weights....

(http://i378.photobucket.com/albums/oo221/rsterne/30%20cal%20Disco%20Double/DD%20Cothran%20Preload_zpsna5he1sx.jpg) (http://s378.photobucket.com/user/rsterne/media/30%20cal%20Disco%20Double/DD%20Cothran%20Preload_zpsna5he1sx.jpg.html)

Next the measured lift, and the calculated FPE/CI, at those same preload settings....

(http://i378.photobucket.com/albums/oo221/rsterne/30%20cal%20Disco%20Double/DD%20Cothran%20Lift_zpspt32gfuk.jpg) (http://s378.photobucket.com/user/rsterne/media/30%20cal%20Disco%20Double/DD%20Cothran%20Lift_zpspt32gfuk.jpg.html)

Note that when the valve was working properly (ie not falling off the cliff), the lift was at least 0.065", and peaked at 0.125".... The gun was tethered to a regulator set at 2900 psi for these tests.... It had a 28" barrel, with exhaust, transfer and barrel ports of 0.258", and the valve had a 0.335" throat with a stem of 0.175" (stock Cothran valve), so the equivalent throat was 0.284"…. The hammer spring was 1.89" LOA 0.30" OD and made from 17 coils of 0.035" wire, with a rate of 8.7 lb/in. and the hammer weighed 82 gr. and had a stroke of 0.75".... Max. preload was coil bound, which occurs at a length of 0.60" at a load of about 11 lbs.... The minimum lift when the valve was on the plateau was 19% of the throat diameter, and at maximum it was 37%, so flow limiting from the curtain area would have certainly been happening.... I hope you find this information useful....

Bob
Title: Re: Simplified Balanced Valve
Post by: rsterne on January 13, 2019, 10:35:42 PM
Here is another set of valve lift measurements, this time on a .308 cal with a 21" barrel.... First, the shot strings, so you can see how the gun shoots at the various preload settings....

(http://i378.photobucket.com/albums/oo221/rsterne/30%20cal%20Disco%20Double/30DiscoDoubleShortBarrel_zps82907bb6.jpg) (http://s378.photobucket.com/user/rsterne/media/30%20cal%20Disco%20Double/30DiscoDoubleShortBarrel_zps82907bb6.jpg.html)

Now here are the corresponding valve lift measurements, taken at the beginning and end of each string, along with the average lift.... Note that the lift during each compete string (-6T out or more) increases by 60-80% from the high pressure start to the low pressure end.... This is typical for a 4% ES.... The lift roughly doubles during a shot string if you allow a 5-6% ES.... With a 10% ES it more than doubles during the string....

(http://i378.photobucket.com/albums/oo221/rsterne/30%20cal%20Disco%20Double/308%20Disco%20Double%20Valve%20Lift_zpspuneg9fi.jpg) (http://s378.photobucket.com/user/rsterne/media/30%20cal%20Disco%20Double/308%20Disco%20Double%20Valve%20Lift_zpspuneg9fi.jpg.html)   

At that time I was just using calipers, so I was rounding to 2 decimal places when recording the lift.... I was only interested in getting a rough idea of the lift, but it certainly show the trend, with the lift increasing as the pressure drops during the string.... and also that the higher the FPE, the greater the lift.... This gun had a throat of only 0.234" with a stem of 0.115" (0.203" equivalent) and exhaust port of 0.200", with transfer and barrel porting of 0.219".... I was using a QB hammer spring, LOA 2.34", 0.33" D, 20 turns of 0.047" wire, 17.4 lb/in, coil bound at 0.95".... The hammer weighed 82 gr. and had a travel of 0.72".... Max. preload was again when the spring was coil bound, which occurs at a load of about 24 lbs, and the preload adjuster was 24 TPI (0.042" per turn)…. I was shooting .30 cal JSB 46 gr. pellets which were "bumped up" to 0.308" in a die I made....

Oh, one other thing that is not on the graph, the efficiency for each string, by preload setting....

Max.... 0.49 FPE/CI
-2 T.... 0.58
-4 T.... 0.69
-6 T.... 0.72
-8 T.... 0.89
-10 T....0.91
-12 T.... 0.90

The strings are moved to the right to indicate the start and end pressure on the appropriate pressure line.... For example, the last string at -12 T was shot filling to 1900 psi and stopping at 1220....

Again, I hope this data gives you something useful....

Bob
Title: Re: Simplified Balanced Valve
Post by: mann on January 13, 2019, 10:35:55 PM
With that style ssg do you set the preload with the nut and use the bolt to adjust your gap . I was using the bolt to add preload and the nut to adjust the gap now that I think about it I wasn't doing the adjustments right because an adjustment on the bolt also make the gap to have to be adjusted oops
Title: Re: Simplified Balanced Valve
Post by: rsterne on January 13, 2019, 10:43:31 PM
Mark, that is correct.... I usually use two nuts for the preload adjuster, locked against each other so the preload can't change.... The gap is the primary adjustment, the preload is used to get you in the ballpark, and provide enough load on the guide that when the hammer is thrown back by the spring it can't store energy in the spring, it just rattles around between the end of the guide and the valve stem.... I use a minimum of 3 lbs. of preload, typically 5 lbs., and have used as much as 8 lbs.... Using a long, soft spring with a lot of preload makes the cocking buttery smooth, because once your muscles pull hard enough to start pulling the bolt back, they hardly notice the increase in force.... With a SSS, with no load at the beginning of the cocking stroke, and a lot at the end, it is easy to not quite cock the gun, resulting in a double pellet fees with a magazine like on the MRod….

Bob
Title: Re: Simplified Balanced Valve
Post by: mann on January 13, 2019, 10:54:07 PM
I've only used the style where the hammer is on the bolt to and the whole bolt moves to strike the stem  which is a different style now that I looked at this style again it hit me how it works I'll be making a new one for my brod also thanks Bob
Title: Re: Simplified Balanced Valve
Post by: PikeP on January 14, 2019, 02:46:33 AM
Rising air pressure in transfer plenum has a velocity closer to 1125 not 1650...

1125*12/1000 = 13.5 inches per ms

1.5 inches (my full long distance seat to pellet) / 13.5 = 110 micro seconds

Or 1 inch (shortest available path) = 70 micro seconds..

Air doesn't change direction well on it's own, it is not sentient. There is randomness to its movement (bouncing around varying travel distance and speed) hence variance in muzzle velocity regardless how consistent the conditions...air takes path of least resistance like water..similar flow profiles, air is not a racecar that takes sharp corners very well..

The time it takes to release enough air to move pellet is roughly 70 micro seconds..that's not factoring in its travel through two dimensions...space and time

Air cannot skip either dimension...

At merely 50 micro seconds I calculate 1125 micro grams of air per 50 micro seconds which is 1.25 mg.. which equates to 1.4 psi...required psi to begin pellet movement is 4 to 5 over atm...

So in summary, with NO losses, and air traveling the shortest distance like you were behind the wheel of a race car...straight lined and only taking the shortest distance..pellet movement can not begin any sooner than 70 micro seconds...assuming air is leaving the starting line at 1125 fps and maintaining that speed the entire path..and that the lift generated to release said air skipped the dimension of time and instantly released said 2500~ micro grams to begin pellet movement.

Trying to scope down to such a level of time is really difficult and if you do it with absolutely zero losses you're bound to be off by a large factor.
Title: Re: Simplified Balanced Valve
Post by: rsterne on January 14, 2019, 02:51:21 AM
Sound perfectly reasonable.... I was trying to put a logical (to me) reasonable number on the time during which all that was happening was the pressure in the transfer port was increasing.... If it is 70-100 microsec. instead of 50, I'm 100% OK with that....

Bob
Title: Re: Simplified Balanced Valve
Post by: PikeP on January 14, 2019, 05:37:33 AM
I find it odd that classical mechanics didnt predict hammer weight and spring requirment from the get go, even for a balanced valve... My formula predicted 79 gr and 11 lb spring at full balance and 79 gr and 12.8 at partial balance...

Here is another way i can go about to estimate your pcps performance...


Your port can flow 3700 mg per ms... at 28% thermal efficiency and a 2 ms dwell time I get 274.8 fpe/ 896 fps with 154 gr....

With a 3ms dwell time you would have a thermal efficiency of 19% or under 1 fpe per ci...
Title: Re: Simplified Balanced Valve
Post by: PakProtector on January 14, 2019, 08:29:41 AM
Rising air pressure in transfer plenum has a velocity closer to 1125 not 1650...


Given the ability to deliver light pellet velocity in excess of 2000 fps I don't think that is valid. The rise in pressure is going to be moving at least that fast. If it were not, we'd never see those higher than average molecular velocity shots being recorded.
cheers,
Douglas
Title: Re: Simplified Balanced Valve
Post by: MJP on January 14, 2019, 11:20:49 AM
I'm curious where did you guys get the 1650fps port velocity?
Speed of sound at pressure?
Then how do we see velocity exceeding this?

Marko
Title: Re: Simplified Balanced Valve
Post by: PakProtector on January 14, 2019, 12:42:49 PM
Have some fun at the maximum velocity thread Marko.

There has been recorded MV at over 2000 fps...and I made the claim that pressure change velocity in the port has got to proceed faster than a pellet that was getting pushed by it...:) I took exception to Mike's 1150-ish one, and for the same reason 1650 fps which is air at STP average velocity. And yes, I realize it is probably one small bit o' the picture, but we clearly have evidence that pressure wave propagation goes very quickly indeed, esp compared to C or avg. velocity.
cheers,
Douglas
Title: Re: Simplified Balanced Valve
Post by: rsterne on January 14, 2019, 12:43:05 PM
Marko, the 1650 fps is the average "speed" (it isn't a velocity, since the directions are random) of air molecules at room temperature…. There was (and still is, for some people) a theory that that velocity set an upper limit on the expansion of air through a parallel tube (eg. a barrel)…. This was promoted very vocally (by one airgun guru in particular on another Forum), and when Lloyd made his first historic shots over 2000 fps, there were suggestions of improper technique; the Chrony was set up or lighted wrong, the shots were taken too quickly after the reservoir was filled, and hence the temperature was elevated.... anything that could be said to disparage Lloyd's achievement was pretty much done, and of course debunked and the results (and others which followed) now are allowed to speak for themselves, that velocities of over 2000 fps, using expanding air, are possible.... Here on the GTA we spent a long time debating a more reasonable "upper limit" (I proposed twice the 1650, or 3300 fps, and gave what I though was a reasonable argument to support it)….

Quite recently, a new member, DomingoT, who is a professor of Thermodynamics, had a brief stint here on the GTA, during which he used lengthy equations to predict quite closely PCP behaviour, and in fact got extremely close agreement to Lloyd's 2162 fps shot (within a few fps) using his approach.... Unfortunately, he found our voracity for knowledge on the subject was taking too much of his time, and "scaled back his web presence" and we haven't heard from him since.... His "upper limit" on velocity is the "Mach 5 at prevailing temperature and pressure" widely accepted by those designing and using Light Gas Guns.... He says the same limit applies, but of course in reality is completely out of reach for PCPs....

I don't know Mike's background, but he is obviously a bright guy, with a penchant for calculations, and a knowledge of flow calculations.... We are fortunate to have his input, even if I don't understand much of it.... Now I know how some of you guys feel when I use "too much math" in some of my posts.... *LOL*…. I have always said that my theories are only valid until experimental data exceeds them, in which case it's time for a new theory.... I'm still stuck in the realm of Newtonian mechanics, Thermodynamics and Flow Theory are far beyond my understanding, unfortunately.... However, I welcome anyone who can show the theory behind our observable facts.... It is only in that way that our knowledge of PCPs can advance.... Doing it is not good enough, we need to know the "why" it works, and not just the "how" to do it.... IMO, anyways....

Bob
Title: Re: Simplified Balanced Valve
Post by: rsterne on January 14, 2019, 12:47:10 PM
Quote
With a 3ms dwell time you would have a thermal efficiency of 19% or under 1 fpe per ci...

That sounds 100% correct, from my experience.... In fact "dump shots", where the valve is open until after the pellet exits the barrel can be less than half that value (eg. 0.4 FPE/CI)…. To be truthful, I have never tried to model how the hammer strike relates to the way the valve opens.... I have math for the hammer energy and momentum, and intuitively (and through experiment) know how that affects the valve cycle.... and we have a Newtonian model for the Internal Ballistics (thanks to Lloyd)…. but I have never tried to work out the math of how the hammer strike, per se, relates to valve lift and dwell....

Did you try and model the lower power, .224 cal shots, in Reply # 416, where the valve is no longer tuneable?.... We need to know why it isn't working, as a conventional valve will certainly still work in that situation.... So for that matter will the SS valve....  ???

Bob
Title: Re: Simplified Balanced Valve
Post by: MJP on January 14, 2019, 02:56:18 PM
For me the why's and if's aren't so important but how. I can't explain everything for why and how I designe stuff. I just see it in my head how it should be.
I have made in the past one of the most powerful and fastest 2 stroke engines, but Why everything in it is like they are I can't explain it just feels right.

I make it as I go, no drawings no dimensions it just comes together in the end. All of the guns that I have made are without blueprints except the Savage, that was drawn by Timo. I make the drawings if I need to make another based on the previous one.

Sorry for the OT,

Marko
Title: Re: Simplified Balanced Valve
Post by: MJP on January 14, 2019, 03:01:52 PM
What is the speed of a single molecule of air inside the airtank at 300bar? Pressure is just air molecules colliding against the cylinder walls as they are never stationary.

Marko
Title: Re: Simplified Balanced Valve
Post by: rsterne on January 14, 2019, 03:42:05 PM
The average speed of air molecules at room temperature is ~1650 fps, independent of the presssure.... At high pressure, you just have a lot more of them colliding with the walls of the container.... At very high pressures, they are also colliding with each other more frequently, which actually reduces the pressure, but they are packed more tightly together (less vacant space between), which increases the pressure.... These two factors are taken into account in the VanDerWaal's equations, which is the reason that pressure builds faster than density above about 3000 psi for air.... It is no longer acting as an "ideal gas" like Boyle's Law is based on....

That explanation just gave me an idea that may explain partly why you were able to exceed my 50% rule of thumb.... At 4500 psi, you are getting more force from less mass of air being expelled (accelerated) out the muzzle.... Just like in using Helium (a lower mass gas), you get a similar (but much reduced) effect.... While very high pressure air loses shot count compared to 3000 psi air.... it should actually gain velocity....  8)

At 4500 psi, the air "pushes" on the bullet with 50% greater force than at 3000 psi... However, it only has a density 38.7% higher.... That should give about an 8% advantage to 4500 psi air in my "lofty goal" equation, compared to 3000 psi (which I am used to working with, and used when I made that approximation).... When we incorporate the VanDerWaals correction, it makes your results make sense.... 8) ;D ;)

Bob
Title: Re: Simplified Balanced Valve
Post by: mann on January 14, 2019, 06:09:28 PM
Got the ssg made using tss end cap and a 13 lb flat spring may have to thread it some more once I get it set up and need to drill a hole in my transfer port thinking about try around a .150 to hole
Title: Re: Simplified Balanced Valve
Post by: oldpro on January 14, 2019, 06:32:28 PM
https://youtu.be/u427RHkSy4o
Title: Re: Simplified Balanced Valve
Post by: triggertreat on January 14, 2019, 06:51:58 PM
WOW Travis...That's very impressive!!!  You know I/we want that for sure.  Just curious if we can swap out the innards of our gen 1 SS valves or do we need to order a new valve.  Can't wait to get back to easy cocking and no stiction.  Thank you for all you do for us!
Title: Re: Simplified Balanced Valve
Post by: oldpro on January 14, 2019, 06:59:26 PM
WOW Travis...That's very impressive!!!  You know I/we want that for sure.  Just curious if we can swap out the innards of our gen 1 SS valves or do we need to order a new valve.  Can't wait to get back to easy cocking and no stiction.  Thank you for all you do for us!
Keith i was going to send you Python internals but thought twice about it so YES I will send you new gen 2 SS internals when I get back from the Shot Show.
Title: Re: Simplified Balanced Valve
Post by: rsterne on January 14, 2019, 07:41:21 PM
Today I removed the .224 cal barrel and installed the .257 cal.... It is a 28" long 14" twist TJ's.... I tethered the gun at 3000 psi and got the following data.... I was getting low on the Lyman 257420s, so I bracketed the weight of that with an NOE 260-63 HP and an RCBS 257-85 HP, the weights are shown on the graph below....

(http://i378.photobucket.com/albums/oo221/rsterne/Hayabusa%20PCP/Hayabusa%20257%20Balanced%20Valve_zpspxfpqaej.jpg) (http://s378.photobucket.com/user/rsterne/media/Hayabusa%20PCP/Hayabusa%20257%20Balanced%20Valve_zpspxfpqaej.jpg.html)

You can see that the gun is not quite reaching the velocity plateau, even at zero SSG Gap.... With the original valve and hammer it peaked at 160 FPE, at zero gap it is 146 FPE with the same bullet.... I don't really care, because I never max. out the gun when shooting anyways, because you get a declining shot string and lousy efficiency.... This could also be due to the small plenum of 108 cc.... I then filled the gun to 3000 psi and shot strings at four SSG Gap settings until the velocity fell 4% below the peak.... The resulting shot strings are shown below.... Remember that the reservoir volume, including the hose, gauge and valve is only 120 cc, when the 22 CI bottle is reinstalled the reservoir volume will be 460 cc, so I should get close to 4 times the number of shots.... depending on the effect of the expected power increase with less pressure loss during the shot from the larger reservoir....

(http://i378.photobucket.com/albums/oo221/rsterne/Hayabusa%20PCP/Hayabusa%20257%20Balanced%20Strings_zpsizgrffwu.jpg) (http://s378.photobucket.com/user/rsterne/media/Hayabusa%20PCP/Hayabusa%20257%20Balanced%20Strings_zpsizgrffwu.jpg.html)

I have not made ANY changes to the .357 cal lower, which has the balanced valve I just built, a 77 gr. hammer and an SSG with an 11 lb/in. hammer spring.... The transfer port is the same tapered one I had on the .224 version (they share the same receiver), the barrel port on the .257 cal barrel is oblong and equivalent to the caliber, and the most restricted point is the chamber, which has the same 0.088" probe as the .224 cal (they share bolts), so the annular area around the probe is the smallest point in the porting system, equivalent to a hole of 0.241" diameter....  I also tested all the different weight bullets I have kicking around, with the SSG adjusted to zero gap.... The results are in the table below....

(http://i378.photobucket.com/albums/oo221/rsterne/Hayabusa%20PCP/257%20Hayabusa%20Balanced%20Weights_zpstzcnoeou.png) (http://s378.photobucket.com/user/rsterne/media/Hayabusa%20PCP/257%20Hayabusa%20Balanced%20Weights_zpstzcnoeou.png.html)

The FPE was between 145-151 with all bullets tested, peaking with the Lyman 257420 FN at 73.5 gr.... The one low FPE was a cast bullet I got from Doug Noble which had many lube bands.... and despite all bullets being sized the same at 0.256", it had a lower than expected velocity.... I suspect extra friction from all the drive bands was the cause.... One other note.... The 98 gr. bullet I tested was the HP version of my NOE 101 gr. BBT, which is 0.873" long.... Despite my backstop only being at 20 feet, it was keyholing on impact, the holes were about 1/2" long.... This is proof positive that bullet is NOT stable in a 14" twist....

So far, the new valve has worked properly in .357 cal, .224 and .257 cal.... Next I will prep the .30 cal LW barrel I have by enlarging the barrel port, and make a new bolt probe for it that is 7/64" diameter to replace the 0.140" removable probe currently on the .357 bolt.... The .308 and .357 barrels share the same receiver and bolt.... After I have tested that barrel, I will have to do some significant alteration to my 7 mm barrel and receiver to adapt it to the existing lower.... When all is said and done, I will have five calibers that all fit the same lower, using the same valve, hammer and SSG setup.... at least I see no reason now why that should not be possible, since the smallest (0.224") and largest (0.357") both worked properly at the 3000 psi fill pressure I am using....

Bob
Title: Re: Simplified Balanced Valve
Post by: rsterne on January 14, 2019, 07:49:30 PM
Well done, Travis.... It looks like a pretty sudden increase in velocity from 521 to 669 in 1/4 turn, as we would expect somewhere in that range.... but still lots of adjustment either side of that.... Looks like you are getting about 250 fps in the upper range.... Good job !!!!

Bob
Title: Re: Simplified Balanced Valve
Post by: triggertreat on January 14, 2019, 07:59:12 PM
WOW Travis...That's very impressive!!!  You know I/we want that for sure.  Just curious if we can swap out the innards of our gen 1 SS valves or do we need to order a new valve.  Can't wait to get back to easy cocking and no stiction.  Thank you for all you do for us!
Keith i was going to send you Python internals but thought twice about it so YES I will send you new gen 2 SS internals when I get back from the Shot Show.



That's great Travis!  I have been following along and could tell the Python wasn't happening.  Have fun at the Shot Show and be safe.  I'm looking forward to seeing whatcha got to show us.
Title: Re: Simplified Balanced Valve
Post by: oldpro on January 14, 2019, 08:13:03 PM
WOW Travis...That's very impressive!!!  You know I/we want that for sure.  Just curious if we can swap out the innards of our gen 1 SS valves or do we need to order a new valve.  Can't wait to get back to easy cocking and no stiction.  Thank you for all you do for us!
Keith i was going to send you Python internals but thought twice about it so YES I will send you new gen 2 SS internals when I get back from the Shot Show.



That's great Travis!  I have been following along and could tell the Python wasn't happening.  Have fun at the Shot Show and be safe.  I'm looking forward to seeing whatcha got to show us.
The Python works awesome its just not what your looking for at your power level. Im going to make both valves eventually. 
Title: Re: Simplified Balanced Valve
Post by: oldpro on January 14, 2019, 08:36:19 PM
Well done, Travis.... It looks like a pretty sudden increase in velocity from 521 to 669 in 1/4 turn, as we would expect somewhere in that range.... but still lots of adjustment either side of that.... Looks like you are getting about 250 fps in the upper range.... Good job !!!!

Bob
I went and reran it and used 1/8 turns and I get a 300 fps window which I think is plenty in most applications. I have to tell you I have been working off and on with this for 3 months now and until you  guys made the spread sheet I was getting nowhere. The secret for me was reducing the area in the vent chamber to as small as I could get it and that made it work I was nearly twice the size it is now before. MUCH Thanks Gentlemen.   
Title: Re: Simplified Balanced Valve
Post by: rsterne on January 14, 2019, 09:42:52 PM
I agree, 300 psi is lots for a tuning range.... more than I have seen on any balanced valve....

Just think when we started playing with these, there was NO adjustability unless you changed the pressure (Cothran)…. We've come a long ways since then....

Bob
Title: Re: Simplified Balanced Valve
Post by: PikeP on January 14, 2019, 10:03:03 PM
Update to where sheet currently is. It's basically done once I run numbers on more versions, calibers, and energy levels.

Lots of approximations going on so dont nitpick..added a lot of metric conversions for outputs but inputs are still mostly imperial. Sorry Marco..
Title: Re: Simplified Balanced Valve
Post by: rsterne on January 14, 2019, 10:28:39 PM
The spreadsheet is looking great, Mike.... Nothing wrong with approximations, particularly where they make the results agree with the testing.... As long as you don't have to make drastic changes in those assumptions when you change the test criteria (eg. caliber), that's the important part.... When you are happy with it, I would love to see the inputs use my spring chamber and spring (diam. = 0.203", height = 0.40", spring vol. = 0.09 cc; hammer sprung travel 1.09 max. - 0.1 gap = 0.99"; port = 0.328", throat = 0.375",)…. Some of your values have drifted a bit from what I have (in the interests of optimizing the design, I realize that)…. One other thing, the barrel, from the base of the bullet to the muzzle, measures 27.5", not 28".... At that 2T Gap setting the velocity with the 154 gr. bullet is 860 fps.... efficiency is 1.33 FPE/CI....

Once you have that, I would love to see the other calibers input (just changing the specs. on the upper) and see how close the outputs are to my measured tests.... If it doesn't require tweaking between calibers, that would be a pretty good indication you're there....  8)

Bob
Title: Re: Simplified Balanced Valve
Post by: oldpro on January 14, 2019, 10:42:11 PM
I agree, 300 psi is lots for a tuning range.... more than I have seen on any balanced valve....

Just think when we started playing with these, there was NO adjustability unless you changed the pressure (Cothran)…. We've come a long ways since then....

Bob
That’s a fact Bob! We’ve moved the needle a bit. Now we’ve found a way to make a trouble free adjustable valve the sky’s the limit my friend.
Title: Re: Simplified Balanced Valve
Post by: PikeP on January 15, 2019, 12:14:57 AM
So after studying dwell some I believe 1/2 barrel is 1.0 fpe per ci, 1/3rd is roughly 1.43 fpe/ci..and 1/4th is 1.85 fpe/ci....thats with a projectile that is 1/2 gr per fpe or greater, peller mass certainly effects the above..I dont know how well that holds up universally but I think Bob has always advocated about barrel distance for valve closure closely relating to volumetric efficiency..I certainly agree and have finally understood the connection myself..

Attached is the same graph as above but with a recorded efficiency of 1.0 fpe/ci
Title: Re: Simplified Balanced Valve
Post by: rsterne on January 15, 2019, 01:46:39 AM
I think your FPE/CI vs the dwell is a bit optimistic, but then I could be wrong about how short I think the dwell is on the really efficient shots.... We both agree that there is a direct relationship between where the valve closes and the volumetric efficiency....

I have a question about your valve dwell lift in the lower left corner.... Is that the "effective" dwell, taking into account curtain limiting.... or do you think that is how high the poppet lifts from the seat?.... I ask because you only have a 0.002" difference in the lift, even though the dwell increases from 2.11 mS to 2.79 mS.… I don't see any difference in the hammer strike, so I don't see how all those factors can interrelate.... With the same hammer mass, the relationship between lift and dwell is somewhat proportional, and governed by hammer velocity.... Lift should increase with the square of residual hammer energy, and dwell in proportion to the residual momentum.... at least that is my understanding.... How can you get a 1/3 increase in dwell without a corresponding large increase in lift?....

Bob
Title: Re: Simplified Balanced Valve
Post by: PikeP on January 15, 2019, 02:18:14 AM
Bob I added a valve close checker...it verifies close distance based on your formula that I've modified down to within 1% accuracy based on a given barrels length volume...then you match your volumetric efficiency until your thermally projected FPE output matches...once both figures match you should know approximate close distance and efficiency...

Title: Re: Simplified Balanced Valve
Post by: rsterne on January 15, 2019, 12:20:07 PM
HI Mike....

It is cool to see the volumetric efficiency being tied into the valve dwell, and the point where the valve closes as the pellet moves along the barrel.... Lloyd's spreadsheet, once set up for the known quantities, ends up with two numbers that must be changed to come up with the observed FPE/CI.... One is the valve dwell, and the other is an overall "efficiency factor" that can run anywhere from 50-80%.... There is only ONE combination of those two inputs that will produce the observed FPE/CI at the observed velocity/energy.... By using Thermodynamics, it appears you have eliminated the "fudge factor" (always a good thing)…. I am wondering, however, it that is still there to some degree in your choice of 28% thermal efficiency.... Surely not all airguns have that same value?.... I assume if you change that, then the relationship between dwell, FPE and efficiency all changes....

Still, I am delighted to see that the relationships between FPE and barrel length, port size, plenum volume, projectile weight and caliber are being clarified, as I knew they would.... If each of us can come up with small pieces of the puzzle, and we all keep an open mind, we can accomplish a lot....  8)

Bob
Title: Re: Simplified Balanced Valve
Post by: mann on January 15, 2019, 02:40:38 PM
Ok I have a question . Won't changing the transfer port to a smaller size make the chamber fill faster
Title: Re: Simplified Balanced Valve
Post by: PikeP on January 15, 2019, 03:40:26 PM
Bob the 28% rule only applies when operating at peak efficiency and power combined...imo..for example your 274 fpe shot was in the neighborhood of 22%..and the 250 fpe shot was probably 27%or so..

28% is just a baseline to want to be at..which translates to roughly 1.4 fpe/ci which I think you can agree is a good place to tune for both air use and power.

I think I figured lift and dwell to some degree...at least getting within spitting distance. I think the valave opens up 10% or so more than what an equivalent port would flow...

Bob, can you for a giggle run a simulated 150~ fpe shot with the 154 grain through Lloyd's spreadsheet so I can see where I currently stand in comparison on lift and dwell? It's really hard to solve for x and y when you only know the median of z..but I think it's possible. I get around 1.5 to 1.8 ms dwell depending on efficiency but I haven't found a way to modify your formula for less than peak performance ie low lift conditions..if I figure out that solve I'll be golden..lift, dwell and volumetric efficiency is all I need to compare. Thanks.
Title: Re: Simplified Balanced Valve
Post by: rgb1 on January 15, 2019, 03:42:34 PM

"The average speed of air molecules at room temperature is ~1650 fps, independent of the presssure.... "


rms molecular velocity (denoted by lower case c) is pressure dependent
just like sonic velocity (a) and they are related by


       
      c/a = sqrt(3/gamma)


Hope this helps, Bob.


                                                                                 Ron
Title: Re: Simplified Balanced Valve
Post by: PikeP on January 15, 2019, 04:18:14 PM
Thanks Ron. My sheet isn't using the air velocity to calculate much currently so I havent put focus or time into it...but I put brief thought into it this morning..although with the distances I'm calculating even large velocity shifts aren't changing my calculatios more than .05% because air velocity is not the largest factor for my current formulations...

I changed to the following to get velocity based on KE and mass...however it may not be the best or most precise I think it's good enough for what I'm doing..thanks again!


Sqrt(2*ke/mass)

This puts atm air doing 1650~ and air at 4500 going 2850~...roughly

In most pcps air flow rate limits your pellet velocity more than air velocity...so it's not THAT important here as it would be in a theoretical maximum velocity event..which I'm not currently considering ..not saying air velocity plays no role it's just much less of one until you start going for absolute peaks..meaning air flow rate causes more delay through small orifices and at lower lifts. Where as air velocity + ke have more impact at peak flow rates with large orifices..

I'm calculating fill rates from 100 to 1500 micro seconds through orifices from .01 to .05. Air could move 1000 feet per second and still not effect the end result by much..going from 1400~ fps to 2700~ fps for example changes my estimated fill rate by .05%.
Title: Re: Simplified Balanced Valve
Post by: rsterne on January 15, 2019, 06:08:24 PM
Hey, Ron.... good to see you again.... I have a question about that formula.... If the quantity c/a can be determined by sqrt(3/gamma)…. or for that matter any quantity, fixed or variable, lets call it X = sqrt(3/gamma).... doesn't that mean that c is proportional to a ?.... What I mean is, the equation could be rearranged to....

c/a = X …. or  c = aX …. or  a = cX …. So, if you don't know the value of c, you can't know a.... and vice versa.... or am I missing something?.... We know that gamma varies somewhat with pressure, and we know that a also varies somewhat with pressure.... but is that because c is constant?.... Without more information I'm still a dummy....  ::)

I always used this calculator for the molecular speed....

http://hyperphysics.phy-astr.gsu.edu/hbase/Kinetic/kintem.html#c4 (http://hyperphysics.phy-astr.gsu.edu/hbase/Kinetic/kintem.html#c4)

I don't see pressure or density there, just temperature and the atomic number (molar mass).... What am I missing?....

Bob
Title: Re: Simplified Balanced Valve
Post by: PikeP on January 15, 2019, 06:15:36 PM
For a giggle I ran calcs as low as 10 micro seconds. With my assumption that nearly no air flow occurs in the first 10 micro seconds you have to add that to the time pellet starts movement. From there I let the air go full speed 1650 fps...which is probably way high...ever catch a leak on your pcp and see bubbles slooowly grow when you use soap?

1650 fps eh?..Anyhow. Short distance .065ms long distance .091ms... I personally feel confident in these numbers and the margin of error considering the scale of time involved. I certainly didnt add any losses to the above times either with the exception of 10 micro seconds added to generate lift that can flow any appreciable air over time..and that is being very giving. And in air resistance the very low flow profile encounters among other losses and the long distance looks better and better.
Title: Re: Simplified Balanced Valve
Post by: rsterne on January 15, 2019, 06:43:12 PM
Mike, if I set Lloyd's spreadsheet up for 860 fps with 154 gr. bullet in a 27.5" barrel, using 108 cc of 3000 psi air, at 73% efficiency (actually pretty high, but that's what it takes to balance), using 2 lbs. of bullet drag and 5 lbs. of breakaway, with a 1.64 cc wasted transfer port volume, I get 2.44 mSec. for the dwell at 1.32 FPE/CI, and the valve is closing at 36% of the barrel length.... That's as close as I can get to my operating conditions for the .357 with 2T of gap on the SSG....

If I change ONLY the dwell and leave the efficiency at 73% (which certainly isn't the case for higher power, longer dwell shots, they get less efficient), I get the following results....

4.45 mS.… by adjusting the efficiency down to 68%, this is the dwell when the valve closes at pellet exit (100%), @ 0.66 FPE/CI.... reasonable assumption....
4.0 mS.… 921 fps @ 0.77 FPE/CI, valve closes at 88%.... To keep the velocity at 890, efficiency must be reduced to 69%....
3.0 mS.… 897 fps @ 1.07 FPE/CI, valve closes at 53%.... Velocity a bit too high, using efficiency of 71% I get 883 fps, which agrees with observed results at zero gap....
2.0 mS.… 810 fps @ 1.58 FPE/CI, valve closes at 25%.... Pretty good agreement with observed....
1.5 mS.… 725 fps @ 1.94 FPE/CI, valve closes at 14%.... Valve has gone "over the cliff" at this point, no valid test results....
1.22 mS.… 662 fps @ 2.16 FPE/CI, valve closes at 9.5%....   ditto.... This would be 150 FPE....
1.0 mS.… 605 fps @ 2.34 FPE/CI, valve closes at 6.4%....   ditto....
0.5 mS.… 467 fps @ 2.62 FPE/CI, valve closes at 1.6%....   ditto
0.1 mS.… 398 fps @ 2.63 FPE/CI, valve closes at 0.1%....   ditto

It is pretty obvious that Lloyd's spreadsheet doesn't work once the dwell is on the order of the lag time to fill the transfer ports, as it assumes the pellet is being accelerated from the get-go.... Perhaps if we added 100 uS (ie 0.1mS) to all those dwell times to allow for that, it might be a much better model.... Lloyd and I have discussed that, but as of yet that hasn't been done.... I hope you find the above useful....

Bob

PS.... I understand now that the 28% is not always applied, only for "good" PCPs.... makes perfect sense, thanks....
Title: Re: Simplified Balanced Valve
Post by: mann on January 15, 2019, 06:54:40 PM
So I tried a .150 transfer port Which is .050 smaller than what I had in place it seemed to give me more tunability tuned from 690 fps up to 800 fps is where I stopped I have to readjust the gap which after trying more tension on the ssg got to wide and I didn't have any more time to keep testing
Title: Re: Simplified Balanced Valve
Post by: rsterne on January 15, 2019, 07:04:57 PM
WHOA !!! …. Back up a minute, Mike !!! …. Where did THIS formula come from ? ….

Quote
Sqrt(2*ke/mass)

This puts atm air doing 1650~ and air at 4500 going 2850~...roughly

If you have some way to calculate maximum air velocity of 2850 fps at 4500 psi I need to know about it....  :o :D 8)

Bob
Title: Re: Simplified Balanced Valve
Post by: rgb1 on January 15, 2019, 07:36:05 PM

I always used this calculator for the molecular speed....

http://hyperphysics.phy-astr.gsu.edu/hbase/Kinetic/kintem.html#c4 (http://hyperphysics.phy-astr.gsu.edu/hbase/Kinetic/kintem.html#c4)

I don't see pressure or density there, just temperature and the atomic number (molar mass).... What am I missing?....



The answer is right there at the top ......."for an ideal gas"........

Title: Re: Simplified Balanced Valve
Post by: PikeP on January 15, 2019, 08:04:13 PM
WHOA !!! …. Back up a minute, Mike !!! …. Where did THIS formula come from ? ….

Quote
Sqrt(2*ke/mass)

This puts atm air doing 1650~ and air at 4500 going 2850~...roughly

If you have some way to calculate maximum air velocity of 2850 fps at 4500 psi I need to know about it....  :o :D 8)

Bob

Well it better explains the current obtained velocities no? Do you think 2200 + fps was obtained with no losses in air speed? Idk...and that 2850 at 4500 psi is theoretical max before any adiabatic cooling occurs which slows air speeds no?...its not what you'd ever obtain from a projectile...

I'm definitely open to different methods of obtaining airs *average* velocity and *peak* so I'll check out your link.

Dropping temp just a small amount of degrees reduces speed greatly, reducing KE due to losses takes that 2850 down further...see where I am trying to go? If your peak 2k+ fps shots were recorded when air was moving its peak velocity I'd be quite impressed! I'll calculate a few losses and report back with a new practical maximum out of a pcp..
Title: Re: Simplified Balanced Valve
Post by: PikeP on January 15, 2019, 08:15:44 PM
Bob, thank you very much for all that data. I'll try to tie a lot in to my sheet/brain and maybe make a dwell model from one of your tested shots comparing flow rates with dwell and lift so I can attempt to match lift/dwell somehow by simpy knowing flow. I'm going to have my work cut out for me...but I think itll help me understand the relationship between lift, dwell and flow rate better.  I think my guess at 1.5ms wasnt top far off for just doing a napkin guess..if I put eff to what lloyd predicts I get 1.37ms currently without tweaking a thing...how crazy is that? Two entirely different methods of obtaining lift and dwell in almost perfect agreement..within 10% or less of eachother... remarkable.
Title: Re: Simplified Balanced Valve
Post by: PikeP on January 15, 2019, 08:28:19 PM
Another thought on practical tune range..notice at very little close distance you still get lots of energy..the ejection rate can only be practically reduced x amount from peak before either valve doesn't open or acts very funny with huge swings in velocity when well below optimal velocity..but as you get to larger calibers that suggest you cant reduce power by near the % from peak compared to smaller calibers due to flow rates..unless we greatly choke off the transfer port or as you have on a build, at the bolt probe. So I think the tune range we found on yours is near perfect..certainly if you were up to my last revision. Gotta say I'm still beside myself how well this valve is operating.
Title: Re: Simplified Balanced Valve
Post by: PikeP on January 15, 2019, 09:10:05 PM
So I simply scaled lift to 25% more than the required lift to flow a set amount of air or rather KE at a specific efficiency...and my dwell times are all within a few micro seconds...I arrived at 2.87 vs 3.0 ms...and 1.32 ms vs 1.22 ms...next I will model both with flow and see what makes sense so I can tweak further. Thanks again Bob. I also get 14.8" valve close on the 270+ fpe shot now where lloyd predicted 14.84... 😁

Pretty crazy to arrive at the same figures using different methods..seems to solidify things a tad.
Title: Re: Simplified Balanced Valve
Post by: rsterne on January 15, 2019, 09:12:48 PM
Conventional valves can be tuned wayyyyyyyyyy down, even in a .457 cal.... They just don't exhibit the drop off like we see with any of the balanced valve when we back the hammer strike off too much.... I sure wish we could get our valves to open like a balanced valve and be adjustable like a conventional one....  ::)

Yeah, I want to have my cake and eat it too....  :o  ;)

Bob
Title: Re: Simplified Balanced Valve
Post by: rsterne on January 15, 2019, 09:25:06 PM
Don't forget, Lloyd's spreadhsheet runs strictly on Newtonian mechanics.... It includes the air mass that has been released by the valve with the mass of the projectile to be accelerated.... A later version, which I don't use, has that fraction adjustable.... IIRC, DomingoT said that using 1/3 the mass was a closer match to reality.... but that makes the air work like a spring (which it does after the valve closes)….  but during the valve open stage Lloyd found that including the air mass previously released worked the best, as that air, plus the mass of the bullet, is what is going to have to be accelerated in the next 10 uS (Lloyd's spreadsheet does a calculation each 0.00001 sec)....

