GTA
All Springer/NP/PCP Air Gun Discussion General => Machine Shop Talk & AG Parts Machining => Engineering- Research & Development => Topic started by: sb327 on June 27, 2020, 06:48:38 PM
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While letting my other project ‘simmer’ a bit, I started another. I usually have several projects going at one time.
I eventually want to build a breakover pcp with an exhaust on the valve as close to the pellet as I can get. That puts controlling the valve from behind. I realize Air Force exhausts this way but gets controlled up front.
I came up with this idea. Again, may have been done, not sure.
I bias the valve to open itself with a 1/4” oring seal up front and a 5/16” out back with valve stem sticking out the back.
I have a shuttle in between the two valves that is only sealed on it’s outer edge but not on the valve shaft. This makes a leaky seal between the two chambers it creates.
The valve is held shut by a sear at the rear. The sear is tripped by the trigger with a disconnector. When valve flies open, it moves disconnect and allows sear to fall back down. At this point, the shuttle flies forward due to pressure drop up front and closes valve allowing the sear to catch it.
As the pressure in the two chambers equalizes, a spring moves the shuttle back to an adjustable stop.
It works. I’ve only shot it up to 1200 psi. It appears to be quite violent internally. The sleeve I used to upsize the stainless rod in the center is aluminum. I cross drilled and pinned it, in two spots, with 1/16” drill bit shanks and it breaks them off. That can be sorted.
The good news is, it is amazingly consistent. I had several dup’s on the chrony. Wasn’t expecting that. I am running off a reg and the valve does dispense the same each time, so it makes sense.
Still needs quite a bit of tweaking but the idea works.
The tube is 3/4” id. It’s a piece of 4130 I had on hand.
No drawing yet, just pictures.
Dave
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I don't understand the operation of the valve.... but because you say the operation is "quite violent internally", and that it has broken two 1/16" shear pins, at only 1200 psi.... it sounds like you need a better way to stop the moving parts without them coming to a crashing halt.... I assume this is a "dump valve"?....
Bob
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It is a dump of sorts given the fact it dumps the front chamber. But, the front chamber dimenishes in size, holding the pressure higher, longer by the shuttle, then abruptly closes. So it doesn’t react exactly like a dump in that respect.
I think I have a solution for the ‘violent’ issue. The valve at present has quite a bit of free travel rearward. I am going to limit it some to decrease velocity of the valve.
I am also going to drop down a size on the rear oring seal to have less bias between front and rear.
I will try to sketch something up with notes to help explain my theory here.
Dave
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This should help explain what’s going on inside.
So I know the theory is sound, I just need to experiment with some things. I’m liking this design better than my electric one at this point.
Dave
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OK, I now understand the operation.... It becomes immediately obvious to me that your "firing volume", ie the air on deck and available to create the shot, is basically only that between the valve seat and the shuttle.... That portion is "dumped", just like in a pumper.... In that case, you must look at the volume of that as if it was a pumper.... The small volume severely limits the power and the efficiency.... At a maximum, you should stay less than 1/2 the barrel volume, otherwise the efficiency tanks.... Pumpers typically run from 1/4 -1/3 the barrel volume, and even then, the efficiency is not great.... The consistency of a dump valve, however, is very good.... This valve design will lend itself to low power applications....
Bob
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The front chamber, upon closing, is effectively smaller, due to the shuttle closing in on it. Making it unlike a dump valve. This should, ideally give it a little better efficiency than a pumper.
Unless I’m seeing it wrong.
Dave
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I guess it depends on at what time in the valve cycle the shuttle forces the poppet to close.... If it does it late, at low pressure, then most of the air is dumping, with a large pressure drop.... If it does it early, at higher pressure, then less of the air is dumping, with a smaller pressure drop.... It is pretty simple to do the calculation to show how much air is released, if you know when the shuttle closes the valve.... I still think that your effective plenum size (between the poppet and shuttle) is tiny.... This will make the valve OK for low power, but limit the ability to generate high FPE.... just not enough "air on deck" available....
Bob
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That is why the position of the shuttle is adjustable. It is returned, after firing, to the adjustable stop by the return spring.
As this is my first attempt, just to prove concept, my next version will have more adjustability built in.
I was able to shorten the valve throw and put a shoulder on the part that was getting beat up. I put an oring between the shoulder and the back and this solved the issue. My last regulator adjustment was 1400. I will continue testing up to approx 1800, then I will redo my setup, switching to threaded end caps vs the pinned ones I currently have. Decrease rear portion of valve od. Then continue on up.
At 1410 psi I was shooting a 15.5 gr @ 820 FPS. I would charge the ‘gun’, turn off tank and after firing, the gun, hose, and valve would have 1200 Psi left in it. Recharge to 1410 and shoot again.
Dave
Dave
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I'll be following this with much interest, I see you took my bait! ;)
Hammer-less valves baby, yeaaaa
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Not sure what bait you are referring to. Maybe in my electric valve thread? BTW, I did download your spreadsheet. I will use it further down the road once I get through the mechanical part here. So thanks👍
This one here has my attention right now. I think with some tweaking it will be pretty neat. Different anyway. And I won’t have to cock it. I’m still trying to figure how I am going to connect barrel to action. However I do it, I want the chamber sitting directly in front of valve. So a break, slide or twist seem to be my options. I’m a single shot kinda guy, so no need for speed here.
I think on my electric one, I’ll switch to a regular balanced valve next time I tinker with it.
Dave
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Not sure what bait you are referring to. Maybe in my electric valve thread? BTW, I did download your spreadsheet. I will use it further down the road once I get through the mechanical part here. So thanks👍
This one here has my attention right now. I think with some tweaking it will be pretty neat. Different anyway. And I won’t have to cock it. I’m still trying to figure how I am going to connect barrel to action. However I do it, I want the chamber sitting directly in front of valve. So a break, slide or twist seem to be my options. I’m a single shot kinda guy, so no need for speed here.
