Simplified Balanced Valve

[MJP]

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

[rsterne]

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....



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....



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

[rsterne]

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

[PikeP]

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...

[rsterne]

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

[PakProtector]

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

[shorty]

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 ).

[rsterne]

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

[PakProtector]

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

[MJP]

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

[PikeP]

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.

[PikeP]

Marko,

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

[rsterne]

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....



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....

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....

[Motorhead]

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 ...

[Hobbyman2007]

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 .

[rsterne]

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

[rsterne]

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:

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.... 

Bob

[Hobbyman2007]

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 ?

[rsterne]

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....



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

[shorty]

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.