BTW, you can toggle including the air mass on or off.... it makes a HUGE difference.... For the 2T Gap shot at the beginning of my last long post, which is 253 FPE, if you toggle the air mass off, and just accelerate the pellet.... you get 335 FPE.... The mass of gas in the barrel for that shot was 57.16 grains....

Bob
Title: Re: Simplified Balanced Valve
Post by: mann on January 15, 2019, 09:33:59 PM
I gained adjustability from using a smaller transfer port but it is no where near a conventional valve I wonder why any ideas Bob
Title: Re: Simplified Balanced Valve
Post by: mann on January 15, 2019, 09:40:57 PM
Is the tunability due to the valve not letting enough air threw to be able to fill the chamber. That why Travis said in order to get more he had to make the chamber as small as he could
Title: Re: Simplified Balanced Valve
Post by: mann on January 15, 2019, 09:44:15 PM
So really only way to get the adjustability would be to change the chamber size or to change the transfer port size . Need a adjustable transfer port like in the original mrod valve then you could tune it to where ever you want it
Title: Re: Simplified Balanced Valve
Post by: mann on January 15, 2019, 09:48:15 PM
Couldn't  a person just drill a hole into the valve transfer port like 8/32 or larger and use a long set screw to adjust enough so adjustability would be there
Title: Re: Simplified Balanced Valve
Post by: mann on January 15, 2019, 09:56:12 PM
I might do that so I could run my .200 port and not have to change to a different port just turn the screw to be able to take it to what ever fps you want to
Title: Re: Simplified Balanced Valve
Post by: PikeP on January 15, 2019, 11:40:04 PM
Yes man, if you read one of my messages up top I touch on transfer port restriction s furrher helping...if I were you I'd squeeze out volume like travis did...you have 3 other solutions if that isn't feasible but others require more work than the former. GL it's very achievable
Title: Re: Simplified Balanced Valve
Post by: PikeP on January 15, 2019, 11:42:18 PM
Bob I can understand why Domingo uses 1/3rd mass of air...another way to look at the air column is like a 3 car train...once the first train collides with the projectil it gets "derailed"...itll still exit at great speeds but not as if there were no projectile to derail it...that's my analogy ...in fact dry fires are incredibly louder...likely due to the vastly increased air speed and muzzle pressure combined

Alternatively if I simply calculate pressure drop and KE loss drop the more likely air speed at muzzle is 2200-2400 in the best conditions...that's using very raw napkin math but 2800~ peak at 4500 psi doesn't seem too unreasonable, only if you were able to shoot and measure just air...maybe that 2900 fps Texan shot? Idk..not giving credit but between your losses measuring 2200+ fps projectiles and a Texan measuring 2500+ unknowns I cant really discount the possibility of a 2850~ peak fps for air at 4500 psi
Title: Re: Simplified Balanced Valve
Post by: mann on January 15, 2019, 11:47:24 PM
I was thinking it would be easier to put in the transfer port adjuster in the valve that way you can adjust to what ever you want to do it. .050 reduction moved me down almost 200 fps which isn't severely choking the Valve and I can still get to my desired power level
Title: Re: Simplified Balanced Valve
Post by: PikeP on January 15, 2019, 11:52:34 PM
It's a very viable approach mann. That's why I mentioned it a few posts earlier. You're on the right track with your thinking. Either greatly choke the flow to create a range to tune in or solve it at the valve itself as discussed at length here. There should be no question as to how to do it provided you're measuring volumes and venting correctly with a reasonable balance ratio.
Title: Re: Simplified Balanced Valve
Post by: mann on January 16, 2019, 12:00:41 AM
Yeah everything is working properly other wise and it would be a set screw in the valve which the air tube all ready has a hole for it so it can be adjusted from the outside of the tube and wouldn't have to pull the valve if I wanted to change it . That's what I'm going to do .put in my .200 transfer port and restrict the tp at the valve . Thanks guys for all the help
Title: Re: Simplified Balanced Valve
Post by: PikeP on January 16, 2019, 02:00:22 AM
Ok I chose the 3ms dwell to model. Here are my results. These are approximate models not actual interpreted data..

Both charts make sense in terms of flow..

3ms dwell is 1.07 fpe/ci  with roughly 5370 mg ejected at an average rate of 1790 mg per second..

2.66ms dwell is 1.156 fpe/ci with roughly 4670 mg ejected at a rate of 1759 mg per second.

Bob would have to confirm which efficiency above represents his real world results as I cannot..they are both so close...

Notice I clip the flow once lift is beyond the point where it equals the ports ahead flow value.

I am sure Bob would rather the 2.66ms prediction be correct but it very well may be the 3ms...I thought a flow model would throw it off but its seemingly feasible! I find the 3 ms much more reasonable now although I was only figuring a few tenths less..and I was under the impression of higher efficiency but I believe that was before Bob determined it to be off by a small factor which threw me off..
Title: Re: Simplified Balanced Valve
Post by: rsterne on January 16, 2019, 02:20:20 AM
Domingo's 1/3 factor was (I think) based on the mass you include for a spring, fixed at one end and expanding at the other.... like a hammer spring.... You include 1/3 of the spring mass along with the hammer when calculating the acceleration due to the force of the spring.... An air spring would work in exactly the same way, and that would apply after the valve closes.... but I think not valid while the valve is open.... Think of the mass of a "packet" of air released each uS as becoming part of the mass that now must be accelerated by the next "packet" of air released in the next uS…. The mass to be accelerated keeps increasing every uS as long as the valve is open....

Mike, like you say, the models are very close, I have no way to choose between them.... One thing bothers me about your lift curves, though.... They have two distinct slopes to each side, four slopes in total.... How is that even possible?.... Should not the lift curve be something of a parabola?.... I get it that the flow rate may not be, particularly if the flow is restricted by the curtain effect, or port size.... but I can't wrap my brain around the poppet having four different, and symmetrical, parts to the acceleration/deceleration.... which is the only way you can end up with a curve that isn't a smooth one....

Bob
Title: Re: Simplified Balanced Valve
Post by: rkr on January 16, 2019, 03:33:24 AM
A question, what material and wall thicknesses could be used for the thimble? I mean we have full reservoir pressure against atmospheric pressure but much smaller diameter "tube" in this case. Would delrin be practical material and what wall thickness is needed? How about aluminium and brass?
Title: Re: Simplified Balanced Valve
Post by: PikeP on January 16, 2019, 06:11:56 AM
A quick side note. Added wasted volume resulting from a balance valve proportionally effects efficiency by your shot volume...so for a small bore shooting 1 to 4 ccs per shot, a .25 cc chamber would use 25% to 6.25% more air each shot for equal energy of a unbalanced...no way around it...where as with Bob's shot at 19~ ccs his chamber volume is adding only 2%~ more wasted volume.. its definitely worth it for big bores but small bores have a larger trade off the smaller in caliber you go.
Title: Re: Simplified Balanced Valve
Post by: PikeP on January 16, 2019, 06:22:19 AM
Bob, I tried to be clear those were approximate models not actual representations and more based on what's required to flow the discharged air at those dwells..its simply your dwell time divided by 10 with its peak lift mid way.. if you didnt notice..I dont know your poppet lift time to the curtain or its curtain to close time but if you do and want to share I can model based off those...I also want to note the behavior of the poppet is probably weirder than you think..it goes from having 200 lbs against it to transitioning to ~200 lbs assisting all while its opening in under .5~ ms..not sure it's a perfect parabola with all the transitions it faces. But.. I'm not trying to produce actual representations, I cant make that clearer. I dont mind making corrections but throw me a bone or something. Any lift data would be nice.
Title: Re: Simplified Balanced Valve
Post by: PakProtector on January 16, 2019, 07:35:46 AM
A question, what material and wall thicknesses could be used for the thimble? I mean we have full reservoir pressure against atmospheric pressure but much smaller diameter "tube" in this case. Would delrin be practical material and what wall thickness is needed? How about aluminium and brass?

For a first cut, use the hoop stress equation. I don't think it matters if the hoop is under tension( pressure inside), or compression( this case; pressure outside). For a cylinder it is Pressure*radius/wall thickness. Do mind the units, yes? If the stress is acceptable, consider the Youngs modulus, and see how much the tube will shrink under this load; that could indeed cause binding you'd never see unless you hired one of Maxwell's demons to go inside and look...:) Just keep in mind, the likely dimensions are out of the range of the20:1 ratio of diameter to wall thickness...

Bob, the forces acting on the poppet are not symmetrical, and even work to push it open until the balance chamber fills( IIRC you posted this graph earlier). I can see this making an asymmetric lift profile.
cheers,
Douglas
Title: Re: Simplified Balanced Valve
Post by: rkr on January 16, 2019, 07:48:39 AM
A question, what material and wall thicknesses could be used for the thimble? I mean we have full reservoir pressure against atmospheric pressure but much smaller diameter "tube" in this case. Would delrin be practical material and what wall thickness is needed? How about aluminium and brass?

For a first cut, use the hoop stress equation. I don't think it matters if the hoop is under tension( pressure inside), or compression( this case; pressure outside). For a cylinder it is Pressure*radius/wall thickness. Do mind the units, yes? If the stress is acceptable, consider the Youngs modulus, and see how much the tube will shrink under this load; that could indeed cause binding you'd never see unless you hired one of Maxwell's demons to go inside and look...:)
cheers,
Douglas

Well, I'm not a math guy so I was more looking for guidelines with serious overkill. Like acceptable materials and wall thickness for say 1/4" or smaller ID thimble. I know it needs less thickness than bigger tubes. I have some aluminium bar and delrin I could use but I'm uncertain of delrin and uncertain of the wall thickness needed for aluminium. I could get some brass rod if aluminium is a bad idea but again I have no idea of the wall thickness. I assume someone did the math before they made their thimble?
Title: Re: Simplified Balanced Valve
Post by: MJP on January 16, 2019, 08:42:40 AM
Rkr how about actually calculating something, it is not that hard. There are even good calculators for pipe strength at engineersedge.
Put some effort in to it and don't expect a ready answer.

Marko
Title: Re: Simplified Balanced Valve
Post by: mann on January 16, 2019, 09:23:46 AM
I used aluminum for thimble 1/4 in hole inside outside diameter I left at .400 seems to be working fine
Title: Re: Simplified Balanced Valve
Post by: PakProtector on January 16, 2019, 12:38:20 PM
I used aluminum for thimble 1/4 in hole inside outside diameter I left at .400 seems to be working fine

With Pr/t the stress at 3000 psi of a .250 ID and .02 wall is just under 20,000 psi. Given the repetitive loading, and 6061T6 yeild strength of about 35,000 psi, this is pushing it. If you choose 1144 steel, a .02" wall for a .25" balance piston should be sufficient. Even 1045 cold drawn at 78ksi looks good. The precision of keeping the hole on center with the OD comes into play of course...:)
cheers,
Douglas
Title: Re: Simplified Balanced Valve
Post by: rsterne on January 16, 2019, 12:50:21 PM
Mike, I don't have any actual lift or dwell data for this valve, or I would gladly share it.... I realize that the lift curve will not be a perfect parabola, after all, the forces go from 200 lbs. holding it close to over 100 lbs. negative when it cracks, to 40 lbs. closing it again once the balance chamber fills (sometime before full open)…. After that, however, the force is pretty constant (stem only), particularly with the poppet being shrouded by the thimble, and not subjected to much airflow, except a bit of surface friction as the airflow velocity increases.... At the very end of the valve cycle, when the flow chokes, then the closing forces increase again.... However, this should leave the center and most of the closing cycle somewhat of a parabola, at least that is how I envision it.... If your lift curves are only a representation it doesn't matter anyways.... I'll just ignore the shape and look at the maximum lift and dwell....

I used 1144 Stressproof steel (115K tensile) for my thimble, and on the SS valve on my .457 the big end (1/2" ID) is only 0.030" wall.... That gave me a 3.6:1 safety margin at the working pressure of 3600 psi in that gun.... For the much smaller ID chamber in this valve, I didn't even run the math, but I will now.... Using 6061-T6 aluminum (45K tensile), with a 1/4" ID and a 5/16" OD (0.031" wall) you would have a 3.3:1 safety factor at 3000 psi.... which considering it is contained inside the valve, and that inside a tube, would not concern me.... On my valve, with a 0.315" ID on the balance chamber, I would have to switch up to 2024-T3 (70K tensile) with  a 0.030"wall (3/8" OD), but the SF would be 4:1....

I have tensile strengths of 8.5K for Delrin and 16K for PEEK.... Using that with a 1/4" ID at 3000 psi would require much thicker walls.... With Delrin, the OD would have to exceed 3/4", so that is not practical.... With PEEK, you could get away with a 9/16" OD, resulting in a 0.156" wall with a 1/4" ID and have a 3.6:1 safety margin at 3000 psi.... Plastic, as you can see, is NOT very good as a pressure vessel, I would not recommend it....

Bob
Title: Re: Simplified Balanced Valve
Post by: mann on January 16, 2019, 02:46:15 PM
It came out to .413 I think is where I left it but I'm also running it In a regulated gun at 2100 psi after I did few tests from my spare tube from 3000 psi down. It will now stay in the regulated tube
Title: Re: Simplified Balanced Valve
Post by: PikeP on January 16, 2019, 04:29:15 PM
Bob not only does what you state effect the shape of lift curve over (dwell) time...but so does the flow through the valve..low lift low flow is going to act way differently than high lift high flow on both the open and close side...I wouldnt theorize anything as ideal or perfect..certainly in those conditions with wide variance of forces in play in short order. Jmo!

The thimble should ideally be so small that the material strength can be very forgiving..at least imo. I'd still use high quality metal rated for HPA as itll allow thinner walls that reduce volume taken away in the valve. I think a failure event would be fairly harmless unless a pellet were loaded..plastic versions more so as they could be the next projectile if they break..






Title: Re: Simplified Balanced Valve
Post by: rsterne on January 16, 2019, 04:39:53 PM
I think I may have a way to measure the actual valve lift.... If it works, I will give you a table of lifts at various SSG Gaps and two tethered pressures....

Bob
Title: Re: Simplified Balanced Valve
Post by: PakProtector on January 16, 2019, 04:55:24 PM
I'd still use high quality metal rated for HPA as itll allow thinner walls that reduce volume taken away in the valve.

What steel's are 'rated for HPA'? Or for that matter, any metal? Are you serious?
cheers,
Douglas
Title: Re: Simplified Balanced Valve
Post by: PikeP on January 16, 2019, 05:34:29 PM
I'd still use high quality metal rated for HPA as itll allow thinner walls that reduce volume taken away in the valve.

What steel's are 'rated for HPA'? Or for that matter, any metal? Are you serious?
cheers,
Douglas

Are you serious? Do your own research...rating for hpa would be based on Tensile strength and wall thickness and can be nearly any metal, provided you size it right...I was vague  because I'm not going to go through a list of every element in earth comparing tensile strengths and thicnkess... thats not what I signed up for...if you're building this valve or anything to do with HPA then that is YOUR responsibility..
Title: Re: Simplified Balanced Valve
Post by: PikeP on January 16, 2019, 05:35:49 PM
I think I may have a way to measure the actual valve lift.... If it works, I will give you a table of lifts at various SSG Gaps and two tethered pressures....

Bob

Bob that is fantastic..I'll eagerly await your results and cant wait for you to share the method. Any and all data is useful!

A 1,000,000 fps camera is all we truly need to get the perfect dwell and lift model that'll give us micro second resolution :o
Title: Re: Simplified Balanced Valve
Post by: PakProtector on January 16, 2019, 06:50:49 PM
I'd still use high quality metal rated for HPA as itll allow thinner walls that reduce volume taken away in the valve.

What steel's are 'rated for HPA'? Or for that matter, any metal? Are you serious?
cheers,
Douglas

Are you serious? Do your own research...rating for hpa would be based on Tensile strength and wall thickness and can be nearly any metal, provided you size it right...I was vague  because I'm not going to go through a list of every element in earth comparing tensile strengths and thicnkess... thats not what I signed up for...if you're building this valve or anything to do with HPA then that is YOUR responsibility..

Everything I build is made from rated materials then...thanks.

No need for 1,000,000 fps...what you do is interleave. Or with one, you just adjust the start, and repeat.
cheers,
Douglas
Title: Re: Simplified Balanced Valve
Post by: PikeP on January 16, 2019, 07:15:26 PM
Bob, does Lloyd's sheet have a coefficient of diffusion factor? If not I highly recommend integrating one for low lift conditions and probably all around. If he already has it then that's awesome. Ficks law explains why I argued  the pellet moves at a later time then you think. At the time it was a concept in my head till I researched it..
Title: Re: Simplified Balanced Valve
Post by: rsterne on January 16, 2019, 08:21:22 PM
Mike, Lloyd's spreadsheet, as I said, works on Newtonian physics, good ol' F=ma (or rather a = m/F)….

Well, guys, I Rube Goldberged together a method to make direct measurement of the lift on my Hayabusa…. I couldn't do it through the back because the SSG was in the way.... and then in the middle of the night I woke up and smacked myself in the head.... This gun has an EXTERNAL COCKING HANDLE mounted directly on the hammer....  ::) …. All I had to do was make an indicator that showed how far ahead of the rest position (against the valve stem) the handle moves during firing.... Here it is....

(http://i378.photobucket.com/albums/oo221/rsterne/Hayabusa%20PCP/Hayabusa%20Lift%20Measurement_zps3rlqrkr2.jpg) (http://s378.photobucket.com/user/rsterne/media/Hayabusa%20PCP/Hayabusa%20Lift%20Measurement_zps3rlqrkr2.jpg.html)

The brass tube is sitting against the breech band so it can't slide forward, and held in place by two cable ties and a couple drops of glue.... The aluminum tube slides inside it, and an O-ring slides on that inner tube.... You slide the O-ring forward before you cock the gun, so it rests against the end of the brass tube when the end of the aluminum tube is against the cocking handle, while the hammer sits against the end of the valve stem.... You cock the gun, load a bullet and take aim through the Chrony, fire it, the cocking handle slides the aluminum tube forward, and the O-ring slides back to create a gap (as shown in the photo above) between itself and the end of the brass tube.... You push the aluminum tube back against the cocking handle, which you force to sit tight against the end of the valve stem my putting a turn of preload on the SSG.... Measure the gap between it and the end of the brass tube, and you know the valve lift.... I checked to see if firing a second time slid the O-ring back further and found that it didn't, within my ability to measure the gap.... I was using the 77.2 gr. bullet in the .257 version for this testing.... I was able to measure the lift to the nearest 0.005".... Here are the results....

(http://i378.photobucket.com/albums/oo221/rsterne/Hayabusa%20PCP/Hayabusa%20257%20Balanced%20Lift_zpsjcfxjdbb.jpg) (http://s378.photobucket.com/user/rsterne/media/Hayabusa%20PCP/Hayabusa%20257%20Balanced%20Lift_zpsjcfxjdbb.jpg.html)

The lift at 3000 psi went from 0.125" at zero gap down to 0.040" at 6 turns out, and then dropped to zero lift at 8 turns because the gun would not fire at that gap.... The velocities were quite close to my previous data, so the lift indicator device I am using is not slowing the hammer enough to worry about.... Trying a second shot after the O-ring had already moved on the aluminum tube made no consistent difference to velocity or O-ring position.... I then tethered the gun to my other regulator, which is set at 1850 psi, and repeated the tests....

This series was quite interesting.... I expected to measure greater lift, because with only 62% of the pressure, you only have 62% of the opening and closing forces for the hammer to overcome.... That was indeed the case, the lift was 0.190" at zero gap, decreasing to 0.110" at 6 turns of gap, during which time the velocity sat solidly on the plateau at just over 800 fps.... The velocity dropped off over 100 fps to 689, and the lift decreased to only 0.035", during the next 2 turns on the SSG.... This means that the spring I am using for 3000 psi is way too strong at 1850 psi.... I suspect if I used a much lighter hammer spring I would be able to get a decent adjustment range at the lower pressure.... 

If you look at the lift where the velocity started to drop at 1850 psi, it looks like it was about 0.125".... That is the same as the starting lift at 3000 psi.... This means that if the lift exceeds that amount, you are basically up on the plateau, you get no further velocity increase at either pressure.... That happens to be 1/3 of the throat diameter.... This leads me to conclude that if I allow a maximum poppet travel of 0.150", that should be sufficient.... I currently have 0.250" of balance chamber height in the thimble, so I can put in a spacer to make the volume smaller.... It should make quite a difference in the tuning range of the valve, I would think.... It would also be a good idea if I do that to make sure that the hammer can't drive the poppet into that spacer, as it could break things.... I am going to ponder removing the valve and changing these thing before I fit the .308 cal barrel, which is now ready for testing.... I'll ponder that overnight.... It's nice to know how much lift I have to allow for, and 0.150" should be plenty....

Bob
Title: Re: Simplified Balanced Valve
Post by: PikeP on January 16, 2019, 10:56:58 PM

I have told enough for those that can listen and understand basics that can build similar valves that I have made, I just don't make pictures and diameters available in open forum.

It's ticking me off that some of the manufacturers use forums as R&D and then make profit out of it, patenting someone's ideas!

Marko

You weren't wrong by having these feelings or beliefs and I whole heartedly understand why now. Hindsight is 20/20
Title: Re: Simplified Balanced Valve
Post by: rsterne on January 17, 2019, 12:08:41 AM
From the very first post of this thread, the intention was to bring balanced valves into the limelight, and to develop them openly.... Little did I know that it was first tried over 17 year ago, and the guy that did it, Brian, shared what he did in this thread!!!!….  8) 8)

Quote
Anyways, there is the idea for a simple balanced valve, with minimum parts, that is relatively easy to machine.... By putting this out in the public domain, I hope to encourage others with the skills and equipment to jump on the train and let's get these balanced valves out of the station, and roaring down the track, into the mainstream of PCP airgunning….

If that results in some companies making a buck off them, so be it, we all benefit in the long run.... I am very proud of what all of us have accomplished in this thread, and I thank each and every one of you for your input.... We still have a lot more to learn, but we are well on the way.... Congratulations, all....  8) 8) 8) 8)

Bob
Title: Re: Simplified Balanced Valve
Post by: oldpro on January 17, 2019, 12:51:29 AM
From the very first post of this thread, the intention was to bring balanced valves into the limelight, and to develop them openly.... Little did I know that it was first tried over 17 year ago, and the guy that did it, Brian, shared what he did in this thread!!!!….  8) 8)

Quote
Anyways, there is the idea for a simple balanced valve, with minimum parts, that is relatively easy to machine.... By putting this out in the public domain, I hope to encourage others with the skills and equipment to jump on the train and let's get these balanced valves out of the station, and roaring down the track, into the mainstream of PCP airgunning….

If that results in some companies making a buck off them, so be it, we all benefit in the long run.... I am very proud of what all of us have accomplished in this thread, and I thank each and every one of you for your input.... We still have a lot more to learn, but we are well on the way.... Congratulations, all....  8) 8) 8) 8)

Bob
I agree sharing is how we all learn. When Brian said he built his 17 years ago for me it was like saying they found computers in the pyramids  thousands of years old  😀
Title: Re: Simplified Balanced Valve
Post by: MJP on January 17, 2019, 01:46:55 AM
Now we just wait for the Hammer to come out, now they have a working solution at hand.
Its down to the most basic things of human nature that makes me mad, greed.
I do respect your decision to do it openly for progress, let's just hope it won't come back to bite us in the end.

There are people just for this type of forums, scavenging information and patenting everything just that everyone else needs to pay to them to use "their" inventions.
People too stupid to make anything without directions or blueprints but sly enough to profit from others work when handed out in a silver platter.
Yes I have seen it, from too close.

Marko
Title: Re: Simplified Balanced Valve
Post by: oldpro on January 17, 2019, 02:00:23 AM
Now we just wait for the Hammer to come out, now they have a working solution at hand.
Its down to the most basic things of human nature that makes me mad, greed.
I do respect your decision to do it openly for progress, let's just hope it won't come back to bite us in the end.

There are people just for this type of forums, scavenging information and patenting everything just that everyone else needs to pay to them to use "their" inventions.
People too stupid to make anything without directions or blueprints but sly enough to profit from others work when handed out in a silver platter.
Yes I have seen it, from too close.

Marko
I’d like to see if their patients are infringements on my older balanced valve patent and maybe this is why they haven’t released it???? Hhhmmmm
Title: Re: Simplified Balanced Valve
Post by: Motorhead on January 17, 2019, 02:09:13 AM
Why is it when a TEAM does much good ... there are those in said team that feel slighted ???

Great job guys !!  take a bow and be proud of your contributions .... take a chill pill or have a beer with a buddy and smile .... PLEASE !
Title: Re: Simplified Balanced Valve
Post by: MJP on January 17, 2019, 04:36:34 AM
Well I wasn't born yesterday, so I view my world the way I see fit.
Think back a decade or two, and I would have seen it your way, now its all about the big eating the small that has the ideas.

Tell me Scott that the world hasn't changed in that time and for the worst.

The team might have this one, but it's the corporate bosses who'll have the last laugh on this one also.

More money and better lawyers is the name of the game these days.

I'm just a bystander, my contributions don't really matter much at least to me.
I gave my all one time and there's a company logo on it somewhere.
Its called business you see, that's what they tell you.
Sorry for the ot.

Marko
Title: Re: Simplified Balanced Valve
Post by: MJP on January 17, 2019, 04:42:42 AM
Bob how large port did you try for the balancer?
When you have two or three bigger ports to fill the chamber immediately after valve opening you'll endup with hammer driven dwell like regular non balanced poppet.
I found that not good for my application as I don't care for bellcurve, but for you it'll work.

Marko
Title: Re: Simplified Balanced Valve
Post by: PikeP on January 17, 2019, 06:16:49 AM
All data approximate. 2 small bore revisions, cannot comment as to any potential end results or towards the practicality of either models. Good luck building old friends..I have a few different approaches to this valve but I think itll all figure itself out in time.  ;)

Title: Re: Simplified Balanced Valve
Post by: rsterne on January 17, 2019, 12:03:53 PM
Marco, I currently have a single 0.052" (1.32mm) vent.... I am going to try reducing the volume in front of the poppet by installing a spacer in the balance chamber, since I have determined I allowed for more lift than I need....

The valve is perfectly usable for my needs the way it is now.... Ideally what I would like is a balanced valve on opening that reverts to a conventional valve on closing.... That would be the best of both worlds, IMO.... and the hammer strike would still be reasonable....

Bob
Title: Re: Simplified Balanced Valve
Post by: rsterne on January 17, 2019, 12:08:36 PM
Mike.... Those look good.... I find the colours quite difficult, in particular the grey background makes the red hard to read on the screen for my colourblind eyes....  ::)

There is a LOT of data there, I would have to print them out to try and absorb it all....

Bob
Title: Re: Simplified Balanced Valve
Post by: Motorhead on January 17, 2019, 12:36:23 PM
Well I wasn't born yesterday, so I view my world the way I see fit.
Think back a decade or two, and I would have seen it your way, now its all about the big eating the small that has the ideas.

Tell me Scott that the world hasn't changed in that time and for the worst.

The team might have this one, but it's the corporate bosses who'll have the last laugh on this one also.

More money and better lawyers is the name of the game these days.

I'm just a bystander, my contributions don't really matter much at least to me.
I gave my all one time and there's a company logo on it somewhere.
Its called business you see, that's what they tell you.
Sorry for the ot.

Marko

I'm 60 and been around long enough to see exactly what you state ... But then again YOU DO HAVE A CHOICE to fall into feeling the victim or empower yourself to continue in doing what you love to do in spite what others may do with your contributions what ever they may be.  I'm sour enough in my age to have some hard feelings too .. but have made the choice in my life to share what i can to the benefit of those who know less and be humble enough to listen & learn from those who know more.  This Life trip we're all on is a one way journey and getting caught up on what's just and fair is a waste of ones energy & talent. 

JMO ...
Scott
Title: Re: Simplified Balanced Valve
Post by: triggertreat on January 17, 2019, 01:16:12 PM
Mike.... Those look good.... I find the colours quite difficult, in particular the grey background makes the red hard to read on the screen for my colourblind eyes....  ::)

There is a LOT of data there, I would have to print them out to try and absorb it all....

Bob


I agree...Separate out the sections with different colors for easier reading.  Kinda something along these line, but make it your own.  Great graph!  A little over my head, but Looking forward to it to learn from.
Title: Re: Simplified Balanced Valve
Post by: oldpro on January 17, 2019, 03:44:11 PM
Pastels work great for this sort of thing. Looks real good and data flow looks good. Excellent work
Title: Re: Simplified Balanced Valve
Post by: rsterne on January 17, 2019, 04:10:29 PM
 I took the gun apart and made a spacer for inside the thimble to fill the volume I don't require.... Here it is sitting on the valve spring....

(http://i378.photobucket.com/albums/oo221/rsterne/Hayabusa%20PCP/Poppet%20Spacer_zpsxpqhyf7e.jpg) (http://s378.photobucket.com/user/rsterne/media/Hayabusa%20PCP/Poppet%20Spacer_zpsxpqhyf7e.jpg.html)

The front part reduces the diameter of the spring chamber from 1/4" to 13/64".... and the flange portion takes up 0.090" of length, to reduce the maximum poppet movement from 0.240" to 0.150".... I determined yesterday that I don't need more than about 1/8" of lift.... This spacer will reduce the volume of the balance plus spring chamber (when the volume of the spring and seat are deducted) from 0.52 cc to just 0.29 cc.... When the poppet is open 0.090", like it is when I have 2 T of SSG Gap, the volume is further reduced by 0.11 cc, which means the balance chamber volume that needs to be filled through the vent drops from 0.41 cc to just 0.18 cc.... nearly a 56% reduction.... This should make a big difference in the tunability of the valve....

I still have to shorten the poppet stem so that the hammer can't drive the poppet into the space and break something.... and I plan to add another O-ring to the flange on the large end as a thicker bumper for added protection....

Bob
Title: Re: Simplified Balanced Valve
Post by: Brian W Cook on January 17, 2019, 04:20:01 PM
My inspiration was back when LD built his piston assist valve . Other than thinking he put a piston between the valve and the hammer i had no idea how it was configured.    I think i started to build a valve going that direction but decided to try and simplify it a bit and i started drawing up stuff .   I think the patent idea crossed my mine once but i was working night shift and it seemed like a lot of trouble.   
I love all the nice compact versions you guys have came up with .   
Title: Re: Simplified Balanced Valve
Post by: rsterne on January 18, 2019, 01:49:37 AM
Well, Brian, you certainly contributed to this round of development.... It will be nice to see balanced valves work into the mainstream of airgunning…. I hope this thread has given that a push....

Bob
Title: Re: Simplified Balanced Valve
Post by: oldpro on January 18, 2019, 12:14:13 PM
 I can tell you this much we will be launching several guns this year and all will have the option of a balanced valve.
Title: Re: Simplified Balanced Valve
Post by: mann on January 18, 2019, 11:04:44 PM
Well I got the adjustable transfer port screw in it wasn't the easiest after I snapped a cheap 8/32 tapp off in it but I got it finally
Title: Re: Simplified Balanced Valve
Post by: rsterne on January 18, 2019, 11:15:26 PM
That looks like it will work....

Bob
Title: Re: Simplified Balanced Valve
Post by: mann on January 18, 2019, 11:20:22 PM
10/32 threw side of the valve like the original mrod valve and can adjust it threw the original hole in the air tube  . I need to pick up another to lock it down and some new screws for the breech to many times on and off being the gun I tinker with ever winter it seems like
Title: Re: Simplified Balanced Valve
Post by: mann on January 19, 2019, 03:52:05 PM
Well I got it tuned down to 815 fps before I couldn't get below 850 31 gram peek hammer  13 lb flat spring on ssg had to order some new breech screw other than that check it for leaks and it is down i hope
Title: Re: Simplified Balanced Valve
Post by: Brian W Cook on January 20, 2019, 04:16:16 PM
Staying on track with the balanced valve business.   Where do most of you get your peek at ?  Is $39 a foot for .750 the going rate ?
I’ve kinda been out of the fabricating airgun parts loop for about 5 years.   
All this has got me interested in retrofitting a piston to my .45 Lasso rifle .   It’s kinda maxed out on hammer weight and stroke and it’s limited to about 3100 psi.     
Would like to be able to run 35 or 3600
Title: Re: Simplified Balanced Valve
Post by: PakProtector on January 20, 2019, 04:46:15 PM
Staying on track with the balanced valve business.   Where do most of you get your peek at ?  Is $39 a foot for .750 the going rate ?
I’ve kinda been out of the fabricating airgun parts loop for about 5 years.   
All this has got me interested in retrofitting a piston to my .45 Lasso rifle .   It’s kinda maxed out on hammer weight and stroke and it’s limited to about 3100 psi.     
Would like to be able to run 35 or 3600

$33 here: https://drakeplastics.com/peek-rod/

but yes, it is a bit pricey...:)
Douglas
Title: Re: Simplified Balanced Valve
Post by: shorty on January 20, 2019, 04:48:52 PM
Not to get off topic but, is PikeP AKA Ackuric ?
Title: Re: Simplified Balanced Valve
Post by: oldpro on January 20, 2019, 05:46:07 PM
Not to get off topic but, is PikeP AKA Ackuric ?
Yes
Title: Re: Simplified Balanced Valve
Post by: mann on January 20, 2019, 06:01:23 PM
I'm thinking about building another balance valve and use the 25 mrod original valve and I may order a Breech and put another  marauder together  . Question I have is how far can I open the throat on the original mrod valve 
Tia mark
Title: Re: Simplified Balanced Valve
Post by: PakProtector on January 20, 2019, 06:42:13 PM
If you don't touch the seat on a 2563 valve, you can take the throat to about .234" Now if you have a 2263 valve, and you pull the sleeve, you can go significantly bigger. Now I am going to find out if the 2563 body can stand having its OE seat removed, and re-created after turning it to chips with a .281 drill. The remaining knife edge seat will need flattened, so a turned dowel chucked in the lathe and sandpaper glued to the flat end should do...:)
cheers,
Douglas

PS: WTB any/all 2263 valve bodies...:)
Title: Re: Simplified Balanced Valve
Post by: mann on January 20, 2019, 07:10:53 PM
I wasn't to worried about the original seat I just didn't want to get into mounting screw holes .280  was about where I want to be
Title: Re: Simplified Balanced Valve
Post by: rsterne on January 20, 2019, 07:27:56 PM
Well, it's been an interesting and educational couple of days.... The smaller balance chamber REALLY changed things.... I had installed the .308 cal. upper on the gun before testing, even though I know it's not a good idea to make 2 changes at once....  ::) …. I still had the same hammer and SSG spring installed, and with 118 gr. bullets it peaked at 846 fps (188 FPE), which was quite a drop from the 219 FPE I had with the conventional valve, which had smaller ports.... I know I have a much smaller plenum on this gun at the moment, with the tiny tank installed, but that was a big drop in power.... The tuning range, however, was much wider, now up to 200 fps with the smaller balance chamber.... I suspected that perhaps I had cut too much off the valve stem, or stacked too many O-rings on the shoulder on the poppet as a safety bumper, and that the valve was no longer able to "blow open" sufficiently to give me the power I felt I should have had.... I even tried a stronger hammer spring, and all that did was increase the SSG gap required, I could not get the plateau velocity to go over 850 fps.... At small gap settings the velocity dropped, a sign the hammer was bouncing off the back of the valve.... All in all, pretty frustrating....

I pondered it for a couple of days, and then decided that before I pulled the valve out and changed things again, I should try reinstalling the heavier steel hammer, which weighs 123 g. with the cocking handle installed.... With the shortened valve stem, the hammer stroke has increased to 1.18".... I was running low on the 118 gr. bullets, so I grabbed some of the 109 gr. HP version to continue testing.... I tried a shot with the heavy hammer spring and got well into the 900s with a big gap, so I reinstalled the 0.047" wire spring and did some proper testing with the gun tethered at 3000 psi.... Here are the results....

(http://i378.photobucket.com/albums/oo221/rsterne/Hayabusa%20PCP/Hayabusa%20308%20Balanced%20Valve_zpsdehvbvfz.jpg) (http://s378.photobucket.com/user/rsterne/media/Hayabusa%20PCP/Hayabusa%20308%20Balanced%20Valve_zpsdehvbvfz.jpg.html)

The velocity peaked at 938 fps at 2 turns of gap on the SSG, which with the 109 gr. bullets is 213 FPE, pretty close to what I had previously, with the full size bottle in place.... The fall off with less gap is because the hammer is bouncing off the back of the valve.... The big surprise was the HUGE increase in tuning range with the small balance chamber, about 300 fps....  8) …. This pretty much proves that the small balance chamber, along with a generous vent, is the key to a wide tuning range.... However, it does need a heavier hammer to create the dwell needed to get maximum power.... The valve is operating like a balanced valve on opening, but a conventional valve on closing, so you need hammer momentum to fully open the valve and keep it open long enough to get maximum power.... The efficiency is pretty decent, I have no problem with those numbers.... certainly a huge improvement with the balanced valve and the SSG.... I ran some short shot strings (still with the tiny tank, remember), as follows....

(http://i378.photobucket.com/albums/oo221/rsterne/Hayabusa%20PCP/Hayabusa%20308%20Balanced%20Strings_zpsqp9tvesw.jpg) (http://s378.photobucket.com/user/rsterne/media/Hayabusa%20PCP/Hayabusa%20308%20Balanced%20Strings_zpsqp9tvesw.jpg.html)

You will note the nice bell-curves, and that the fil pressure drops as the velocity decreases, just as it should.... I didn't stop the last string (in red) until the pressure was down to 1300 psi, so the valve is perfectly stable, with no sign of hammer bounce.... I also tested the maximum velocity with 4 bullet weights at 2T of gap on the SSG, as follows....

79.5 gr.... 1047 fps (194 FPE)
98 gr..... 958 fps (200 FPE)
109 gr.... 938 fps (213 FPE)
118 gr.... 899 fps (212 FPE)

To put this performance in perspective, compared to the 154 gr. bullet in the .357 cal, the 118 gr. bullet is a slightly higher SD, and yet it is shooting faster in the .308 cal, 899 fps instead of 883 fps.... so I certainly don't seem to have lost any performance with the smaller balance chamber and larger vent.... I think before I try the 7 mm upper I will reinstall the .357 upper, just make sure.... All in all, I am very pleased with the way this balanced valve has turned out.... It is MUCH easier to cock than the conventional valve, I can run an 11 lb/in hammer spring instead of the 15 lb/in spring I had previously.... with a lighter hammer, less travel, and the cocking force has dropped from 23 lbs. to just 13 lbs.... Yes, I had to reinstall the steel hammer from the .224/.257 cal version instead of the MDS hammer, but the range the valve can be tuned over is now double what I started with (actually, the original version of this valve was not tuneable at all)…. I would say this valve is a screaming success....  8)

Bob
Title: Re: Simplified Balanced Valve
Post by: mann on January 20, 2019, 07:43:42 PM
Yes it is a great success good job Guys
Title: Re: Simplified Balanced Valve
Post by: rkr on January 21, 2019, 03:35:35 AM
I'm wondering how it would work if you left the valve spring out? That would allow even smaller chamber in the thimble. Or perhaps use a weak spring from thin wire that would just have enough power to push the valve against the seat when the gun is empty.
Title: Re: Simplified Balanced Valve
Post by: MJP on January 21, 2019, 05:06:02 AM
The spring is not needed, at least I have not found any use for it.  ;)

Marko
Title: Re: Simplified Balanced Valve
Post by: rkr on January 21, 2019, 08:34:01 AM
The spring is not needed, at least I have not found any use for it.  ;)

Marko

Well, it could be useful to get the fill started with an empty gun. IIRC some guns without valve spring require a very healthy blast of air from the tank to get started ;)

After drilling 4 thimbles off the center I started thinking that perhaps there's an easier way of doing it - extension nut + some thread bar or extension stud. Just drill out the threads for the chamber and screw in a thread bar that attaches thimble to the valve housing.

https://www.ebay.com/itm/M3-M4-L-6mm-Hexagonal-Hex-Thread-Extension-Brass-Studs-Pillars-Standoff-Spacers/132771163663?hash=item1ee9c72e0f:m:mku3oMYAmH78XxWnb_o2AKg:rk:8:pf:0 (https://www.ebay.com/itm/M3-M4-L-6mm-Hexagonal-Hex-Thread-Extension-Brass-Studs-Pillars-Standoff-Spacers/132771163663?hash=item1ee9c72e0f:m:mku3oMYAmH78XxWnb_o2AKg:rk:8:pf:0)

Now if I wanted to use a steel extension nut + thread bar for extra strength, could locktite or epoxy be used to form a pressure tight bond in the threads?