I think on my electric one, I’ll switch to a regular balanced valve next time I tinker with it.
Dave
Haha, inception baby, yea! In your electric valve thread yes I implied that you can achieve all that you were attempting pneumatically and with one energy source instead of introducing another, and felt it more elegant to arrive at such a solution. Hope the spreadsheet provides some use on any of your builds in determining optimal parameters.
Don't get me wrong, I am not against the idea of introducing electronically driven functions/operations into a pcp valve, but I feel they should absolutely be more basic when doing so (electronically driven adjustment that's 'coded' to adjust for a particular range, such as a lift limiter that is able to make adjustments on the fly based on logistics of prior outputs, the only electronic parts being the software back end and the hardware front end that controls said adjustment), or simple electronic triggers...and sure possibly a little tap for a near fully balanced valve...but short of that, I still find controlling the majority in a pneumatic way more appealing.
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David, have a look at what I've done.
Perhaps you'll find it helpful.........
https://www.gatewaytoairguns.org/GTA/index.php?topic=138392.msg1391435#msg1391435 (https://www.gatewaytoairguns.org/GTA/index.php?topic=138392.msg1391435#msg1391435)
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Thanks for the link. Interesting design.
I viewed the pictures linked in your first post of that thread and they do not appear to match the conversation within the thread. The pictures are of a pumper and the thread discusses a pcp.
Dave
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Just an update. I’m still working on this when I get time.
15 grandkids + summertime = not much shop time for poppa.
I have most of the platform worked out and most of how I want to put it together. Just a lot of odds and ends now.
It will be a little more exciting when I get to start test/tune.
Dave
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Not sure if it was brought up but maybe you should not quite go with so much differential between your seals . Maybe make the rear one around 7mm or so . It might cut down on the violent spool shift .
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Thanks for the suggestion.
I have changed the design to be neutral front and back. Now I open the valve with a solenoid and the spool closes it. This has taken care of the violence within.
I was able to test the valve function this morning. No projectile, regged to 2000. It appears to function correctly. I still have a few more hours of work before actual testing but I’ll be back at work tomorrow so it gets to sit for a bit.
Thanks again for the input. If the solenoid doesn’t work reliably I will change that back seal to just a tad bigger than front.
Dave
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I have had a couple of days to play with this. I’ve been working out the bugs with the electric solenoid firing it. At first I had the front oring too far engaged to allow my little solenoid to unseat it and have enough travel to open. I now have the center of the oring about .010” inside the front valve and it seems to be working well.
It is shooting around 890 FPS with 18.5 gr. H&N’s.
I need to get into cad and open up my mag well on the grip so it will accept the boost converter and a 9 volt. My capacitor will be in the ‘frame’ tube just forward of my on/off valve.
So far so good.
Dave
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Just an update. Still playing with this as time allows.
I boosted the pressure up to 2800. Was giving just a little over 1000 FPS with 14.3 gr.
I decided I needed more air ‘behind’ the shuttle to keep the pressure on the air in ‘front’ of shuttle. I made a sealed chamber and transfer from it to the main chamber via a block. It helped a bunch. Gained over 200 FPS. Got to here the ‘crack’.
I’ve turned the pressure down to 2400 and adjusted the shuttle forwards. It is back down to the high 900’s now.
Anyway, it’s still getting worked on. Along with other projects.
Dave
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I made an adjustable reg because the China adjustable would blow an oring after minimal adjusting. The tolerance was just way too loose. The one I made is a great deal beefier with more threads engaged on both the Belleville retainer (I made that up, I have no idea what it’s really called) and the body/adjustment threads.
I shot a string of 32 shots today at pressure from 1800 to 2000 reg pressure. Best groupings were at 1900psi/890ish fps.
So here are the numbers for the string
3250 start psi
2400 stop
0.2l bottle
893.6 fps avg.
14.3 gr benji discovery pellet
32 shots
Next time out, I’ll be trying 2100-2300 psi.
Dave
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Away from home for a couple weeks so I only get to ponder for a bit.
From that shot string I had
812.8 total fpe
With a pressure drop of 850 psi from a 12.2ci tank.
If my math is correct, I am getting 1.1 fpe/ci of air. It’s definitely not great but it’s not terrible. I know with higher pressure I have shot it at 1230 with same pellet. So it can make at least some power. I think if these numbers are correct, further testing is warranted. It is a fun shooter.
Let me know if y’all find problems with my math.
Dave
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Excellent work!
I took the liberty of making an animation based on your drawing to illustrate my understanding of the concept:
(https://i.imgur.com/9M9iGfJ.gif)
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Thanks a million. I can muddle through freecad but don’t have the animation ninja skills!
Dave
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Awesome work dave.. I think im all caught up.. Is the solenoid releasing the spool?
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It does since the spool is the same diameter front and back. (Only on the solenoid model). Once the seal breaks open at the pellet end, the rear seal pushes spool full open. Then shuttle brings it back closed.
The shuttle actually has a very tiny bleed hole in it so pressure can equalize after shot cycle. Allowing spool to return to the adjustable stop.
Dave
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3 o-rings in DYNAMIC application of which ALL are subject to the operating pressure. I detect MAJOR sticksion issues having erratic consistency potential.
just sayin ....
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I agree with Scott.... Both the O-rings on the valve are loaded in the direction to increase stiction on firing.... The HPA is pressing them into the same corner that the direction of travel of the valve stem will be dragging them towards, the combination of the two causing a wedging action into that corner.... That is the perfect setup to invite stiction when the valve sits, under pressure, between shots....
(https://hosting.photobucket.com/albums/oo221/rsterne/Parts%20for%20Sale/.highres/O-ring%20Wedging_zpsxxalcs6g.jpg) (https://app.photobucket.com/u/rsterne/a/ec7c3593-4578-4151-a54b-04e884d967df/p/53b28b81-acaa-4c24-9524-72f39430f3f0)
The arrow shows the relative motion of the parts that increases this wedging action, and causes increased stiction problems.... Incidently, for the front O-ring, that HPA behind and under the O-ring will want to blow it off the valve stem when it opens....