Title: Re: Simplified Balanced Valve
Post by: TPL on January 21, 2019, 11:15:15 AM
Epoxy will do the job well, just remember it's not so strong mechanical bond where that is needed. It is preferable as sealing, no guessing if it hardens and it is easier to open than locktite. Just a little warming is enough.
Title: Re: Simplified Balanced Valve
Post by: rsterne on January 21, 2019, 01:45:08 PM
After seeing what happened when I drastically shortened the balance chamber in this valve, I think I have a "rule of thumb" for how much travel you need to allow for in one of these valves.... This is also based on the lift measurements I have done on this and other valves.... Originally I had 0.250" of room for the poppet to lift before the small end bottomed out in the thimble, or the spring went coil bound.... I shortened that to 0.150" of physical room, then limited that to 0.140" with the O-ring bumper riding on the poppet, and then shortened the valve stem so that the hammer could only drive the stem 0.130" before it hit the back of the valve.... This provided a couple of safety margins so that the poppet could not crash into the end of the chamber in the thimble with great force and end up destroying itself.... I had determined with my lift measurements that 0.125" of available lift should be enough to give full power with the 0.375" throat diameter of my valve....

Now that I have tested the above, while I still think that having 1/3 of the throat diameter for the poppet lift is probably enough to provide full power.... I don't think I have really left enough travel inside the valve.... I think it likely that the valve is still "blowing open" to some degree, and the poppet may be travelling far enough for the O-ring bumper to be limiting the travel.... While that is its intended job, I think I have gone just a bit too far for the ultimate safety and longevity of the valve.... I think a better way to go would be to allow for a poppet travel of 1/2 the throat diameter, or 0.187".... I would then make sure that the hammer could not drive the stem physically past about 0.150", have the O-ring bumper hit at about 0.170", and still have a safety margin of 0.017" to allow for O-ring compression....

The next time I have the valve apart (which may not be for a very long time, or may be tomorrow) I will carefully examine it for any signs that the end of the poppet has bottomed out in the thimble.... Perhaps it hasn't, and this precaution is not necessary.... However, I feel that if followed, this guideline (allowing for 1/2 the throat diameter for maximum poppet travel) should avoid any damage.... when accompanied by a stem length that will prevent the hammer from driving the poppet that far....

Bob

Title: Re: Simplified Balanced Valve
Post by: rsterne on January 21, 2019, 04:46:46 PM
One of the tests for a tunable valve is to turn down the pressure and use a lighter bullet and see if it is still tuneable.... I tethered the .308 Hayabusa with the balanced valve at 1850 psi, and used a 79.5 gr. BBT to test it, and here are the results, plotted on the previous graph with the 109 gr. bullet at 3000 psi....

(http://i378.photobucket.com/albums/oo221/rsterne/Hayabusa%20PCP/Hayabusa%20308%20Bal%20Vlv%201850_zps5db6cxui.jpg) (http://s378.photobucket.com/user/rsterne/media/Hayabusa%20PCP/Hayabusa%20308%20Bal%20Vlv%201850_zps5db6cxui.jpg.html)

Note that the curve is moved to the right because it takes less hammer strike to get to the velocity plateau, in this case the maximum is at 8 turns of gap instead of just 2 turns.... After that, the velocity drops in a nice smooth curve, as you would expect, and is still reasonably stable 300 fps below the peak.... At that point, the SSG gap is 14 turns, or 0.7" (the spring is only being compressed another 0.48" to full cock), so the free flight of the hammer is longer than the acceleration.... I am sure that with a lighter hammer spring and/or hammer the consistency even at these low velocities could be improved even more.... I have no doubt that using this valve in a regulated PCP would achieve good stability and efficiency.... I shot 4 different weight pellets at the maximum velocity setting of 8 turns of gap, with the following results....

44.8 gr.... 1076 fps (115 FPE) with JSB .30 cal. Exact
59.2 gr.... 1000 fps (131 FPE) with NOE Magnum Hunter (light)
65.7 gr.... 958 fps (134 FPE) with NOE Magnum Hunter (heavy)
79.5 gr.... 885 fps (138 FPE) with Accurate 31-079A BBT

Keep in mind that this performance level is being achieved with only 1850 psi and a 108 cc plenum.... I also did a short shot string with the SSG Gap set to 11 turns, filling to just 1800 psi.... With the 79.5 gr. BBT the velocities were 799, 812, 794 fps (average 113 FPE) and the end pressure was 1300 psi.... That means that the efficiency for that very flat 2% ES was 1.35 FPE/CI.... I'm very pleased with how well this valve performs when dialed back.... With that velocity stability over a 500 psi range, it should be great in a regulated PCP.... It is hard to imagine a .30 cal regulated PCPs spitting out Magnum Hunters in the 900s with an 1800-2000 psi setpoint....  8)

Bob
Title: Re: Simplified Balanced Valve
Post by: Hobbyman2007 on January 21, 2019, 05:49:58 PM
Very impressive Bob . I have given up on my attempt for this valve in my converted Winchester in .257 . I just dont have the materials or machining skills to accomplish what I was looking to get ... more power and better efficiency. I’ll wait to see what JSAR comes out with and hopefully get to 1.4 at 150fpe.
Title: Re: Simplified Balanced Valve
Post by: oldpro on January 21, 2019, 06:12:11 PM
Remember the higher the power lower typically will be the efficiency but the larger bores kind of make up for this a little having more total area for the HPA to push on. 1.4 at 150 should be doable.
Title: Re: Simplified Balanced Valve
Post by: Hobbyman2007 on January 21, 2019, 07:16:08 PM
Remember the higher the power lower typically will be the efficiency but the larger bores kind of make up for this a little having more total area for the HPA to push on. 1.4 at 150 should be doable.


Send me the bill I’ll take one . ;)
Title: Re: Simplified Balanced Valve
Post by: rkr on January 22, 2019, 05:24:28 AM
One thing worth consideration is to have the vslve return spring where the o-ring buffer is right now. It would allow much smaller thimble volume to be used.
Title: Re: Simplified Balanced Valve
Post by: rsterne on January 22, 2019, 12:32:33 PM
I had actually thought of removing the outer part of the thimble and installing the valve spring over the (then smaller) OD of it and having it bear on the larger part of the poppet DO where the O-ring is now.... The other possibility is to create a recess inside the poppet for the spring, which would not reduce the volume inside as much, but it would drastically shorten the length of the vent.... There are definitely more ways to configure this valve we haven't tried yet.... The key thing we have confirmed (through both spreadsheet and building them) is that you want a small balance chamber and a large diameter vent.... so that the pressure equalizes as quickly as possible.... The downside is that more hammer strike is required once you get the valve to stop blowing open....

Bob
Title: Re: Simplified Balanced Valve
Post by: rsterne on January 22, 2019, 08:14:37 PM
With what we have learned since I introduced this thread, I thought I would put all the ideas together in a drawing, and add one thing I thought about a week or so ago.... Instead of having the thimble extend down over the OD of the larger part of the poppet, I wondered about shortening it and fitting a spring over the outside, instead of having the spring inside the balance chamber where it increased the volume.... Note that this has NOT yet been tried, but it should work just fine.... I also incorporated the idea of a shorter balance chamber, with enough depth to safely allow the poppet to travel 1/2 the throat diameter.... In addition, I shortened the stem, since it is no longer needed to create a spring seat on the front of the poppet, and drilled a hole in front of the stem, slightly larger than the vent diameter, to keep the resistance to the airflow filling the balance chamber, and the chamber volume itself, to a minimum.... This stepped hole helps avoid too little room between the OD of the stem and the bottom of the O-ring groove.... Here is the drawing with all those changes.... It is "generic" in that the proportions are basically correct, but no dimensions are shown....

(http://i378.photobucket.com/albums/oo221/rsterne/Parts%20for%20Sale/Balanced%20Valve%20External_Spring_zpscg16atbi.png) (http://s378.photobucket.com/user/rsterne/media/Parts%20for%20Sale/Balanced%20Valve%20External_Spring_zpscg16atbi.png.html)

I feel that the range of balance chamber diameters that will work OK are from 60% to 72% of the diameter of the outer sealing edge of the poppet.... With all the changes we have made, you might even get to 75%.... I would still use 71% as my goal, which means that the cracking force of the valve is reduced by half.... The back of the poppet is undercut slightly (about 5 deg.) to insure a narrow seal, right at the outside edge.... Here is what the cracking force is, as a percentage of what it would be without the balancing chamber, relative to the diameter of the balance chamber as a percentage of the seat diameter....

60% balance chamber diameter reduces the cracking force by 36%
66% balance chamber diameter reduces the dracking force by 44%
71% balance chamber diameter reduces the cracking force by 50%
75% balance chamber diameter reduces the cracking force by 56%

Here are some examples for the dimensions you might like to try for a valve for a full power .257 cal. bullet shooter.... (could also be used for smaller PCPs)….

Throat ID 0.312"
Stem OD 0.125" (using 5-40 threads on the forward 1/4" to provide shear strength)
Vent Hole ID 0.052" (hole forward of stem 0.062" ID)
Exhaust Port ID 0.257"
Poppet OD at Valve Seat 0.375"
Balance Chamber ID 0.250"
Balance Chamber Length (ahead of poppet) 0.170"
Poppet Travel Before O-ring Bumper Contact 0.156"
Stem Protrusion Behind Valve Body 0.150"
The length of the larger part of the poppet would be about 0.25"
The length of the smaller part of the poppet would be about 0.50"
The front OD of the thimble is 0.250" and threaded inside 8-32
The overall length of the thimble would be about 1.00"
The center of the perforated mounting wheel is drilled 0.187" and counterbored 0.281" for the front of the thimble
This assures a loose fit between the thimble, thimble screw, and the supporting wheel to allow some radial movement for self-alignment
The thimble is secured to the perforated wheel with an 8-32 screw cut to length to give minimum end float when tightened
The OD of the thimble, the poppet at the spring seat, and the spring would be about 0.42" minimum (matching the spring OD)
A good spring would be the Century #71332, which is 1"LOA, 0.42" OD, 0.038" wire, 0.344" ID, 11 lb/in, and 0.26" length at coil bind
Nearly identical is the McMaster Carr # 9657K307, same specs except the wire is 0.039", 0.342" ID, and 0.29" length at coil bind
The ID of the valve would be about 0.625" minimum, and larger is better, to provide double the throat area past the poppet, thimble and spring
You would want 8 holes of 0.156" min. ID in the front mounting wheel, to provide double the throat area into the valve
That means the mounting wheel needs to be 0.75" OD or larger, it is retained with a circlip
That circlip groove OD in turn dictates the minimum OD of the valve body, in the case of a 0.75" front wheel, the valve must be at least 0.875" OD
The overall length of the valve would be about 2.75"

I hope this will give you a basic "road map" to follow if you want to try a balanced valve....

Bob
Title: Re: Simplified Balanced Valve
Post by: mann on January 22, 2019, 08:37:25 PM
I was think about converting the Cobra valve I have . The poppet is drilled in the center and the Cobra chamber rides in the center of the poppet so essentially the chamber would be on the inside of the poppet and the vent hole would be shorter yet . I haven't taken it apart to get any measurements but I would think that the chamber volume could also be kept small doing it that way
Title: Re: Simplified Balanced Valve
Post by: Brian W Cook on January 22, 2019, 10:50:35 PM
You might be careful about having a spring out in the edge of the main air flow around the poppet .   I had a valve return spring work it’s way all the way out into the barrel of my .58 .  It had my hollow bolt nose locked in place and i had to reach down the reservoir and drag it back out to get it apart .   I was helping with a big bore airgun demonstration for a large group of hunter safety people from all over the US  when an old Hawaiian dude was taking the last shot of the day it dumped all the air out.   
Title: Re: Simplified Balanced Valve
Post by: MJP on January 23, 2019, 12:12:09 AM
Brian is right, you'll endup ruining a completely good valve. The spring will blow out of the transfer for sure.
And you need to cut back the valve seat quite much to get it seal again.

Marko
Title: Re: Simplified Balanced Valve
Post by: rsterne on January 23, 2019, 01:01:03 AM
Thank you for the warning, gentlemen.... I can't understand what airflow forces could straighten out 0.038" spring wire.... but perhaps the O-ring could disintegrate and allow the spring to move off-center…. I still don't understand how a 0.344" ID spring could fit over a 0.420" OD poppet.... I replaced the drawing above with one having a spring seat machined in the poppet, the shelf for the spring is the same width as the spring wire.... so the O-ring is no longer locating the spring, it is only a bumper....

I would like to know how what I am doing is different than a conventional PCP valve, such as this one on my Chief.... The spring, as in most PCPs is right out in the airflow, and I've never seen one peel over the edge of the poppet.... The stock valve is on top, my slimmed down one on the bottom....

(http://i378.photobucket.com/albums/oo221/rsterne/Beeman%20Chief/PEEK%20Poppet_zpsxty8facv.jpg) (http://s378.photobucket.com/user/rsterne/media/Beeman%20Chief/PEEK%20Poppet_zpsxty8facv.jpg.html)

The ridge that the spring seats against is only 0.030" wide, and the 0.035" spring wire is actually wider than that, so the spring OD is larger than the poppet OD by about 0.010".... That gun runs at 3000 psi with no problems.... In the post above I specified that the poppet OD is the same as the spring OD.... now it has a rigid shelf to indicate that.... Bear in mind I only showed the spring as a dotted line, the wire is actually the same width as the spring seat....

Bob
Title: Re: Simplified Balanced Valve
Post by: rkr on January 23, 2019, 03:28:14 AM
What ID spring wires are you guys talking about? My idea was to use a short and stiff spring in place of that bumper o-ring, actually the same diameter and wire as the original valve spring was - only shorter. IMO it would make the o-ring unnecessary as the spring itself would act as the bumper. My plan is actually to do this for one of my BSAs and use the original poppet. Just add the o-ring seal at the end of the poppet, ventilation hole, the thimble and cut down the valve spring so it fits in between the thimble and the poppet.
Title: Re: Simplified Balanced Valve
Post by: Brian W Cook on January 23, 2019, 10:57:51 AM
My spring wasn’t that heavy of wire .    I was playing around trying to eliminate poppet drag so i made one for my .58 that resembled a Sierra match king . And then i made a spring loaded telescoping brass tube for my valve return.     Was just trying different stuff. 
Title: Re: Simplified Balanced Valve
Post by: rsterne on January 23, 2019, 12:22:07 PM
rkr, I think you may have a space problem putting the return spring where the O-ring was.... When at full lift, there is only enough room for the O-ring.... You could, of course make the small part of the poppet longer to allow you to put the spring in place of the O-ring, and then move the thimble forward.... While the spring acts somewhat like a bumper, if it went coil bound, then you effectively have a "hard crash" of the poppet against the thimble, which is what I am trying to avoid with the O-ring.... and the smaller space you allow for lift, the more likely that becomes.... It's like hitting something with a hammer, the force is extremely high.... Put an O-ring in between as a bumper, the peak force (and hence destructive power) drops by an order of magnitude at least....

Brian, I really appreciate the warning, I could see how a loosely coiled spring of relatively thin wire could have that problem.... Adding a rigid spring seat to the poppet is a far better idea than relying on the O-ring to locate it.... a minor change but a valulable one....

Bob
Title: Re: Simplified Balanced Valve
Post by: rkr on January 23, 2019, 01:24:56 PM
Well I don't think a long spring is needed, maybe two coils or thereabouts. As I see it it's only purpose is to push the valve against the seat when you fill the gun from empty. Also short springs are usually stiffer so when pushing it to coil bind it should slow down the hammer quite a bit. I can get around 9mm length for the narrow part of the poppet, at 12 fpe power level that should leave room for a 2-3 coil spring.
Title: Re: Simplified Balanced Valve
Post by: rsterne on January 23, 2019, 04:09:56 PM
3 coils of 1mm wire would still leave you with 6mm of movement, which is plenty.... providing the unloaded length of that 3 coil spring is 12mm or so, to give you some pressure on the seat....

Bob
Title: Re: Simplified Balanced Valve
Post by: mann on January 24, 2019, 10:57:54 PM
Well I started making a new vavle for a marauder build took the 25 original valve bored out to a 1/2 inch and punched out the throat to .280 ran a 1/2 end mill all the way down to flatten the seat then polished it drilled transfer port to .170 took the thimble from SS valve and shortened it made a poppet   .280 with the oring and .375 on the lower end of it  I shortened the chamber to just under a 1/4 inch planning on using a larger vent hole . It's a derlin poppet and I cut in a snap ring to hold the thimble .  I have a 25 breech and a  bolt coming . I have a .30 Cal barrel also  I'd like to try pellets threw it  I don't know how they will do I believe it is a faster twist in it 
Title: Re: Simplified Balanced Valve
Post by: rsterne on January 25, 2019, 01:24:37 AM
I reinstalled the .357 cal barrel this afternoon on the Hayabusa with the balanced valve, now with the smaller balance chamber volume and the heavier hammer.... The velocity peaked at 883 fps at 2 turns of Gap on the SSG, exactly the same as the previous peak.... However, I was able to tune the velocity down lower.... ie the tuneable range of the valve has definitely increased with the smaller balance chamber....

I then milled out the receiver for the 7 mm, made a stepped transfer port (I had to because of the way it fits to the barrel in that version), with an ID tapering from 0.328" at the valve to 0.281" at the barrel.... The barrel has an oblong, full area barrel port, and this version has a flat nosed, retractable bolt.... I tried a few shots, tethered at 3000 psi, and the velocity was virtually the same as what I had when maxed out with the conventional valve, with both the 96.5 gr. BBT FN bullets and the 91.0 gr. HPs.... The gun peaked at 190 FPE....

I have been contemplating stripping the valve out of the gun and machining a bit off the end of the spacer and removing an O-ring from the bumper, to allow the poppet to move a bit more.... but the gun is shooting so well I think I will leave it alone.... I never shoot my PCPs maxed out anyways, they just use too much air that way....I am getting very close to installing the 22 CI bottle so that I can test the gun with the full size reservoir, and as that will increase the average pressure during the shot, I may have to use a bit less gap anyways.... Just tuning by reducing the preload on the SSG spring, or maybe reducing the hammer weight a bit, may be all I will need....

Bob
Title: Re: Simplified Balanced Valve
Post by: MJP on January 25, 2019, 04:04:50 AM
Looking forward to see your test on a bigger reservoir. How much is the difference when pressure stays higher during the shot.

Have you experienced any machine gunning?

Marko
Title: Re: Simplified Balanced Valve
Post by: rkr on January 25, 2019, 06:27:06 AM
A bit different approach, poppets I can make - stems I need to buy as spares:

(https://farm8.staticflickr.com/7897/32994765298_cd32997726_c.jpg) (https://flic.kr/p/SgCNcL)balanced-valve (https://flic.kr/p/SgCNcL) by abbababbaccc (https://www.flickr.com/photos/11843711@N08/), on Flickr

After making that hole through the poppet I can say that it would be easier to file a flat on the stem.
Title: Re: Simplified Balanced Valve
Post by: MJP on January 25, 2019, 08:47:01 AM
Rkr, you need to buy a lathe!
Much easier to make stuff even with a small chinese mini lathe.

I hope you didn't buy that stem, it looks kind of rough.

Marko
Title: Re: Simplified Balanced Valve
Post by: rkr on January 25, 2019, 09:18:40 AM
Rkr, you need to buy a lathe!
Much easier to make stuff even with a small chinese mini lathe.

I hope you didn't buy that stem, it looks kind of rough.

Marko

I've considered getting one but it would be a real squeeze to fit one in my garage, perhaps one day. That's standard BSA valve stem that has seen some use, new ones are 19£ + postage with a poppet.
Title: Re: Simplified Balanced Valve
Post by: Hobbyman2007 on January 25, 2019, 09:32:27 AM
RKR,

I agree with MJP , a lathe would make the task a lot easier to accomplish . However I’m pretty sure you’re more than able to polish the valve stem if it was needed with some Emory cloth while spinning in a drill . I’m impressed with what you get done with the tools you have .

Marco ,
I’m not sure if it’s the Finn to English translator you use or maybe you’re just arrogant . It might be a good idea to read your posts a few times before posting them on a public forum . For the most part you come across as quite the D%=K . Good luck to you , I was always told to treat others as you wished to be treated . I sure hope it’s a translator problem and not the latter .I know I’d hate to go through life with a demeanour that made EVERYONE think I was an A-$#*le.  ;D
Title: Re: Simplified Balanced Valve
Post by: rsterne on January 25, 2019, 12:23:33 PM
*LOL*….

Marco, the only way I can make this valve machine-gun is to run the SSG in so that there is "negative" gap.... ie the preloaded spring is pressing against the stem by a couple of turns.... Since there is already about 3.5 lbs. of preload on it, that means about 4.5-5 lbs. of preload against the stem, just to try and introduce runaway hammer bounce.... I have not even tried to induce machine-gunning with the latest version of the valve, although I did try a turn of preload (negative gap) without getting it.... It's pretty hard on the valve, and since I have to force the gun to do it, in a mode I have no reason to ever use because it is past the point where the hammer is bouncing off the back of the valve, and past where the maximum plateau velocity occurs.... I don't see anything to worry about.... Nor do I see a reason to try it, just to see if I can abuse the valve....

Bob
Title: Re: Simplified Balanced Valve
Post by: MJP on January 25, 2019, 12:52:21 PM
Rkr, you need to buy a lathe!
Much easier to make stuff even with a small chinese mini lathe.

I hope you didn't buy that stem, it looks kind of rough.

Marko

I've considered getting one but it would be a real squeeze to fit one in my garage, perhaps one day. That's standard BSA valve stem that has seen some use, new ones are 19£ + postage with a poppet.

You can make pretty good stems out of m5 or m6 long 12.9 bolt that are only partially threaded. Saw drill file type of deal.
Title: Re: Simplified Balanced Valve
Post by: rsterne on January 25, 2019, 01:06:57 PM
OK, guys, that's enough.... The thread, IMO, has a lot of valuable information, but I will lock it if necessary.... or delete posts if they are simply insulting or derogatory.... Some guys have impeccable machining (and life) skills, others, me included, do not.... but that is no reason to make negative comments that have no purpose other than to hurt or insult.... Please be considerate of others, and offer constructive criticism only.... Treat others the way you wish to be treated.... If you do not wish to follow these simple rules, the door to the workshop is over there.... *pointing*….

Bob
Title: Re: Simplified Balanced Valve
Post by: ezman604 on January 25, 2019, 01:26:46 PM
Sorry Bob, I beat you to it and removed a post. We do not want nor allow such attitudes. They don't belong here. And we don't bow to anyone when it comes to keeping the forum positive.
Thank ya sir and to all that contribute to our goal.
Title: Re: Simplified Balanced Valve
Post by: rkr on January 25, 2019, 04:12:27 PM
Rkr, you need to buy a lathe!
Much easier to make stuff even with a small chinese mini lathe.

I hope you didn't buy that stem, it looks kind of rough.

Marko

I've considered getting one but it would be a real squeeze to fit one in my garage, perhaps one day. That's standard BSA valve stem that has seen some use, new ones are 19£ + postage with a poppet.

You can make pretty good stems out of m5 or m6 long 12.9 bolt that are only partially threaded. Saw drill file type of deal.

Good point, I hadn't considered that. It's 3,2 mm shaft so I could order some 1/8" bolts from ebay. I've used drill bit shafts previously, do you reckon there's any difference?

Edit, I'm a metric guy so I ran in to trouble with terminology when checking e-bay. What would you guys across the big pond call/name/number a bolt that would fit the purpose?
Title: Re: Simplified Balanced Valve
Post by: MJP on January 25, 2019, 04:19:27 PM
I have used good quality 12.9 bolts for stem material many times with zero problems.
It's hard enough to take the hammering with no problem.
And there's the plus side it has threads already on one end.

Drill rod planks work just the same, and dont cost much.

Edit: drill the valve to accept 4mm stem and everything will be easier.
Or send it to me and I will drill it for you.

Marko
Title: Re: Simplified Balanced Valve
Post by: shorty on January 25, 2019, 04:39:09 PM
I was planning to use a shoulder bolt.Grind the head off,drill the hole, and then harden. They even make some shoulder bolts that have internal threads and you can run a die over it to thread it then cross hole it.

https://www.mcmaster.com/92183a152 (https://www.mcmaster.com/92183a152)

https://www.mcmaster.com/96655a116 (https://www.mcmaster.com/96655a116)
Title: Re: Simplified Balanced Valve
Post by: rkr on January 25, 2019, 04:57:58 PM
I have used good quality 12.9 bolts for stem material many times with zero problems.
It's hard enough to take the hammering with no problem.
And there's the plus side it has threads already on one end.

Drill rod planks work just the same, and dont cost much.

Edit: drill the valve to accept 4mm stem and everything will be easier.
Or send it to me and I will drill it for you.

Marko

BSA uses JB's self centering firing valve system where the valve stem is supported by only the o-ring. I just checked and 3mm drill shaft falls through while 3.2 (or 3.175 to be more precise) works. Larger valve stem would require enlarging the o-ring holder and all parts associated so it would be easier to just get a fitting 1/8" bolt. Besides, as you can see from photo there's not that much space in between the 3.2mm shaft and 6.5mm poppet head. But yes, I'll work it out - that's part of the challenge and makes things interesting :)
Title: Re: Simplified Balanced Valve
Post by: shorty on January 25, 2019, 05:04:55 PM
Vented screw too. 4/40 has .035"vent and 10/32 has .046" vent.

https://www.mcmaster.com/93235a116 (https://www.mcmaster.com/93235a116)

https://www.mcmaster.com/93235a250 (https://www.mcmaster.com/93235a250)

Title: Re: Simplified Balanced Valve
Post by: TPL on January 26, 2019, 04:48:23 AM
I wouldn't use stainless for any moving part. It has high galling tendency.
Title: Re: Simplified Balanced Valve
Post by: rsterne on January 26, 2019, 08:41:35 PM
I installed the 22 CI bottle today, along with the .357 cal. barrel.... The final version of the valve has the internal spacer to reduce the balance chamber volume and the 0.052" vent.... along with a reduction in stem length to limit the travel to 0.125".... This means that when the SSG Gap is set to zero, the hammer bounces off the back of the valve and the velocity drops a bit below maximum.... However, I never shoot my guns maxed out anyways, because they waste air and end up with a Korean Cliff tune.... so the fact I have to run a bit more SSG Gap is not an issue... I am running the steel hammer, which weighs 113 gr. including the cocking handle.... The SSG is using an 11 lb/in. spring with 0.30" of preload (3.3 lbs) and with 2 turns of gap it takes 15 lbs. of force to cock the gun, which is wayyyyy less than the 23 lbs. it required with the conventional valve.... At 8 turns of gap, the cocking effort is less than 12 lbs.... Here is how the velocity works out at various SSG Gap settings....

(http://i378.photobucket.com/albums/oo221/rsterne/Hayabusa%20PCP/Hayabusa%20357%20Final%20Velocities_zpsnwhkxqxt.jpg) (http://s378.photobucket.com/user/rsterne/media/Hayabusa%20PCP/Hayabusa%20357%20Final%20Velocities_zpsnwhkxqxt.jpg.html)

As you can see, the tuning range is much increased with the small balance chamber volume and larger vent.... The gun can be tuned over a 300 fps range, which is way more than I would ever need.... The maximum velocity occurs at 2 turns of gap (260 FPE), at which point the efficiency is 1.09 FPE/CI.... With the conventional valve, at slightly less FPE, I was only getting 0.74 FPE/CI.... At 5 turns of gap (240 FPE), which is about 3% below the peak, the efficiency has increased to 1.19 FPE/CI, and with 8 turns of gap it is up to 1.36 FPE/CI, and the gun is still producing 210 FPE.... At a similar power level the original version of the Hayabusa was getting 1.13 FPE/CI, so I am getting the same power on 17% less air.... Here are some sample shot strings....

(http://i378.photobucket.com/albums/oo221/rsterne/Hayabusa%20PCP/Hayabusa%20357%20Final%20Strings_zpsqvplxbwk.jpg) (http://s378.photobucket.com/user/rsterne/media/Hayabusa%20PCP/Hayabusa%20357%20Final%20Strings_zpsqvplxbwk.jpg.html)

With the 131 gr. bullets tuned at 8 turns of gap, to peak just below 850 fps, I am now getting 13 shots per fill averaging 202 FPE.... compared to 8 shots previously.... Not only is the new valve more efficient, I can also shoot down to 2000 psi and stay within a 4% ES, whereas before I had to stop at 2200 from the same 3000 psi fill.... At 5 turns of gap, I am getting 6 shots in a nice bell curve within a 4% ES at 240 FPE with either bullet.... If I choose to tune for maximum power, at 2 turns of gap, I am getting 260 FPE, but after 3 shots the ES drops more than 4%.... While this is OK for hunting, dialing the power back to 4-5 turns of gap gives nearly the same FPE and more velocity except for the first 2 shots....

Something interesting, and a bit unexpected occurred when I fitted the 22 CI bottle instead of the tiny tank.... I had expected a bit of a power increase, but basically it didn't occur.... It appears that with the higher efficiency the 108 cc plenum, which was only 0.42 cc per FPE, wasn't really costing me any significant FPE.... This could be because this balanced valve is opening very quickly, while the pressure is still high in the plenum.... Certainly, compared to a conventional valve, where you can continue to get a small amount more FPE by keeping the valve open a long time, that isn't happening here.... I'm not complaining, mind you.... I'm getting more power and using less air....  8)

This concludes the development of this new balanced valve design.... I had a few nay-sayers at the beginning, but I had a gut feeling this valve was going to work, once I found the right combination.... As with any balanced valve the devil is in the details.... It was really interesting to see that Brian built one of these over 17 years ago.... My gut feeling about what was required to get this valve to work was beautifully calculated by Mike (aka Matt/akuric) in his spreadsheet, and I really do have to thank him for quantifying what was happening inside this valve.... When he showed that the flow rate into the balance chamber, relative to the volume of that chamber, was allowing the valve to "blow open" for more than 50% of the dwell, it became crystal clear that reducing the balance chamber volume and increasing the vent diameter was critical to getting the tuning range we all desired.... So, thanks to Matt for his help....  8)

There you go, guys.... A simplified balanced valve that works, is easy to cock, tunable, and efficient.... Have fun !!!

Bob
Title: Re: Simplified Balanced Valve
Post by: ezman604 on January 26, 2019, 09:12:29 PM
Great work from team effort for sure!!!!
Title: Re: Simplified Balanced Valve
Post by: JTB530 on January 27, 2019, 10:16:45 AM
Thank you Bob and to all those who have contributed to this. I've been lurking in the background excitedly watching as this project progressed! An amazing industry changing collaboration which I have no doubt will appear in production guns in the years to come. For me the lack of tools and time leave purchasing one of them as an only option. Thank you guys again!
Title: Re: Simplified Balanced Valve
Post by: jackssmirkingrevenge on February 02, 2019, 09:45:59 AM
I've considered getting one but it would be a real squeeze to fit one in my garage, perhaps one day. That's standard BSA valve stem that has seen some use, new ones are 19£ + postage with a poppet.

Sherline have some examples of compact workshops (https://www.sherline.com/workshop/#shop2) on their website, for making small parts you really don't need a setup that takes up a lot of space.
Title: Re: Simplified Balanced Valve
Post by: mann on February 02, 2019, 10:39:42 PM
Well I got peek poppet to seal in the old marauder valve with a .280 throat .250 balance chamber and a .350 lower end of the poppet and exhaust port around .175  I had derlin sealed up twice but I blew off the end of the poppet where the oring was derlin is ok at lower pressure in regulated gun but if it sits at 3000 psi for a little bit it blows apart at oring groove with a .050 vent hole threw the center
Title: Re: Simplified Balanced Valve
Post by: Gippeto on February 02, 2019, 11:21:09 PM
Ain't that a booger lol. ;D

Didn't "blow" apart at all...was PULLED apart...ie failed in tension. Need to understand what happened if you're going to prevent making the same mistake over and over...

The "fix" for the problem...a delrin seat in the valve body and a one piece valve stem. ;)

Just watch those little drill bits...they break easy.

(https://i.imgur.com/vJYfH2Um.jpg)

Al
Title: Re: Simplified Balanced Valve
Post by: mann on February 03, 2019, 12:35:00 AM
Peek is holding up so far but That would work to thanks .
Title: Re: Simplified Balanced Valve
Post by: mann on February 03, 2019, 12:37:54 AM
Yeah air pressure pushing up on the oring and pushing down on the lower part of stepped poppet
Title: Re: Simplified Balanced Valve
Post by: rsterne on February 03, 2019, 01:26:06 AM
Good analysis of the failure, Al.... The balancing force against the O-ring is exceeding the tensile strength of the cross section of the Delrin poppet at the bottom of the O-ring groove (minus the area of the vent hole)…. I had an SS poppet fail, but that was a completely different mode of failure.... The O-ring groove was too close to the shoulder at the end of the large diameter part of the poppet and it sheared off the end of the gland.... failing towards the atmospheric pressure section in the middle of the thimble.... Putting the O-ring twice as far from the shoulder cured it....

When we are working with plastics holding pressure, we still have to think of the stresses involved and engineer an appropriate safety margin into the parts....

Bob
Title: Re: Simplified Balanced Valve
Post by: Lob0426 on February 03, 2019, 02:49:56 PM

Quote
Sherline have some examples of compact workshops on their website, for making small parts you really don't need a setup that takes up a lot of space.


The Sherline Mill and Lathe are good quality. They indeed are "desktop" machining. I have the 5400 mill and 4400 lathe both CNC. You do have to remember to take smaller cuts as they are not as stiff as a shop lathe. For an airgun valve, hammer and such they will be great. But the passthrough is too small for barrel work and the mill can be a bit cramped on some parts.
Title: Re: Simplified Balanced Valve
Post by: RichH on February 03, 2019, 07:04:04 PM
This is quite a bit over my head, but what happened to that Pike guy? Seems like he is the one who broke this technology open and now that he disappeared no more advancement.
Title: Re: Simplified Balanced Valve
Post by: mann on February 03, 2019, 07:07:00 PM
The valve works what more advancement do you want also his spread sheet has it all mapped out
Title: Re: Simplified Balanced Valve
Post by: rsterne on February 04, 2019, 02:04:39 PM
Yeah, the development is done, from my point of view, I'm on to the next project.... Mike/PikeP, aka Matt/ackuric, made noises about making his spreadsheet available to all, but changed his mind I guess.... I can understand, because it's a lot of work to just "give away".... It's a pity, though, because he apparently had a pretty good handle on what was going on, I know I used his data to confirm the direction I went, and thanked him for that in Reply #573 above....

I posted a lot of data towards the end of my valve development, including actual lift measurements and what happened regarding the increased hammer strike when I filled a lot of the balance chamber with a spacer, to help him hone his spreadsheet, but he never responded to any of that input.... Without his spreadsheet to assist anyone with further development, all I can suggest is that you keep the balance chamber volume to a minimum and use the largest diameter, shortest vent possible.... to get the pressure in the balance chamber to rise to equal that in the exhaust port in the shortest possible time.... That increases the closing force during the valve cycle, and will increase the hammer strike required to get back the dwell you lose, but you will still get a large decrease in the initial hammer strike required to crack the valve....

Bob
Title: Re: Simplified Balanced Valve
Post by: jackssmirkingrevenge on February 04, 2019, 02:55:39 PM
But the passthrough is too small for barrel work and the mill can be a bit cramped on some parts.

It most certainly has its limitations but if you don't have a lot of space available and want to make small parts it's a great setup.
Title: Re: Simplified Balanced Valve
Post by: Lob0426 on February 04, 2019, 09:29:47 PM
But the passthrough is too small for barrel work and the mill can be a bit cramped on some parts.

It most certainly has its limitations but if you don't have a lot of space available and want to make small parts it's a great setup.

I have an old small dining room table (4'X6'), in the spare bedroom, as my work space. The CNC computer, display, Mill and Lathe all reside there. Most of the tooling is in a plastic toolbox under the table. You can fit it all into a pretty small area. The CNC adds a lot of versatility if you are willing to learn how to use it.

I think I am going to make the Poppet/balance out of drill rod. Then put a PEEK "washer" to seal the valve. I am thinking of center drilling a small spring run in the center of the balance. Then continue an 0.052" through stem. This of course will add volume that needs to be filled but hopefully not to much.

Trying to decide what to use for the thimble material. All I have here is 6061 and some 1018. I will be making the valve body fron 1.25" 6061 round bar. This is for one my brothers mrods. He has not gotten the valve to me yet to try to copy it.

I included an image of the spreadsheet I am working on. 
Title: Re: Simplified Balanced Valve
Post by: Gippeto on February 04, 2019, 11:45:44 PM

I think I am going to make the Poppet/balance out of drill rod. Then put a PEEK "washer" to seal the valve. I am thinking of center drilling a small spring run in the center of the balance. Then continue an 0.052" through stem. This of course will add volume that needs to be filled but hopefully not to much.

Trying to decide what to use for the thimble material. All I have here is 6061 and some 1018.

Ask yourself why you're thinking to use peek. Is there a VALID reason to use it or just "flavor of the day"? Remember that you're working on a valve that has LESS force holding it closed. Give some thought to what the actual seat pressure is...lbs force on seat area. If the seat pressure isn't causing permanent deformation...where's the benefit?

Of the two choices, would use the 6061, 1018 IMO should not be used in a valve.

Al
Title: Re: Simplified Balanced Valve
Post by: Lob0426 on February 05, 2019, 12:47:27 AM
Delrin could be used. It will be supported by the poppet/balance. I will be using a larger throat than stock but not by much. PEEK is tougher than Delrin and I have to buy either as I do not have any. Machineability appears to be about the same for both materials. So why not buy the PEEK? Yes it is more expensive but I will not need much of it. I do have some Nylon rod here. I don't think that will work.

I will be using 6061 for the body I have it in many sizes of round and square. I am not sure what to use for the thimble in the balanced design. I think rsterne used 1144, so that might be what I will try. 1018 is just what I have here. I don't think it is what I want to use either. Again I will have to order something.
Title: Re: Simplified Balanced Valve
Post by: rsterne on February 05, 2019, 01:46:03 AM
I think what Al is getting at, is that PEEK, being harder, is more difficult to get to seal at low force levels, compared to Delrin.... I have found that the trick with PEEK is to use VERY narrow seat margins.... I use a flat seat in the valve body, and undercut the poppet by 5 deg. to force the seat to the very outside edge....

Bob
Title: Re: Simplified Balanced Valve
Post by: Lob0426 on February 05, 2019, 02:14:37 AM
I see what you are saying. I remember you mentioning undercutting to get it to seal. So Delrin it is.

There will be a flat seat as I do not intend to even try to recreate the stock seat.

Probably biting off more than I can chew for a first project on an air gun. We will just have to see. Having something to copy will help. Figure I have to start someplace.

Thank you both for the advice.
Title: Re: Simplified Balanced Valve
Post by: jackssmirkingrevenge on February 09, 2019, 09:08:13 AM
I wonder if a balanced hammer valve with a much weaker spring needed to knock the valve open would make a Caselman-style blowback repeater more practical. 

(https://i.imgur.com/EoCEBvO.gif)
Title: Re: Simplified Balanced Valve
Post by: rsterne on February 09, 2019, 12:35:39 PM
That is a beautiful drawing, and I understand the principle involved.... However with the proportions drawn, that valve would blow open and could even dump the bottle.... Once the valve is cracked, there is equal pressure surrounding the poppet head, and since the balance chamber is vented to atmosphere the valve would blow open.... The only opposing closing forces are the air pressure acting on the (much smaller diameter) valve stem and the valve spring.... It would remain open until at least when the BB exited the muzzle, and likely longer.... If you increased the diameter of the valve stem to equal that of the balance chamber, then the forces would cancel and the valve spring could close the valve (eventually)…. By careful choice of balance chamber and stem diameter, you could get the valve to shut with acceptable dwell....

Otherwise I see no reason the concept would not work.... and the much lighter valve strike required should make it function more easily....  8)

Bob
Title: Re: Simplified Balanced Valve
Post by: jackssmirkingrevenge on February 09, 2019, 01:23:03 PM
Thanks, woke up way too early for a Saturday.  Point taken about not venting to atmosphere, you're right that it would be a poor choice here.

Many paintball markers work on more or less the same principle but they require the pressure also pushing on the hammer face in order to generate enough force to blow back the mechanism against the hammer spring, this is what your typical "standard" marker mechanism would look like conceptually with the transfer port also venting into the hammer tube:

(https://i.imgur.com/6MKH7ce.jpg)

This obviously wastes a lot more air per shot.  The balanced valve certainly seems to offer a lot of potential for a repeater in my view, because so much less work is required to actuate it so the system can be much more efficient.

 
Title: Re: Simplified Balanced Valve
Post by: rsterne on February 09, 2019, 01:49:11 PM
Agreed.... Instead of venting the balance chamber to atmosphere as in your first .gif I would think that the balanced valve developed in this thread, which vents the balance chamber to the exhaust port, could be made to work....

As with any system, much development work would be required, unless you were incredibly lucky the first time around.... The devil is, most certainly, in the details....

Bob
Title: Re: Simplified Balanced Valve
Post by: Brian W Cook on February 09, 2019, 02:17:33 PM
Caselman’s rifles were dependent on the moment of inertia created by the air pressure pushing back on the bolt to re cock the bolt and hammer assemblies .   I think the atmosphere vented valve wouldn’t be that bad as long as the poppet isn’t shrouded from the air flow like in  Bob’s design . 
Title: Re: Simplified Balanced Valve
Post by: jackssmirkingrevenge on February 10, 2019, 09:13:52 AM
I think the atmosphere vented valve wouldn’t be that bad as long as the poppet isn’t shrouded from the air flow like in  Bob’s design.

For a repeater I think Bob is right that this risks the valve locking open.

I updated the animation to reflect this valve configuration:

(https://i.imgur.com/6rqk8FA.gif)
Title: Re: Simplified Balanced Valve
Post by: Hobbyman2007 on February 10, 2019, 09:47:20 AM
That sure looks a lot like the Evanix air speed mechanism . As Bob mentioned the devil is in the details . Great work on the animation . Wish I had the time to work on stuff like that . I suffer from paper design and animate in my head . Which usually translates to missing a few key steps .
Title: Re: Simplified Balanced Valve
Post by: jackssmirkingrevenge on February 10, 2019, 10:47:11 AM
That sure looks a lot like the Evanix air speed mechanism.

That's interesting, I've never seen the mechanism for this one.  I had an FX Monsoon which used air pushing on a piston in the shroud to recock the mechanism but wasn't aware that there are rifles on the market that use direct blowback to cycle the action.

Quote
Great work on the animation . Wish I had the time to work on stuff like that . I suffer from paper design and animate in my head . Which usually translates to missing a few key steps .

Thanks, I find that when you're trying to flesh out an idea, drawing and animating it forces you to take into account the proportions and any consequences of motion that you might not have considered just by looking at a paper sketch.
Title: Re: Simplified Balanced Valve
Post by: rsterne on February 10, 2019, 12:15:45 PM
Beautiful job on the animation, for sure.... Wish I had that talent....

Bob
Title: Re: Simplified Balanced Valve
Post by: jackssmirkingrevenge on February 10, 2019, 12:40:03 PM
Beautiful job on the animation, for sure.... Wish I had that talent....

Cheers!  I wouldn't call it a "talent", just copy-pasting on MS Paint to make each individual frame then combining them on this nifty website (https://ezgif.com/maker).

Here's a quickie with the subject of this thread made with just 3 unique frames:

(https://i.imgur.com/SegZX2Z.gif)

edit: or if one was feeling a little silly, voila

(https://i.imgur.com/M64eh5y.gif)
Title: Re: Simplified Balanced Valve
Post by: Hobbyman2007 on February 10, 2019, 04:35:49 PM
Well look at that , a Quebecois and Ontarien actually getting along . Again good work Jack . I’m up in Northern Labrador for work right now . -40c and blowing snow 30 to 40cm . Can’t wait to get home to the -30c . The mine site has been on shut down for the last 18 hours , pretty nasty out . I haven’t seen a winter storm like this since the early 80’s .
The Evanix is similar with blowback ,but not quite . It doesn’t blow back directly on the hammer . There’s another mechanism involved .
Title: Re: Simplified Balanced Valve
Post by: jackssmirkingrevenge on February 10, 2019, 04:43:06 PM
Well look at that , a Quebecois and Ontarien actually getting along .

Well I'm Toronto born and raised irredeemably Anglophone so that must explain it ;) 

Quote
I’m up in Northern Labrador for work right now . -40c and blowing snow 30 to 40cm . Can’t wait to get home to the -30c . The mine site has been on shut down for the last 18 hours , pretty nasty out . I haven’t seen a winter storm like this since the early 80’s .


Nice and warm with -12 degrees here ;) It does seem to be particularly harsh this Winter though.

Quote
The Evanix is similar with blowback ,but not quite . It doesn’t blow back directly on the hammer . There’s another mechanism involved .

Is there an exploded view online somewhere?  I'm curious as to how it works exactly.
Title: Re: Simplified Balanced Valve
Post by: Hobbyman2007 on February 10, 2019, 07:07:39 PM
No blown up pics available or exploded parts diagram available as of yet . You know how straws a fast food joints come with a paper cover , if you remove just one end of the paper and blow into the end of the straw the cover goes flying . That’s how it works. Now just think of how the hammer would be the paper cover .
Title: Re: Simplified Balanced Valve
Post by: Lob0426 on February 10, 2019, 08:56:10 PM
Edit: Yes some paintball guns vent gas from the exhaust to the hammer near the valve stem. Some have a grub screw in the vent to adjust the flow to the hammer.

Efficiency is effected by venting to the hammer and the bolt opening while still pressure in the bore. Need a way to separate bolt movement from hammer movement. Or keep the chamber sealed longer. Like hammer hitting a spring loaded bolt farther back than sear. Separated bolt from hammer.

Might be a system to consider for higher performance semi airguns. Might work better with larger calibers, poppets and pressures.
Title: Re: Simplified Balanced Valve
Post by: rkr on February 12, 2019, 11:25:49 AM
That sure looks a lot like the Evanix air speed mechanism.

That's interesting, I've never seen the mechanism for this one.  I had an FX Monsoon which used air pushing on a piston in the shroud to recock the mechanism but wasn't aware that there are rifles on the market that use direct blowback to cycle the action.


There's Steyr, Crosman Nightstalker and now Evanix. Evanix is the only one with a probe, others fire from magazine.

Edit, that is they use air from transfer port to cock the mechanism. Caselman uses air at the probe, heavy mass and long soft spring.

Edit 2, there's also another reason why Caselman works, the probe can retract a long way before it wents out air giving it decent speed before the bullet leaves the barrel. I tried similar approach with a normal .177 airgun and while the probe shot back it gave a loud pop once it exited the barrel and stopped quickly when it hit the hammer. A much softer spring for the hammer with hammer+bolt locked together and some 1" or so retraction before venting out could have made it work. So yes, this balanced valve may help in development of simple semi/full auto airguns. 
Title: Re: Simplified Balanced Valve
Post by: Jim Holmgren on February 15, 2019, 06:10:49 PM
I did just skimmed thought this thread and wondering.

1. Is there any advantages of this design compared with a valve with the balancing cylinder behind the poppet, (like the one that Lloyd did make?)

2. Why do you put the bleed hole in the valve stem and not though the poppet? A smaller stem in the throat would help flow but if you have a hole in it, it must be thicker right?

3. Does it matter if the thimble have to poppet inside or the poppet is hollow going over a fixed rod. (If not would this be easier to machine)?

4. I think I read something about interchangeable bleed jets? Were would you put them in that case so it could easily be exchanged?

My idea was to machine a valve now in the weekend and consider to make one based of Lloyds design, but I will maybe reconsider and make something like this instead.
Title: Re: Simplified Balanced Valve
Post by: rsterne on February 15, 2019, 07:37:27 PM
Hey, Jim....

1. A balancing cylinder behind the poppet like Lloyd's or the one used by AAA is harder to make, because the poppet must be made in two piece so that it can be assembled.... AAA use a jig to hold the parts aligned while they are pressed together while in the valve body....

2. There isn't much room between the bottom of the O-ring groove and the stem for a vent hole.... certainly if you wanted a single straight hole.... Depending on the size of the parts, you may be able to have two holes intersecting, with the front hole on an angle.... If the front part of the poppet is large enough, and the stem small enough, you may have room for a vent hole paralled to the stem....

3. You could use a poppet with the outer portion hollow at the front, going over a (semi) fixed rod, however you would have to make sure the wall of the poppet is strong enough to not collapse from the pressure outside it and only atmospheric pressure inside it.... The Cothran valve does this but uses a metal sleeve for the front hollow section of the poppet.... I would allow the rod to move radially to allow for self-alignment with the poppet, like Cothran does....

4. The interchangeable bleed jets on the front of the valve are not used in this design.... only in the SS valve and the Cobra/Python valves.... The purpose is to control the airflow out of the front chamber which acts as an air spring (some SS valves don't use that feature, particularly in high power applications)…. This valve has no vent from the inside of the valve body to the balance chamber, only the rear vent through the poppet to the exhaust port....

Something else to consider.... One of the guys in this thread had some poppets pull apart at the bottom of the O-ring groove.... The main body of the poppet is held back against the seat by air pressure, and the balancing force is acting forward on the O-ring, effectively trying to stretch the poppet lengthwise.... His problem was that the cross sectional area below the O-ring groove where the vent hole is, was insufficient for the Delrin he used, and the poppet was pulling apart and failing at the bottom of the O-ring groove.... He made a PEEK one, and I understand hasn't had that occur since.... My valve has the threaded stem continue all the way to the front of the poppet, in fact it becomes the spring seat.... Therefore, the stem takes some of the tensile load.... That is the advantage to continuing the stem all the way past the O-ring groove, I kind of lucked into that feature, and it resulted in me not having any poppets pull apart.... You need to consider that tensile load in your poppet design.... If you are going to make the front of the poppet tubular, and of metal, that should not be an issue.... but of course the stem you use, fastened to the front of the valve, will end up with that tensile load at the bottom of the O-ring groove, so allow for it there....

Bob
Title: Re: Simplified Balanced Valve
Post by: HYspd on February 17, 2019, 12:31:14 AM
I'm also still learning how to do some of these things on the lathe so it's a learning experience and gives me something to tinker with 

Like using a butter knife to carve prime rib ..... yea that would be rather difficult.
Doable but not pretty.

Yea the tolerances there talking here requires good tooling and established technique .... Tho half the fun and learning comes from our mistakes & there is nothing wrong with that !


old post and off topic, BUT when  I cook a prime rib you can cut with a fork!
Title: Re: Simplified Balanced Valve
Post by: mackeral5 on February 17, 2019, 06:46:54 PM
Beautiful job on the animation, for sure.... Wish I had that talent....

Cheers!  I wouldn't call it a "talent", just copy-pasting on MS Paint to make each individual frame then combining them on this nifty website (https://ezgif.com/maker).

Here's a quickie with the subject of this thread made with just 3 unique frames:

(https://i.imgur.com/SegZX2Z.gif)

edit: or if one was feeling a little silly, voila

(https://i.imgur.com/M64eh5y.gif)

Very cool and very clear demonstration. 

This looks very similar to a Cothran works minus the rod.  i'd love to see a Cothran animation. 
Title: Re: Simplified Balanced Valve
Post by: jackssmirkingrevenge on February 17, 2019, 09:42:41 PM
This looks very similar to a Cothran works minus the rod.  i'd love to see a Cothran animation.

Is there a diagram for this valve?  Best I could find was this image:

(https://i.imgur.com/algbCm3.jpg)

Not 100% clear on how it's put together though.
Title: Re: Simplified Balanced Valve
Post by: rsterne on February 18, 2019, 12:39:33 AM
There is no specific diagram for the Cothran valve, this is close to how it operates, but the front of the poppet is reversed (it is hollow inside, instead of carrying the O-ring)....

(http://i378.photobucket.com/albums/oo221/rsterne/Parts%20for%20Sale/Balanced%20Poppet_zpsysyicmhc.jpg) (http://s378.photobucket.com/user/rsterne/media/Parts%20for%20Sale/Balanced%20Poppet_zpsysyicmhc.jpg.html)

In the Cothran valve, the front end of the poppet is tubular, and the rod which carries the O-ring is fastened to the front of the valve, with no axial movement but some radial movement to allow for self-alignment of the rod with the poppet.... The poppet is made in 3 pieces (4 if you count the metering rod inside it), the front tubular section, the rear stem, and the clear plastic seat, which is held in place between those two parts when they are threaded together....

The stem is hollow and the small "metering rod" fits inside that, and works like a "leaky check valve".... There is a cross hole in the stem, barely visible in that photo, you can see it in the side of the stem immediately below the O-ring.... In operation, when the valve is closed, the balance chamber is at atmospheric pressure, and provides a "lifting force" on the poppet to reduce the hammer strike required to crack it.... Once cracked, HPA from the exhaust port travels through the cross hole, along the close-fitting sides of the metering rod through the hollow stem, and raises the pressure inside the balance chamber.... This helps close the valve.... Once the valve closes, that HPA changes direction, and has to again leak around the metering rod to escape into the exhaust port and out the barrel.... This takes a small amount of time, and during that time the force holding the valve closed is greater, to resist any hammer bounce reopening the valve....

The valve "blows open" in a definite cycle.... If you don't hit it hard enough, it barely "pops" (100-300 fps)…. Hit it a bit harder, and it cycles normally.... You cannot tune it with hammer strike, it either works or it doesn't, a complete "cliff".... The only way you can adjust the velocity is by changing the pressure....

Bob





Title: Re: Simplified Balanced Valve
Post by: jackssmirkingrevenge on February 18, 2019, 06:26:52 AM
Thank you Bob for the explanation, I have drawn it based on your description:

(https://i.imgur.com/ConVUvx.png)

Let me know if this is accurate and I will animate it.

Title: Re: Simplified Balanced Valve
Post by: mackeral5 on February 18, 2019, 07:07:28 AM
Excellent description and the diagram is almost perfect.   The stem port does not pass completely through the stem.  It only penetrates one side.  The stem is bored slightly larger than the rod, with the rod also being slightly undersized/stepped on 1 end.  The rod undersize is approximately 1/4 the length of the rod.  The undersized end is towards the stem port
Title: Re: Simplified Balanced Valve
Post by: jackssmirkingrevenge on February 18, 2019, 07:28:46 AM
Thanks, just one more thing, how deep can the rod go in the stem?

edit:  Here's a more complete diagram, roughly to scale and just missing the return spring:

(https://i.imgur.com/uV7zsPR.png)
Title: Re: Simplified Balanced Valve
Post by: mackeral5 on February 18, 2019, 11:51:31 AM
Thanks, just one more thing, how deep can the rod go in the stem?

edit:  Here's a more complete diagram, roughly to scale and just missing the return spring:

(https://i.imgur.com/uV7zsPR.png)

I dont have a valve in front of me right now but I think your diagram is correct in all aspects now.  The only uncertainty I have is the precise location where the stem port intersects the stem bore. Great job 
Title: Re: Simplified Balanced Valve
Post by: rsterne on February 18, 2019, 12:48:33 PM
Pretty much perfect diagram, IIRC the hole intersects the stem about the middle of the exhaust port when closed.... I think you can see that in the upper photo.... I believe there is a slight bevel on the ends of the rod.... At rest (as shown), the front end of the rod sits a bit below flush in the end of the hollow stem.... The exhaust port is 0.257", the stem diameter is 0.175", and the throat ID is 0.335".... The stock vent hole is 0.025" (one side only), and the valve works better (easier to tune near the cliff) IMO with that at 0.032" for most applications.... I tried sanding down the metering rod by 0.003" and got a wider adjustment range but much increased ES.... I also tried a 0.035" vent, with the same results.... Removing the metering rod destroyed the soft seat within a few shots, it hammered a huge groove into it, so the valve was slamming shut without the rod.... The stem projects 0.200", and I ran mine with a #210 O-ring against the back of the valve to limit the hammer travel.... It hits the O-ring when the lift is about 0.075, but that does little if anything to the velocity, which to me proves that the valve is "blowing open" when cycling....

Bob
Title: Re: Simplified Balanced Valve
Post by: jackssmirkingrevenge on February 18, 2019, 01:29:12 PM
Thanks Bob.

Here's my interpretation:

(https://i.imgur.com/k5ZsYG0.gif)
Title: Re: Simplified Balanced Valve
Post by: rsterne on February 18, 2019, 05:19:32 PM
I believe that the rest position of the metering rod is back inside the stem (the last airflow was out of the balance chamber)…. It accelerates forward with the stem, and momentum likely carries it on until it hits the back of the stationary rod carrying the O-ring.... and it remains there as the pressure leaks past it to increase that inside the balance chamber.... Once the poppet hits the seat, the pressure in the exhaust port drops, and the air in the balance chamber pushes the metering rod back to the rear of the hole in the stem.... The last HPA anywhere except inside the valve body would be inside the balance chamber....

That what I think is happening, anyways....  ::)

Bob
Title: Re: Simplified Balanced Valve
Post by: jackssmirkingrevenge on February 18, 2019, 05:30:52 PM
It was a guess on my part but on the other hand, if the thing is loose in the stem and there isn't a return spring, won't the rod move forward and backwards depending on the attitude of the rifle?  It seems to me that the de facto rest position would be determined by gravity more than anything else... or am I missing something?
Title: Re: Simplified Balanced Valve
Post by: rsterne on February 18, 2019, 06:00:16 PM
Could very well be.... I guess the only thing reasonably certain is that is would be forward during the early part of the shot cycle, when the balance chamber is filling, and back during the latter part when that pressure exceeds the pressure in the exhaust port.... I likely doesn't matter where it is between shots.... I still think describing is as a "leaky check valve" is the best way to think of it....

Bob
Title: Re: Simplified Balanced Valve
Post by: jackssmirkingrevenge on February 19, 2019, 09:19:01 AM
Something like that?

(https://i.imgur.com/VOGwOhy.gif)
Title: Re: Simplified Balanced Valve
Post by: mackeral5 on February 19, 2019, 10:10:35 AM
That is very much how I envisioned the rod functioning.

i have a question around running the Cothran with and without the rod.  I read Bob's previous posts around destroying a poppet without the rod.  I am curious as to why this happens with the Cothran vs. other balanced valve designs.  Is this due to the volume of the stem bore?  Could this be mitigated by decreasing volume of the stem bore, by reducing its diameter?

I have a Cothran with approximately 100 or so shots with the rod removed and haven't noticed any changes in performance.  It has a .032 stem vent.  What I do notice is a very nice snappy shot cycle and very consistent velocity.  It is also somewhat responsive to preload changes.  It is a relatively low power (55-70fpe) application with a 19" barrel.  With the rod it kept the valve open way too long and wasted a ton of air.  I've yet to have a reason to disassemble so I can't speak to the condition of the poppet seal, but its not leaking, no preload changes have been required, and velocity is consistent---at least for now. 
Title: Re: Simplified Balanced Valve
Post by: rsterne on February 19, 2019, 12:49:04 PM
The Cothran valve uses a very soft sealing washer, softer than Delrin.... It got a groove pounded into it in just a few shots with the rod removed, and Travis had the same thing happen I believe.... The poppet failure is likely related to the soft seal.... On the other hand, the low cracking force means a low sealing force, so a soft seal helps do that....

The lack of a tuning range is more than likely due to the large balance area of the Cothran valve, compared to the seat diameter.... The closer to zero force you get for cracking the valve, the more likely it is to "blow open" and provide only a plateau and cliff.... I was able to get some tunability with a Cothran valve, but it was accompanied by a very large ES when you operated close to the cliff.... I had some tunes that were only 100 fps below the plateau, but the shot to shot variation was 200 fps.... eg. plateau at 900, and when I decreased the velocity to about 800 fps, some shots were as low as 600 fps.... so in practical terms, that was not "tuneable", it was simply "unstable" operation....

I'm not saying that you can't get a Cothran valve to operate with an acceptable ES at 10% below the plateau velocity.... or get one to produce a bell curve.... just that I have not been able to do either....

Bob
Title: Re: Simplified Balanced Valve
Post by: mackeral5 on February 19, 2019, 06:34:09 PM
Thank you for the additional explanation Bob.  So far my poppet hasn't shown any signs of failure, at least not yet.....I"ll be watching it.  Eventually i'm sure I will have to replace it based on your and Travis' experience. 
Title: Re: Simplified Balanced Valve
Post by: jackssmirkingrevenge on March 13, 2019, 05:13:31 AM
Some thoughts on this based on recent experiences:

- The vent hole from the balancing chamber to the transfer port is absolutely necessary if you don't want the valve to lock open from the overpressure on firing

- having the balancing chamber on a separate part isn't a terribly good idea for sealing because it's more difficult to guarantee that all parts are on the same axis inside a tube.  My latest prototype was built with the configuration illustrated in the first diagram, however I think the configuration in the second diagram would work better:

(https://i.imgur.com/R0OkPSb.png)
Title: Re: Simplified Balanced Valve
Post by: rsterne on March 13, 2019, 11:47:34 AM
The thimble (part that encloses the balance chamber) is mounted via a single screw at the front to a perforated wheel that allows air to enter the valve.... The mounting hole is oversize, to allow radial movement of the balance chamber, but I use a shouldered screw (SHCS with a spacer on it) to prevent more than a couple of thou of axial movement of the thimble.... This arrangement (which is also used by the Cothran valve) allows the thimble to self-align with the poppet.... Simple and effective....

Bob
Title: Re: Simplified Balanced Valve
Post by: jackssmirkingrevenge on March 13, 2019, 12:02:04 PM
Thanks for the tip Bob, I'm going to re-make the "thimble" and see if leaving it loose will solve the intermittent sealing issues I've been having.
Title: Re: Simplified Balanced Valve
Post by: skorec on March 13, 2019, 02:20:56 PM
With what we have learned since I introduced this thread, I thought I would put all the ideas together in a drawing, and add one thing I thought about a week or so ago.... Instead of having the thimble extend down over the OD of the larger part of the poppet, I wondered about shortening it and fitting a spring over the outside, instead of having the spring inside the balance chamber where it increased the volume.... Note that this has NOT yet been tried, but it should work just fine.... I also incorporated the idea of a shorter balance chamber, with enough depth to safely allow the poppet to travel 1/2 the throat diameter.... In addition, I shortened the stem, since it is no longer needed to create a spring seat on the front of the poppet, and drilled a hole in front of the stem, slightly larger than the vent diameter, to keep the resistance to the airflow filling the balance chamber, and the chamber volume itself, to a minimum.... This stepped hole helps avoid too little room between the OD of the stem and the bottom of the O-ring groove.... Here is the drawing with all those changes.... It is "generic" in that the proportions are basically correct, but no dimensions are shown....

(http://i378.photobucket.com/albums/oo221/rsterne/Parts%20for%20Sale/Balanced%20Valve%20External_Spring_zpscg16atbi.png) (http://s378.photobucket.com/user/rsterne/media/Parts%20for%20Sale/Balanced%20Valve%20External_Spring_zpscg16atbi.png.html)

I feel that the range of balance chamber diameters that will work OK are from 60% to 72% of the diameter of the outer sealing edge of the poppet.... With all the changes we have made, you might even get to 75%.... I would still use 71% as my goal, which means that the cracking force of the valve is reduced by half.... The back of the poppet is undercut slightly (about 5 deg.) to insure a narrow seal, right at the outside edge.... Here is what the cracking force is, as a percentage of what it would be without the balancing chamber, relative to the diameter of the balance chamber as a percentage of the seat diameter....

60% balance chamber diameter reduces the cracking force by 36%
66% balance chamber diameter reduces the dracking force by 44%
71% balance chamber diameter reduces the cracking force by 50%
75% balance chamber diameter reduces the cracking force by 56%

Here are some examples for the dimensions you might like to try for a valve for a full power .257 cal. bullet shooter.... (could also be used for smaller PCPs)….

Throat ID 0.312"
Stem OD 0.125" (using 5-40 threads on the forward 1/4" to provide shear strength)
Vent Hole ID 0.052" (hole forward of stem 0.062" ID)
Exhaust Port ID 0.257"
Poppet OD at Valve Seat 0.375"
Balance Chamber ID 0.250"
Balance Chamber Length (ahead of poppet) 0.170"
Poppet Travel Before O-ring Bumper Contact 0.156"
Stem Protrusion Behind Valve Body 0.150"
The length of the larger part of the poppet would be about 0.25"
The length of the smaller part of the poppet would be about 0.50"
The front OD of the thimble is 0.250" and threaded inside 8-32
The overall length of the thimble would be about 1.00"
The center of the perforated mounting wheel is drilled 0.187" and counterbored 0.281" for the front of the thimble
This assures a loose fit between the thimble, thimble screw, and the supporting wheel to allow some radial movement for self-alignment
The thimble is secured to the perforated wheel with an 8-32 screw cut to length to give minimum end float when tightened
The OD of the thimble, the poppet at the spring seat, and the spring would be about 0.42" minimum (matching the spring OD)
A good spring would be the Century #71332, which is 1"LOA, 0.42" OD, 0.038" wire, 0.344" ID, 11 lb/in, and 0.26" length at coil bind
Nearly identical is the McMaster Carr # 9657K307, same specs except the wire is 0.039", 0.342" ID, and 0.29" length at coil bind
The ID of the valve would be about 0.625" minimum, and larger is better, to provide double the throat area past the poppet, thimble and spring
You would want 8 holes of 0.156" min. ID in the front mounting wheel, to provide double the throat area into the valve
That means the mounting wheel needs to be 0.75" OD or larger, it is retained with a circlip
That circlip groove OD in turn dictates the minimum OD of the valve body, in the case of a 0.75" front wheel, the valve must be at least 0.875" OD
The overall length of the valve would be about 2.75"

I hope this will give you a basic "road map" to follow if you want to try a balanced valve....

Bob

Bob, nice work as always .
Am I  right if I am thinking that larger vent hole and smaller balanced chamber increase velocity of valve closing ?

Title: Re: Simplified Balanced Valve
Post by: jackssmirkingrevenge on March 13, 2019, 06:26:08 PM
Mr. Sterne I owe you a beer, I machined a looser fitting cup at it worked like a charm!  I was focusing too much on the poppet itself and neglecting alignment as the primary cause of my woes.  Now it seals on the first stroke from a hand pump.
Title: Re: Simplified Balanced Valve
Post by: rsterne on March 13, 2019, 08:16:51 PM
Peter, I don't think you can state that directly.... What they do is prevent the valve from blowing open as quickly/easily.... and make the valve more "tuneable".... If you have no vent hole, the valve would blow open and stay open until the reservoir was empty.... As you make the hole larger and the balance chamber smaller, it takes less time for the pressure in the balance chamber to rise.... That increased pressure make the valve act more like a conventional valve.... If you did nothing to the hammer strike, then indeed the valve would have less dwell, and likely less lift as well.... You would definitely get less power from the gun, because less air would be released.... However, this allows you to add hammer strike to get the dwell back, making the valve act more like a conventional valve once it is cracked.... and giving you a larger tunable range....

Jack, sometimes the simplest solutions are the best ones....  ;)

Bob
Title: Re: Simplified Balanced Valve
Post by: skorec on March 15, 2019, 11:48:57 AM
A bit different approach, poppets I can make - stems I need to buy as spares:

(https://farm8.staticflickr.com/7897/32994765298_cd32997726_c.jpg) (https://flic.kr/p/SgCNcL)balanced-valve (https://flic.kr/p/SgCNcL) by abbababbaccc (https://www.flickr.com/photos/11843711@N08/), on Flickr

After making that hole through the poppet I can say that it would be easier to file a flat on the stem.

I also want to make venting hole easier way ( channel across the stem M3,5 spire )  see my picture.
https://www.gatewaytoairguns.org/GTA/index.php?topic=155953.0 (https://www.gatewaytoairguns.org/GTA/index.php?topic=155953.0)

But I am  not sure if  air turbulences  across the M3,5 nut  spire will not delay filling of balance camber too much.

Title: Re: Simplified Balanced Valve
Post by: mann on April 06, 2019, 11:33:44 PM
I was thinking to machine the poppet out of metal and put the chamber in it like the cothran valve then just need to put a center rod in threw the thimble of what ever size the the chamber is . I was thinking I'd machine a poppet out of metal one piece drill a 1/4 inch hole in and slide a 1/4 inch rod down threw the thimble after drilling it .put a oring on the rod you could thread the rod to be able to adjust the chamber size and poppet lift. . I could use a bolt to make the poppet and another bolt for the rod . Then thread the stem next to the poppet and use a nut to hold on the derlin seat . Vent hole would probably be a pain to do though
Title: Re: Simplified Balanced Valve
Post by: rsterne on April 07, 2019, 01:47:28 AM
If you want to make a metal poppet, why not make a Delrin seat insert like on a Hatsan…. It is basically a thick Delrin washer (donut) with the throat through the middle, and sits in a recess in the valve body.... There is an O-ring around the outside to seal the Delrin seat to the valve body....

Bob
Title: Re: Simplified Balanced Valve
Post by: jackssmirkingrevenge on April 07, 2019, 10:48:32 AM
There is an O-ring around the outside to seal the Delrin seat to the valve body....

If you make the seat a little oversize and hammer it I find that usually does the trick without an o-ring.
Title: Re: Simplified Balanced Valve
Post by: rsterne on April 07, 2019, 12:28:29 PM
As long as it doesn't leak, that will work fine....  ;)

Bob
Title: Re: Simplified Balanced Valve
Post by: mann on April 07, 2019, 01:21:38 PM
That would be easier than trying to put it on the back of the poppet
Title: Re: Simplified Balanced Valve
Post by: tnt76 on June 01, 2019, 10:19:01 PM
Several weeks back I decided it was time to go back to a balanced valve in my gen2 MRod. It did have a Cothran in it when I had the .257 cast slug barrel on it and performed well when on the bench, tethered.
I later decided to go back to the .25 barrel shooting pellets for plinking and rabbit control, regulated with my custom conventional valve and with the shroud.
After reading this thread and seeing Bob’s achievements of obtaining a bell curve with the balanced valve, I thought I’d whip one up with smaller dimensions to suit a .25 cast slug shooter.
I fully intended to scale down Bobs valve, however trying to turn an O-Ring groove on the poppet with an 1/16 id and including a .045 - .060 vent hole in the stem would be very difficult. So whilst waiting for some 1mm cross section O-Rings, I decided to experiment with an “over balanced” valve just to see what would happen.

My poppet is .320 od big end and .250 od small end, resulting in a balance ratio of around 61% by area and diameter ratio of 78%.

I have turned the poppet from stainless steel and have a delrin seat insert with .290 throat to fit the WAR valve body. The 1/8 stem is drilled .063 with a single sided vent of close to .050 to start with.
The thimble contains a small valve spring around 3/16 od. and .750 long, however version 2 will be an external, over poppet style spring like the Cothran.
I have a .250 exhaust and oringed delrin transfer port into a bore size oblong barrel port. The hammer is a brass/nylon piece around 40grams.

First shots I tethered to 3000psi and recorded fps from -0.5 turns(preload) to 3 turns of gap on the SSG with a std mrod spring with 2 turns of preload.  The gap adjuster is a 14 x 1.5mm (.060) thread and the ssg preload is a 6 x 1mm (.040) thread, so .060" and .040" per turn respectively.

Results with the 51.5gr BBT show I reached the plateau of 952fps (103fpe) at -0.5 turns preload and only lost 3fps at zero gap.  Increasing the gap 1/2 turn at a time, resulted in declining fps with a solid opening until 3 turns out 700fps, where it became erratic and 3.5 turns failed to open.

I next did a few strings untethered and adjusted until i had a 1000psi bell curve with matching 1st and last shots.
Same again with 51.5gr BBT

3000psi - 2000psi
815 fps
885
915
907
896
882
869
859
850
835
824
814

I will retest this at a later date, as the first couple shots ramped up much faster than the last several, so maybe a hint of stiction?
 
I'm happy with result from what started as a "lets see what happens" poppet.  Now I think I will refine it further and test for any unsafe trigger bumps etc. It is very easy opening.
I will also add more pics and dimensions when I tear it down again.

PS. Disregard the legend and secondary axis on the preload graph.
Title: Re: Simplified Balanced Valve
Post by: rsterne on June 02, 2019, 01:58:45 AM
Certainly looks like a workable valve, Trent.... Having 250 fps of adjustment before it falls over the cliff should be plenty.... This type of valve design should not be subject to stiction, because there is no additional wedging action of the O-ring when the poppet opens.... Perhaps you have too little difference between the bottom of the O-ring groove and the ID of the thimble, causing too much compression on the O-ring material.... Alternately if could be the large balance chamber diameter that is causing that, I don't know.... That would certainly make the valve very easy to open....

Bob
Title: Re: Simplified Balanced Valve
Post by: tnt76 on June 02, 2019, 07:51:49 AM
Thanks Bob, I have now stripped the gun down for the next change and a few more measurements that were not recorded, as I machined on the fly.
I have remeasured the poppet O-Ring groove and found the groove id to be right (.004 over size actually) but did not allow a wide enough groove, I needed a .094” groove for the .070 wide O-Ring, it was a snug fit.  Thanks google.
I am now working on the balance chamber volume, as I have quickly calculated it to be 0.44cc.
Back to the lathe tomorrow.
Title: Re: Simplified Balanced Valve
Post by: rsterne on June 02, 2019, 12:41:21 PM
Actually, you don't need to go to 0.094", I use about 0.080", particularly for a dynamic O-ring.... but yes, you certainly need somewhere for the rubber to move to when compressed radially....

Bob
Title: Re: Simplified Balanced Valve
Post by: tnt76 on June 12, 2019, 01:02:54 AM
So a quick little update.
I may have found the point of over balance.  Between a compressor rebuild, lead pot PID rewire, casting more BBT's and general life.
I decided to do away with the valve spring completely and fill the spring cavity inside the thimble with a spacer and an small o-ring, reducing the balance chamber from .38cc to .23cc.
Having no compressor running I was left to test from 2000psi, so I loaded up the 25gr jsb to do a low pressure test starting with zero preload on the ssg and 3-4 turns of gap it barely fired. Decreasing the gap until it finally sent pellets at 900+fps. At this point I was at 1900psi and turned the gap setting to roughly -1/16 turn, or preload on the valve stem. Then BANG, 900psi valve dump, blowing my delrin shroud end cap off and all the baffles flew through the chrony and into the pellet trap.....at 1016 fps! This valve does not like preload on the stem!

Will add more details later, I did some more tests today with pellets at 1200psi (compressor back together)  @ 860fps with an SSG gap this time.
Title: Re: Simplified Balanced Valve
Post by: rsterne on July 12, 2019, 05:49:22 PM
Looks like Travis has finally got his version of this valve in production as the "JSAR Gen 2 Balanced Valve".... I don't know the dimensional details of it, but I'm looking forward to hearing your results with it....

Bob
Title: Re: Simplified Balanced Valve
Post by: grand-galop on July 12, 2019, 05:59:54 PM
Is this JSAR GEN2  valve is in the RAPTOR????
Title: Re: Simplified Balanced Valve
Post by: rsterne on July 12, 2019, 06:27:53 PM
I assume so, but you would have to ask Travis....

Bob
Title: Re: Simplified Balanced Valve
Post by: oldpro on July 13, 2019, 01:25:50 PM
Is this JSAR GEN2  valve is in the RAPTOR????

Yes it is
Title: Re: Simplified Balanced Valve
Post by: Motorhead on July 31, 2019, 05:06:12 PM
Ran with a few ideas and build one from scratch ( well used a recycled valve body )
https://www.gatewaytoairguns.org/GTA/index.php?topic=160916.msg155791292#msg155791292 (https://www.gatewaytoairguns.org/GTA/index.php?topic=160916.msg155791292#msg155791292)
Title: Re: Simplified Balanced Valve
Post by: TF89 on July 31, 2019, 07:40:10 PM
I know others have said this before, yet I still wish I understood half of this. 
Title: Re: Simplified Balanced Valve
Post by: Motorhead on August 02, 2019, 07:25:38 PM
Got a bit more aggressive and retrofit another valve .... that thread here:  https://www.gatewaytoairguns.org/GTA/index.php?topic=160999.msg155792422#msg155792422 (https://www.gatewaytoairguns.org/GTA/index.php?topic=160999.msg155792422#msg155792422)
Title: Re: Simplified Balanced Valve
Post by: PCPhack on August 02, 2019, 09:30:37 PM
Someone should now do the retrofit for the gen1 JSAR SS valves.
Title: Re: Simplified Balanced Valve
Post by: oldpro on August 03, 2019, 12:58:37 PM
Someone should now do the retrofit for the gen1 JSAR SS valves.
It could be done but would require some mill work and new seat/poppet/thimble etc. expensive retrofit unless your doing it yourself really.
Title: Re: Simplified Balanced Valve
Post by: PCPhack on August 03, 2019, 10:26:01 PM
Someone should now do the retrofit for the gen1 JSAR SS valves.
It could be done but would require some mill work and new seat/poppet/thimble etc. expensive retrofit unless your doing it yourself really.

Yes, but better than throwing it in the trash. ;)

Now I can blame you for buying a high end mill and lathe. Heh.
Title: Re: Simplified Balanced Valve
Post by: rkr on May 03, 2020, 12:38:58 PM
A question, what happens with fps spread (shot to shot variation) when using balanced valve. Does it increase or decrease or does it stay the same? I'm wondering if it would be a good or bad thing for long range shooting where small fps spread is required.
Title: Re: Simplified Balanced Valve
Post by: Motorhead on May 03, 2020, 01:15:37 PM
A question, what happens with fps spread (shot to shot variation) when using balanced valve. Does it increase or decrease or does it stay the same? I'm wondering if it would be a good or bad thing for long range shooting where small fps spread is required.

This is a GENERAL statement because so much changes when using these type valves ....

If simply changing from a conventional valve to a balanced valve ... ES figures very likely will open up ... a LOT
Power will go way up too in all likelihood.

because these valves open so much easier .. FAR far less hammer strike required. this not only being LESS spring rate BUT a lighter hammer too !   being able to control poppet lift becomes something one needs to address when applying these valves when a tight ES is required.
This can be done as JSAR does using a buffering system while still using a fairly heavy hammer or IMO better yet is to use an SSG devise with a light hammer and a tad stronger spring at a reduced hammer stroke.

Scott S
Title: Re: Simplified Balanced Valve
Post by: triggertreat on May 03, 2020, 01:21:35 PM
A question, what happens with fps spread (shot to shot variation) when using balanced valve. Does it increase or decrease or does it stay the same? I'm wondering if it would be a good or bad thing for long range shooting where small fps spread is required.


I haven't had any issues with balanced valves and a tight ES.  I have tested many variations of them as well.  It's all still a balance of parts and tuning as usual that gets you a tight ES.
Title: Re: Simplified Balanced Valve
Post by: MJP on May 03, 2020, 01:35:24 PM
There is no noticeable spread from shot to shot, all the shots are with in 1m/s that I have shot with my guns with Labradar.

Marko
Title: Re: Simplified Balanced Valve
Post by: rsterne on May 03, 2020, 07:00:12 PM
I agree, when properly tuned a low ES is quite possible....