Bob
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Thanks for the lesson in stiction ::)
I am aware.
I have shot this design several times and at different pressures. I have yet to lose the front oring. I do know there is a chance to blow it out though. I never claimed this to be a perfect design. It is more a proof of concept and is something I enjoy doing.
Now, back to the stiction. I feel it is a non issue. Because....the length of the shot cycle is not dependent on an external energy source where stiction may rob some of that energy one time and not the next. As long as the shot cycle is started, tripping the sear in the case of my mechanical one, the valve is blown open. The time it stays open is dependent on the length the spool moves (all things being equal for sake of conversation)
Also, the shuttle oring sees pressure from both sides between shots and therefore, again, non issue.
Now, M-head allows I will have erratic consistency potential. Either he did not read my first post in this thread or he is suggesting I am a liar.
Just saying.....
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I think the shuttle o-ring could be left out entirely and just have a tight fit, after all it does not need to be completely airtight.
You can also have a two-part spool to have a more immediate exposure of the breech:
(https://i.imgur.com/S59gSUy.png)
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I have considered that two part spool after seeing your animations in the other thread
You are correct in that the spool can get away without an oring. I really only put it in as an expendable element to keep wear off the spool. It is toleranced to be an easy slider.
Thanks for the excellent suggestion.
This will get a redesign I’m sure and suggestions for improvement are always welcome.
Thanks,
Dave
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I meant to say two part VALVE.
I am also considering attaching the adjustment rod to the spool. I want to see if it will take the place of the spring to move the spool back to position. If that works, I can collapse the front chamber even more. Similar to what you talked about in the Huben as related to keeping that volume small.
I know it does introduce yet another dynamic oring to the equation. Keep in mind though, the one I’m using now is tiny. It was a chore finding an oring that small.
Dave
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Glad you know how stiction works, most do not.... It is the bane of most balanced valve designs....
The time it stays open is dependent on the length the spool moves (all things being equal for sake of conversation)
By "all other things being equal", I assume you mean pressure, pellet weight and fit, barrel length, etc.etc.etc.... Would not the dwell change when you change pellet weight, because the pressure differential across the spool (yellow part) would change at a different rate?.... How do you adjust that?....
Is there something I am missing, or is the volume of HPA available for the shot only that to the left of the spool?.... ie the valve dumps all the HPA in that chamber, but only that air?....
Bob
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I believe that is correct Bob about the pellet weight changing the diff pressure. All things you listed will have an effect on the closing rate of this valve.
You are not missing anything Bob about that being the only available air. It is ‘metered’ so to speak. But a dump valve in the normal definition, it is not.
My reasoning being that at the end of the shot cycle, the volume of that ‘deck’ has been minimized. It collapses so therefore, that ‘metered’ volume is now in the barrel only, behind the pellet. And not the barrel + deck volume. If it closes before Elvis leaves the building of course.
Now I am aware there are losses due to accelerating the mass of spool and valve, as well as friction and obviously the force required to negate the effect of the rear ‘blow open’ part of the valve. But the pressure in chamber B will exert its same pressure, minus losses, upon chamber A.
I can’t recall exactly what I read a typical dump valve’s efficiency to be but in my last configuration of this valve, I was a touch over 1. I think through continued refining, it will do a little better but I’m not too dreamy about that aspect. A little over 1 is fine with me, especially if I don’t have to cock it.
Dave
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Sorry, forgot the ‘how do you adjust that?’
There are two adjustments on this thing.
The position of shuttle before firing. I have a .062” rod that extends in from the back of valve and passes through a small oring. The rearmost part of that hole is threaded 4-40 with a set screw.
The regulator.
So essentially I can change swept volume and operating pressure.
Dave
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What sort of volume is the firing chamber?.... From the drawing it would appear to be quite small.... What sort of FPE are you getting, in what caliber, with what pellet, using what barrel length and pressure?....
Bob
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I checked the cc’s of that chamber early on but can’t remember offhand. Of course I would need to check again at current setting.
I am at work (away from home) so I don’t have my notes. And I’ve built 2 scratch builds since this one so my memory of exacts is fuzzy. Original drawing is not to scale. The tube is 1” od .065 4130.
Replies 18, 19, and 20 give some specifics.
At 1900 psi
890 FPS
14.3 gr
Approximately 23” barrel
22 cal
From reply 18 you can see I made a change to the design that had a dramatic effect. I substantially increased the volume of rear chamber. I consider this my plenum volume.
Increasing plenum volume doesn’t mean we necessarily use all that air, it does have the effect of keeping the air available at a higher pressure. IN CONVENTIONAL VALVES In my case, it means keeping more air pressure on the shuttle which transmits to the air in chamber A. (With losses of course)
I could probably figure the volume of REGULATED air used each shot, based on the numbers I have available at present. That would tell how much air gets ‘metered out’ each shot. Which would ‘very loosely’ translate to the volume in chamber A. But in reality, the chamber does not collapse to zero, so a little would need to be added to that.
I may do that when I get a moment later.
Dave
ETA
from reply 20
812fpe shot string
850psi pressure drop
12.2 ci bottle
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So we're looking at 25 FPE from 1900 psi, with a typical airgun barrel length.... Not too shabby, accompanied with efficiency in the 1.14 range, for a unique concept that self cocks.... Well done!.... 8)
Bob
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I’m only part way to my goal.
To me, only accurate guns are interesting.
My favorite aspect of this valve is it’s ability to meter air out in a consistent manner. I have never shot as many dups across a chrony in all my 50 years.
I still have hurdles. I like the inline valve but it is a pain to ‘properly’ load. The best alternative seems to be the af style sliding breech. I want my projectile to be seated in the lands on takeoff.