Bob
Title: Re: Simplified Balanced Valve
Post by: rkr on May 04, 2020, 03:57:20 AM
Thanks guys! I was worried that with reduced forces acting on the hammer small things like friction variations would become more pronounced and cause more spread in fps. I may have to start looking for a balanced valve for my Blizzard, it would benefit from reduced trigger pull associated with reduced hammer spring tension.
Title: Re: Simplified Balanced Valve
Post by: Motorhead on May 04, 2020, 12:40:31 PM
Thanks guys! I was worried that with reduced forces acting on the hammer small things like friction variations would become more pronounced and cause more spread in fps. I may have to start looking for a balanced valve for my Blizzard, it would benefit from reduced trigger pull associated with reduced hammer spring tension.

They will !!   All the effects of force or drag within the system get amplified.     It just requires finer details in the parts and pieces and tuning to get a low ES reestablished.
Having now made over a dozen versions having varied balance ratios too ... i'm speaking from hands on experience here.
Title: Re: Simplified Balanced Valve
Post by: rkr on May 04, 2020, 03:39:54 PM
Hmm, i do have pretty good fps spread right now ... perhaps I'll start with bench rest stock and see if that's enough to get rid of those flyers caused by me and trigger not being in sync.
Title: Re: Simplified Balanced Valve
Post by: skorec on May 06, 2020, 01:46:52 AM
If  balance valve  increase the power at about  30% the ES have increase at about 30% too ???.
Title: Re: Simplified Balanced Valve
Post by: PCPhack on May 06, 2020, 02:19:37 AM
No it doesn't.
Title: Re: Simplified Balanced Valve
Post by: Motorhead on May 06, 2020, 02:46:42 AM
No it doesn't.

Would agree ... percentiles of cause and effect are not proportional to power produced.
Tho said, if the tune is really out of balance the ES very easily could be much worse than an out of balance conventional valve.

Every thing is amplified if out of wack ... Tho with correct tuning and balance of parts they can be just a stable and low ES as a conventional valve.
Title: Re: Simplified Balanced Valve
Post by: skorec on May 06, 2020, 06:10:15 AM
YES practical experiences are most importance.

Another theoretical ideas for poorer ES for balanced valve  :
1.   Longer valve dwell mean also higher difference between individual  dwells .
2.   Small venting hole and balanced chamber may  be not stable via different temperature or dirty
3.   Sealing O-ring may add different dragging

I see only  one idea for better ES may. Lower spring tension that may be  means also lower/less difference at hammer string energy.
Title: Re: Simplified Balanced Valve
Post by: Motorhead on May 06, 2020, 01:49:48 PM
YES practical experiences are most importance.

Another theoretical ideas for poorer ES for balanced valve  :
1.   Longer valve dwell mean also higher difference between individual  dwells .
2.   Small venting hole and balanced chamber may  be not stable via different temperature or dirty
3.   Sealing O-ring may add different dragging

I see only  one idea for better ES may. Lower spring tension that may be  means also lower/less difference at hammer string energy.


Your beating this horse unnecessarily ....... Read up on the valve and most of what you think is going on will become clear as to what actually is going on   ;)
Start by reading this thread from the beginning.
Title: Re: Simplified Balanced Valve
Post by: rsterne on May 06, 2020, 04:55:10 PM
Quote
If  balance valve  increase the power at about  30%

Simply stated, it doesn't increase the power, all it does is reduce the hammer strike.... You need to read this thread to understand what is going on....

Bob
Title: Re: Simplified Balanced Valve
Post by: skorec on May 07, 2020, 03:23:47 AM
I know and sorry because  I again  forgot to mentioned/accent “if”. If the hammer strike energy is the same we can use higher shooting air pressure  which produce  the higher bullets energy. 

For me using higher shooting air pressure for slugs is tautology and main reason why to use balanced valve.
Sorry again.
Title: Re: Simplified Balanced Valve
Post by: Scotchmo on May 07, 2020, 10:51:32 PM
.... It is becoming increasing more obvious that you can't make the chamber too small, ...


I'm going to take exception to that statement. Yesterday I made some changes to the porting outside the valve. The only change I made to the valve on that  tear down was to reduce the balance chamber volume. After doing so, the gun would no longer produce ANY significant energy. Occasionally, it would fire, though very low fpe. If I really leaned on the hammer, it would fire more often but still very low energy. I think I was at the point of the balance chamber volume being TOO small for any significant assist.

This is what I had when it was working more consistently:
Balance chamber volume
valve closed: 0.1016cc
valve fully open: 0.0295cc

This is what I had when it would no longer work as a balanced valve:
Balance chamber volume
valve closed: 0.0836cc
valve fully open: 0.0115cc

That is a very small change. I'll speculate that the poppit had insufficient time to escape the Bernoulli effect before the small balance chamber pressurized.

I switched back to the larger balance chamber volume, and that fixed it.

I'm going to try adding an additional 0.03cc and see what happens.

Title: Re: Simplified Balanced Valve
Post by: rsterne on May 08, 2020, 01:12:42 PM
Admittedly that statement is from over a year ago, during development of the prototype.... However, the point I was trying to make is that as you make the chamber smaller, the valve acts more and more like a conventional valve, with the exception that you are reducing the cracking force (and only the cracking force)…. If the chamber is so short that it, or the spring, bottoms out before the valve opens, limiting the travel, then of course it is too small.... I had that occur, even though measurements said it should not, because to get usable dwell I needed a greater hammer strike, which caused the valve to open so fast that the poppet was driving the stem past it's normal lift and bouncing off the coil bound spring and slamming shut again.... I actually destroyed one poppet from that internal collision, even though the hammer struck the back of the valve body before the poppet spring went coil bind.... It looked from the damage to the poppet like the hammer was driving the poppet into the spring, but that was impossible, the poppet was accelerating into coil bind with the spring as it "blew open"....

Sometimes it is difficult to separate one effect from another and come to the wrong conclusion.... Other times, the conclusion was, indeed wrong.... Just like the quote from George Bernard Shaw....

"All generalizations are false.... including this one"....  ;) ::) :o

Here is another generalization that I feel applies to the simplified balanced valve.... The larger the balance chamber, and the smaller the vent, the more tendency for the valve to "blow open" once cracked.... This reduces the hammer strike required to produce a given dwell, but tends to make the valve almost impossible to tune, it either cycles or it doesn't.... developing a "plateau and cliff" like the Cothran valve.... The point of reducing the balance chamber volume (and increasing the vent size) is to avoid that situation....

Bob
Title: Re: Simplified Balanced Valve
Post by: Scotchmo on May 08, 2020, 03:35:17 PM
...
Here is another generalization that I feel applies to the simplified balanced valve.... The larger the balance chamber, and the smaller the vent, the more tendency for the valve to "blow open" once cracked.... This reduces the hammer strike required to produce a given dwell, but tends to make the valve almost impossible to tune, it either cycles or it doesn't....

That might be what I'm getting. It either cycles or it doesn't. Because of the light hammer and short stroke, I might be relying on the "blow open" for it to work. I'm not yet convinced that "blow open" is necessarily a bad thing, as long as it closes when I want. OK - I'll work on it some more.
Title: Re: Simplified Balanced Valve
Post by: MJP on May 09, 2020, 04:21:12 AM
Blow open is good at least it has worked for me in all my guns. You tune the closing with the port and not with the hammer strike. You use the lightest possible hammer and spring that can consistently open the valve.

No point in searching for a curve where it is not needed. Tuning the chamber venting gives you your dwell and you get max flow from the valve as it blows wide open.

Want a shorter dwell make a larger vent port.
Or better yet make the vent size adjustable.

Marko
Title: Re: Simplified Balanced Valve
Post by: PikeP on May 09, 2020, 02:01:29 PM
Balance chamber fill time / flow rate of air into a balance chamber is determined by pressure, altitude, temperature, vent length, and most importantly, Vent OD.

Timing this event to get a desired closure event similar to a conventional valve, yet all the benefits of a balanced valve with reduced cracking/opening forces (resulting in ONLY less hammer strike, nothing more), requires both a properly sized vent OD and balance chamber volume. One can simply just throw in the smallest possible chamber that will allow full lift, and the largest vent od that doesn't compromise their poppets structural integrity, but they will simply not obtain the ideal chamber volume fill time that provides maximum benefits of a 'hybrid-semi balanced valve', unless the stars and planets align just right for them...

The goal to be able to tune with hammer strike with a hybrid valve solely relies on timing this event correctly to achieve maximum tune-ability for YOUR desires. One can setup this valve to have hammer spring adjustment resulting in a variance of 600 fps, where as another can set up this valve to have a variance of 20 FPS, or anywhere in between the two. Depending on the application, your needs may vary, as so will your required vent od / chamber volume ratios.

I showed this much earlier in the thread using flow rate formulas while we settled on ideal fill times to achieve proper tune-able ranges in Bob's build, and its tried and proven, I have no doubt he's content with the range of dwell he can manipulate with hammer strike, those ratios are for his application.

Its a VERY delicate process when it comes to timing the transitional event of going from semi-balanced to non-balanced...

The formula required to obtain the approximate ideal ratios require a lot of data, the formulas are not simple, nor overly complex. It requires calculating flow rate through a static port, so that the balanced chambers volume is filled within .5 ms - 3ms...the desired fill time (in ms) is dependent primarily on your desired tuning range, AND barrel length, as valve dwell and barrel length are directly tied together...

In summary...

fill balance chamber too fast, lose some benefit of a balance valve and their reduced hammer strike requirements, wider range of fps / valve dwell with hammer strike, which can exceed whats desired per application.

fill balance chamber too slow, retain benefits of balanced valve through-out shot cycle, less hammer strike needed, severely limited or no range of fps / valve dwell from hammer strikes.

fill chamber at the right time...achieve maximum benefit of both a balanced valve and conventional valve, which means greatly reduced hammer strike required to operate the valve, and a tune-able range that fits within an applications needs, be it 200 fps, or 600 fps...
Title: Re: Simplified Balanced Valve
Post by: MJP on May 09, 2020, 02:20:53 PM
Altitude plays no significant role in valve timing, port and valve vent is not at atmospheric pressure when the valve opens, it has no meaning what altitude you fire that 300bar from the reservoir.
I'm not interested in any conventional valve behavior, but that's just me.

Marko
Title: Re: Simplified Balanced Valve
Post by: Scotchmo on May 09, 2020, 04:25:11 PM
...
The formula required to obtain the approximate ideal ratios require a lot of data, the formulas are not simple, nor overly complex. It requires calculating flow rate through a static port, so that the balanced chambers volume is filled within .5 ms - 3ms...the desired fill time (in ms) is dependent primarily on your desired tuning range, AND barrel length, as valve dwell and barrel length are directly tied together...

In summary...

fill balance chamber too fast, lose some benefit of a balance valve and their reduced hammer strike requirements, wider range of fps / valve dwell with hammer strike, which can exceed whats desired per application.

fill balance chamber too slow, retain benefits of balanced valve through-out shot cycle, less hammer strike needed, severely limited or no range of fps / valve dwell from hammer strikes.

fill chamber at the right time...achieve maximum benefit of both a balanced valve and conventional valve, which means greatly reduced hammer strike required to operate the valve, and a tune-able range that fits within an applications needs, be it 200 fps, or 600 fps...

Best I can calculate (choked flow through a static port), the no go fill rate for my balance chamber was about 0.2ms. At 0.3ms-0.4ms, the valve opened somewhat reliably. Enlarging it further (0.6ms) did not seem to make a measurable difference in projectile velocity. Maybe I would need >1ms to notice any dwell increases from the balance chamber.

What I'm learning -

1) For a balanced valve that cracks only, use standard tuning of the striker mass/momentum/energy to control dwell (and FPE for a given projectile).

2) this is where we actually are for most "balanced valves" - somewhere between (1) and (3)

3) For a balanced valve that blows fully open, use chamber fill rate to control dwell (and FPE for a given projectile).

Or maybe we could leave the dwell constant and just vary the fill pressure. That won't work with a conventional valve (heavy mass striker) as dwell varies greatly with pressure. But for a blow open valve, velocity should be mostly proportional to pressure, without any other tuning.

Note:
you said: "Balance chamber fill time / flow rate of air into a balance chamber is determined by pressure, altitude, temperature, vent length, and most importantly, Vent OD."

The balance chamber is filled by the plenum air at high pressure, so I don't see how altitude would matter. Vent length should make little difference as long as the minor diameter of the vent is at the balance chamber. The approximate fill time of the balance chamber could be as simple as this:

balance-volume/(vent-area x SOS)
Title: Re: Simplified Balanced Valve
Post by: Brian W Cook on May 12, 2020, 05:03:25 PM
If you build the front of your valve so the air flows over the poppet head there won’t be any of the “blowing open “ going on .   You can even vent your chamber to the atmosphere and it will still work just fine
Title: Re: Simplified Balanced Valve
Post by: Jenny domansky on May 13, 2020, 02:49:14 PM
I've got a melon scratcher that frustrating me. .I'm building 3 mrods ...1 with a war cobra valve ,just put it together and perfect.
The 2 others are using Jefferson state ss valve, built them, started to gas and on both the air runs straight through and out the barrel, what is happening tried using the port with the o rings and without....HELP PLEASE
Title: Re: Simplified Balanced Valve
Post by: rsterne on May 13, 2020, 04:17:46 PM
My guess is that your hammer spring is holding the valve open.... Try cocking the gun before filling.... Once you have air pressure in the reservoir it should be OK.... but you may need a lighter hammer spring so as to not waste a lot of air....

Bob
Title: Re: Simplified Balanced Valve
Post by: Motorhead on May 13, 2020, 04:39:41 PM
If Bobs suggestion does not work ? ... May need to spin the valve stem in a drill with a bit of pull back pressure to burnish in the seat.
Title: Re: Simplified Balanced Valve
Post by: Scotchmo on May 13, 2020, 05:20:23 PM
My guess is that your hammer spring is holding the valve open.... Try cocking the gun before filling.... Once you have air pressure in the reservoir it should be OK.... but you may need a lighter hammer spring so as to not waste a lot of air....

Bob

+1
When filling my Skyhawk, if there is any air pressure in the tank, I don't need to cock it to fill up. But when totally empty, I often need to cock it to relieve the hammer spring pressure from the valve stem.
Title: Re: Simplified Balanced Valve
Post by: rkr on August 30, 2020, 05:04:49 AM
A sizing question. I have 3mmx1mm o-rings and want to build a "cup" style balanced valve. What dimensions should I have for the cup (ID) and for the plunger (OD) to make this size o-rings to work?
Title: Re: Simplified Balanced Valve
Post by: Motorhead on August 30, 2020, 12:39:07 PM
JMO .... but a 1mm cross section o-ring offers so little compression yield the fit ( If you can get it to seal ) is going to require a very tight tolerance. The assembled alignment / TIR will need to be dead nut for there to be no binding and not have the o-ring leaking.  Static application with such small o-rings is one thing .. DYNAMIC motion is an entirely different animal.
That fit to get just right will take some trial & error IMO.

Going with a thicker cross section o-ring will buy you being able to run within a slightly looser tolerance while also allowing some TIR or alignment errors.

I've build a few now with X / Quad rings and results have been good in the short term thus far.


Scott S
Title: Re: Simplified Balanced Valve
Post by: rkr on August 30, 2020, 01:58:29 PM
So BS003 or BS004 would be better then, which one would you recommend for 7.2mm diameter poppet and what dimensions for bore and rod?
Title: Re: Simplified Balanced Valve
Post by: rkr on August 31, 2020, 01:19:38 AM
So BS003 or BS004 would be better then, which one would you recommend for 7.2mm diameter poppet and what dimensions for bore and rod?

Thinking it a bit further, BS004 is 1.78x1.78mm o-ring and it would give about 50% reduction is area for a 7.2mm poppet. In practice I would probably make the poppet 7.5mm in diameter and use 5.5mm hole inside, would that work for PEEK poppet? What would then be the needed gap for the o-ring? BS003 at 1.52x1.42mm would give 40% reduction in area which is still good and about 0.5mm thicker walls for the poppet if that's needed ...

Edit, groove design for o-rings: https://www.marcorubber.com/o-ring-groove-design-dynamic-piston.htm (https://www.marcorubber.com/o-ring-groove-design-dynamic-piston.htm)
Title: Re: Simplified Balanced Valve
Post by: skorec on August 31, 2020, 02:06:32 AM
JMO .... but a 1mm cross section o-ring offers so little compression yield the fit ( If you can get it to seal ) is going to require a very tight tolerance. The assembled alignment / TIR will need to be dead nut for there to be no binding and not have the o-ring leaking.  Static application with such small o-rings is one thing .. DYNAMIC motion is an entirely different animal.
That fit to get just right will take some trial & error IMO.

Going with a thicker cross section o-ring will buy you being able to run within a slightly looser tolerance while also allowing some TIR or alignment errors.

I've build a few now with X / Quad rings and results have been good in the short term thus far.


Scott S

Thanks for interesting/important notice.
Which material?
Title: Re: Simplified Balanced Valve
Post by: Motorhead on August 31, 2020, 02:26:49 AM
BUNA-N
Title: Re: Simplified Balanced Valve
Post by: rkr on August 31, 2020, 02:44:31 AM
BUNA-N

Scott, you've been building these. That groove design site I linked says just 0.002" difference from piston diameter to bore diameter of the cylinder. Based on your experience - is that correct?
Title: Re: Simplified Balanced Valve
Post by: rkr on August 31, 2020, 05:22:38 AM
BUNA-N

Scott, you've been building these. That groove design site I linked says just 0.002" difference from piston diameter to bore diameter of the cylinder. Based on your experience - is that correct?

Another source said 0.002-0.005" / side, that sounds more realistic. That would be about 0.2mm difference in cylinder and piston diameters.
Title: Re: Simplified Balanced Valve
Post by: Motorhead on August 31, 2020, 12:21:49 PM
BUNA-N

Scott, you've been building these. That groove design site I linked says just 0.002" difference from piston diameter to bore diameter of the cylinder. Based on your experience - is that correct?

There are a few factors that dictate what the I.D to O.D. Should or Could be set at ???
Vertical alignment if off requires more clearance to prevent binding ... doing so gap increases and use of a 90 duro over a 70 required to prevent extrusion.
Material for thimble as well post used and how stable it is when subjected to high pressure may become as issue ?
O-ring or X ring HARDNESS used .. as above, harder rings can run with greater clearance than softer.
Cord thickness and the Friction when used Dynamically increases with larger, decreases with smaller having Surface finish and lubrication used becoming very important.


This is WHY I did not start rattling off design spec numbers .... every one I've built has been different is materials, design etc ....


Scott S
Title: Re: Simplified Balanced Valve
Post by: mackeral5 on December 11, 2020, 09:07:24 PM
I've read most of this thread 3+ times........

Over the past few years I have been exposed to the Cothran Powerhouse valve I have been on a mission to tame it a bit.  When I say tame it, I mean to make it responsive to hammer strike adjustments across a broad pressure range.  As Don C has made it very clear, this was not his intention for a valve named the Powerhouse, so I was pursuing something that was not within the intent of the designer.  Fighting an uphill battle so to speak.

Why go against the grain? 

 1)  These are the only off the shelf valves readily available for Mrod and 7/8" tubed guns that support large throats and  exhaust ports.  As delivered, Mrods have .350 throats and .250 exhaust, there is enough meat to port exhaust to .280ish.  the 7/8 valves have enough meat to port them similarly.  2)  They don't require excessive hammer strike due to having a balanced chamber.  3)  I do not have the tools nor skills to make my own valves.  4) I've read most everything Bob, Scott, and Travis have written about balanced valves and their ability to deliver high power and high efficiency with reasonable hammer mass and hammer spring weights, I wanted to experience that without the ability to make my own valves.

I convert my Powerhouse valves to Simplified Balanced valves by making 2 modifications.  1)  remove the rod  2)  change the seal material to a delrin washer.  This results in a very snappy valve, that is very efficient and capable of producing mid-high energy for a given caliber/barrel length.  However it is still plagued by one of the Powerhouse's issues---it is not very tuneable at any given pressure.  it is more tuneable than a powerhouse, but it is still a narrow range, less than 100fps of tune available by adjusting hammer strike.  When the valve operates too low in the range ES can be excessive.  Too high in the range and efficency goes to &^^&. 

After a few tanks of nitrogen and associated lead, I never could get around the narrow powerband, so to speak.  it is actually a much longer story than that, but a lot of it is documented in various threads over the past couple of years. 

Then one day I read and paid closer attention to Bob's final development of his balanced valve for his Hyabusa (I believe the summary is found in post 573).  it is there Bob reinforced the primary factors around balanced valve design.   For me, 3 primary realizations came from it.  1)  keeping balance chamber volume to the bare minimum.  2)  limiting valve travel, in this instance by controlling stem protrusion.  3)  using a fairly large stem vent. 

Buy a Powerhouse valve and buy a spare poppet assembly.  This gives you a valve that can be easily converted from Powerhouse, first shot is the most powerful, descending string to a more tame, more efficient Simplified Balanced valve that has a broad tuning range.  2 totally different applications for the same valve by simply changing poppets.  You don't modify your original poppet so you still have the ability to restore your valve to an unmolested Powerhouse format.

For the Mrod Powerhouse valve---  Stem protrusion is like any other valve, trim the stem to length, in this instance I used Bob's data as a guide and trimmed my stem to protrude .130.  You keep balance chamber volume to a minimum by screwing the balance piston carrier in/out with the valve at full lift.  Making a large stem vent can be accomplished many ways, I use pointed diamond burrs.  My stem vent is around .055, again following Bob's example with his Hyabusa. 

Similar work can be done with the 7/8" Powerhouse, but it does not have the feature of an adjustable balance piston carrier. 

I've used this valve design in various applications ranging from a 28" barreled, 320fpe Bulldog, to a 12.5" barreled 80fpe .357 pistol to a 18.25" barreled 70fpe .25.   In the .357 pistol and .25 carbine I have seen efficiency numbers greater than 1.6 at medium/high fpe levels, which for me is a first, especially with relatively short barrels. 

The .357 pistol journey is documented here in this thread with the latest development around efficiency and a bell curve across a broad pressure range in post  35. 

https://www.gatewaytoairguns.org/GTA/index.php?topic=180012.20 (https://www.gatewaytoairguns.org/GTA/index.php?topic=180012.20)

Bob, Scott, Travis, and everyone else that contributed thank you for so openly sharing your research.....

Title: Re: Simplified Balanced Valve
Post by: rsterne on December 12, 2020, 12:33:30 PM
Mike, you get full marks for persistence in taming the Powerhouse valve to get a usable bell curve.... When I destroyed a poppet by removing the metering rod, I gave up on it and just started working on the simplified balanced valve detailed in this thread.... Getting a curve starting with the Powerhouse, using methods that don't require a lot of machine work, was a worthwhile endeavour.... Congratulations, and thanks for sharing your methods and results....  8)

Bob
Title: Re: Simplified Balanced Valve
Post by: mackeral5 on December 12, 2020, 02:22:45 PM
Mike, you get full marks for persistence in taming the Powerhouse valve to get a usable bell curve.... When I destroyed a poppet by removing the metering rod, I gave up on it and just started working on the simplified balanced valve detailed in this thread.... Getting a curve starting with the Powerhouse, using methods that don't require a lot of machine work, was a worthwhile endeavour.... Congratulations, and thanks for sharing your methods and results....  8)

Bob

Thanks Bob.  It was a very frustrating ride, but when I finally paid attention to the 3 factors I listed in the post above, it came together.  One of the lowest moments was scattering the chronograph and light kit across the shop, 3 times in a row due to machine gunning tank dumps on my QB .357 Double, tuned in the 280fpe range.  This was when I was experimenting with a peek seal.  At the time I blamed it on the peek seal and switched to Delrin.  The machine gunning stopped, but I was still left with a very narrow "power band" the valve wanted to run in.  In hindsight, I was fighting the effects of excessive balance chamber volume and too much valve lift.  Perhaps a peek seal could be reintroduced, but that experience "left a mark" so I doubt I will revisit it.
Title: Re: Simplified Balanced Valve
Post by: PikeP on December 13, 2020, 12:16:14 AM
I've read most of this thread 3+ times........

Over the past few years I have been exposed to the Cothran Powerhouse valve I have been on a mission to tame it a bit.  When I say tame it, I mean to make it responsive to hammer strike adjustments across a broad pressure range.  As Don C has made it very clear, this was not his intention for a valve named the Powerhouse, so I was pursuing something that was not within the intent of the designer.  Fighting an uphill battle so to speak.

Why go against the grain? 

 1)  These are the only off the shelf valves readily available for Mrod and 7/8" tubed guns that support large throats and  exhaust ports.  As delivered, Mrods have .350 throats and .250 exhaust, there is enough meat to port exhaust to .280ish.  the 7/8 valves have enough meat to port them similarly.  2)  They don't require excessive hammer strike due to having a balanced chamber.  3)  I do not have the tools nor skills to make my own valves.  4) I've read most everything Bob, Scott, and Travis have written about balanced valves and their ability to deliver high power and high efficiency with reasonable hammer mass and hammer spring weights, I wanted to experience that without the ability to make my own valves.

I convert my Powerhouse valves to Simplified Balanced valves by making 2 modifications.  1)  remove the rod  2)  change the seal material to a delrin washer.  This results in a very snappy valve, that is very efficient and capable of producing mid-high energy for a given caliber/barrel length.  However it is still plagued by one of the Powerhouse's issues---it is not very tuneable at any given pressure.  it is more tuneable than a powerhouse, but it is still a narrow range, less than 100fps of tune available by adjusting hammer strike.  When the valve operates too low in the range ES can be excessive.  Too high in the range and efficency goes to &^^&. 

After a few tanks of nitrogen and associated lead, I never could get around the narrow powerband, so to speak.  it is actually a much longer story than that, but a lot of it is documented in various threads over the past couple of years. 

Then one day I read and paid closer attention to Bob's final development of his balanced valve for his Hyabusa (I believe the summary is found in post 573).  it is there Bob reinforced the primary factors around balanced valve design.   For me, 3 primary realizations came from it.  1)  keeping balance chamber volume to the bare minimum.  2)  limiting valve travel, in this instance by controlling stem protrusion.  3)  using a fairly large stem vent. 

Buy a Powerhouse valve and buy a spare poppet assembly.  This gives you a valve that can be easily converted from Powerhouse, first shot is the most powerful, descending string to a more tame, more efficient Simplified Balanced valve that has a broad tuning range.  2 totally different applications for the same valve by simply changing poppets.  You don't modify your original poppet so you still have the ability to restore your valve to an unmolested Powerhouse format.

For the Mrod Powerhouse valve---  Stem protrusion is like any other valve, trim the stem to length, in this instance I used Bob's data as a guide and trimmed my stem to protrude .130.  You keep balance chamber volume to a minimum by screwing the balance piston carrier in/out with the valve at full lift.  Making a large stem vent can be accomplished many ways, I use pointed diamond burrs.  My stem vent is around .055, again following Bob's example with his Hyabusa. 

Similar work can be done with the 7/8" Powerhouse, but it does not have the feature of an adjustable balance piston carrier. 

I've used this valve design in various applications ranging from a 28" barreled, 320fpe Bulldog, to a 12.5" barreled 80fpe .357 pistol to a 18.25" barreled 70fpe .25.   In the .357 pistol and .25 carbine I have seen efficiency numbers greater than 1.6 at medium/high fpe levels, which for me is a first, especially with relatively short barrels. 

The .357 pistol journey is documented here in this thread with the latest development around efficiency and a bell curve across a broad pressure range in post  35. 

https://www.gatewaytoairguns.org/GTA/index.php?topic=180012.20 (https://www.gatewaytoairguns.org/GTA/index.php?topic=180012.20)

Bob, Scott, Travis, and everyone else that contributed thank you for so openly sharing your research.....

May the real merits of those who are summed up in such empty words such as "everyone else" be never forgotten, for those with true value will step forth to be anointed with such, where those without will continue as they have.
Title: Re: Simplified Balanced Valve
Post by: mackeral5 on December 13, 2020, 08:36:39 AM

[/quote]

May the real merits of those who are summed up in such empty words such as "everyone else" be never forgotten, for those with true value will step forth to be anointed with such, where those without will continue as they have.
[/quote]


Sorry about that PikeP,.  You were included in the "everyone else."    Your contributions were not unnoticed.  But, perhaps,, they were overshadowed.

Looking back on my exclusion,in your particular instance, it was not intentional.  Subconsciously the value I place on memebers' contributions to a community as a whole is based on a weighted average, which includes a "plays well with others" factor.  Maybe including such a factor is wrong of me, this is something I will at least give a but of reflection.

Title: Re: Simplified Balanced Valve
Post by: Motorhead on December 13, 2020, 12:35:49 PM


SOLID Content always has merit ... force feeding it not so much.
Title: Re: Simplified Balanced Valve
Post by: rsterne on December 13, 2020, 12:54:17 PM
Enough, guys.... Matt contributed a lot to this thread.... let's not derail it over personalities....

Bob
Title: Re: Simplified Balanced Valve
Post by: mackeral5 on December 13, 2020, 01:17:32 PM
Enough, guys.... Matt contributed a lot to this thread.... let's not derail it over personalities....

Bob

Understood and agreed.
Title: Re: Simplified Balanced Valve
Post by: Rallyshark on December 19, 2020, 04:02:49 PM
After talking to Mike D about unrelated barrel stuff, the conversation eventually came to the balanced valves.  That prompted me to finally read this whole thread, until I could wrap my head around it.  I'm pretty sure I understand the concept now, and thank you guys for all of the valuable info!!!  Admittedly, I did get lost in a lot of the math involved, because I'm much better off when I can apply all of that to a visual representation.  I feel like I can probably make one, but I'm not so sure if it is totally worth the inevitable failure that will be involved in me getting to a functional solution.  I'm stating all of this, to avoid be told "you need to run the numbers to find out if it will work", or "you're just being lazy, and wanting someone else to solve the problem for you".  Lazy isn't my problem, but I don't trust fully trust my own abilities running the numbers without mistakes.  Time is also a pretty major part of it.  I am willing to try and find the time, if there is some potential there.

I guess I'll direct this at you Mr. Sterne, since you have known experience with Hatsan valves.  In my case, the Flash valve specifically, which is mechanically the same as an AT44 valve.  It has the same valve pin and seat.  I have converted them to PEEK seats with .210-.215 seat opening.  The Flash has a direct pull bolt, and I'm having to use some pretty massive HS to get the power I'm getting.  That is why I'm considering trying this.  I'm not looking for specific numbers or sizing of poppets or vents or any of that.  I would just like to know:  In your opinion, would it be worth attempting this on a Hatsan valve?  As you know, there isn't a ton of room to work with in there, and I wonder if I'd have the room to make it work, without negatively affecting the flow potential of the valve.  I'll also note that I'm only dealing with small bores here(.177 and .22), and I saw in the thread where the benefits of this decline on smaller bore guns.  At least, that's the impression I got. 

All of that being said...  What do you think Bob(or anyone else willing to chime in)?  Any insight is appreciated, as always!   
Title: Re: Simplified Balanced Valve
Post by: rsterne on December 19, 2020, 05:28:52 PM
I haven't attempted this on a Hatsan valve, but you are correct, there is not a lot of room inside, without boring it out.... IIRC, there is a fair amount of material, but not a lot of length.... You might have to make a whole new valve that projects into the air reservoir to get the length for the balance chamber.... Just a thought....

Bob
Title: Re: Simplified Balanced Valve
Post by: Rallyshark on December 20, 2020, 12:21:18 AM
I haven't attempted this on a Hatsan valve, but you are correct, there is not a lot of room inside, without boring it out.... IIRC, there is a fair amount of material, but not a lot of length.... You might have to make a whole new valve that projects into the air reservoir to get the length for the balance chamber.... Just a thought....

Bob

Thank you Bob, point well taken!  I will say the Flash valve is considerably deeper than the AT valves, since the gauge is installed in it. I don't think length would be the issue as much as diameter?  You are correct about there being more material that could be removed.  I don't think I could remove as much as it looks like, since I have to consider wall thickness where the gauge and bleed screw are.  I'd also need to change the material of that spring retainer, because plastic won't cut it for balanced valve use.  I would need to shorten that bleed screw a bit too, since it comes into the inside of the wall of the valve.
The gun I'm most interested in trying it on is the .177 slug gun, because it takes quite a bit of HS to get those little ice picks moving.  Here's a few pictures that may help:
Title: Re: Simplified Balanced Valve
Post by: rsterne on December 20, 2020, 01:37:12 AM
Looks pretty tight, unless you can increase the inside diameter safely....

bob
Title: Re: Simplified Balanced Valve
Post by: Rallyshark on December 20, 2020, 01:55:19 AM
Yessir, my thoughts exactly.  I'm just trying to weigh whether or not the effort will be worth the benefit on the .177 slug gun...
Title: Re: Simplified Balanced Valve
Post by: jackssmirkingrevenge on March 06, 2021, 09:06:52 AM
I'll just leave this here as an example of how a balanced valve can make a huge difference to an antique (https://www.gatewaytoairguns.org/GTA/index.php?topic=184456.0).

https://youtu.be/60AmSPaHMmI (https://youtu.be/60AmSPaHMmI)

There was no real question of tweaking the hammer mechanism, but by using the same lock and switching to a balanced valve, I was able to raise maximum operating pressure from 600 psi to 1700 psi and effectively double the muzzle energy from about 40 ft lbs to just under 80 ft lbs.
Title: Re: Simplified Balanced Valve
Post by: MJP on June 25, 2021, 04:29:49 AM
So who has done any calculations on force in the valve balancer on the shot cycle?
I have and still its not good, 450fpe gun on balanced form and after two years of using.
(https://img.aijaa.com/t/00574/14985257.t.jpg) (https://aijaa.com/cj7pbN)
Material is 42crmo4 as you know it 4140 I think.
So the valve blows open and is hammering the cage with pretty substantial force. More so than the static force of pressure, as the cage should have hold that.
There is a buffer inside the cylinder but it seems like its a wear item the cage.

Marko
Title: Re: Simplified Balanced Valve
Post by: rsterne on June 25, 2021, 01:35:15 PM
It looks like there is not much material supporting the cage, Marco.... I had one fail as well, and about tripled the area on its replacement.... I suspect it is either fatigue, or possibly shock loading (or that causing fatigue).... In my design the poppet hits the o-ring buffer against the end of the balance chamber, which in my design is supported by the spider on the front of the valve.... It is that (I think you call it the "cage") which I made stronger.... The o-ring buffer, by slowing the mass of the poppet gradually, should drastically reduce the peak force, and therefore the fatigue....

Bob
Title: Re: Simplified Balanced Valve
Post by: sb327 on June 25, 2021, 01:50:47 PM
Can you show a picture of the rest of the valve?

Dave
Title: Re: Simplified Balanced Valve
Post by: oldpro on June 25, 2021, 08:32:38 PM
So who has done any calculations on force in the valve balancer on the shot cycle?
I have and still its not good, 450fpe gun on balanced form and after two years of using.
(https://img.aijaa.com/t/00574/14985257.t.jpg) (https://aijaa.com/cj7pbN)
Material is 42crmo4 as you know it 4140 I think.
So the valve blows open and is hammering the cage with pretty substantial force. More so than the static force of pressure, as the cage should have hold that.
There is a buffer inside the cylinder but it seems like its a wear item the cage.

Marko
Ive seen that a few times LOL.
Title: Re: Simplified Balanced Valve
Post by: rsterne on June 25, 2021, 10:59:57 PM
Original.... Not enough material left in the 4 webs, too thin in both directions....

(https://hosting.photobucket.com/albums/oo221/rsterne/6mm Sporter/.highres/Broken Valve_zpsa3kdn2zs.jpg?width=1920&height=1080&fit=bounds) (https://app.photobucket.com/u/rsterne/a/2f8e7dd4-f82d-4776-a4ea-72f8a8d34c0a/p/c0388420-5fd7-4536-9f26-59a0410fa75b)

New version.... 8 webs, all of them thicker in both directions.... About 10 times as strong....

(https://hosting.photobucket.com/albums/oo221/rsterne/Hayabusa PCP/.highres/457 Valve Front_zpsju5gsbay.jpg?width=1920&height=1080&fit=bounds) (https://app.photobucket.com/u/rsterne/a/60abf6ff-337f-4270-86ba-4dd32dede705/p/bb846dbd-596a-4c5e-9f73-427492756b05)

Plus an O-ring buffer to cushion the poppet when it hits the balance chamber.... No problem so far, but that doesn't mean it won't fail some day of course....  ::)

Bob
Title: Re: Simplified Balanced Valve
Post by: sb327 on June 26, 2021, 08:42:38 AM
I mentioned in my condor build (and my sidelever I think), how I floated my valve. That way it doesn’t reach the web, the bolt holding it in the web is free to move forward. It also offers the option of adjustability without making new parts.

That’s why I was asking about Marko’s internals.

Dave
Title: Re: Simplified Balanced Valve
Post by: rsterne on June 26, 2021, 12:59:37 PM
Since the balance chamber should always be forced back towards the poppet (the pressure inside it should never exceed the pressure surrounding it), I guess floating it could prevent damage from the poppet crashing into it.... but I think it would complicate tuning, would it not?....

Bob
Title: Re: Simplified Balanced Valve
Post by: sb327 on June 26, 2021, 01:11:51 PM
IMO, it complicates it in that you have another variable to play with but if you want to go back to a limited movement setup, it’s easy to do without making a new cage.

It does get rid of the worry of the hammer and poppet weight crashing into things in case you got over ambitious with hammer strike trying to increase dwell.

Dave

Title: Re: Simplified Balanced Valve
Post by: rsterne on June 26, 2021, 01:44:35 PM
The hammer should NEVER drive the poppet into the end of the balance chamber, and that is VERY easy to avoid.... You shorten the valve stem so that it protrudes from the back of the valve less than the distance the poppet can travel before the O-ring bumper on it contacts the balance chamber.... Easy-peasy.... If you are worried about the hammer hitting the back of the valve too hard, install an O-ring bumper there too....

Valves do not need to open very far, the flow rate does not increase after the lift equals 1/4 of the diameter.... If the valve is opening more than 1/2 it's diameter, I can pretty much guarantee you are wasting air.... as it is likely open long after the bullet exits the muzzle.... The most the cage should have to withstand is the momentum of the poppet, being slowed by the O-ring bumper....

If you go back to Reply #546.... https://www.gatewaytoairguns.org/GTA/index.php?topic=152413.540 (https://www.gatewaytoairguns.org/GTA/index.php?topic=152413.540) .... you will note that the stem protrudes less than the available travel of the poppet, and that is noted in the description.... If you don't do that, you are indeed asking for trouble as the hammer can drive the poppet into the cage....  ::)

Bob
Title: Re: Simplified Balanced Valve
Post by: sb327 on June 26, 2021, 03:49:29 PM
It was only a suggestion and it worked for me……twice…..with good efficiency….

I was merely explaining that overdriving the poppet with the hammer wouldn’t tear up the valve….was not trying to suggest it be done……

Dave
Title: Re: Simplified Balanced Valve
Post by: PikeP on June 27, 2021, 01:58:36 PM
Your balance chamber height, MUST exceed the necessary lift to operate your valve, which is easy as pie to calculate. Alternatively you could round that number to about 50% of your throat diameter...60% if you want a little extra room....

As Bob mentioned, approaching or exceeding 50% of your throat ID in lift is likely just wasting air.

Also, as Bob mentioned, your valve stem should not protrude in any amount that exceeds the above...


All that doesn't matter if your valve is so unevenly balanced, that is BLOWS open due to pressure differential as opposed to hammer force.

That would make for a design flaw, that causes your poppet to hammer the cage on every single opening...and that would make it a wear item that needs replacement every X amount of shots.

Simply put, you shouldn't experience wearing out cages, thimbles, balance valve components other than its dynamic o-ring, if you build it properly.

You can increase your balance chamber vent hole diameter, or decrease your balance ratio to mediate these issues, as that will reduce how much hammering is an end result of your tinkering.

Ideally, one shouldn't build their balance valve with such tight margins (tiny chamber, smaller vent hole, or over balanced). Snapping cages is ultimately the result of getting greedy with any of the above...
Title: Re: Simplified Balanced Valve
Post by: PikeP on June 27, 2021, 02:02:05 PM
How quick does a poppet move when its only motion is influenced by the hammer which is likely moving between 20-30 fps, vs motion influenced by a hammer AND air that moves at speeds in excess of 1500 fps? Well, I don't think anyone here is able to answer it....but those cages sure show it ;)
Title: Re: Simplified Balanced Valve
Post by: Scotchmo on June 27, 2021, 05:02:26 PM
Your balance chamber height, MUST exceed the necessary lift to operate your valve, which is easy as pie to calculate. Alternatively you could round that number to about 50% of your throat diameter...60% if you want a little extra room....