Right now, I’m using a sliding barrel that use linear bearings inside that cf tube. I’m not expecting accuracy, it was just an easy way to test valve.
Like I said, lot more to do on this one.
Dave
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I'll agree that it's a very smart concept, there does seem to be merit in the idea of actively forcing the valve to shut in order to gain efficiency.
One wonders if the same thing could be done with more conventional poppet valves:
(https://i.imgur.com/tn1leGG.png)
The benefit would be that you could use a strong hammer to knock the valve open quickly, without the corresponding long dwell time one expects in a conventional setup.
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I don’t see why it wouldn’t help to speed up valve closing. I’d have to study what the effects would be on the shot itself.
While you got that animation machine on fast draw there, I’ve got a ‘floating balance chamber’ valve design that I have proven to work. It’s in another thread. You might want to play with it.
I’ll get a link
No worries if you don’t. It is Thanksgiving after all.
Dave
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Here’s the link
https://www.gatewaytoairguns.org/GTA/index.php?topic=178164.0 (https://www.gatewaytoairguns.org/GTA/index.php?topic=178164.0)
I reversed the design of the balance chamber from my sketch. The poppet is the outer part of the chamber and the back is a piston.
Dave
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This is a great idea however my main concern would be that the exhaust o-ring may wear out quickly with use. Also the fact that the seer is what's keeping the valve shut would make it hard to use a more traditional delrin poppet as it'd need to apply a lot of pressure.
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There are design elements that I have done to this that are not outright talked about within the thread. If you will notice, there wasn’t much discussion about this after the first go round for a couple of months of me posting design changes so I didn’t get very detailed.
In the electric version, it holds itself closed. Truly ‘balanced’. It relies on an external force to start cycle. My design limits the amount of engagement of that front oring (I describe this in the thread) for the purpose of making that external force as minimal as possible. This design has other positive benefits as well. I’ll sketch that up later.
Do you have a solution to your concern?
Dave
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I think the shuttle o-ring could be left out entirely and just have a tight fit, after all it does not need to be completely airtight.
You can also have a two-part spool to have a more immediate exposure of the breech:
(https://i.imgur.com/S59gSUy.png)
Jacks design here with the two piece poppet is the best way in my opinion. Air pressure can hold the valve closed on the seat and the seer only needs to hold the stem from blowing back, that requires a lot less precision and is less susceptible to wear.
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Ive definitely considered that solution. I would need to come up with a snazzy solution to put it all together within that small space and it still have the strength to handle the ‘jerk’ when you light it off.
It will certainly be on my list to try if that oring proves troublesome.
I need to draw out how I have it now, it seems to be working fine. I’ve not had to change it yet in its current setup.
If I go with the floating poppet, I significantly increase the pressure my sear sees. Which translates to wear and increase trigger pull. (Which can be dealt with
Dave
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Here is a sketch (roughly) of what is working
Dave
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If I go with the floating poppet, I significantly increase the pressure my sear sees. Which translates to wear and increase trigger pull. (Which can be dealt with
Not really, the area being acted on by the pressure in the direction of the sear is the difference between diameters A and B:
(https://i.imgur.com/LkGDSRQ.png)
You can still design it to be only slightly unbalanced.
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I hadn't thought about the increased pressure on the seer but that's a very good point. With no opposing pressure from the exhaust valve the seer would take the full weight of the 5/16 seal.
I am not a machinist by any means so I can't exactly advise you on the best way to actually construct such a valve either. My only idea would be to make the poppet a tube so the stem can pass through with an o-ring and and the edge of the tube seals on the seat, something like a nut threaded onto the end of the stem to catch the poppet as it slid back.
My drawing skills are maybe worse than my machining skills but here's my idea, the other end of the stem could be threaded to screw into the rest of the valve stem/shuttle guide once the the poppet was installed.
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If I go with the floating poppet, I significantly increase the pressure my sear sees. Which translates to wear and increase trigger pull. (Which can be dealt with
Not really, the area being acted on by the pressure in the direction of the sear is the difference between diameters A and B:
(https://i.imgur.com/LkGDSRQ.png)
You can still design it to be only slightly unbalanced.
O-ring A needs to be fairly small to fit within the poppet which limits the size of B, that may or may not be an issue depending on how the other dimensions work out.
Wouldn't it also depend if the o-ring was grooved into the poppet or the stem? If grooved into the poppet itself I don't see how it'll apply forward pressure on the rest of the stem. You'd have to have the stem OD grooved rather than than the poppet ID if I'm understanding right.
Edit: after thinking about it I realize you mean the pressure is just the difference between the diameters assuming the o-rings aren't in the stem OD, though I think my first point still stands. I also think for the o-ring in the poppet, grooving the stem is far easier than trying to do an ID groove in a small hole though.
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To be able to take advantage of subtracting a from b, it would need a vent. (See terrible markup I did)
Again, we are talking about a small area for such detail. Doable but with some difficulty.
Dave
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And shuttle would need to push on stem to get it to reach sear engagement point
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And shuttle would need to push on stem to get it to reach sear engagement point
For initial filling you would either need to use a high pressure source to "shock" the shuttle into cocking the mechanism or to cock it manually.
Again, we are talking about a small area for such detail. Doable but with some difficulty.
I think it could be reconfigured for ease of manufacture in a way that would also vent the space (though the latter is not strictly necessary for the effect), building on what CableStop suggested:
(https://i.imgur.com/zWQLP2g.png)
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That looks a little more achievable.
I also want to figure out a way to move the shuttle back to position without using the big spring up front. I am considering TRYING to attach the adjusting rod (.062”) to the shuttle and have it float to the outside. That would make a tiny piston of it pushing it to an adjustable external stop. I may be pipe dreaming on that though.