As Bob mentioned, approaching or exceeding 50% of your throat ID in lift is likely just wasting air.

Also, as Bob mentioned, your valve stem should not protrude in any amount that exceeds the above...


All that doesn't matter if your valve is so unevenly balanced, that is BLOWS open due to pressure differential as opposed to hammer force.

That would make for a design flaw...


Agree with most of what you say, but blow open is not necessarily a design flaw.

My thoughts:

On any valve, the hammer should not be able to bottom out the stem before the end of hammer travel. So either the stem can pull in below the face of the valve, or use a buffer on the hammer. I spent some time playing with a couple of balanced valves and found that it's easiest to treat them as "blow open" and tune according. Trying to tune via hammer strike is frustrating.

The goal with the hammer is minimal momentum but sufficient energy to crack the valve, and then have it blow open. Dwell is then determined by the design of the balance chamber and venting.

I've built a .257 with a Cothran valve tuned for about 150fpe. The Cothran valve has a fairly long dwell time. 72gr projectiles, and a 36" long barrel make good use of that long dwell. With a light hammer that does little to extend the dwell. For fpe/cu-in, it's one of my my most efficient airguns.
Title: Re: Simplified Balanced Valve
Post by: sb327 on June 27, 2021, 06:30:03 PM
I agree with blow open being a tuning option. That is how my condor valve works. It is relatively efficient but I don’t try overdriving it.

And I don’t let the cage be in the way of the
poppet/balance chamber. The cage DOES NOT control valve lift in any way. Therefore, no need for orings as buffers and no broken cages. If it was wasting air, I would just decrease my bv volume (which is adjustable, no need to make a new part). When I first installed it, I had my bv chamber set small, shot it a few times, then just kept setting larger until I reached my goal, and stopped. I didn’t try overdriving/wasting air.

This means my valve lift/dwell is only controlled by hammer and blow open effect.

Btw, my poppet is the cylinder of the balance valve.

Dave
Title: Re: Simplified Balanced Valve
Post by: rsterne on June 28, 2021, 05:05:17 PM
One thing I do like about your suggestion, Dave, is that by varying the length of the piston rod in the balance chamber, you can vary the volume of it, by threading it into the "cage".... However, as I understand it, you float your piston rod, so would not it basically follow the poppet motion once the valve is cracked and the balance chamber is pressurized?.... While the poppet sleeve is not driven into the piston rod, won't the rod still impact the cage if it moves with the poppet (but with an air cushion inside the balance chamber)?....

If a valve blows open, you can calculate the initial acceleration of the poppet after it cracks by using the throat pressure (ie operating pressure) times the balance chamber area to calculate the force, and knowing the mass of the poppet calculate it's terminal velocity when it travels the distance available to hit the O-ring bumper.... This assumes a large balance chamber and a VERY small vent, of course, but it does give the maximum possible velocity of the poppet when it hits the O-ring bumper.... Using it's momentum, you can calculate the force on the cage from the collision, by plugging in the distance the O-ring compresses.... If it doesn't compress at all (ie no O-ring bumper) the force approaches infinity (the momentum is stopped in zero distance).... I think running this sort of calculation might be a real eye-opener as to the force the cage must withstand....

As you decrease the volume of the balance chamber, and increase the vent size, the pressure differential accelerating the poppet decreases rapidly, eventually dropping to (near) zero, and then the force reverses as the closing force on the stem takes over control of the poppet.... So, not only does following this design principle make the valve more responsive to tuning via hammer strike, since the poppet force is reversing during the shot cycle, it will drastically reduce the load on the cage by reducing or eliminating the poppet impact....

Bob
Title: Re: Simplified Balanced Valve
Post by: rsterne on June 28, 2021, 05:35:45 PM
Thinking about this further, since the area of the balance chamber is known, as is the maximum pressure, we can calculate the maximum force that could ever "blow-open" the poppet by multiplying them together.... Max. F = Area x Pressure.... so for a 3/8" balance chamber at 3000 psi we would have (0.375^2 x PI/4) x 3000 = 331.2 lbf....

If that force is applied to a poppet that has 0.25" available to accelerate, and if further the O-ring can compress 1/10th that distance (0.025"), we don't need to know the mass of the poppet, as it cancels out.... so the peak force exerted by stopping the poppet could be as high as (0.25 / 0.025) x 331.2 = 3312 lbf.... If the cage is not designed to withstand a repeated hammering by that force, then it should eventually fail....  :o

Take the O-ring bumper away, if we assume that the poppet must then stop in 0.0025" (allowing for a bit of spring in the metal and PEEK), the force would be 10 times that great.... I'm guessing the cage would fail immediately.... Now, with a small balance chamber and a large vent, the force on the poppet drops off quickly, so the poppet is accelerating slower, and ends up with less momentum, and creates a lower peak force when it crashes to a stop.... Perhaps it never even reaches the O-ring bumper, and so exerts no force on the cage.... The true force is somewhere between these extremes in most cases.... but it sure shows why some cages fail, and that they are much more likely to do so if the valve "blows open"....

If we look at a cage with 8 webs that are 0.040" thick and 0.25" long, each one is 0.01 sq.in. so the total of the 8 would be 0.08 sq.in.... It we use 2024-T3 aluminum, with a tensile strength of 70,000 psi (shear strength of 42,000 psi).... that works out to (42,000 x 0.08) = 3360 lbs. to shear.... Using 4130 CrMoly would increase that to 4656 lbs.... With only 4 webs, cut that in half.... If the webs are thinner or shorter (less CS area) then reduce it again.... Put in a thicker O-ring bumper, or a softer material (lower durometer), so that it compresses further, the peak force goes down.... Leave the bumper out, and it skyrockets.... Have a small balance chamber and a large, short vent, it reduces, and may drop to zero.... As with much of what we do, the Devil is in the Details....  ;)

Bob
Title: Re: Simplified Balanced Valve
Post by: sb327 on June 28, 2021, 07:05:10 PM
Bob,

One would have to grossly over drive the poppet or something and air use would be through the roof for anything to contact the cage.

In my sidelever, I started with the balance chamber really small and started adjusting hammer strike up until I got a good crack open. Then I adjusted both hammer strike and balance chamber size until my goal was reached. Then stopped.

I didn’t use any orings for bumpers, I just let the cycle go for as far as the hammer and blow open take it.

In my mind, it was the only way I knew I was getting the most out of the balance valve in the form of the lightest cocking effort.

I also didn’t build in (purposely) the inability for the hammer to drive the valve into anything. I just didn’t put anything in its way, so to speak, to be able to hit.

Now, there is a crash that happens. My piston crashes into the bottom of the poppet cylinder. But I have seen no I’ll effects from this happening.

The sketch is obviously nts or proportional.

Dave
Title: Re: Simplified Balanced Valve
Post by: rsterne on June 29, 2021, 12:14:44 PM
I'm definitely glad to see guys trying all sorts of variations, that is how progress is made.... I see you do have a threaded balance chamber volume adjustment.... Do you have to disassemble the valve to adjust it?....

Since a valve that is operating efficiently is usually not opening more than 1/4 of it's diameter, and conventional PCP valves operate without the poppet crashing into anything.... I can't see any problem with that design, or tuning it.... My guess is that since that design has nothing to crash, you can run a TINY balance chamber, and only use it to crack the valve.... In other words, it may only blow open 1/4 the diameter, or maybe less?.... After that, the balance piston travels with the poppet, and you have a conventional valve.... That should make it respond well to tuning via hammer strike....

Bob
Title: Re: Simplified Balanced Valve
Post by: sb327 on June 29, 2021, 12:29:26 PM
I do have to remove the valve from the gun but I don’t have to disassemble the valve. The way I support my cage allows access to the side of the piston. But I actually use a nut on the end of my piston rod. Unlike the rough sketch I did.

Dave
Title: Re: Simplified Balanced Valve
Post by: Motorhead on June 29, 2021, 03:02:32 PM
Can see we are all mostly gravitating towards the thimble being part of the poppet head and chambers end plug connected to the intake grate while utilizing an external spring.
Title: Re: Simplified Balanced Valve
Post by: sb327 on June 29, 2021, 03:20:01 PM
Can see we are all mostly gravitating towards the thimble being part of the poppet head and chambers end plug connected to the intake grate while utilizing an external spring.

Yours and Bob’s (and anyone I may have missed) research on this style valve was exactly how I went about my design. Thank you fellas for sharing all of it.

I think the poppet being the cylinder affords more advantages than the other way.

The only thing I’ve actually changed about y’all’s design is the addition of the moving (floating) piston.

Dave

Title: Re: Simplified Balanced Valve
Post by: rsterne on June 29, 2021, 05:27:59 PM
I haven't yet tried the cylinder on the poppet (other than in a Cothran), but the next time I build a balanced valve I definitely plan on doing that.... I agree that putting the spring on the outside of the balance chamber, as I suggested in my improved design in Reply #546 above, and getting it out of the balance chamber (which can then be made smaller) should be a big plus, although again I haven't made one that way.... yet....  ::)

Bob
Title: Re: Simplified Balanced Valve
Post by: MJP on July 05, 2021, 12:33:52 PM
Can you show a picture of the rest of the valve?
Dave
Small video I made some time ago of this valve on 257 gun
https://youtu.be/qX4EIyGomaA (https://youtu.be/qX4EIyGomaA)

Marko
Title: Re: Simplified Balanced Valve
Post by: Rob M on July 05, 2021, 01:27:13 PM
my guess is the garrett turbo goes on the 20mm rifle ?  ;D
Title: Re: Simplified Balanced Valve
Post by: rkr on December 26, 2021, 10:42:15 AM
I've been thinking, how much is too much or shall I say how little is too much - what's the maximum reduction in pressure related force keeping the valve closed we can go for? What if we do a full poppet diameter balance chamber and use just a stiff valve spring to keep the valve closed - would it work?
Title: Re: Simplified Balanced Valve
Post by: PikeP on December 26, 2021, 12:52:09 PM
I've been thinking, how much is too much or shall I say how little is too much - what's the maximum reduction in pressure related force keeping the valve closed we can go for? What if we do a full poppet diameter balance chamber and use just a stiff valve spring to keep the valve closed - would it work?

Maximum reduction? Well, all of it, you just need a soft enough seal.

Using springs to close valves is far less efficient than using air, in my experience using very heavy springs make an air gun very inefficient...

So that leaves me asking why would you entirely eliminate the greatest, fastest closing force available to your air rifle? Currently in a valve with both spring and valve closing force, air acts as a closing force upon the poppet before the spring is fully compressed, in fact for all we know our valve springs put up a fight, resisting the air flow closing forces due to it containing the residual energy from the hammer strike, if even for a brief moment.

I personally don't see a reason to reduce a closing force beyond less than ~100 lbs, unless you design one that temporarily increases its closing force while opened via some unbalancing act.
Title: Re: Simplified Balanced Valve
Post by: rkr on December 26, 2021, 01:10:34 PM
I've been thinking, how much is too much or shall I say how little is too much - what's the maximum reduction in pressure related force keeping the valve closed we can go for? What if we do a full poppet diameter balance chamber and use just a stiff valve spring to keep the valve closed - would it work?

Maximum reduction? Well, all of it, you just need a soft enough seal.

Using springs to close valves is far less efficient than using air, in my experience using very heavy springs make an air gun very inefficient...

So that leaves me asking why would you entirely eliminate the greatest, fastest closing force available to your air rifle? Currently in a valve with both spring and valve closing force, air acts as a closing force upon the poppet before the spring is fully compressed, in fact for all we know our valve springs put up a fight, resisting the air flow closing forces due to it containing the residual energy from the hammer strike, if even for a brief moment.

I personally don't see a reason to reduce a closing force beyond less than ~100 lbs, unless you design one that temporarily increases its closing force while opened via some unbalancing act.

Valve closing is normal and is the force acting against the area of the valve stem as it is with all poppet valves. The spring is the only thing that keeps the valve closed once it hits the seat and the balance chamber reaches atmospheric pressure in this scenario. What I'm wondering if that's a good or bad thing?
Title: Re: Simplified Balanced Valve
Post by: rsterne on December 26, 2021, 03:34:09 PM
I would think you would need a VERY heavy spring.... In addition, you will end up with a valve that either cycles or doesn't, a plateau and cliff, with NO tunability from the hammer strike.... The valve will blow open the instant it is cracked, so be prepared for poppet to balance chamber impacts, and the subsequent stresses that causes.... Velocity will be completely pressure dependant....

Bob
Title: Re: Simplified Balanced Valve
Post by: PikeP on December 27, 2021, 10:59:30 AM
Quote
Valve closing is normal and is the force acting against the area of the valve stem as it is with all poppet valves. The spring is the only thing that keeps the valve closed once it hits the seat and the balance chamber reaches atmospheric pressure in this scenario. What I'm wondering if that's a good or bad thing?

Closing speed would be theoretically slower in a fully balanced valve with a very strong spring acting. As you said the air flow passing the valve stem is a closing force, but it certainly is not the only. Air flow is directional, if you start evacuating air outside of a pressure vessel, that pressure, more specifically the air molecules, act towards the site of evacuation, which is a force aside from pressure along the valve stem. This is why valves that move MORE air require MORE hammer strike, even with identical valve stem size.

The spring absorbs and conserves the mechanical energy exchanged from your hammer, it takes time for that energy to decay... that time frame is what will make your fully balanced valve less efficient, because we're dealing with dwells in the 1-2 ms range, and a spring conserving energy cannot decay it fast enough.

Hence forth, a VERY stiff spring in the neighborhood of 100 lbs conserving a ton of energy, is not gonna lose a battle to 25 lbs or so of air pressure acting against your valve stem in a fashionable time compared to a light valve spring.

The rating of your spring directly correlates to its ability to conserve energy....which is energy your CLOSING force has to fight against. I thought I made this clear in my first post.
Title: Re: Simplified Balanced Valve
Post by: PikeP on December 27, 2021, 11:27:05 AM
The issue isn't lacking tunability (although the main purpose of the valve designed here is for such), as there are already valves out there that act similarly (blow open or not at all)

The main issue is, would it have any other disadvantages or advantages that are either detrimental, or ground breaking, and IMO its the former...due to the reasons I have alluded to. By all means don't let that discourage you from trying...even more so if efficiency is of no concern, but in the end, I only see disadvantages, and see zero benefit from balancing a valve further than has been recommended in this thread.
Title: Re: Simplified Balanced Valve
Post by: MJP on December 27, 2021, 11:57:16 AM
I've been thinking, how much is too much or shall I say how little is too much - what's the maximum reduction in pressure related force keeping the valve closed we can go for? What if we do a full poppet diameter balance chamber and use just a stiff valve spring to keep the valve closed - would it work?

Just one question, Why? All things have a purpose, why would you need a critically balanced valve with only a spring to keep it shut?
I would rather make a piloted valve than critical balanced one. You could open it just by pushin the pilot open. Or by solenoid or very light hammer. And time the valve with fill port size tuning.
No point by trying to time it with spring pressure.

Marko
Title: Re: Simplified Balanced Valve
Post by: rkr on December 27, 2021, 12:41:31 PM
I've been thinking, how much is too much or shall I say how little is too much - what's the maximum reduction in pressure related force keeping the valve closed we can go for? What if we do a full poppet diameter balance chamber and use just a stiff valve spring to keep the valve closed - would it work?

Just one question, Why? All things have a purpose, why would you need a critically balanced valve with only a spring to keep it shut?
I would rather make a piloted valve than critical balanced one. You could open it just by pushin the pilot open. Or by solenoid or very light hammer. And time the valve with fill port size tuning.
No point by trying to time it with spring pressure.

Marko

Small caliber semi-auto conversion. Smallest quad ring I could find is about the same as poppet OD. I could always make the poppet bigger in diameter but that got me thinking is it needed, which kind of leads to my next question - what would be a good minimum force pushing against the seat? 100 lbs has been suggested, any other opinions?
Title: Re: Simplified Balanced Valve
Post by: MJP on December 28, 2021, 05:47:32 AM
What ever pressure you get it to seal. There really is no minimum, just to get it to seal is enough.
But you need to consider it not being unsafe, too critical and it's going to bump fire if you drop it. And if blow open it's going to be full power cycle at that.

Marko
Title: Re: Simplified Balanced Valve
Post by: PikeP on December 28, 2021, 11:37:27 AM
Fully balance the valve, use minimum spring rating with a softer material to achieve your seal (this would take trial and error as it depends on material used, sealing surface diameter, and spring used)

Then play with larger valve stem sizes, since that is, as you put, primary closing force (which it is in smaller calibers that move little air). If you're talking about a 10-30 fpe rifle with a balance valve, opposed to where they're really needed (150+ fpe rifles), the air movement through the valve is far less, and not as concerning.

Essentially, no one has the answer except trial and error. If you have 120 lbs holding a poppet shut right now, and 25 lbs of closing force,
 your hammer strike is absorbed by both, but no one has a true answer as to what % of that strike is left fighting the 25 lbs of closing force in a very small caliber, probably marginal when compared to the 120 initial #'s holding the valve shut...introducing a larger valve stem diameter thru the valve body would re-introduce hammer strike sensitivity.

Is it possible? Sure. Is it practical? Maybe? Does anyone currently have all the answers? No.

My 100# recommendation at pressure holding a valve shut is mostly for practical purposes and safety precautions.


You also have to consider, if you make a valve open too easily, the hammer strike needed to open it becomes, slow, lazy, weak, and with that more sensitive itself to variation, this is where you find yourself only lightening the hammer itself while keeping the same spring rating, and the end result? A ms or two shaved off hammer lock time which is already in the sub 10 msec range....


Also consider, what is the lightest hammer + spring you would want in your rifle. IMO its vital to find the ideal combo here, where the hammer is not too light, nor heavy, and the spring not too stiff, nor too light... I have all the formulas to approximate that personally, which makes it easier to have my perspective. If one wanted to do a lot of work for near nothing, I suppose they could run a short throw, stiffly sprung, light to medium weight hammer to achieve an incredibly low lock time with a near fully balanced valve, seems like a lot of work to me to cut off a few MS of hammer lock time though...so, to me, that is about the only reason to go this route...
Title: Re: Simplified Balanced Valve
Post by: rkr on December 28, 2021, 02:37:16 PM
Fully balance the valve, use minimum spring rating with a softer material to achieve your seal (this would take trial and error as it depends on material used, sealing surface diameter, and spring used)

Then play with larger valve stem sizes, since that is, as you put, primary closing force (which it is in smaller calibers that move little air). If you're talking about a 10-30 fpe rifle with a balance valve, opposed to where they're really needed (150+ fpe rifles), the air movement through the valve is far less, and not as concerning.

Essentially, no one has the answer except trial and error. If you have 120 lbs holding a poppet shut right now, and 25 lbs of closing force,
 your hammer strike is absorbed by both, but no one has a true answer as to what % of that strike is left fighting the 25 lbs of closing force in a very small caliber, probably marginal when compared to the 120 initial #'s holding the valve shut...introducing a larger valve stem diameter thru the valve body would re-introduce hammer strike sensitivity.

Is it possible? Sure. Is it practical? Maybe? Does anyone currently have all the answers? No.

My 100# recommendation at pressure holding a valve shut is mostly for practical purposes and safety precautions.


You also have to consider, if you make a valve open too easily, the hammer strike needed to open it becomes, slow, lazy, weak, and with that more sensitive itself to variation, this is where you find yourself only lightening the hammer itself while keeping the same spring rating, and the end result? A ms or two shaved off hammer lock time which is already in the sub 10 msec range....


Also consider, what is the lightest hammer + spring you would want in your rifle. IMO its vital to find the ideal combo here, where the hammer is not too light, nor heavy, and the spring not too stiff, nor too light... I have all the formulas to approximate that personally, which makes it easier to have my perspective. If one wanted to do a lot of work for near nothing, I suppose they could run a short throw, stiffly sprung, light to medium weight hammer to achieve an incredibly low lock time with a near fully balanced valve, seems like a lot of work to me to cut off a few MS of hammer lock time though...so, to me, that is about the only reason to go this route...


A light hammer spring would be good for my build, I was thinking of converting one of my BSAs to a balanced valve and to use this "Caselman" principle for cycling: https://www.gatewaytoairguns.org/GTA/index.php?topic=155499.0 (https://www.gatewaytoairguns.org/GTA/index.php?topic=155499.0)
Title: Re: Simplified Balanced Valve
Post by: Motorhead on December 29, 2021, 02:26:22 PM
MATT,

I'm at a loss that your adding OPINION here ???

By your own admission YOU HAVE NEVER EVEN BUILT ONE.  Yet alone experienced first hand the cause and effect of the ratios, sealing, sticksion etc etc etc.
Now I have no issue with sharing, but to toss out ... Data Says / Read it on the web prior / My feeling are this ... WITHOUT stating you have never actually applied what you think you know.

Well ... Lets get real  :-\
Title: Re: Simplified Balanced Valve
Post by: PikeP on December 29, 2021, 05:25:34 PM
MATT,

I'm at a loss that your adding OPINION here ???

By your own admission YOU HAVE NEVER EVEN BUILT ONE.  Yet alone experienced first hand the cause and effect of the ratios, sealing, sticksion etc etc etc.
Now I have no issue with sharing, but to toss out ... Data Says / Read it on the web prior / My feeling are this ... WITHOUT stating you have never actually applied what you think you know.

Well ... Lets get real  :-\

I have built them, I do not use one in my gun, anything else Scott?
Title: Re: Simplified Balanced Valve
Post by: PikeP on December 29, 2021, 05:44:02 PM
Fully balance the valve, use minimum spring rating with a softer material to achieve your seal (this would take trial and error as it depends on material used, sealing surface diameter, and spring used)

Then play with larger valve stem sizes, since that is, as you put, primary closing force (which it is in smaller calibers that move little air). If you're talking about a 10-30 fpe rifle with a balance valve, opposed to where they're really needed (150+ fpe rifles), the air movement through the valve is far less, and not as concerning.

Essentially, no one has the answer except trial and error. If you have 120 lbs holding a poppet shut right now, and 25 lbs of closing force,
 your hammer strike is absorbed by both, but no one has a true answer as to what % of that strike is left fighting the 25 lbs of closing force in a very small caliber, probably marginal when compared to the 120 initial #'s holding the valve shut...introducing a larger valve stem diameter thru the valve body would re-introduce hammer strike sensitivity.

Is it possible? Sure. Is it practical? Maybe? Does anyone currently have all the answers? No.

My 100# recommendation at pressure holding a valve shut is mostly for practical purposes and safety precautions.


You also have to consider, if you make a valve open too easily, the hammer strike needed to open it becomes, slow, lazy, weak, and with that more sensitive itself to variation, this is where you find yourself only lightening the hammer itself while keeping the same spring rating, and the end result? A ms or two shaved off hammer lock time which is already in the sub 10 msec range....


Also consider, what is the lightest hammer + spring you would want in your rifle. IMO its vital to find the ideal combo here, where the hammer is not too light, nor heavy, and the spring not too stiff, nor too light... I have all the formulas to approximate that personally, which makes it easier to have my perspective. If one wanted to do a lot of work for near nothing, I suppose they could run a short throw, stiffly sprung, light to medium weight hammer to achieve an incredibly low lock time with a near fully balanced valve, seems like a lot of work to me to cut off a few MS of hammer lock time though...so, to me, that is about the only reason to go this route...


A light hammer spring would be good for my build, I was thinking of converting one of my BSAs to a balanced valve and to use this "Caselman" principle for cycling: https://www.gatewaytoairguns.org/GTA/index.php?topic=155499.0 (https://www.gatewaytoairguns.org/GTA/index.php?topic=155499.0)

Very interesting and I can see a very light hammer strike benefiting a semi auto action, but again be mindful of what MJP stated about being safe and covering any bump fires or odd scenarios that could cause a mis-fire on a valve thats too easy to open.  I haven't done testing in that department and can only give a number I've safely lowered to which is that 100# mark, maybe others have gone further?
Title: Re: Simplified Balanced Valve
Post by: PikeP on December 29, 2021, 10:19:28 PM
Another thing to consider is the fill rate, depending on the balance ratio, the higher you go the larger vent hole you'll want to help increase your balance chambers fill rate. (larger vent hole = better imo)

Ultimately that is what allows this balance valve to be adjustable via hammer strike, is countering the balancing via fast enough fill rate to return to 'conventional' mid valve opening.

A fully balanced valve with just a strong spring should theoretically still be tunable via hammer strike with a large enough vent hole, because the valves "tunability" occurs after the poppet is cracked off its seat, which takes a fraction of ms compared to the 1-2 ms of dwell you obtain while off the seat and decaying residual "tunable" hammer energy via fill rate. I still believe fully balanced valve with a heavy spring would be quite inefficient compared to one that's balanced 'just right' or compared to conventional, better to use the air that's already present then a stronger valve spring.
Title: Re: Simplified Balanced Valve
Post by: sb327 on December 29, 2021, 10:50:50 PM
It is not the thread to discuss it but the pilot valve I’m using in my l2 inspired build is super easy to open and showing tunability with the venting. And it is easy to make with an inherent stictionless aspect.

Dave
Title: Re: Simplified Balanced Valve
Post by: mackeral5 on February 08, 2023, 08:34:29 AM
Long-ish read, but the primary subject is balance chamber vent sizing.

I have resumed use of my Cothran-Based simplified balanced valve conversions.  These involve converting to a delrin valve seal material and increasing stem vent diameter. 

A key learning....

The large diameter of the Cothran stem hollow effectively adds excess volume to the balance chamber.  The "vent" is at the far end of the hollow stem, creating somewhat of a plenum.  I believe this contributes to a very narrow tuning range.  Setup like this the valves would be very easy to open, very snappy shot cycle.  However they wanted to run where the wanted to run so to speak----they would only function efficiently, without bounce in a very narrow range of hammer strike.  If the output yielded desired energy levels--awesome, I got lucky.  If the output did not achieve desired energy levels it became a frustrating experience of trying to force something to do what it doesn't want to do. 

I can be extremely hard headed, so this part of the journey was long and wasteful.  A brief period of using peek seats (bad idea!) Lots of nitrogen and lead.  A decent amount of damage ranging from sucking the valve spring out the valve exhaust, wrecking the valve seal beyond repair to destroying a light kit and chronograph with a tank dumping machine gun.  There were many more, but those were the highlights that I wish were on video.

I stumbled across the "fix" by accident.  Without going into a long drawn out story, I ultimately moved the vent to the top of the stem, to the base of the balanced chamber.  I did this by plugging the upper end of the stem and redrilling it, creating a jet/vent of sorts.  This mod seems to be key to tuneability. This particular combination allowed a broad tuning range, using hammer strike, and could be shifted up/down in energy like a normal unregulated knock open valve. 

There was a sweet spot of hammer strike where the valve became almost self-regulating, resulting in a very flat bell curve across >1kpsi of pressure.

All of my previous testing/development was with short barrels---16", 12", and 9" in a .357, at energy levels of 50-100fpe-ish.  Almost like the big bore .357 equivalent of a 12fpe .177.  All that was needed was a very short burst of air.  For this testing I ran a relatively large vent of 1/16 or a bit larger. 

Recently I have begun using these valves with longer barrels---in excess of 24".  The current project is a .30 Brod.  My current poppet modifications do not provide enough valve dwell.  I can create a very efficient tune, but it is at relatively low energy levels, those that you would expect out of a well tuned short barreled pcp, not taking advantage of the longer barrel.

I believe I need to decrease stem vent size and will soon test that. 

Bob, Scott, others that have real world experience-----anything to add?  thanks in advance.
Title: Re: Simplified Balanced Valve
Post by: MJP on February 08, 2023, 09:06:07 AM
Smaller vent to get more dwell, or larger volume in the balancer with same port size.
Transfers can be bigger than caliber, no matter what some say about wasted volume.

Marko
Title: Re: Simplified Balanced Valve
Post by: mackeral5 on February 08, 2023, 09:25:46 AM
Smaller vent to get more dwell, or larger volume in the balancer with same port size.
Transfers can be bigger than caliber, no matter what some say about wasted volume.

Marko

Thank you Marko. 
Title: Re: Simplified Balanced Valve
Post by: Scotchmo on February 09, 2023, 01:53:59 AM
...  My current poppet modifications do not provide enough valve dwell.  I can create a very efficient tune, but it is at relatively low energy levels, those that you would expect out of a well tuned short barreled pcp, not taking advantage of the longer barrel.

I believe I need to decrease stem vent size and will soon test that. 

Bob, Scott, others that have real world experience-----anything to add?  thanks in advance.

I'm using a Cothran valve in my Armada big bore. Cothran valves like long barrels. I needed more dwell to take advantage of my even longer barrel (48"). I made a thin section washer to space the front grate out 0.030" for some additional balance chamber volume. And then I trimmed the piston head pack 0.030" to gain even morel balance chamber volume. It helped a little.

https://www.gatewaytoairguns.org/GTA/index.php?topic=183218.msg156376705#msg156376705 (https://www.gatewaytoairguns.org/GTA/index.php?topic=183218.msg156376705#msg156376705)
Title: Re: Simplified Balanced Valve
Post by: mackeral5 on February 09, 2023, 08:30:50 AM
...  My current poppet modifications do not provide enough valve dwell.  I can create a very efficient tune, but it is at relatively low energy levels, those that you would expect out of a well tuned short barreled pcp, not taking advantage of the longer barrel.

I believe I need to decrease stem vent size and will soon test that. 

Bob, Scott, others that have real world experience-----anything to add?  thanks in advance.

I'm using a Cothran valve in my Armada big bore. Cothran valves like long barrels. I needed more dwell to take advantage of my even longer barrel (48"). I made a thin section washer to space the front grate out 0.030" for some additional balance chamber volume. And then I trimmed the piston head pack 0.030" to gain even morel balance chamber volume. It helped a little.

https://www.gatewaytoairguns.org/GTA/index.php?topic=183218.msg156376705#msg156376705 (https://www.gatewaytoairguns.org/GTA/index.php?topic=183218.msg156376705#msg156376705)

Scott, thank you for chiming in.  I have followed your build as it has evolved.  Descriving your journey impressive would be a major understatement....

A  key difference in our applications is that I am not using the valve as designed, I have actually developed a way to make it respond to hammer spring adjustments and operate across a broad pressure range.  At risk of over simplification, I am primarily using Don's valve for its ease of opening/large ports as  I  do not have the capability to machine my own.  The poppet mods I described make for a much more efficent vslve.   Im my conversations with Don over the years he made it very clear that his design intent did not heavily weight efficiency...a powerful first shot, with backup shots at  lower, but acceptable velocities accomplished his primary goals. 

Many of us want to have our cake and eat it too.....

Title: Re: Simplified Balanced Valve
Post by: Motorhead on February 09, 2023, 12:56:13 PM
This Scott knows Nothing of Cothrin valves.  Tho conversations of cause & effect of altering dwell parallel the JSAR architecture valves.

Indeed chamber volume being lower speed up closing, as does larger venting & Visa Versa.

* I've NOT read if or not choking the transfer flow speed up a Cothrin in closing w/o adversely cutting back on power much ( Sonic choking )
In JSAR types, if running rather small vented and dwell is a tad longer than wanted, simply adding a bit of progessive transfer restriction causes valve to chop dwell in a pretty controlled manor.
Title: Re: Simplified Balanced Valve
Post by: mackeral5 on February 09, 2023, 09:04:50 PM
This Scott knows Nothing of Cothrin valves.  Tho conversations of cause & effect of altering dwell parallel the JSAR architecture valves.

Indeed chamber volume being lower speed up closing, as does larger venting & Visa Versa.

* I've NOT read if or not choking the transfer flow speed up a Cothrin in closing w/o adversely cutting back on power much ( Sonic choking )
In JSAR types, if running rather small vented and dwell is a tad longer than wanted, simply adding a bit of progessive transfer restriction causes valve to chop dwell in a pretty controlled manor.

Great info Scott.  As I test further I will share my findings. 
Title: Re: Simplified Balanced Valve
Post by: Scotchmo on February 10, 2023, 02:29:48 AM
…  The poppet mods I described make for a much more efficent vslve.   Im my conversations with Don over the years he made it very clear that his design intent did not heavily weight efficiency...a powerful first shot, with backup shots at  lower, but acceptable velocities accomplished his primary goals. 

Many of us want to have our cake and eat it too.....


With a long enough barrel (36”+), and a heavy projectile, the stock Cothran valve can be very efficient.

“have our cake and eat it too”. High FPE with good efficiency. If you can stand the long enough barrel.
Title: Re: Simplified Balanced Valve
Post by: mackeral5 on February 12, 2023, 04:25:07 PM
Followup to post 743... 

I never measured the vent size in the valve mentioned because it worked so well and it was such a frustrating experience getting it to work I was afraid to touch anything.  At the time I didn't really grasp what change truly yielded the more favorable results. 

Today I measured the vent.  It was almost .060, which BTW, worked very well in a short barreled .300 ported .357 pellet/light slug shooter.  In longer barrels and when attempting to go for higher energy levels I was having to really lean on the HST, excessively preloading the SSG against the valve and things would become very inefficient not to mention hard to cock.

I soldered closed the brass plug that I previously plugged the chamber end of the Cothran stem with.  Then I decided to start with the smallest bit I felt safe using , which ended up being .025.

I had a 18" .25 Green Mountain barrel with the choke removed in the Brod at the time of first testing.  I proceeded to do some testing by using just the Brod tube with the Mrod fill adapter screwed in and connected to my regulated tanks.

To start I set the SSG at 2 turns of preload against the valve and started testing at 3000psi.

At 3kpsi it would push unsized, a bit hard to chamber MP Molds 6.35mm 48gr airgun bullets upwards of 930-940fps.  This is the fasted I've ever pushed these out of the relatively short barrel.  Down at 2400psi they would do 840-850fps.  The smaller vent is indeed helping with dwell.  Shot cycle sounded a lot better too, I believe since the hammer was no longer trying to force the valve to dwell longer than it wanted to.

I did more testing with the 24" .300 barrel and results were very similar.  With the few JSB 44gr I had left I was able to do some lower pressure testing and I found a nice setting of 1700 psi and approximately 900fps.  Once my molds arrive I hope to cast up some pellets and see how it will shoot with a similar tune. 

I appreciate everyone contributing  their experiences. 
Title: Re: Simplified Balanced Valve
Post by: Scotchmo on February 13, 2023, 03:03:24 AM
I have a relatively new Delta Wolf. It came with the standard valve, but I was able to get one of the new high flow valves to test. It’s an interesting type of balanced valve. The balance chamber is vented to atmosphere. And the stem has a fat portion with an o-ring about equal in diameter to the balance piston. It is tunable via hammer strike/dwell.
Title: Re: Simplified Balanced Valve
Post by: mackeral5 on February 17, 2023, 07:44:14 AM
Followup to post 743... 

I never measured the vent size in the valve mentioned because it worked so well and it was such a frustrating experience getting it to work I was afraid to touch anything.  At the time I didn't really grasp what change truly yielded the more favorable results. 

Today I measured the vent.  It was almost .060, which BTW, worked very well in a short barreled .300 ported .357 pellet/light slug shooter.  In longer barrels and when attempting to go for higher energy levels I was having to really lean on the HST, excessively preloading the SSG against the valve and things would become very inefficient not to mention hard to cock.

I soldered closed the brass plug that I previously plugged the chamber end of the Cothran stem with.  Then I decided to start with the smallest bit I felt safe using , which ended up being .025.

I had a 18" .25 Green Mountain barrel with the choke removed in the Brod at the time of first testing.  I proceeded to do some testing by using just the Brod tube with the Mrod fill adapter screwed in and connected to my regulated tanks.

To start I set the SSG at 2 turns of preload against the valve and started testing at 3000psi.

At 3kpsi it would push unsized, a bit hard to chamber MP Molds 6.35mm 48gr airgun bullets upwards of 930-940fps.  This is the fasted I've ever pushed these out of the relatively short barrel.  Down at 2400psi they would do 840-850fps.  The smaller vent is indeed helping with dwell.  Shot cycle sounded a lot better too, I believe since the hammer was no longer trying to force the valve to dwell longer than it wanted to.

I did more testing with the 24" .300 barrel and results were very similar.  With the few JSB 44gr I had left I was able to do some lower pressure testing and I found a nice setting of 1700 psi and approximately 900fps.  Once my molds arrive I hope to cast up some pellets and see how it will shoot with a similar tune. 

I appreciate everyone contributing  their experiences.


More followup.... 

The smaller vent has significantly reduced the amount of hammer strike required.

Had I not been so thick-skulled in this area I could have saved pounds of lead and many cubic feet of nitrogen, lol...

 I use a flat wire.spring in this gun's SSG.  With the previous .060 vent I used 1 and a half  17lb springs.. 

After reducing the vent to .025 the first few test shots indicated excessive hammer strike.  Even with the SSG adjusted to a half inch of hammer gap/free flight, I still could not adjust down off the plateau.

Ultimately i removed the half spring and restored adjustability.  and now cocking effort is significantly reduced. 

I currently do not use any sort of hammer buffer/bumper nor any adjustability in the stiker.
 Stem protrusion is such that the balance chamber/piston cannot bottom out before the hammer contacts the valve body, IIRC, stem protrusion measures in the .190 range. 

Any benefit to adding adjustability and/or buffering to the hammer system?
 

Title: Re: Simplified Balanced Valve
Post by: mackeral5 on February 20, 2023, 08:16:07 AM
Followup to post 743... 

I never measured the vent size in the valve mentioned because it worked so well and it was such a frustrating experience getting it to work I was afraid to touch anything.  At the time I didn't really grasp what change truly yielded the more favorable results. 

Today I measured the vent.  It was almost .060, which BTW, worked very well in a short barreled .300 ported .357 pellet/light slug shooter.  In longer barrels and when attempting to go for higher energy levels I was having to really lean on the HST, excessively preloading the SSG against the valve and things would become very inefficient not to mention hard to cock.

I soldered closed the brass plug that I previously plugged the chamber end of the Cothran stem with.  Then I decided to start with the smallest bit I felt safe using , which ended up being .025.

I had a 18" .25 Green Mountain barrel with the choke removed in the Brod at the time of first testing.  I proceeded to do some testing by using just the Brod tube with the Mrod fill adapter screwed in and connected to my regulated tanks.

To start I set the SSG at 2 turns of preload against the valve and started testing at 3000psi.

At 3kpsi it would push unsized, a bit hard to chamber MP Molds 6.35mm 48gr airgun bullets upwards of 930-940fps.  This is the fasted I've ever pushed these out of the relatively short barrel.  Down at 2400psi they would do 840-850fps.  The smaller vent is indeed helping with dwell.  Shot cycle sounded a lot better too, I believe since the hammer was no longer trying to force the valve to dwell longer than it wanted to.

I did more testing with the 24" .300 barrel and results were very similar.  With the few JSB 44gr I had left I was able to do some lower pressure testing and I found a nice setting of 1700 psi and approximately 900fps.  Once my molds arrive I hope to cast up some pellets and see how it will shoot with a similar tune. 

I appreciate everyone contributing  their experiences.


More followup.... 

The smaller vent has significantly reduced the amount of hammer strike required.

Had I not been so thick-skulled in this area I could have saved pounds of lead and many cubic feet of nitrogen, lol...

 I use a flat wire.spring in this gun's SSG.  With the previous .060 vent I used 1 and a half  17lb springs.. 

After reducing the vent to .025 the first few test shots indicated excessive hammer strike.  Even with the SSG adjusted to a half inch of hammer gap/free flight, I still could not adjust down off the plateau.

Ultimately i removed the half spring and restored adjustability.  and now cocking effort is significantly reduced. 

I currently do not use any sort of hammer buffer/bumper nor any adjustability in the stiker.
 Stem protrusion is such that the balance chamber/piston cannot bottom out before the hammer contacts the valve body, IIRC, stem protrusion measures in the .190 range. 

Any benefit to adding adjustability and/or buffering to the hammer system?
 

I tested with a -118 oring as a buffer.  With such a short stem protrusion this did not allow for the valve to fully open.   Velocities should have been above 880fps, with the buffer velocities would not exceed 770fps.   This particular hammer is not equipped with an adjustable striker, so I could not make any adjustments, perhaps an adjustable striker combined with the oring buffer would yield more desirable results.
Title: Re: Simplified Balanced Valve
Post by: rsterne on February 20, 2023, 12:50:26 PM
Try a 021 instead of the 118, they are the same OD, but the 021 is only 0.070" thick instead of 0.102"....

Bob
Title: Re: Simplified Balanced Valve
Post by: nervoustrigger on February 20, 2023, 02:10:52 PM
...or a softer durometer, or flat sand the current O-ring to reduce its thickness. 
Title: Re: Simplified Balanced Valve
Post by: rsterne on February 20, 2023, 07:44:40 PM
Or use a backup ring, they are thinner as well....

Bob
Title: Re: Simplified Balanced Valve
Post by: mackeral5 on February 22, 2023, 07:06:28 PM
Followup to post 743... 

I never measured the vent size in the valve mentioned because it worked so well and it was such a frustrating experience getting it to work I was afraid to touch anything.  At the time I didn't really grasp what change truly yielded the more favorable results. 

Today I measured the vent.  It was almost .060, which BTW, worked very well in a short barreled .300 ported .357 pellet/light slug shooter.  In longer barrels and when attempting to go for higher energy levels I was having to really lean on the HST, excessively preloading the SSG against the valve and things would become very inefficient not to mention hard to cock.

I soldered closed the brass plug that I previously plugged the chamber end of the Cothran stem with.  Then I decided to start with the smallest bit I felt safe using , which ended up being .025.

I had a 18" .25 Green Mountain barrel with the choke removed in the Brod at the time of first testing.  I proceeded to do some testing by using just the Brod tube with the Mrod fill adapter screwed in and connected to my regulated tanks.

To start I set the SSG at 2 turns of preload against the valve and started testing at 3000psi.

At 3kpsi it would push unsized, a bit hard to chamber MP Molds 6.35mm 48gr airgun bullets upwards of 930-940fps.  This is the fasted I've ever pushed these out of the relatively short barrel.  Down at 2400psi they would do 840-850fps.  The smaller vent is indeed helping with dwell.  Shot cycle sounded a lot better too, I believe since the hammer was no longer trying to force the valve to dwell longer than it wanted to.

I did more testing with the 24" .300 barrel and results were very similar.  With the few JSB 44gr I had left I was able to do some lower pressure testing and I found a nice setting of 1700 psi and approximately 900fps.  Once my molds arrive I hope to cast up some pellets and see how it will shoot with a similar tune. 

I appreciate everyone contributing  their experiences.


More followup.... 

The smaller vent has significantly reduced the amount of hammer strike required.

Had I not been so thick-skulled in this area I could have saved pounds of lead and many cubic feet of nitrogen, lol...

 I use a flat wire.spring in this gun's SSG.  With the previous .060 vent I used 1 and a half  17lb springs.. 

After reducing the vent to .025 the first few test shots indicated excessive hammer strike.  Even with the SSG adjusted to a half inch of hammer gap/free flight, I still could not adjust down off the plateau.

Ultimately i removed the half spring and restored adjustability.  and now cocking effort is significantly reduced. 

I currently do not use any sort of hammer buffer/bumper nor any adjustability in the stiker.
 Stem protrusion is such that the balance chamber/piston cannot bottom out before the hammer contacts the valve body, IIRC, stem protrusion measures in the .190 range. 

Any benefit to adding adjustability and/or buffering to the hammer system?
 

I tested with a -118 oring as a buffer.  With such a short stem protrusion this did not allow for the valve to fully open.   Velocities should have been above 880fps, with the buffer velocities would not exceed 770fps.   This particular hammer is not equipped with an adjustable striker, so I could not make any adjustments, perhaps an adjustable striker combined with the oring buffer would yield more desirable results.

At your recommendations I did order some -021 in 50 durometer.  However I made another change prior to their arrival.

I have tested enough that I am beginning to better understand how vent size affects the valve and I believe I am seeing a trend around tuneability/responsiveness to hammer strike adjustments. 

At lower pressures, say below 2500psi, the small .025 vent was virtually non-adjustable.  The valve blew open and behaved a lot like a Cothran when trying to find the knee.  But when testing at 3000psi it seemed to be responsive to HST adjustments.  With the .025 vent and 3000psi the .300 would push 68gr 1040fps!!!   25" barrel, .281 porting. 

The purpose of this gun isn't to be a 150fpe slug shooter.  It really is intended to be a 100fpe pellet and light slug shooter.  So I proceeded to open the vent up until I found my adjustability with lower pressures, say from 1800-2400psi.  I tried .035, then .045.  Ultimately I ended up at .060 and the shot cycle is nice and snappy again. 

In summary, I believe vent size is also dependent upon operating pressures.  Simply stated, in this particular application, a .025 vent just blew open at 2200psi and lower.  It was not responsive/tuneable with hammer strike.  The same .025 vent seemed close to appropriate at 3000psi. 
Title: Re: Simplified Balanced Valve
Post by: rsterne on February 22, 2023, 11:16:18 PM
Makes perfect sense.... thanks for doing the testing and posting your results....  8)

Bob
Title: Re: Simplified Balanced Valve
Post by: The_Long_Shot on February 28, 2023, 02:15:52 PM
 I haven't posted to airgun forums for a few years now. Good thing I'm sure.
My airgun buddy pointed out a recent post of a very ingenious balance valve designed for my airgun platform.
He also left a piece of PEEK in my shop. Hard to ignore that. So the project began.
  Cutting a part on a gun your pleased with was a little hard to do at first. Knowing there's no going back.
This isn't your simplified valve design, that at least a couple of AG manufacturers have adapted a simular design for thier guns.
It's probably the design JSAR, Bob and others im sure started work on about 5 years ago.
So here's a photo of my copy of others design. This is for a .35 cal. Cricket platform, modified to .25 cal.
  I just didn't want to have the bored drill rod with a hole in the side as a possible weak point. So I made a final version without it.
I can say after a roller coaster ride, and some help from my buddy. This thing has turned out to work better than I thought it would.
HS adjustable from way to slow to the velocity I wanted. A slug @ the 990 FPS range, or a different barrel heavy slug @ 900+ FPS.
Having a dual reg. with external adjustment and a digital plenum gauge has proven invaluable in this process.
Seems there's almost to much adjustment available, to get you in a good or bad balance between slug weight, plenum pressure, HS strenghth and vent size.
Stiction seems to be a tune vairiable that I have been luckly able to get rid of. Easy cocking and quieter with more power.  :o
I used info. from Bobs HAM article and this post to get a grasp on the force needed to open a poppet among other things.
Thanks to all.

Title: Re: Simplified Balanced Valve
Post by: Motorhead on February 28, 2023, 03:52:44 PM
Indeed these valves extract there power from available pressure far easier than a conventional valve.
It is having the control of dwell / lift keeping them efficient that is the real hat trick  :o

Great looking parts you have fabricated & using ... Very nice  ;)
Title: Re: Simplified Balanced Valve
Post by: rsterne on March 03, 2023, 07:23:35 PM
Scott, a question.... If you make your poppet from PEEK, with the balance cylinder part of it and the piston fixed (or sliding) attached to the front cage.... how thick do you need to make the wall of the PEEK cylinder so that it doesn't collapse from the pressure inside the valve when the pressure inside is atmospheric?.... I plan to run the numbers, but I would like to know what you have been using for a wall thickness, and at what pressures?....

Bob
Title: Re: Simplified Balanced Valve
Post by: Motorhead on March 03, 2023, 08:34:58 PM
Scott, a question.... If you make your poppet from PEEK, with the balance cylinder part of it and the piston fixed (or sliding) attached to the front cage.... how thick do you need to make the wall of the PEEK cylinder so that it doesn't collapse from the pressure inside the valve when the pressure inside is atmospheric?.... I plan to run the numbers, but I would like to know what you have been using for a wall thickness, and at what pressures?....

Bob
Regs are from @ 1600 to 2400 psi.  Not gone higher, having no need too.
Most are @ .220" I.D. & .315" O.D.
Have a couple at .250" I.D. with .340" O.D. ( with the 006 Quad rings )
Have experienced no wall collapse so far ... with Peek.

Tho understand most are set up with low chamber volume having piston nearly bottom out at full poppet lift ( This generally  @ .150- .175" ) before stem flushes out to body.
Title: Re: Simplified Balanced Valve
Post by: rsterne on March 03, 2023, 08:55:06 PM
Thanks for that information.... I have not so far been able to find the formula for external pressure.... For internal, 0.250" ID x 0.340" OD with 2400 psi the stress is 8050 psi, so at 3600 psi (my application) it would be 12,075 psi.... PEEK has a tensile and compressive strength of 16,000 psi, so about a 2:1 safety margin for your application (if the pressure was inside).... I plan on a 0.353" OD, so that works out to 16,000 / 10,845 = ~ 1.5:1.... However, I don't know if that applies to external pressure....  ???

Bob
Title: Re: Simplified Balanced Valve
Post by: Motorhead on March 04, 2023, 02:47:51 AM
Had always understood the strength of a cylinder compressed equally inward far exceeded the same cylinder expanded outward.
As in with outside pressure the radius of the cylinder is compressing the material its made from and gains strength similar to a arch under a bridge etc ... so a compression to yield issue.
Where as a compressed cylinder internally is trying to pull the material apart, failure being what the materials shear or stretch yield strength is.

Not a math or physics guy ... I tried it knowing worst case is a non volatile failure, it has not failed   :o
Title: Re: Simplified Balanced Valve
Post by: PikeP on March 04, 2023, 10:39:09 AM
Calculating external pressure is far different and more complicated than Barlow's formula for internal pressure P= (2*T*S/D). Interesting how much length of tube plays a factor in external pressure where as internal it does not.

https://cybra.lodz.pl/Content/6287/APM_56_20.pdf
Title: Re: Simplified Balanced Valve
Post by: rsterne on March 04, 2023, 11:12:18 PM
Thanks for that, Matt.... but I'm too lazy to wade my way through that....

Bob
Title: Re: Simplified Balanced Valve
Post by: PikeP on April 02, 2023, 12:18:44 AM
Tested my balanced valve calculator today and installed a balanced valve into my Marauder...after a few years its about time I got around to testing my own calcs...

Here are my 'build' stats

(https://i.ibb.co/wSXL7Br/image1.png) (https://imgbb.com/)

57% reduction,  67 lbs down from 155 lbs

Hammer weight: 30gram
Hammer springs: 5lb and 7lb

Lubricant: Krytox 205

My calculator recommends filling the balance chamber within 1/3rd to 1/2 of your valve dwell time, which for me is around .5-.75 ms. My calculator estimates .6 ms balance chamber fill time. No clue how close I am to that but I do know I hit the mark with fill time rate because...

I was so far able to tune down to 720 fps (as low as I currently tune) shooting 25.4's on a 5 lb spring with little preload and a 30 gr hammer, I was also able to tune 60 fpe using a 7 lb spring with moderate preload using the same 30 gr hammer.

Shot to shot consistency was no worse than conventional, have yet to test for stiction / breakout friction

Also note currently running far too much hammer gap (.06") as I haven't fine tuned everything, I will be reducing that to .04", and likely lightening my hammer even more, closer to 25 grams.


No magical gains in efficiency, or even real leaps for me personally in reduction of cocking force, I simply was able to greatly reduce my hammer weight. Did this mostly to cross it off my bucket list, while also proving my calculations on chamber fill time. Now, I'd toot my own horn but, my poppet/valve seat has a minor leak so until that is resolved, no toot.
Title: Re: Simplified Balanced Valve
Post by: sb327 on April 02, 2023, 09:18:04 AM
Toot toot!

There, I did it for you, lol.

Very interesting. I’m always curious what is exactly going on inside these critters. I’ve been playing with my oscilloscope and pressure sensors some, trying to fine tune my pilot valve. Baby steps for sure.

Thanks for sharing.

Dave
Title: Re: Simplified Balanced Valve
Post by: PikeP on April 02, 2023, 12:32:10 PM
Toot toot!

There, I did it for you, lol.

Very interesting. I’m always curious what is exactly going on inside these critters. I’ve been playing with my oscilloscope and pressure sensors some, trying to fine tune my pilot valve. Baby steps for sure.

Thanks for sharing.

Dave

It sure does feels good validating approximations you've stood behind blindly with confidence, approximations that calculate a tiny space (.1 CC's in my instance) equalizing its pressure with my throat in under a ms during a sub 1 to 2 ms shot cycle.


I constructed my valve to favor balancing by a total 57% (only .035" walls on delrin balance chamber), proving that when tuned correctly, you can still have your cake and eat it to. I don't believe there is a 'limit' in how much you could effectively balance a valve while remaining tunable, rather limitations on how you must approach and construct. In the given construction (using poppet as a bore, and balance valve as piston) you're limited as your bore requires some material for chamber wall strength while in operation to oppose the internal forces of pressure pressing against the cylindrical poppet.

However a balance valve built in reverse to the above, as originally mentioned in this thread, with the poppet as the moving piston, and the chamber as the bore, you could effectively remove all pressure against your valve poppet from HPA, and balance to 100%, however this configuration would be a pain to seal, and equally a pain to keep from blowing open as all passages would have to be so large you'd waste a lot of air, as well as still have to fight a lot of spring which would have to be used to supplement the lack of force against the valve from pressure, so really its moot to chase 100% or even near 100% balance, as that would be both dangerous, and futile being you'd work backwards, adding back spring force for proper valve operation..

I believe a 50-60% balance ratio is completely safe and sound.

For anyone interested, my conventional valve had 125 lbs holding it closed, and with a 50 gr hammer, the same spring (7lb) under the same preload making around 40FPE made just shy of 60 FPE with a 30 gr hammer. The spring that made 29 FPE (720 fps) shooting 25.4's began shooting them at 42 fpe (870 fps) with that same 30 gr hammer.

Title: Re: Simplified Balanced Valve
Post by: PikeP on April 03, 2023, 10:59:40 PM
I was able to achieve a seal that held 100% overnight and passed a water dunk, so, here is my official toot I suppose.


Below is my hand made balance piston, poppet and stem. The cage was made from a bolt head cut off, crudely rounded, reduced in height, and then tapped 6-32. This arrangement simply fits into the stock marauder valve with the only mod(s) required being reducing the end cap overall length by .1"~ and drilling the spring pocket a tad deeper, otherwise just a drop in to the stock valve. Tolerances were tight but manageable with room to spare. My balance chamber height is adjustable, as I did take it down to .155" from .175" while fixing the leak, (could go further but won't for now), can't give credit to anyone  as I had the idea conceived at the time I made the spread sheet that calculates balance valve fill times, a few years ago, what can I say except great minds think alike. (Anyone casting shade on the thinned stem, I ran the same style stem in a non-balanced valve for 3 years without fail  ;) )

(https://i.ibb.co/Gsx5KLj/IMG-20230402-092529814.jpg) (https://ibb.co/SQs3h8p)

I reduced the hammer to 27 grams and hammer gap to .045 (was 30 gr and .04 before I tore down), fps dropped from 890-900 to 860-870 on a 7 lb spring with barely any preload. Still need to run the valve thru its paces, test for break out friction, and make sure it is reliable from shot to shot, but so far I am impressed overall with the performance, and how much I've been able to reduce hammer weight, I could see going to 10-20 grams on this valve, even in 25 cal doing 60+ FPE. Maybe in time.. as I intend to do a .177/.22 cal upper that will absolutely require a lighter hammer if I only change caliber and hammer spring...

-Matt
Title: Re: Simplified Balanced Valve
Post by: sb327 on April 04, 2023, 11:44:42 AM
I have to say, you must have had some determination to do that by hand. Glad you got it sealing proper.

Dave
Title: Re: Simplified Balanced Valve
Post by: Motorhead on April 04, 2023, 04:47:04 PM
Hard as these valves close, can't see that thin stem area holding up ???
Title: Re: Simplified Balanced Valve
Post by: PikeP on April 04, 2023, 04:58:31 PM
I have to say, you must have had some determination to do that by hand. Glad you got it sealing proper.

Dave

Difficulty rating

Making piston: 2/10
Making poppet: 3/10
Making cage: 4/10
Doing it all right so it lines up: 5/10
Sealing home made poppets: Bane of my existence

Lol :)

Title: Re: Simplified Balanced Valve
Post by: PikeP on April 04, 2023, 04:58:57 PM
Hard as these valves close, can't see that thin stem area holding up ???

I had the same stem area on my previous unbalanced valve hold up for 5 years at 60 fpe? (125 lbs against valve vs 67 lbs)...here it is below, decommissioned for now and in perfect health, may go back to it someday...1000's of shots on it.

(https://i.ibb.co/z8DxyxD/IMG-20230404-141039540.jpg) (https://ibb.co/4s3t6t3)

Also valve closure is not hard on the stem area in question, think about it (what absorbs impact upon open, what absorbs impact upon closure...)...I would wager a healthy amount of money on other things failing long before that stem

Furthermore, you have a stem bore and balance chamber bore keeping the poppet fairly aligned, as well as VERY equal pressure in all directions of the poppet head, and the poppet only lifts 1-2mm from the seat, I highly doubt the stem could bend in any direction during that 1-2 ms of motion...

Lastly, the only risk here, more-so during a valve closure failure of said stem, you consequentially would only be unable to fire the gun...not too catastrophic in that event, nor a valve open failure event where it would likely do the same, or simply drain all the air from the reservoir failing to re-seat...
Title: Re: Simplified Balanced Valve
Post by: sb327 on April 04, 2023, 06:27:06 PM
Hard as these valves close, can't see that thin stem area holding up ???

What is it about a balanced valve that makes it close hard?

My thoughts are that it offers no extra closing force than a standard poppet.

And a significant amount comes from the larger stem diameter pushing back on the hammer. The rest of the closing force comes from spring and sail effect.

Dave
Title: Re: Simplified Balanced Valve
Post by: PikeP on April 04, 2023, 06:39:42 PM
I should add, I did reduce my hammer weight further, fully to 25 grams. No changes in spring preload, I am still slinging 25.4's at 890 with .055" or so gap, on a spring that used to do 720-730 with the unbalanced valve and even less gap.

Have not noticed break-out friction at 45 minute interval which is a start, next test is overnight and then a week if I can go that long without shooting it...

I had some weird experience where my fps went from 880 down to 660, then to 700, then 780, then back to normal...very strange, not sure what to blame there but if anyone wants to solve a mystery, there ya go!
Title: Re: Simplified Balanced Valve
Post by: PikeP on April 04, 2023, 06:42:34 PM
Hard as these valves close, can't see that thin stem area holding up ???

What is it about a balanced valve that makes it close hard?

My thoughts are that it offers no extra closing force than a standard poppet.

And a significant amount comes from the larger stem diameter pushing back on the hammer. The rest of the closing force comes from spring and sail effect.

Dave

Not only that, your poppet head absorbs the impact upon close, the force acting against the valve stem during closure is much less than the force acting upon the stem while opening, the initial force of cracking the valve off the seat is where the stem would see the most impact, all while being lined up with a bore and in this case 2 bores...like I previously stated twice now, my old unbalanced valve that experienced much greater forces from open to close used the same style stem for 3-5 years (time flies too fast I swear)

If you ever cracked a valve by hand (I have, especially balanced, I can actually degas the valve by hand haha), you would note that cracking the poppet from the seat is the hardest part, once that occurs your transfer port equalizes with your throat which reduces the force required to hold the valve open.
Title: Re: Simplified Balanced Valve
Post by: mackeral5 on April 04, 2023, 08:24:13 PM
I was able to achieve a seal that held 100% overnight and passed a water dunk, so, here is my official toot I suppose.


Below is my hand made balance piston, poppet and stem. The cage was made from a bolt head cut off, crudely rounded, reduced in height, and then tapped 6-32. This arrangement simply fits into the stock marauder valve with the only mod(s) required being reducing the end cap overall length by .1"~ and drilling the spring pocket a tad deeper, otherwise just a drop in to the stock valve. Tolerances were tight but manageable with room to spare. My balance chamber height is adjustable, as I did take it down to .155" from .175" while fixing the leak, (could go further but won't for now), can't give credit to anyone  as I had the idea conceived at the time I made the spread sheet that calculates balance valve fill times, a few years ago, what can I say except great minds think alike. (Anyone casting shade on the thinned stem, I ran the same style stem in a non-balanced valve for 3 years without fail  ;) )

(https://i.ibb.co/Gsx5KLj/IMG-20230402-092529814.jpg) (https://ibb.co/SQs3h8p)

I reduced the hammer to 27 grams and hammer gap to .045 (was 30 gr and .04 before I tore down), fps dropped from 890-900 to 860-870 on a 7 lb spring with barely any preload. Still need to run the valve thru its paces, test for break out friction, and make sure it is reliable from shot to shot, but so far I am impressed overall with the performance, and how much I've been able to reduce hammer weight, I could see going to 10-20 grams on this valve, even in 25 cal doing 60+ FPE. Maybe in time.. as I intend to do a .177/.22 cal upper that will absolutely require a lighter hammer if I only change caliber and hammer spring...

-Matt

As another who whittles on these guns with caveman tools, I have to give credit where credit is due.  At one time creating a peek poppet with Cobra chamber/air valve return spring seemed daunting, but now I have a series of operations where it isn't so difficult.  But a balance chamber and the VENT----I have not even come close to considering such a task...  Great job there.

To dabble in this space I have to use Cothran's as a base.....making Don's stem vent larger than needed, and adding a 6/32 set screw, drilled as a jet to the top of the stem/base of the  balance chamber gives me the ability to play in space of simplified, tuneable balanced valves....

Regarding small stems------I am a firm believer.  On my conventional knock-open valves, I modify most of my guns to accept 2mm stems.  I've yet to bend/break one with valve throats up to .3125....I don't get fancy with the stem/peek interace either.  A tight interference fit is all that is needed.  1/16 predrill of the peek to .375 or so deep, hammer the stem in.  Make sure it bottoms out or it will move and you may end up having to get very creative to degas......

I do appreciate everyone's contributions to this thread, it has been very helpful. 
Title: Re: Simplified Balanced Valve
Post by: PikeP on April 04, 2023, 08:54:08 PM
I was able to achieve a seal that held 100% overnight and passed a water dunk, so, here is my official toot I suppose.


Below is my hand made balance piston, poppet and stem. The cage was made from a bolt head cut off, crudely rounded, reduced in height, and then tapped 6-32. This arrangement simply fits into the stock marauder valve with the only mod(s) required being reducing the end cap overall length by .1"~ and drilling the spring pocket a tad deeper, otherwise just a drop in to the stock valve. Tolerances were tight but manageable with room to spare. My balance chamber height is adjustable, as I did take it down to .155" from .175" while fixing the leak, (could go further but won't for now), can't give credit to anyone  as I had the idea conceived at the time I made the spread sheet that calculates balance valve fill times, a few years ago, what can I say except great minds think alike. (Anyone casting shade on the thinned stem, I ran the same style stem in a non-balanced valve for 3 years without fail  ;) )

(https://i.ibb.co/Gsx5KLj/IMG-20230402-092529814.jpg) (https://ibb.co/SQs3h8p)

I reduced the hammer to 27 grams and hammer gap to .045 (was 30 gr and .04 before I tore down), fps dropped from 890-900 to 860-870 on a 7 lb spring with barely any preload. Still need to run the valve thru its paces, test for break out friction, and make sure it is reliable from shot to shot, but so far I am impressed overall with the performance, and how much I've been able to reduce hammer weight, I could see going to 10-20 grams on this valve, even in 25 cal doing 60+ FPE. Maybe in time.. as I intend to do a .177/.22 cal upper that will absolutely require a lighter hammer if I only change caliber and hammer spring...

-Matt

As another who whittles on these guns with caveman tools, I have to give credit where credit is due.  At one time creating a peek poppet with Cobra chamber/air valve return spring seemed daunting, but now I have a series of operations where it isn't so difficult.  But a balance chamber and the VENT----I have not even come close to considering such a task...  Great job there.

To dabble in this space I have to use Cothran's as a base.....making Don's stem vent larger than needed, and adding a 6/32 set screw, drilled as a jet to the top of the stem/base of the  balance chamber gives me the ability to play in space of simplified, tuneable balanced valves....

Regarding small stems------I am a firm believer.  On my conventional knock-open valves, I modify most of my guns to accept 2mm stems.  I've yet to bend/break one with valve throats up to .3125....I don't get fancy with the stem/peek interace either.  A tight interference fit is all that is needed.  1/16 predrill of the peek to .375 or so deep, hammer the stem in.  Make sure it bottoms out or it will move and you may end up having to get very creative to degas......

I do appreciate everyone's contributions to this thread, it has been very helpful.

Thanks for the kind words, my caveman methods improve with each daunting task I take on, this certainly was more daunting mentally beforehand than it was when executing it mindfully. I still hate the final step of getting peek or even white delrin to seal under these types of conditions (balanced valve or valves with little force holding poppet closed)

I drilled my poppet to .06" to begin with, made any needed corrections with a small dremel bit, then drilled it to.106" with a jig to ensure straightness, corrected again if it was off a few thou to .115 tops, then with a dab of red loctite hammered the .125" stem in, my depth was quite limited so I only went .165" deep, probably the tightest space constraint in the entire build, the space between stem head and balance chamber is around .07". My vent is a small area ground out from the head of the stem that goes into the poppet, which I then used as a guide to drill thru, starting the hole with a fine dremel bit then graduating to the .047" drill bit.

Its quite easy to get center by hand with the above method, starting with a small hole and making corrections with dremel and caliper, rinse and repeat. My balance chamber is off at most by .002", which for by hand is quite impressive, but with the above methods not too difficult to achieve.

-Matt
Title: Re: Simplified Balanced Valve
Post by: PikeP on April 05, 2023, 02:26:17 PM
Slightly off topic however I do feel its part of balancing a valve, but speaking about thinned stems and even the use of them in balanced valves had me pondering about my partially thinned stem.

The closing force acting upon a .125" stem at 2030 psi would be about 25 lbs, the force acting upon a .05" stem is only 8 lbs... While the partial stem doesn't cancel or reduce the closing force fully down to that 8 lbs, it does momentarily, even for a fraction for a ms, until the air molecules travel the .4" distance that my stem is slimmed down to. Food for thought on why I favor thinned stems even more, its a fine tuning effect that may not have a large impact, but nonetheless, one can't negate their favorable alteration to valve opening conditions...Air certainly doesn't travel .4" instantaneously...even when adding in upwards of .08" lift the air still must travel .32" before it fully achieves 25 lbs of closing force in a thinned stem arrangement such as mine...

I do think there is an ideal size AND possibly shape to a stem in an airgun (call it another step in tuning)..

Here is a simple graph showing various closing forces at different stem sizes and pressures...and do note, this IS quite a simple way to balance your valve so to speak, as less closing force means your valve is more equalized, favoring a balance between the two forces of open/close...can't personally say where we should draw the line for any particular arrangement (caliber, power output) but I do know a gun operating at regulated 2000 psi with a .125  stem will have nearly the same closure and interaction as a .0984 stem at 3500~ psi
 
(https://i.ibb.co/MhpqMbV/image1.png) (https://ibb.co/H2Ymn0z)
Title: Re: Simplified Balanced Valve
Post by: Motorhead on April 05, 2023, 04:43:15 PM
The stem may fracture DUE TOO Stretch & Not compression.
When the balance chamber become pressurized,  The poppet becomes its own projectile of sorts being literally shot towards the seat.
The head of poppet stops the motion upon seat contact, tho a large if not largest mass is that of the full diameter stem that wants to continue moving towards the retreating hammer.
With the hammer in free flight there is little damping the poppets closing.
Have seen stems get pulled free of the poppet head as well head fractures due to the violent closing nature these valves exhibit.

Been there FYI ..  :o
Title: Re: Simplified Balanced Valve
Post by: sb327 on April 05, 2023, 06:58:31 PM
How can the pressure inside the balance chamber shoot out something that is under the same pressure from the outside?

At best, the pressure only equalizes.

Dave
Title: Re: Simplified Balanced Valve
Post by: Motorhead on April 05, 2023, 08:21:35 PM
How can the pressure inside the balance chamber shoot out something that is under the same pressure from the outside?

At best, the pressure only equalizes.

Dave
Added area of chamber that was never at plenum pressure & Kinetics ... newtons third law.

The balance chamber is at atmosphere and pressure outside the chamber is all the plenum pressure bears against.  Soon as the chamber becomes pressurized it acts like a piston trying to spit out the portion of poppet sealed to the chamber.

The sudden stopping of poppet head once contacting seat has the mass of the stem wanting to still continue in the same direction .... This places STRETCH onto the stem either doing nothing but stop, extract itself from poppet head .. or break it.
Title: Re: Simplified Balanced Valve
Post by: PikeP on April 05, 2023, 08:39:16 PM
How can the pressure inside the balance chamber shoot out something that is under the same pressure from the outside?

At best, the pressure only equalizes.

Dave


+1 Strongly agree, the balance chamber does NOT shoot out the poppet into a throat, physics won't allow it. Your balance chamber NEVER exceeds the pressure of that in the valves plenum or the throat, only equal or less than, therefore no shot. Valve closure events are not that violent, or we wouldn't use soft plastics to seal them

How can the pressure inside the balance chamber shoot out something that is under the same pressure from the outside?

At best, the pressure only equalizes.

Dave

Added area of chamber that was never at plenum pressure & Kinetics ... newtons third law.

The balance chamber is at atmosphere and pressure outside the chamber is all the plenum pressure bears against.  Soon as the chamber becomes pressurized it acts like a piston trying to spit out the portion of poppet sealed to the chamber.

The sudden stopping of poppet head once contacting seat has the mass of the stem wanting to still continue in the same direction .... This places STRETCH onto the stem either doing nothing but stop, extract itself from poppet head .. or break it.


Any pressed in home made poppet is prone to losing its stem from a sudden stop, but that is so unlikely and would take an incredibly lose fit, I've never had that happen out of the half a dozen stems I personally made...

The poppet stem is not stretching when it comes to a stop, and certainly isn't failing in such manner even if it were. The young modulus would have to be so low for that material to stretch in such event, that it would flail. The collision event from our valves closing is not stretching valve stems, even when thinned to 1-2mm...and again, I highly disagree that this is more stressful on a valves stem area then the opening event of a valve, neither being catastrophic in the event of failure
Title: Re: Simplified Balanced Valve
Post by: PikeP on April 05, 2023, 09:30:56 PM
I'll additionally say, long before a piece of hardened steel stretches, an interference fit of metal to plastic (stem into poppet) will fail, meaning  as I said before, there will be other failure modes before this stem area in my application, fails. Toss this stem into a gun with 200-300+ lbs of force holding it closed, and it will likely fail upon attempting to open said valve before it fails on a closure event...

-Matt
Title: Re: Simplified Balanced Valve
Post by: mackeral5 on April 05, 2023, 10:27:46 PM
How can the pressure inside the balance chamber shoot out something that is under the same pressure from the outside?

At best, the pressure only equalizes.

Dave


+1 Strongly agree, the balance chamber does NOT shoot out the poppet into a throat, physics won't allow it. Your balance chamber NEVER exceeds the pressure of that in the valves plenum or the throat, only equal or less than, therefore no shot. Valve closure events are not that violent, or we wouldn't use soft plastics to seal them

How can the pressure inside the balance chamber shoot out something that is under the same pressure from the outside?

At best, the pressure only equalizes.

Dave

Added area of chamber that was never at plenum pressure & Kinetics ... newtons third law.

The balance chamber is at atmosphere and pressure outside the chamber is all the plenum pressure bears against.  Soon as the chamber becomes pressurized it acts like a piston trying to spit out the portion of poppet sealed to the chamber.

The sudden stopping of poppet head once contacting seat has the mass of the stem wanting to still continue in the same direction .... This places STRETCH onto the stem either doing nothing but stop, extract itself from poppet head .. or break it.


Any pressed in home made poppet is prone to losing its stem from a sudden stop, but that is so unlikely and would take an incredibly lose fit, I've never had that happen out of the half a dozen stems I personally made...

The poppet stem is not stretching when it comes to a stop, and certainly isn't failing in such manner even if it were. The young modulus would have to be so low for that material to stretch in such event, that it would flail. The collision event from our valves closing is not stretching valve stems, even when thinned to 1-2mm...and again, I highly disagree that this is more stressful on a valves stem area then the opening event of a valve, neither being catastrophic in the event of failure

Valve closure events are not that violent.........I think you may rephrase that as "should not be that violent" when designed and built to not be. 

I do not think it was just airflow that did this.  And let me assure you, it was a bit on the violent side....

(https://i.imgur.com/dtUKb43.jpg)

(https://i.imgur.com/Dkt55f6.jpg)

(https://i.imgur.com/qlq8Im6.jpg)
Title: Re: Simplified Balanced Valve
Post by: PikeP on April 05, 2023, 10:56:00 PM


Yea..something more than just air and a typical valve closure happened there....trust. The spring damage seems more likely to occur during the open event (WAY over hammered, this is one reason why I have 2 built in measures to keep the valve from being over-hammered personally, a valve lift limiter that I can adjust, and my stem itself only protrudes enough to lift the valve .14" in a .155" balance chamber.), it looks like that gun went on auto mode with the spring itself lodged under the poppet head jack hammering into the valve seat? Correct me if I am wrong..

Also I have only personally seen a spring unwind like that from rotational force, never direct blunt impact, impressive feat, unless it was conical and poorly made.
Title: Re: Simplified Balanced Valve
Post by: Motorhead on April 06, 2023, 12:13:49 AM
Lol ... laughing at the obvious MISS of what is going on.   Add pressure to a greater area starting out isolated, the push will exponentially increase as this area comes into the reactive forces of surface area at work.

Nothing more to add ... Figure it out
 
Title: Re: Simplified Balanced Valve
Post by: PikeP on April 06, 2023, 12:25:14 AM
Lol ... laughing at the obvious MISS of what is going on.   Add pressure to a greater area starting out isolated, the push will exponentially increase as this area comes into the reactive forces of surface area at work.

Nothing more to add ... Figure it out

I'm no teacher here, rather a student, but care to show your work or how you arrive at such conclusions? Because you're speaking a foreign language to me and possibly others. Clarity on what your trying to convey certainly doesn't hurt to ask for...


The force you're speaking of that I am familiar with is what allows us to simply tune the valve so it doesn't remain blown open until pressure drops enough for the valve to shut itself, not so much a destructive force that slams the poppet into the seat any more than a conventional valve...add to that, how much inertia or momentum do you think a 2 gram poppet can build up traveling within the .05-.09" or 1-2mm journey back to the seat? Lol, I laugh because you clearly haven't done that math, and I have...
Title: Re: Simplified Balanced Valve
Post by: sb327 on April 06, 2023, 09:19:14 AM
Lol ... laughing at the obvious MISS of what is going on.   Add pressure to a greater area starting out isolated, the push will exponentially increase as this area comes into the reactive forces of surface area at work.

Nothing more to add ... Figure it out

You are correct in that the force pushing against the poppet from the inside increase. But the force can only rise to the same level of force that is pushing from the outside of it (which is the blow open effect). Once the pressure inside the balance chamber equals the plenum pressure, the force opening vs closing is neutral.

According to your thoughts, a balanced valve simply laying on a bench, atmospheric pressure inside and out, would push itself apart. We know that doesn’t happen.

Also something to consider, I float my balance piston, if what you say is correct, my system would spit my piston out. It does not.

Laughing at someone is an insult, something that doesn’t promote progress or learning for anyone. It tends to show one’s true colors during a conversation.

As far as the ‘figure it out’, you have offered nothing to make me re-think the way I have already figured it out.

Dave
Title: Re: Simplified Balanced Valve
Post by: PikeP on April 06, 2023, 09:34:23 AM
I semi - float my balance cage, its under slight tension from spring while under no pressure...HPA definitely changes that dynamic within the valve. A fully floated piston would destroy itself if what Scott said is factual.

The "I'm right, and you're wrong" attitude, with no other constructive contributions is certainly revealing, and while it is an attempt to insult, I find myself chuckling at how low people go..
Title: Re: Simplified Balanced Valve
Post by: mackeral5 on April 06, 2023, 11:05:57 AM


Yea..something more than just air and a typical valve closure happened there....trust. The spring damage seems more likely to occur during the open event (WAY over hammered, this is one reason why I have 2 built in measures to keep the valve from being over-hammered personally, a valve lift limiter that I can adjust, and my stem itself only protrudes enough to lift the valve .14" in a .155" balance chamber.), it looks like that gun went on auto mode with the spring itself lodged under the poppet head jack hammering into the valve seat? Correct me if I am wrong..

Also I have only personally seen a spring unwind like that from rotational force, never direct blunt impact, impressive feat, unless it was conical and poorly made.

Way over hammered as an attempt to get the dwell up and not understanding what was really going on.
 Machine gunning tank dumps.....scattered a chrony and light kit across my shop, lol.  At the time I blamed it on peek bouncing, but going to delrin did not solve the problem.  Much later I learned I was just WAY over vented....

The spring was a quality unit, not conical and sized tight to the poppet. 
Title: Re: Simplified Balanced Valve
Post by: PikeP on April 06, 2023, 11:13:13 AM


Yea..something more than just air and a typical valve closure happened there....trust. The spring damage seems more likely to occur during the open event (WAY over hammered, this is one reason why I have 2 built in measures to keep the valve from being over-hammered personally, a valve lift limiter that I can adjust, and my stem itself only protrudes enough to lift the valve .14" in a .155" balance chamber.), it looks like that gun went on auto mode with the spring itself lodged under the poppet head jack hammering into the valve seat? Correct me if I am wrong..

Also I have only personally seen a spring unwind like that from rotational force, never direct blunt impact, impressive feat, unless it was conical and poorly made.

Way over hammered as an attempt to get the dwell up and not understanding what was really going on.
 Machine gunning tank dumps.....scattered a chrony and light kit across my shop, lol.  At the time I blamed it on peek bouncing, but going to delrin did not solve the problem.  Much later I learned I was just WAY over vented....

The spring was a quality unit, not conical and sized tight to the poppet.

Yea I didn't imagine you'd make a poorly designed conical, so my original assumption was spot on! Lol, a spring wedged under a poppet head, jack hammering into a seat sounds like a nightmare. Cothran valves are definitely different animals.
Title: Re: Simplified Balanced Valve
Post by: rsterne on April 06, 2023, 11:25:58 AM
The pressure in the balance chamber starts at atmospheric, leading to a "blow-open" effect until that pressure rises through the vent from the throat.... Since there must be at least a few psi loss past the poppet and through the throat, the pressure in the throat cannot exceed that in the valve, and likewise the pressure in balance chamber cannot exceed that in the throat, so until the pellet leaves the barrel and the valve closes, the pressure in the balance chamber cannot cause the valve to slam shut.... If the valve is still open at that point (this would only happen in a valve intended to blow open and stay there, with a large balance chamber and small vent), then as the pressure in the barrel suddenly drops, the pressure in the balance chamber could indeed slam the valve shut.... as would the pressure in the valve itself....

In conclusion, it is possible to design a valve that will blow open and stay open until after the pellet has left the muzzle (a Cothran will do that in a short barrel), and that will deliver maximum power for that barrel, at the expense of being very inefficient.... However, most of this thread has been devoted to developing a semi-balanced valve that can be tuned to be not only easy to open, but one where the dwell can be tuned through hammer strike, and improve efficiency.... This means, of course, that the valve must be closing while the pellet is still in the barrel, in which case the balance chamber pressure will never exceed the pressure inside the valve, and it will not slam the poppet closed.... In a properly tuned "semi-balanced" valve, once the pellet is travelling down the barrel, the main closing forces on the poppet are the throat pressure working on the stem area, the valve spring, and the "drag" on the poppet head due to air rushing past it, and causing a pressure differential across it.... Since the pressure in the balance chamber does not exceed the pressure inside the valve, in fact it is still countering that closing force to a small degree....