Dave
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This concept is getting better and better.... Don't have anything to add, but am fascinated with how this valve is developing. Hammerless valve=shorter action; shorter action=more air volume/less bulky gun (or a longer barrel in the same platform).
Watching,
Jesse
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And shuttle would need to push on stem to get it to reach sear engagement point
Cutting a step into the stem so it engages the shuttle first is the easiest way I can think of. Unfortunately it doesn't help the initial cocking issue at all.
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This has been nagging me the past few days but I think I came up with a concept that solves all the problems in theory. Only downside is it's longer than the original design.
Basically take the sliding valve stem and use it to cock an external hammer that slides rearward Airforce style, the hammer cracks the valve so the only pressure on the seer is from the hammer spring.
Have a balance chamber in the back that pressurizes and pushes the valve closes while cocking the hammer, the springs are just for keeping things in place when there is no pressure in the gun so they can be fairly light.
Edit: On further thinking you may be able to put a true balancing chamber around the poppet and valve spring. The rear chamber is more of an imbalance chamber because it doesn't equalize on both sides. It probably does need a vent in the middle chamber to deal with oring seepage. So you either have to put a second balancing port in the stem and balance the rear piston (maybe necessary anyway) or just a hole to ATM in the side of that chamber.
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Since it's dead at work and another thread was talking about short valves. Here's an iteration that lead to the hammer design. This uses a piston attached to the valve stem with two different size faces and a vent to allow the valve to close without pressure drop. The sizing of the poppet is important. The walls of the poppet tube need to be as thin as possible and the inner portion needs to be sized appropriately for the small face of the piston.
The small face has enough force to crack the outer poppet tube off the seat which relieves the forward pressure on the combined poppet assembly. The small piston can then continue back until the vent balances the rear chamber, because of the larger surface area it can push the whole valve assembly closed again and the seer can engage. Again, springs are just for when the guns empty.
I always forget to draw the transfer port, just imagine it where it is on the other valve somewhere in the front chamber.
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I believe the back piston (closing piston) would need to be acted on, only on the back. Through the vent. Otherwise it would simply be equalized.
I believe for it to work as intended, you would need to make a couple of changes. The red arrow would vent to atm. The extension of the center piston would keep plenum pressure off of front of rear piston.
This would be very close to one of Jacks animations that I’m going to try sometime.
Dave
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On a slight tangent, I'm currently in the process of rebuilding a Duk Il King Hunting Master (https://www.gatewaytoairguns.org/GTA/index.php?topic=180527.0).
Like many Korean guns it's a notorious air hog. I never fired this particular one as it came to me in a non-firing state but here is some published data for a similar model (https://www.gatewaytoairguns.org/GTA/index.php?topic=143635.0):
3000 psi with JSB Monster 25.39 gr, Max 71 fpe
1128, 1113, 1100, 1079, 1064, 1047, 1031, 797, 1004, 992, 978, 961, 947, 938, 926, 911, 897, 883
Impressive power that tails of fairly rapidly, I'm looking to flatten that curve.
I am wondering if the best way to go about it would be to include a shuttle that knocks the poppet closed in order to reduce the valve dwell.
This is what I have in mind to scale:
(https://i.imgur.com/14A0S1o.gif)
The major issue is that it isn't really adjustable, so it would basically be a guess as to what "plenum" volume would be adequate.
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Quite similar to my design in that it uses a shuttle in the plenum.
An obvious way to flatten and have adjustable would be to regulate. I’m sure you thought of that though.
Is the hammer strike adjustable?
Dave
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Quite similar to my design in that it uses a shuttle in the plenum.
That was the inspiration, hence it being posted here ;)
An obvious way to flatten and have adjustable would be to regulate. I’m sure you thought of that though.
Sure, but it's too conventional a solution...
Is the hammer strike adjustable?
It does a have a high/low power setting, my understanding is that the way the low power works is to have a synthetic buffer placed in the path of the hammer to limit its travel after impacting with the valve stem.
The way it's made prevents much being done behind the action due to the stock attachment, which is why I'm looking at alternative ways to get around this.
In my mind I really like the idea of an "assisted shut-off" because at least in theory, it offers the option of air economy without compromising power.
If you weaken the hammer strike, you're obviously going to use less air but the valve will open slower and you will have less velocity.
On the other hand with the same hammer strike but a mechanism to quickly re-close the poppet, you should have a valve that opens quickly to give the projectile a good acceleration but also shuts off rapidly to prevent air being wasted after the pellet has left the muzzle.
One possible consequence of shunting the poppet closed could be to relaunch the hammer rearwards and cause the valve to flutter...
I might just give it a go, not too much machining involved.
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I misunderstood. I thought the animation was already in the gun from factory.
I think it is definitely worth a shot to try. In my mind, the theory is sound.
On the plenum volume.
Obviously you can’t think conventional valve when you start thinking of a ‘collapsing’ plenum.
You have to see a pressure drop for it to have its intended result (valve close or assist) So, the smaller the volume initially, the faster and more pronounced the effect. And vice verse
The smaller the diameter of the ‘shuttle’, the more distance the shuttle will move with same air use.
Since plenum collapses, you don’t have to start with a conventional valve size plenum to have same effect.
Adjustable? I can’t think of a way, externally. I’ll study some though.
Dave
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On reflection I would probably start with something closer to this:
(https://i.imgur.com/daMIPhx.png)
Adjustable? I can’t think of a way, externally. I’ll study some though.
I can't think of a feasible manner to do this without taking it apart.
The variable I would introduce is an adjustable port in the shuttle that would regulate the refill rate of the plenum.
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Or change the shuttle position relative to poppet.
I’m not sure how this type of valve will effect shot string with a declining pressure though. I never checked it on mine to see. I just figured it would decline as well due to the nature of ‘dispensing’ a set VOLUME of air. Reducing the pressure of that volume would obviously have an effect. (Which is what I want)
Of course your design introduces a variable of a spring between the poppet and shuttle. That may have some effect to level the string without adding a reg.