Bob
Title: Re: Simplified Balanced Valve
Post by: mackeral5 on April 06, 2023, 12:14:59 PM


Yea..something more than just air and a typical valve closure happened there....trust. The spring damage seems more likely to occur during the open event (WAY over hammered, this is one reason why I have 2 built in measures to keep the valve from being over-hammered personally, a valve lift limiter that I can adjust, and my stem itself only protrudes enough to lift the valve .14" in a .155" balance chamber.), it looks like that gun went on auto mode with the spring itself lodged under the poppet head jack hammering into the valve seat? Correct me if I am wrong..

Also I have only personally seen a spring unwind like that from rotational force, never direct blunt impact, impressive feat, unless it was conical and poorly made.

Way over hammered as an attempt to get the dwell up and not understanding what was really going on.
 Machine gunning tank dumps.....scattered a chrony and light kit across my shop, lol.  At the time I blamed it on peek bouncing, but going to delrin did not solve the problem.  Much later I learned I was just WAY over vented....

The spring was a quality unit, not conical and sized tight to the poppet.

Yea I didn't imagine you'd make a poorly designed conical, so my original assumption was spot on! Lol, a spring wedged under a poppet head, jack hammering into a seat sounds like a nightmare. Cothran valves are definitely different animals.

If I would have made a spring I can assure you it would have been poorly designed.  I would have no idea where to even start....  The spring was original to the valve.   IIRC, I seem to recall it was pulled down over itself, top to bottom, like pulling down a sock from the top.   

Regarding the uniqueness of a Cothran valve, I still cannot fathom how/why Don arrived at the rod/leaky check valve vs what is described in this thread.
Title: Re: Simplified Balanced Valve
Post by: sb327 on April 06, 2023, 01:05:16 PM
Bob,

An eloquent way of trying to save face for someone but in the end, M-head is wrong.

 
M-head,
Seriously, the kind of snobbery by you and the ‘my way or the highway’ bs is what drives others away from sites such as this. I’m not a punk or some idiot, I came here to learn and share ideas. Laugh at me on the internet….you prove who you are. Not very gentlemanly for sure. That keyboard sure makes some folks big n bad, at least in their own minds.

Dave
Title: Re: Simplified Balanced Valve
Post by: PikeP on April 06, 2023, 03:10:56 PM
(Anyone casting shade on the thinned stem, I ran the same style stem in a non-balanced valve for 3 years without fail  ;) )

(https://i.ibb.co/Gsx5KLj/IMG-20230402-092529814.jpg) (https://ibb.co/SQs3h8p)

-Matt

Bob,

An eloquent way of trying to save face for someone but in the end, M-head is wrong.

 
M-head,
Seriously, the kind of snobbery by you and the ‘my way or the highway’ bs is what drives others away from sites such as this. I’m not a punk or some idiot, I came here to learn and share ideas. Laugh at me on the internet….you prove who you are. Not very gentlemanly for sure. That keyboard sure makes some folks big n bad, at least in their own minds.

Dave

Not only that but this thread took a derail trying to understand the mode of failure Scott was attempting to proclaim (a thinned stem made with hardened steel stretching during valve close). Clearly he didn't read the above bold text...

I as well am here to live, learn and share ideas/concepts in a hobby I thoroughly enjoy. I know my thinned stem can and under certain circumstances absolutely will fail, circumstances outside of my use case...that applies to nearly everything we do though, we design within our safety factor / limitations, be it thinned walled tubes, thinned stems, or thin walls on entry points for connectors ect...thinned balanced valve cages that fail (ahem), the list can go on...it simply boils down to personal grievances / differences that spill over into a forum that should only contain discussions in good nature, even when heeding caution to fellow members, such as voicing ones concerns over a design or idea.

Balance valves, in their worse design, blow OPEN, not closed, and when designed as we intend here, operate nearly identical to conventional valves with the benefit of reduced pressure holding it shut and for the first few fractions of a ms. Even a Cothran style valves, an over vented valve with too large of a balance chamber should not SLAM shut, because it will have lost so much pressure in the system to remain open, that there won't be enough force TO slam it shut...

The most vicious close cycles I can think of are, such as mackerals, with a spring underneath your poppet head, which is obscure but certainly a possibility in a really overdriven valve, or one that is jack hammering over and over repeatedly with excessive lift (clearly in this situation excessive lift is most likely, allowing more inertia and momentum to build between each strike than a situation with nominal lift...) which is an entirely different mode of failure
Title: Re: Simplified Balanced Valve
Post by: mackeral5 on April 06, 2023, 08:21:10 PM
Matt, there is no value in continuing to attempt and rub Scott's nose in it. You have to acknowledge that you, as well,  have a history of let's just say not playing very nice with others at times.  Examples lie in this particular thread....

You like to poke the bear, and I get it.  But it is not necessary to continue beating this particular drum so to speak..... 

Not everyone has been around long enough to know  that you are here under at least your second profile, largely due to taking things like this a bit too far, IIRC???

Each of you greatly contribute greatly to the community, there is no reason for either party to try and belittle the other. 

Being "right" isn't the most important thing in life. 
Title: Re: Simplified Balanced Valve
Post by: rsterne on April 07, 2023, 10:06:55 PM
IMO, this thread has been hugely interesting, and provided a wealth of knowledge over it's life.... However, if people cannot leave personalities out of it, I will lock it, and you can play elsewhere.... This is not aimed at anyone in particular, it is just embarrassing and silly to see what has happened here, and I won't tolerate it much longer.... Stay on topic, and leave your egos in the shop.... 'Nuff said!....

Bob
Title: Re: Simplified Balanced Valve
Post by: PikeP on April 10, 2023, 03:12:02 PM
Further testing done today. Testing how LOW can you GO (balance valve reaction time/minimum obtainable fps.)

How deep into that Goldilocks zone am I you ask? Too deep...

I was able to launch a 25.4 across the chronograph to where IT COULD NOT READ, AND I COULD VISUALLY SEE THE PELLET CROSS. Pretty neat!

Adding a little spring tension to my 3 lb spring and 25 gr hammer, I launched a 25.4 pellet across my chronograph @ 215 FPS for 2.6 FPE....Wow.

Needless to say, my balance valves reaction time is TOO fast. I must admit a minor flaw in my prior calculation that used vent distance as a volumetric dimension instead as a distance in the dimension of time, so it skewed my calcs...a lot...but I can admit when I make a mistake or fail, and although I didn't fail, I did make an error that put me deeper into the 'Goldilocks Zone' of tunability than desired.

Attached is my updated calc which seems pretty inline with what I am witnessing at the chronograph...

(https://i.ibb.co/PYgmGTH/image1.png) (https://imgbb.com/)

Next step would be to reduce the vent size from .047" to .031", I can always go to .035" and then to .039" if .031" is too small. .031" should give me a fill time of .055-.065 which is the upper end of my estimated Goldilocks Zone, which I am determined to seek out to a degree for not just personal fine tuning reasons, but for the sake of my balance valve model.

 I will also be trying a peek poppet with smaller margins which will reduce the need for hammer striker further, possibly combined with an even lighter hammer in the range of 10-20 grams opposed to the current 25 gr, all the above will take a few weeks to get the parts gathered and my compressor up and running so my degas/regas is not reliant on hand pumping. I have a lot of fun changes (fun personally at the least) that I am making to my marauder which I will cover in its own thread in the following weeks as they all come to fruition.
Title: Re: Simplified Balanced Valve
Post by: PikeP on April 14, 2023, 07:41:34 PM
Got around to testing a new poppet / balance chamber made from peek @ .234" ID / .297" OD with a .035" vent...thats a peek poppet with only 55 lbs of force holding it shut!

Here are the initial results with my .25 cal marauder shooting 25.4's

Unbalanced     .276" poppet    50 gr hammer    7 lb hammer spring       no vent      = 600-800 fps tuning range       (0% reduction, used 8-9lb springs for more oomph)

55% Balanced .307" poppet    25 gr hammer    5 lb hammer spring      .047" vent   = 600-800 fps tuning range      (56% reduction, still needed 8-9lb spring for peak power)

60% Balanced  .297" poppet    25 gr hammer    3.5 lb hammer spring   .035" vent   = 600-800 fps tuning range      (60% reduction, 7lb spring gets to peak power)
 

My balance valve calculator is now pretty spot on, approximating the valve to close in around .4 ms with my latest .035" vented balance chamber. I didn't test .031" as I mentioned I would earlier as I didn't have confidence it would be enough to hit my lower fps tunes easily, and even so, .035" still pushes that margin right to the edge, the difference between .035" and a .031" vent is approximated at nearly a full tenth of a ms difference which, for those seeking a less tunable range it absolutely could and would work, depending on your air guns variables such as pressure, barrel length, balance chamber height/od...that said I am pretty confident .031"-.039" venting is within the Goldilocks range for MOST pcp's utilizing a balanced valve, and my model certainly can calculate better results for the few pcps outside of these parameters, those with possibly much smaller balance chambers, or those with much larger, the model scales very well. Thanks for reading.

-Matt
Title: Re: Simplified Balanced Valve
Post by: PikeP on April 15, 2023, 01:43:33 AM
Graph showing how much pressure will effect your balance chambers fill rate in ms, following graph is done using a .1 cc volume chamber with modest .25" vent length and .1" distance to vent from throat, of course there are many more variables other than pressure that effect your fill rate which have been covered extensively through-out this thread.


(https://i.ibb.co/fFx6Y6z/image1.png) (https://ibb.co/Gp5YvY4)

It is quite imperative that if building a balance valve, you do not over vent as this really counter-acts the benefits of these valves, hopefully this chart can help guide a DIYer or two.

I chose .1 cc's in balance volume because extrapolation from there is quite easy... if you have .15 cc's you'd be 50% more on the fill time. A good target fill time (imo) is .4 ms, but .3-.6 ms is likely acceptable for most applications, and certain specific applications will need much more or less than that.

*interesting to note that the slope flattens as you go too large of a vent, and is considerably steeper when you under-vent.*


-Matt
Title: Re: Simplified Balanced Valve
Post by: sb327 on April 15, 2023, 08:11:07 AM
One could presume from the graph that it would be possible to ‘align the stars’ such that you could have unregulated AND a reasonably flat shot string. I know some have had this be the case (my AEA bv is surprisingly flat unregged), my case was kinda by accident and kinda by the fact I can easily change the bv volume externally.

Obviously other factors (hammer weight, projectile weight, target velocity, etc) all play into these  ‘stats’.

Dave
Title: Re: Simplified Balanced Valve
Post by: PikeP on April 15, 2023, 08:59:59 AM
One could presume from the graph that it would be possible to ‘align the stars’ such that you could have unregulated AND a reasonably flat shot string. I know some have had this be the case (my AEA bv is surprisingly flat unregged), my case was kinda by accident and kinda by the fact I can easily change the bv volume externally.

Obviously other factors (hammer weight, projectile weight, target velocity, etc) all play into these  ‘stats’.

Dave

Without a doubt, imo a properly balanced valve can handle the pressure drop over a shot string just as well as a conventional valve, as the primary actor in these conditions is a heavy valve return spring that is at least 10% if not more of the force holding your valve shut.

Below is a graph comparing forces holding an unregulated valve shut at 2000-3000 in both conventional and balanced.

(https://i.ibb.co/frvcbJc/image1.png) (https://ibb.co/h2fqk0q)

As you can see the balanced valve change over the 1000 psi appears flatter than the conventional valve, lending itself to....equal or better self regulation.

The conventional valve would need a lot of more valve return spring to counter act the change from 220 to 150 lbs (32%) as pressure drops, where as the balanced valve goes from 82 lbs down to 56 lbs, which is also roughly 32% drop in force holding the valve shut over the 1000 psi. The conventional valve would lend itself to a 15-30 lb valve return spring where the balanced valve should suffice with 5-10 lbs of return spring..

In addition to the above, by finding the right vent size in an unregulated rifle, you can absolutely align the stars, and have the fill times assist you in regulating the rifles power output as well. If you want a bit more lift as pressure drops, you'd want fill times to slow as you drop pressure (smaller vent), if it were better to have flatter fill times, one would lean towards the over venting end. With adjustable chamber height (within your margins of valve lift, ideally no less than around .125" for most pcps for peak power output) you can fine tune quite a bit, but the slope seen on my previous post, is dependent more so on vent size.

(While chamber height and vent size both effect fill times, they absolutely effect them quite differently when altered, more so in an unregulated rifle)

-Matt
Title: Re: Simplified Balanced Valve
Post by: PikeP on April 15, 2023, 10:29:29 AM
Goldilocks Test .036" vent @ .14" chamber height, roughly .1 cc chamber volume, 2000 psi regulated.

Testing how low I can go on a .036" vent...I got a pellet stuck in the barrel with a 25 gr hammer and 3.5 lb spring with nearly 0 preload, so you could say...pretty ' low...a bit more preload, and shes shooting 230 fps across the chronograph...yea, this arrangement works fine...and even the 230 fps was repeatable and consistent in operation. No signs of blowing open or wasting air. Could the .031" vent work..perhaps, but the closer to blow open boundary you get, the more each incremental thousandths makes difference. I personally don't want to cross that boundary so, here I stay at .036"~

Also the closer you get to the blow open boundary, the more sensitive the valve becomes to spring preload change through-out its entire range, where as the closer you get to near instant-transition to conventional, the less sensitive the valve will be to preload changes (will require a wider range of preload).

To this note, on my low fps tunes I prefer to use valve lift limitation to aide in consistent fps for balanced valves, and even in general, where you tune a bit over your intended fps, then use a means to only allow the hammer to lift the valve X amount off the seat, in my case that may be as low as .02", or nearly .5mm, or upwards of .125"~, depending on my tune. I thankfully do have an externally adjustable lift limiter present.

For anyone concerned with the 3.5 lb spring and this particular balanced valve being too easy to open/operate, I can drop the gun on its butt from over 1 foot and it does not discharge a peep of air...


Oh and for the claim that hammer weight significantly changes the relationship between lift and dwell, I hard disagree and have further proven this to myself. I have a lift limiter in my valve set at the same .09" limitation, and achieve at least 53~ FPE at said lift limitation on both 25 gr hammer w/ balanced valve and 50 gr hammer w/ conventional valve, so any change in that relationship is quite negligible unless you make drastic changes in weight, more drastic than 50% reduction...probably need 500% weight change to really start noticing drastic changes in that relationship imo, I calculated my max lift in my chamber knowing how my 50 gram hammer acted, and I certainly am not limited by this going down to 25 gr hammer...Plus this argument makes no sense, ports flow X amount of air regardless how hard the valve is hit...and flow thru the throat and ports determines valve open time which provides X amount of FPE based on a set of variables.



-Matt

Title: Re: Simplified Balanced Valve
Post by: rsterne on April 15, 2023, 01:17:32 PM
Quote
I have a lift limiter in my valve set at the same .09" limitation,

The relationship between lift and dwell does not apply if you have a lift stop, that should be obvious.... The poppet has to be able to coast for it to occur, not have a hard stop....

Bob
Title: Re: Simplified Balanced Valve
Post by: PikeP on April 15, 2023, 02:56:20 PM
Quote
I have a lift limiter in my valve set at the same .09" limitation,

The relationship between lift and dwell does not apply if you have a lift stop, that should be obvious.... The poppet has to be able to coast for it to occur, not have a hard stop....

Bob

How does it not, if the lift required to produce equal power at 25 gr hammer changed substantially over a 50 gr hammer, then the lighter hammer that *should* require more lift should bounce off the valve lift limiter just as any hammer would the back of a valve once you exceed a set lift limit while producing much lower power than the same lift limitation and a heavier hammer...

That is like saying the stem protrusion from the rear of your valve doesn't matter and negates the hammer weight having a substantial effect on your lift/dwell relationship...

Make it make sense, or just provide data to prove otherwise because every data point of mine personally suggests there is no substantial change  in lift/dwell when altering hammer weights as little as 50-100% while altering spring rating to retain identical power output.

Wonder how the lift/dwell relationship is with hammerless valves  ::)

If there was some magic sauce to low dwell valves that produce the same output as another valve that requires more dwell, well you'd be more efficient, and you'd make money selling these valves, please produce these asap.

-Matt

Title: Re: Simplified Balanced Valve
Post by: PikeP on April 15, 2023, 03:19:46 PM
My reason to bring light to the relationship of lift and dwell with hammer weight, is so many others, as people in the past, do not over size their balance chambers height in anticipation of needing much more lift when going with a much lighter hammer....

Having a poppet able to coast past your intended lift results in over striking the valve (inefficient) or creating more power than intended..

Over sizing your balance chamber height, moreso one that is static, will result in the need to over size your vent, and waste a tiny bit more air, an adjustable simply can be adjusted down.

-Matt
Title: Re: Simplified Balanced Valve
Post by: PikeP on April 16, 2023, 11:36:58 AM
Is my 25 gram hammer light, or wait, is it heavy? Guess that depends who/what you ask, yourself, a scale or the valve which the hammer functions in...

My current hammer weight in my 60% balanced valve is objectively heavy, it only needs 3.5 lbs of spring @ 25 grams to make 40 fpe, where as I needed 7 lbs of spring and 50 grams of hammer in my conventional valve to produce equal power.

While many may think subjectively, oh a 25 gram hammer making 40-60 fpe is light, its not when your valve is held closed with 55 lbs, whereas in a conventional valve it certainly is very light...

So, am I running a light hammer, or a heavy hammer? Its gotta be one way or another....

Just more food for thought. Seems relative.
Title: Re: Simplified Balanced Valve
Post by: rsterne on April 16, 2023, 06:46:44 PM
You made a blanket statement, and I provided the counter-argument.... Hammer energy produces lift, while hammer momentum produces dwell, in a conventional knock-open valve.... Period.... The hammer energy is produced by the spring (average force times travel) and while the hammer velocity changes with weight, the energy does not.... If you change the hammer weight, for the same energy the momentum IS changed, however (heavier hammer more momentum, and vice versa).... Therefore, the relationship between energy and momentum changes as you change the hammer weight....

Note, this only applies if the poppet travel is not artificially limited in some way, and all of the RESIDUAL hammer energy and momentum is not wasted by hitting the back of the valve (or the poppet hitting a stop).... The residual energy, of course, is the energy remaining after the valve cracks from the seat, which removes part of the energy (and momentum) by slowing the hammer.... These relationships are also affected by the closing force on the popper, which is spring force, plus poppet drag (pressure differential across it), and in a balanced valve, any net force provided by the balance chamber.... Again, the relationship between hammer weight and momentum (and hence dwell) for a given hammer energy, is simply dictated by physics.... I presume you are not suggesting those laws are wrong?.... As an aside, don't forget that flow through the valve reaches a limit when the lift equals 1/4 of the diameter, caused by the curtain effect.... Therefore, adding lift after that doees not increase flow.... This occurs at 1/16" lift on a 1/4" throat....

There is no question that the balance chamber in a semi-balanced valve can be made to do virtually anything you want it to.... from blowing the poppet open and dumping the reservoir, to only reducing the cracking force on the poppet, and anything in between.... Before you get all riled up, it would perhaps help to take a deep breath and look at what YOU said, and my response.... Believe it or not, sometimes we can both be right, and a pi$$ing contest is not necessary.... Your experiments are valued, and help all of us understand the complicated dynamics of semi-balance valves.... Let's not lose sight of that, please....

Bob
Title: Re: Simplified Balanced Valve
Post by: PikeP on April 17, 2023, 09:46:39 AM
You made a blanket statement, and I provided the counter-argument.... Hammer energy produces lift, while hammer momentum produces dwell, in a conventional knock-open valve.... Period.... The hammer energy is produced by the spring (average force times travel) and while the hammer velocity changes with weight, the energy does not.... If you change the hammer weight, for the same energy the momentum IS changed, however (heavier hammer more momentum, and vice versa).... Therefore, the relationship between energy and momentum changes as you change the hammer weight....

Note, this only applies if the poppet travel is not artificially limited in some way, and all of the RESIDUAL hammer energy and momentum is not wasted by hitting the back of the valve (or the poppet hitting a stop).... The residual energy, of course, is the energy remaining after the valve cracks from the seat, which removes part of the energy (and momentum) by slowing the hammer.... These relationships are also affected by the closing force on the popper, which is spring force, plus poppet drag (pressure differential across it), and in a balanced valve, any net force provided by the balance chamber.... Again, the relationship between hammer weight and momentum (and hence dwell) for a given hammer energy, is simply dictated by physics.... I presume you are not suggesting those laws are wrong?.... As an aside, don't forget that flow through the valve reaches a limit when the lift equals 1/4 of the diameter, caused by the curtain effect.... Therefore, adding lift after that doees not increase flow.... This occurs at 1/16" lift on a 1/4" throat....

There is no question that the balance chamber in a semi-balanced valve can be made to do virtually anything you want it to.... from blowing the poppet open and dumping the reservoir, to only reducing the cracking force on the poppet, and anything in between.... Before you get all riled up, it would perhaps help to take a deep breath and look at what YOU said, and my response.... Believe it or not, sometimes we can both be right, and a pi$$ing contest is not necessary.... Your experiments are valued, and help all of us understand the complicated dynamics of semi-balance valves.... Let's not lose sight of that, please....

Bob

There was no blanket statement. Keep your emotions and personal feelings out of it, there is also no ^*%$#@ contest except the one you create yourself. I stated there is no substantial change in lift / dwell when altering your hammer weight and spring within a specific range of 50%-100% (the range I have been able to personally test) to retain identical power output, what is blanket about that? Wheres the fallacy?

If you have such an issue with my so called blanket statement that this relationship does not change significantly, and as you say, it's simply physics, I kindly await the formulation of math or data to concretely disprove it.

-Matt
Title: Re: Simplified Balanced Valve
Post by: rsterne on April 17, 2023, 02:34:30 PM
Thank you for destroying a very valuable thread with your rant....  >:(....  I see that your "Watched" label is still required, something I will be requesting....

I, Scott, Travis, Lloyd, and many others have built way more custom PCPs, valves and hammers than you could ever hope to achieve, and the relationship between hammer mass and momentum is well documented.... With a conventional valve, if you lighten the hammer (less dwell), you must increase the energy (more spring force and/or travel) to compensate and keep the FPE (area under the lift/dwell curve) unchanged.... The opposite also applies, a heavy hammer can deliver the same FPE with less energy (lift).... The Physics comes into the basic understandings of lift being proportional to energy, while dwell is proportional to momentum (once the energy to crack the valve is subtracted).... As I tried to explain, the flow through the valve, if opened more than 1/4 of its diameter, no longer increases with lift, so for a valve that is ACTUALLY opening that far (easy to measure, but also quite rare in an efficient PCP), all you are left with to change the FPE is a change in dwell with hammer momentum, be that achieved by mass or spring energy.... Just because you happen to disagree is no reason for the rest of us to throw out that valuable piece of information.... or a reason to rant....

While there may be certain valve configurations (balanced, semi-balanced, operating with a hammer or poppet stop, etc.) where the lift does not change (because it cannot), the lack of relationship between lift and dwell as you change hammer mass is caused by those other factors, and your statement, if applied only to those situation, may well be correct.... There is your middle ground.... Accept the fact that you are not always right, or leave the Workshop, please....

Bob
Title: Re: Simplified Balanced Valve
Post by: PikeP on April 18, 2023, 11:31:03 AM
Thank you for destroying a very valuable thread with your rant....  >:(....  I see that your "Watched" label is still required, something I will be requesting....

I, Scott, Travis, Lloyd, and many others have built way more custom PCPs, valves and hammers than you could ever hope to achieve, and the relationship between hammer mass and momentum is well documented.... With a conventional valve, if you lighten the hammer (less dwell), you must increase the energy (more spring force and/or travel) to compensate and keep the FPE (area under the lift/dwell curve) unchanged.... The opposite also applies, a heavy hammer can deliver the same FPE with less energy (lift).... The Physics comes into the basic understandings of lift being proportional to energy, while dwell is proportional to momentum (once the energy to crack the valve is subtracted).... As I tried to explain, the flow through the valve, if opened more than 1/4 of its diameter, no longer increases with lift, so for a valve that is ACTUALLY opening that far (easy to measure, but also quite rare in an efficient PCP), all you are left with to change the FPE is a change in dwell with hammer momentum, be that achieved by mass or spring energy.... Just because you happen to disagree is no reason for the rest of us to throw out that valuable piece of information.... or a reason to rant....

While there may be certain valve configurations (balanced, semi-balanced, operating with a hammer or poppet stop, etc.) where the lift does not change (because it cannot), the lack of relationship between lift and dwell as you change hammer mass is caused by those other factors, and your statement, if applied only to those situation, may well be correct.... There is your middle ground.... Accept the fact that you are not always right, or leave the Workshop, please....

Bob

I see no formula, nor data sets here to prove that when altering your hammer weight by 50-100% and spring rating in a manner to retain the same power output, that the relationship between lift and dwell changes significantly. This is a contribution to this thread, as lift plays a large part in a balanced valves chambers height requirements.

Thanks,

-Matt
Title: Re: Simplified Balanced Valve
Post by: rsterne on April 18, 2023, 01:38:51 PM
You are a decade too late to take part in those discussions.... Here is a simple chart from 2012 showing the relationships, developed using Newtonian mechanics.... It was presented to many, including Steve in NC on the Yellow and Green forums, and nobody (until you came along) disagreed with the science behind it, nor the real-world observed effects....

(https://hosting.photobucket.com/albums/oo221/rsterne/Important/.highres/ValveLift1_zps2fe4f599.jpg) (https://hosting.photobucket.com/albums/oo221/rsterne/Important/.highres/ValveLift1_zps2fe4f599.jpg)

V is the residual hammer velocity after the valve is cracked off the seat, and M is hammer mass.... The closing force on the poppet is assumed to be a constant.... That force slows the hammer/poppet combination and returns it to the seat, with the time required to do that being the dwell....

Bob

Title: Re: Simplified Balanced Valve
Post by: Motorhead on April 18, 2023, 09:36:33 PM
Thank you for destroying a very valuable thread with your rant....  >:(....  I see that your "Watched" label is still required, something I will be requesting....

I, Scott, Travis, Lloyd, and many others have built way more custom PCPs, valves and hammers than you could ever hope to achieve, There is your middle ground.... Accept the fact that you are not always right, or leave the Workshop, please....

Bob

Fancy charts, talking louder, slighting others work etc .... THIS THREAD should be LOCKED. 
If Matt feels he has something to teach us all, Let him create his own thread and then see who contributes or pays attention.
Title: Re: Simplified Balanced Valve
Post by: rsterne on April 19, 2023, 01:46:19 PM
One more chart, for those who do not understand what I mean by flow limiting (the "curtain effect") when the valve lift exceeds 1/4 of the seat diameter.... The flow through the valve is represented by the area under the curve....

(https://hosting.photobucket.com/albums/oo221/rsterne/PCP%20Internal%20Ballistics/.highres/ValveFlow1_zps5a9bbe8d.jpg) (https://hosting.photobucket.com/albums/oo221/rsterne/PCP%20Internal%20Ballistics/.highres/ValveFlow1_zps5a9bbe8d.jpg)

This occurs because the throat area is PI/4 x D^2, while the area between the poppet and the seat is PI x D x L, where L is the lift.... Those areas are equal when....

PI x D x L = PI/4 x D^2 .... simplified to D x L = D^2/4 .... which is L = D/4

This is a well known effect in any poppet style valve (eg. auto engines), and part of camshaft design....

I have done a lot of direct measuring of valve lift, and have found that in efficient PCPs (1.0 FPE/CI or greater) the lift seldom exceeds 1/4 of the diameter.... However, if that is not the case, which could easily occur in a balanced valve, then the only way to vary (or maintain) the area under the curve is to work with the dwell.... If you fit a lighter hammer, you need to increase the spring force and/or travel to get back to the same dwell, and hence the same area under the curve, and FPE of the PCP.... While the lift may be changing (or not, if there is a mechanical stop), you don't see the effect, because of the flow being limited by the curtain effect....

Bob
Title: Re: Simplified Balanced Valve
Post by: oldpro on April 19, 2023, 03:18:09 PM
Thank you for destroying a very valuable thread with your rant....  >:(....  I see that your "Watched" label is still required, something I will be requesting....

I, Scott, Travis, Lloyd, and many others have built way more custom PCPs, valves and hammers than you could ever hope to achieve, There is your middle ground.... Accept the fact that you are not always right, or leave the Workshop, please....

Bob

Fancy charts, talking louder, slighting others work etc .... THIS THREAD should be LOCKED. 
If Matt feels he has something to teach us all, Let him create his own thread and then see who contributes or pays attention.

  Matt had to take a vacation. David took him to the train station  ;)
Title: Re: Simplified Balanced Valve
Post by: mackeral5 on August 19, 2023, 10:12:30 AM
I've shared this elsewhere but since this thread has seen little activity as of late decided to add it here....

In toying around with Cothran-based versions of the simplified balanced valve I was able to achieve good results and with a bit of trial and error on vent size could tune for fairly tight ES across a 1000-1200psi pressure range.  The key was placing the vent at the base of the balance chamber, in turn reducing volume and allowing dwell to be more responsive to vent size. 

The later developments of this thread took a while for me to digest, but once I did I implemented some of it on my Bulldog's Cothran-based valve.  The key change from my previous implementations of this valve is the variable balanced chamber volume achieved by adjustable piston height, and the piston being allowed to move away from the valve seat with the poppet when less blow open is desired. 

This was the final version of the valve components, here you can clearly see the modified Cothran poppet and balance piston.  Piston height is adjusted by loosening the 6-32 nyloc serving as a jam nut screwing the 6/32 screw in or out of the Cothran piston. 

(https://i.imgur.com/ndhrN0W.png)

Piston height can be adjusted in from an extreme of blowing open like a Cothran, with very little tuneability, to the other extreme of almost no balanced chamber volume and closing very much like an traditional knock open valve. 

Balance ratio was not defined by any desired specification, it would be whatever the available combination of parts would yield as I do not have the ability to fabricate such precise components.  The delrin poppet sealing washer has a sealing margin of approximately .420 over the .375 valve throat.  Piston is .250".

The vented disc/bushing/spider whatever we want to call it rests in the Bulldog's tube adapter.  As Matt tried explaining to me on many previous occasions, there is no requirement to firmly attach this to anything.  the same closing force that is removed from the sealing margin of the poppet is transferred to the piston, thus the vented disc will stay located rearward as long as the gun is pressurized.  I put an oring around the disc to keep it from rattling around loose, should the gun depressurize.  Filling from empty is a simple process, to date I have experienced no problems with this particular detail. 

(https://i.imgur.com/a5vZuIn.png)

(https://i.imgur.com/eajnoQK.png)

(https://i.imgur.com/BWZKYEm.png)


A bit of damage from the development process.......

Here the closing forces sheared a piece of threaded brass tubing I used in the first version, as a threaded coupler, to facilitate piston height adjustment.  In the current version the brass tubing is just a sleeve, a bearing surface if you will.  The 6/32 ss screw is solid  and piston height adjustment occurs in the piston itself. 

(https://i.imgur.com/jFC9UPK.png)

Here the stem sheared where it threads into the balance chamber of the Cothran poppet.  Please understand this is not any indicator of lack of robustness of the Cothran parts.  These parts have seen thousands upon thousands of rounds of abuse and in conditions they were never designed for.  I take full credit for the demise of this component.

(https://i.imgur.com/15vwq33.png)

Based on all of my reading around balance valves and tuning, some type of adjustable valve lift is good to have. 

This came in the form of a brass cored MDS hammer with peek striker.  Here are a couple versions of the hammer as well as the crudely made proof of concept/prototype.

(https://i.imgur.com/QrN1ZaL.png)

(https://i.imgur.com/2eoKwWu.png)

(https://i.imgur.com/4lpWe0o.png)

The Bulldog valve stem sits inside a valve body retention nut, the protruding striker is required  due to this.  Adjusting striker protrusion reduces/increases hammer induced valve lift.  Unfortunately this arrangement also varies hammer travel, so the adjustable striker is not influencing valve lift solely in the area of hammer induced lift, but also hammer strike due to increasing/decreasing hammer travel....

Pics of a spare bulldog valve body/retention nut, showing why the protruding stem is required.  Note this particular peek poppet has an oring,  it is for a cobra chamber, another valve configuration developed during my bulldog journey.  IMO 3-5 shot for unregulated, max energy applications, this valve/poppet is hard to beat.  Swap barrels/bolt probes to .357 and to a 2024t3 unregulated tube and it will do a 3 shot tune a little over 380fpe on 3500psi.  Not the most pleasant shooting gun at this tune, but dialed down to 350fpe it is a sweet shooter.

 (https://i.imgur.com/VFXEp1J.jpg)

(https://i.imgur.com/Vckk5pq.jpg)

Later I drilled the hammer side of the valve retention nut with 6 holes and inserted/glued cut sections of 90 duro -118 oring.  the rubber protrudes approximately 1/16 from the nut's face, serving as a hammer buffer.  I tried the bstaley oring buffer, but I cannot get those to stay in place....at some point I will try to get pics of this area....

 













Title: Re: Simplified Balanced Valve
Post by: oldpro on December 27, 2023, 06:07:00 PM
 The alloy holder with all the holes will need to be made of steel or very thick. Ive snapped my fair share of them.
Title: Re: Simplified Balanced Valve
Post by: Rairgunner on December 27, 2023, 06:17:57 PM
Thank you for destroying a very valuable thread with your rant....  >:(....  I see that your "Watched" label is still required, something I will be requesting....

I, Scott, Travis, Lloyd, and many others have built way more custom PCPs, valves and hammers than you could ever hope to achieve, and the relationship between hammer mass and momentum is well documented.... With a conventional valve, if you lighten the hammer (less dwell), you must increase the energy (more spring force and/or travel) to compensate and keep the FPE (area under the lift/dwell curve) unchanged.... The opposite also applies, a heavy hammer can deliver the same FPE with less energy (lift).... The Physics comes into the basic understandings of lift being proportional to energy, while dwell is proportional to momentum (once the energy to crack the valve is subtracted).... As I tried to explain, the flow through the valve, if opened more than 1/4 of its diameter, no longer increases with lift, so for a valve that is ACTUALLY opening that far (easy to measure, but also quite rare in an efficient PCP), all you are left with to change the FPE is a change in dwell with hammer momentum, be that achieved by mass or spring energy.... Just because you happen to disagree is no reason for the rest of us to throw out that valuable piece of information.... or a reason to rant....

While there may be certain valve configurations (balanced, semi-balanced, operating with a hammer or poppet stop, etc.) where the lift does not change (because it cannot), the lack of relationship between lift and dwell as you change hammer mass is caused by those other factors, and your statement, if applied only to those situation, may well be correct.... There is your middle ground.... Accept the fact that you are not always right, or leave the Workshop, please....

Bob
wow. What a clown. First you say no ego allowed then you post this &^^&. You have a huge huge ego problem. This is enough to make me leave this forum and never come back. Absolute nonsense
Title: Re: Simplified Balanced Valve
Post by: avator on December 27, 2023, 06:31:00 PM
Thank you for destroying a very valuable thread with your rant....  >:(....  I see that your "Watched" label is still required, something I will be requesting....

I, Scott, Travis, Lloyd, and many others have built way more custom PCPs, valves and hammers than you could ever hope to achieve, and the relationship between hammer mass and momentum is well documented.... With a conventional valve, if you lighten the hammer (less dwell), you must increase the energy (more spring force and/or travel) to compensate and keep the FPE (area under the lift/dwell curve) unchanged.... The opposite also applies, a heavy hammer can deliver the same FPE with less energy (lift).... The Physics comes into the basic understandings of lift being proportional to energy, while dwell is proportional to momentum (once the energy to crack the valve is subtracted).... As I tried to explain, the flow through the valve, if opened more than 1/4 of its diameter, no longer increases with lift, so for a valve that is ACTUALLY opening that far (easy to measure, but also quite rare in an efficient PCP), all you are left with to change the FPE is a change in dwell with hammer momentum, be that achieved by mass or spring energy.... Just because you happen to disagree is no reason for the rest of us to throw out that valuable piece of information.... or a reason to rant....

While there may be certain valve configurations (balanced, semi-balanced, operating with a hammer or poppet stop, etc.) where the lift does not change (because it cannot), the lack of relationship between lift and dwell as you change hammer mass is caused by those other factors, and your statement, if applied only to those situation, may well be correct.... There is your middle ground.... Accept the fact that you are not always right, or leave the Workshop, please....

Bob
wow. What a clown. First you say no ego allowed then you post this &^^&. You have a huge huge ego problem. This is enough to make me leave this forum and never come back. Absolute nonsense
Or you can just wait until we ban you...  again.
Title: Re: Simplified Balanced Valve
Post by: Motorhead on December 27, 2023, 07:04:47 PM
Thank you for destroying a very valuable thread with your rant....  >:(....  I see that your "Watched" label is still required, something I will be requesting....

I, Scott, Travis, Lloyd, and many others have built way more custom PCPs, valves and hammers than you could ever hope to achieve, and the relationship between hammer mass and momentum is well documented.... With a conventional valve, if you lighten the hammer (less dwell), you must increase the energy (more spring force and/or travel) to compensate and keep the FPE (area under the lift/dwell curve) unchanged.... The opposite also applies, a heavy hammer can deliver the same FPE with less energy (lift).... The Physics comes into the basic understandings of lift being proportional to energy, while dwell is proportional to momentum (once the energy to crack the valve is subtracted).... As I tried to explain, the flow through the valve, if opened more than 1/4 of its diameter, no longer increases with lift, so for a valve that is ACTUALLY opening that far (easy to measure, but also quite rare in an efficient PCP), all you are left with to change the FPE is a change in dwell with hammer momentum, be that achieved by mass or spring energy.... Just because you happen to disagree is no reason for the rest of us to throw out that valuable piece of information.... or a reason to rant....

While there may be certain valve configurations (balanced, semi-balanced, operating with a hammer or poppet stop, etc.) where the lift does not change (because it cannot), the lack of relationship between lift and dwell as you change hammer mass is caused by those other factors, and your statement, if applied only to those situation, may well be correct.... There is your middle ground.... Accept the fact that you are not always right, or leave the Workshop, please....

Bob
wow. What a clown. First you say no ego allowed then you post this &^^&. You have a huge huge ego problem. This is enough to make me leave this forum and never come back. Absolute nonsense
Or you can just wait until we ban you...  again.

PRICELESS
Title: Re: Simplified Balanced Valve
Post by: Rocker1 on December 27, 2023, 07:22:34 PM
 I hit him again gentlemen i wasnt sure if it was him but its kinda obvious. what is he possibly getting out of this. David
Title: Re: Simplified Balanced Valve
Post by: avator on December 27, 2023, 07:25:06 PM
He'll be back. They always do.
Look back in this thread to Bob's post in April.. the one he quoted. Same fool.... different name.
We appreciate our members having patience with the staff while we wack these moles.
Meantime, best to just report and not feed the animals.
Title: Re: Simplified Balanced Valve
Post by: Hoosier Daddy on December 27, 2023, 07:30:32 PM
Un-friggin real.
Rubbish
Title: Re: Simplified Balanced Valve
Post by: only1harry on December 27, 2023, 07:52:41 PM
Un-friggin real.
Rubbish

You are not used to this yet Scott?  ;D   
I hate to say it but unfortunately it's not the first time and won't be the last that someone with major issues joins our forum.  It happens, but until next time we can enjoy our forum and this wonderful thread and advice from some of the most experienced air-gunners in the world.
Title: Re: Simplified Balanced Valve
Post by: triggertreat on December 27, 2023, 09:44:21 PM
I hit him again gentlemen i wasnt sure if it was him but its kinda obvious. what is he possibly getting out of this. David

Thanks David!
Title: Re: Simplified Balanced Valve
Post by: Motorhead on December 27, 2023, 11:20:10 PM
I hit him again gentlemen i wasnt sure if it was him but its kinda obvious. what is he possibly getting out of this. David

The always present EGO STROKE of someone siding with him, that he is right, just or some form of validation.
Sideline judging & commenting w/o actually putting forth the effort doing what is being critiqued to prove of disprove your position ... is just trolling.