Dave
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Wouldn't the shuttle spring need to go around the poppet instead of on top. Maybe I misunderstand the layout but if the spring is between the poppet and the shuttle it'll sort of cancel itself out.
If it seats around the poppet and only acts on the shuttle then it will curve the shot string.
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I got a little bit done on my next iteration/application of this valve.
I have confidence in the theory because it’s been proven in two applications.
So now I’m changing the arrangement of things up just a bit. It won’t be inline. I’m going to use a rotating breech/transfer like the Thomas rifle. It affords the most capable way of loading at the same time keeping overall length vs barrel length to a manageable ratio. (Not counting bullpups in this thought process)
I’m starting with a big chunk of 6061 and will cut away what’s not needed. Bottle will screw into a plenum area and feed valve above it. The barrel will be just above that.
Valve will be controlled mechanically on front of block. I’ll have to figure out where grip will go.
Anyway, a couple of pics. Not much done cuz I’ve been messing with my newly acquired Texan too. That thing is a beast.
Dave
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looking good.. if the valve works well , all the ergonomics will fall into place after
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Just some progress pics. The big block is starting to shed a little weight. Still pretty bulky. I did the bottom of transfer/breech but not the top yet. Lot left to do.
Dave
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that looks greeat.. the top block that rides that stud is the swing breech right ?
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Yeah. I’m gonna run a shim between it and the body to prevent galling.
Dave
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thrust bearing make it smooth as glass ;D
https://www.bocabearings.com/products/nta512-21293?utm_source=google&utm_medium=cpc&scid=scplp21293&sc_intid=21293&gclid=Cj0KCQiA8dH-BRD_ARIsAC24umaADQ6AU7pvKSr27cFAXznx5siT_mBF8Q8IZVbNTblnqd3unqRjdmYaAs9vEALw_wcB (https://www.bocabearings.com/products/nta512-21293?utm_source=google&utm_medium=cpc&scid=scplp21293&sc_intid=21293&gclid=Cj0KCQiA8dH-BRD_ARIsAC24umaADQ6AU7pvKSr27cFAXznx5siT_mBF8Q8IZVbNTblnqd3unqRjdmYaAs9vEALw_wcB)
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That is a big block!
I’m going to use a rotating breech/transfer like the Thomas rifle.
Had never heard of this, is this (https://www.gatewaytoairguns.org/GTA/index.php?action=dlattach;topic=159427.0;attach=275383;image) what it looks like? (from another thread (https://www.gatewaytoairguns.org/GTA/index.php?topic=159427.msg155770860#msg155770860))
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Yeah, that’s the basic idea. Not sure what problems will follow but I won’t know till I try. I have a few thoughts up my sleeve if sealing is an issue. Since this is .22 on regged air, my forces should be kept reasonable.
Dave
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An interesting breech for an interesting valve; a fitting combination. Looking good;
Jesse
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Just some more progress pics. Got the barrel clamp/rail done. It kinda gives an idea of how much will get shaved from the sides of the ‘chunk’.
Trimmed the swing breech down a bit. It still has some profiling that needs done and the tp drilled.
Dave
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everything looks awesome Dave.. dont worry about losing the baby fat till everything is functioning , god forbid a slight redesign is needed and the material isnt there anymore.. .. How many fpe are you predicting ? whats the reg setting ?
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Not going for power as much as accuracy on this one. Obviously it’s gonna be a slug gun cuz all I have are old .22 barrels. I’ll probably stay around 2000+\- psi.
Like I mentioned before, my first version of this valve gave a lot of duplicates on the chrony. I’m hoping this version will be just as consistent.
Dave
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The one thing people may underestimate ( as I did with Rons SSP initially ) is the ability for the shuttle to maintain shot pressure as the air exits the valve .... This valve is really quite elegant in the amount it accomplishes per shot cycle..
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Thank you for taking the time to understand the valve.
A couple of concerns I will address that have been mentioned.
Oring blowout.... I didn’t have any issues on my mechanical or electrical versions. I believe this is mostly due to the fact it is a 1/4” od x 1/16” cs. 90 duro. So it has to stretch a very large amount PROPORTIONALLY to get loose, as compared to a larger oring.
Breakout friction (stiction) of orings effecting consistency......bo friction is gone once the oring moves and starts to slide, this is BEFORE the shot cycle starts. This valve is open/close, once the seal is broken on the throat, the valve fully opens by stem end effect. MEANING... it does not rely on a specific amount of external energy (hammer strike) to control any duration of the shot cycle.
bo friction does not effect the shuttle oring due to it being in a pressure neutral position when shot cycle starts.
It’s not a perfect valve though. It relies heavily on a consistent regulator. That is a concern. And one reason for me building my own reg.
There is one area of this valve I’ve not tested much and that is how it performs at lower velocities.
Thanks again
Dave
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So I gave this (https://www.gatewaytoairguns.org/GTA/index.php?topic=175248.msg156057171#msg156057171) a go and oh boy, the poppet did not enjoy it one bit...
(https://i.imgur.com/wT0l2rV.jpg)
I've guessing it was due to fail anyway, most synthetic parts on the rifle were crumbling away... but still.
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The shuttle doesn’t seem damaged. Poppet must have been degraded. What gun is this in?
Dave
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It's the Korean Hunting Master I mentioned here (https://www.gatewaytoairguns.org/GTA/index.php?topic=175248.msg156057073#msg156057073), all the synthetic material on it was in a very poor state so I'm not surprised.
I made another poppet out of acetal but now the thing won't seal...
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It's the Korean Hunting Master I mentioned here (https://www.gatewaytoairguns.org/GTA/index.php?topic=175248.msg156057073#msg156057073), all the synthetic material on it was in a very poor state so I'm not surprised.
I made another poppet out of acetal but now the thing won't seal...
i put the valve in the lathe chuck , with the stem facing the tailstock.. then lock the tailstock to the stem , and lock the tailstock into place.. spin up to 600, then i retract the tailstock till theres a constant pressure between the delrin poppet and the seat of the valve .. this is generally .2 mm or so , not much to make friction..then i let itt run 30 seconds .. I forgot to mention , i oil the seat before doing this.
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Hey Bob,
I was reading through old posts and ran across this https://www.gatewaytoairguns.org/GTA/index.php?topic=73506.0 (https://www.gatewaytoairguns.org/GTA/index.php?topic=73506.0)
I see a lot of similarity between your idea in that thread and what I’ve got going on here. Although your idea was for different intent than mine initially, they are similar.
Dave
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Hey Bob,
I was reading through old posts and ran across this https://www.gatewaytoairguns.org/GTA/index.php?topic=73506.0 (https://www.gatewaytoairguns.org/GTA/index.php?topic=73506.0)
This is basically what I'm working on actually. Mine is a stand alone plenum for now though, not integrated into the valve. I don't see how the piston here resets, mine uses a double ended piston with seals at each. It's also proving difficult to make the rear seal reliably and is cumbersome to regulate. If there's a better way to do it I'd like to know.
The regulated side of this valve must have a lower pressure than the reservoir so I don't see what pushes it back. I could easily be missing something I'm more of a visual learner as they say.
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Sorry about kind of hijacking the thread but here's a basic drawing of the design I was talking about just for reference. It's completely air driven and you can see how the different piston diameters allow for the more force on the plenum side than the reservoir side when the valve is closed.
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Yes, David, the concept is similar.... and I abandoned it because of the likelihood of the extreme deceleration force on the piston destroying things.... ::)
I think the poppet Jack destroyed may be an example?.... ???
Bob
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Bob,
Maybe since I’m not running a conventional poppet is why I’m not having that issue. The only destruction problem I had was at the blow open piston end and have since got that under control.
Cablestop,
I’m not sure on your last drawing where the flow occurs to really speak to it. I’m not clear on intake, exhaust, etc.
And I don’t mind thread derail, it’s all just something to discuss.
Dave
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Basically the vent allows the plenum area in front of the valve to fill to reservoir pressure pushing the piston away from the valve. The space between the two o-rings is ambient and needs a vent to ATM somewhere. Then when the valve opens and pressure drops the reservoir pressure on the smaller rear piston drives it towards the valve again to shrink the plenum and drive out the air. It's an evolution of the collapsing plenum idea from my other thread.
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As long as what you are doing works, carry on.... I was merely suggesting that could have been the cause of Jack's exploded poppet.... The shuttle ends up being a hammer (albeit a light one), driven at extremely high speed.... If it travels 1/2" in 1 mSec., then it has a terminal velocity of about 1000 fps.... Multiply that by the mass, and you can see how much that is.... That energy/momentum must be dissipated when it stops at the end of its travel.... The more sudden the deceleration, the higher the resulting force required....
Bob
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I was merely suggesting that could have been the cause of Jack's exploded poppet
It was definitely the cause, but the caveat is that it was an old part and like the rest of the synthetic parts on this particular rifle, particularly prone to failure.
In spite of several attempts I still haven't managed to make a new poppet that seals properly, I never seem to have luck with the tapered variety. The flat on a raised lip seat seem to work better.
I tried "lapping" it as Rob suggested further up but no joy. Perhaps I'm not taking it to a high enough pressure, but I figured if it doesn't seal completely at 1000 psi then there's no point in pumping further.
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As long as what you are doing works, carry on.... I was merely suggesting that could have been the cause of Jack's exploded poppet.... The shuttle ends up being a hammer (albeit a light one), driven at extremely high speed.... If it travels 1/2" in 1 mSec., then it has a terminal velocity of about 1000 fps.... Multiply that by the mass, and you can see how much that is.... That energy/momentum must be dissipated when it stops at the end of its travel.... The more sudden the deceleration, the higher the resulting force required....
Bob
Is that milli or micro seconds?
Dave
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Cablestop,
As drawn, res to right, the pressure at valve will have to drop extremely low before piston starts to move. You can achieve the same ‘self reset’ feature by making the res end of piston just slightly smaller than valve side. See the top drawing. This would cause piston to move with less pressure drop.
If you are fine with spring reset, it will move with the least amount of pressure drop. Bottom drawing.
Unless this piston interacts with valve some how or limits amount of air somehow, it would AT BEST only act as an open plenum.
Dave
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Velocity = distance over time.... 0.5" / 0.001 sec. = 500 in/sec.... Oops, divide by 12 in/ft.... Average velocity = 42 fps, so the peak velocity is about twice that (84 fps).... However, at one point you mentioned a travel of over 2", which would multiply that by 4.... My point is that you have a LOT of energy in that shuttle, and it has a lot of momentum.... If you stop that in 0.010", the forces is astronomical.... Even if it takes 0.050" to stop, that means 10 X the force required to slow it than to accelerate it in 1/2"....
Not much wonder Jack's poppet exploded.... and exactly why I never pursued my idea from that thread from 6 years ago....
Bob
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Not trying to argue, but
6061 aluminum weighs .0975 lbs. per ci
My piston is .800” od. Spool shaped. Let’s guess at equivalent to .5” long solid.
So, that’s 0.2531 ci x .0975= 0.0245 lbs.
.0245lbs. = 171.5 grains
That’s equivalent to a 171.5gr bullet traveling @ 85 FPS. When I put that into the calculator, I get 2.8 fpe.
That doesn’t seem astronomical, unless I missed something. I had to guesstimate at the piston weight because I’m away from home and can’t measure directly. I cant get 2” of stroke on mine because the cylinder is only 2” long and piston is approximately .8” long.
I’m really trying to understand why I had no issues with mine. I did run a small oring between my spool and where it pushes on valve. And I had a spring pushing back on the spool.
If I needed to release more air (increase power) and keep max shuttle speed slower, I could move up a size on the cylinder id.
Dave
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Take that 2.8 FPE and stop it in 0.010" and see what force that requires.... 2.8 / (0.010/12) = 3360 lbs.... Now apply that force to the contact area of whatever the shuttle/piston hits and see what the pressure is.... :o
This is the same reason that a bolt handle that is perfectly capable of retaining a bolt when a PCP is fired providing it is locked down, can shear off if the bolt is not locked down when the gun is fired.... There is a thread about that in "The Workshop", with a Video by Lloyd.... Think driving a nail into a board with a hammer, compared to trying to push it in with the same hammer.... Impacts have a way of destroying things very quickly.... and the less "give" (or compression) there is in what the object in motion hits, the higher the force....
Like I said, if it is working for you, great.... It didn't work for Jack.... and may not even with "new" parts of the same dimensions and materials.... Put a Belleville washer stack in there to absorb the momentum of the shuttle, stopping it over a larger distance, and you lower the impact force.... Put an O-ring bumper on the end of the poppet, where the shuttle hits, and it might survive.... Having a metal shuttle crashing into a plastic poppet CAN shatter the poppet.... I'm just trying to explain why.... Taken to extremes, with metal to metal contact, it might even shear valve screws or threads.... something to think about.... ???
Bob
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Taken to extremes, with metal to metal contact, it might even shear valve screws or threads.... something to think about.
A very valid point, it's the same dynamic we see in a Quick Exhaust Valve. In high performance applications, you definitely need some sort of bumper to mitigate the impact from the piston when it reaches the end of its travel. I will try and give my setup another go this evening to see what sort of damage one can expect.
At this point it might be worth trying it out as a single component as first suggested, now that I need to make another poppet anyway:
(https://i.imgur.com/tn1leGG.png)
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In Dave's design, could the rear piston that provides opening force also be working as a damper to slow the valve/shuttle as it closes?
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I have things going on that definitely must be absorbing this energy. I think the fact that the shuttle picks up the valve and seats it must use a lot of it. And the oring. And the spring.
I may try making my spool from delrin to drop some weight from it though just for safety sake.
Dave
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If there is some mechanism occurring that slows the shuttle/piston slowly, then the force is much reduced.... If instead of 0.010", it slows over 0.100", the force required drops to 336 lbs....
Bob
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I was able to get a little done on last days off in spite of very little shop time.
I got the shuttle made, most of the trigger/disconnect, grip frame and got the swing block functional. (Tp drilled and oring groove cut)
The shuttle rods work like I had hoped. They return the shuttle to adjustable stops. The valve blows open like it should but I need to make a stronger spring for the sear to catch it. I had the same issue with my first all mechanical setup.
It’s taking some shape, just not a very pretty one. I cut a piece of cardboard to cover up some of the ugly and if I squint hard I can see it with a forestock. :o
Couple of pics
Dave
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looks good to me.. soo long as it works as designed
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That's some nice machining work.
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Thanks.
I’ll be home in a couple days so hopefully get to see some progress on this one.
I may print a 1911 style grip for it.
Main thing will be getting all functional parts done and tested. And maybe some more fat trimming on that big chunk.
I may use a trick from the fashion gurus. Something like paint it black and machine a stripe long ways. Give it that slimming appearance......lol
Dave
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Finally got back to this the last few days. Aesthetically it’s better but still ugly as homemade soap to me. But....she functions great and is really fun to shoot.
Part of this project was making a bullet mold. I made it off of Bob’s design (thanks again Bob). It weighs in at 43.5 gr.
I’ve got the gun tuned to shoot this at about 800fps.
It doesn’t do to bad for an old .22 take off barrel. A little over 1/2” group at 50.
The heavier spring took care of the resetting issue I had before. Seems to be rocking along pretty good now.
Plenty left to do on this one but overall am liking it.
Dave
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that looks awesome , lots of material removal on that block took place.. can you feel the trigger reset after the shot ?
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When you pull the trigger, you feel nothing but a regular trigger pull. The shot cycles with no interaction with the trigger due to the fact the valve (being held by sear) trips the disconnector, thereby releasing the trigger from the sear. Once fired however, the disconnector resets with a light ‘click’, ready for the next shot cycle, upon releasing trigger.
As far as the shuttle coming back into place, I don’t notice it at all. It all happens fast.
Kind of a long way of explaining that...lol.
Dave
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Nice job, David.... 8)
Bob
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Coming along nicely! It would be interesting to see some shot string data to be able to compare the performance to more conventional setups.
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Thank you guys for the compliments. I appreciate the feedback.
I’ll definitely get the shot data as time allows.
I may try to make a lighter slug based on Bobs boattail design. I would like to get up to 900fps or so without pushing too hard. I’ve had this up to 65 fpe with current BBT. 43.5gr @ 826fps.
Maybe in the 35 gr range would be about right. ?
Making molds is a pain in the backside but saves a bunch of money in the long run. Plus, right now, not many molds in stock to choose from.
Dave
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The 30 gr. BBT would probably work OK for you.... Your FPE will likely drop a bit with a lighter slug....
(https://noebulletmolds.com/site/wp-content/uploads/2019/01/220-30-HP_BT_BK1_.jpg)
or you could make something similar but a bit longer....
Bob
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Very cool... :D
Jesse
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The 30 gr. BBT would probably work OK for you.... Your FPE will likely drop a bit with a lighter slug....
(https://noebulletmolds.com/site/wp-content/uploads/2019/01/220-30-HP_BT_BK1_.jpg)
or you could make something similar but a bit longer....
Bob
That looks good to me Bob. I may stretch it just a touch. I’m not concerned about power at all. I really just referenced the power it’s making at present as kind of a idea what it’s doing (with reasonable pressure) now. My goal being an accurate slug at 900-950. (Not really sure why, just what I want.... lol)
Thanks again, I appreciate it.
Dave