GTA
All Springer/NP/PCP Air Gun Discussion General => Machine Shop Talk & AG Parts Machining => Engineering- Research & Development => Topic started by: NCmountainShooter on August 04, 2014, 04:49:05 PM
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To preface, I'm trying to think of different ways to feed an axial air system with in-line bore diameter porting. It would be a regulated system to remove the need for varying dwell to pressure amounts.
That being said, has anyone ever used a rotating cylinder to open and close the valve instead of the more typical axially oriented poppet? Picture a solid vertical cylinder with a hole through it horizontally and put that up against a semicircular concave port. In starting position the hole through the cylinder is orthogonal to the port and rotated 90 degrees it is in line with the port. The cylinder could be powered by a hammer strike 90 degrees to the cylindrical surface, likely hitting a flat protrusion at the bottom near the edge of the cylinder. If a spring gives a counter force, the cylinder would rotate a certain amount then rotate back shut. Timing the dwell would depend on how fast the cylinder spins open and shut. Another mechanism for powering the cylinder would preload a certain amount of rotational tension on a trigger mechanism such that the release of the catch would let the cylinder spin 180 degrees open and shut to block the hole again. This could be externally controlled if the spring tension were connected to a dial. This would require rotational springs rather than the more typical length oriented springs.
My main mental conundrum would be how to seal between the cylinder and the port. An o-ring or possibly tight fit plastic rim could possibly work. It would just need to be able to withstand the friction from the spinning cylinder.
If this is completely non-feasible, please pardon my mechanical daydreaming.
Chris
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I find written descriptions of such mechanisms almost impossible to understand.... A diagram, showing the parts in various stages of firing, would allow my brain to wrap around it.... at least I think it would....
Bob
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In such Rotary or Spool type Valves, FRICTION between the drum/spool and body is super critical effecting the rotational or sliding speed it can and will move with any know & fixed amount of spring effort exerted.
Making it able to seal means a tight tolerance between parts ... which equals DRAG being created by VERY CLOSE fitted parts has this fit changing with temperature as well.
Have worked extensively with rotary drum and flat gillitine type valves in small 2 stroke race engines, there tricky buisness when asked to move at very high speed .. yet alone stop and start obtaining a very high surface speed to open/ close the intake aperture quickly then abruptly stop.
Honestly DON'T see it practical for an air gun valve ... not at all !!
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Thanks Motorhead! I didn't even know the name for the type of valve. I thought that might be tricky. Unless someone else pipes up with suggestions, I'll file this one in the no-go folder.
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Chris,
The method you describe can be made to work at low pressures, but at 2000+ psi, quite doubtful. Anything that will seal and hold 2000 psi will experience a cheese grater affect as it is rotated across the port under pressure. There might be some ultra precision ceramic materials with zero clearances that would work, but I have not seen them.
But, I do have a little shut-off valve that fits on top of a paintball bottle that opens and closes with a 90 degree twist, similar to a ball valve. It seals with an o-ring that is on the out-put side of the valve so that it isn't forced into the moving part of the valve as the stem is rotated. The actual flow passage is only about .050", and that helps it to work properly.
There are other methods of sealing a "valve" in a PCP, though.
Lloyd
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What are the other valve types that would work in line with the bore?
I'm trying to eliminate any obstruction to flow, like the stem from a poppet. What about something as simple as a ball valve? Use a hollow cylindrical hammer, through which the air would pass, to impact a ball or some other obstructing device that is only being pressed forward by a spring. The hammer would need to have a stop to keep it form following the ball and obstructing flow. It would still need to be a regulated system, but I don't see that as a problem with today's technology.
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Balanced chamber quick exhaust valve that uses a spring to upest the ballance. pressur released fom backside of piston allows piston to move rearward thus removing poppet from flow path. this allows contained pressure to evacuate bore obstruction violently. work s like a dump valve and will require a shut off from reservoir during the cycle.
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(http://i226.photobucket.com/albums/dd79/loyd500/Patent-pg-8_zps4e3cc365.jpg) (http://s226.photobucket.com/user/loyd500/media/Patent-pg-8_zps4e3cc365.jpg.html)
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Too small for my old eyes.... *sigh*....
Bob
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Sorry Bob, found out I couldn't read it either, LOL.
Here is a "viewing friendly" version. Annular face seal. Even though it isn't a straight in-line flow-through design, it dumps radially 360 degrees right into the barrel.
Lloyd-ss
(http://i226.photobucket.com/albums/dd79/loyd500/Prototypes/1-Crosssectionwithflow_zpsd26a2c99.jpg) (http://s226.photobucket.com/user/loyd500/media/Prototypes/1-Crosssectionwithflow_zpsd26a2c99.jpg.html)
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Got it!.... 150 psi air moves the tubular shuttle open or closed (so must be timed for required dwell).... Amount of flow can be controlled by the position of the maroon inner plunger relative to the throat.... right down to virtually nothing.... Would work great, once tuned, for a regulated gun, would need some kind of timing adjustment for non-regulated....
Like the Condor, the loading port would have to be to the left of the valve, in line with the barrel.... and like the Condor, it will have a lot of volume downstream of the valve seat.... Better, more unrestricted flow (after all, the valve can be made larger than boresize with no penalty).... but a slight pressure drop depending on the relationship between the reservoir and the downstream volume....
This has made me wonder.... What, other than higher opening force (which the balanced design eliminates).... is the downside of running larger than boresize valving and porting in a conventional PCP?....
Bob
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Got it!.... 150 psi air moves the tubular shuttle open or closed (so must be timed for required dwell).... Amount of flow can be controlled by the position of the maroon inner plunger relative to the throat.... right down to virtually nothing.... Would work great, once tuned, for a regulated gun, would need some kind of timing adjustment for non-regulated....
Like the Condor, the loading port would have to be to the left of the valve, in line with the barrel.... and like the Condor, it will have a lot of volume downstream of the valve seat.... Better, more unrestricted flow (after all, the valve can be made larger than boresize with no penalty).... but a slight pressure drop depending on the relationship between the reservoir and the downstream volume....
This has made me wonder.... What, other than higher opening force (which the balanced design eliminates).... is the downside of running larger than boresize valving and porting in a conventional PCP?....
Bob
The bore or larger sizing eliminated sonic choking does it not?
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Sorry Bob, found out I couldn't read it either, LOL.
Here is a "viewing friendly" version. Annular face seal. Even though it isn't a straight in-line flow-through design, it dumps radially 360 degrees right into the barrel.
Lloyd-ss
(http://i226.photobucket.com/albums/dd79/loyd500/Prototypes/1-Crosssectionwithflow_zpsd26a2c99.jpg) (http://s226.photobucket.com/user/loyd500/media/Prototypes/1-Crosssectionwithflow_zpsd26a2c99.jpg.html)
Neat design! I had something similar that was still axial I'll post later to see what you think. Bob has already seen it but maybe more eyes can see a better solution to the problem.
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...............
Like the Condor, the loading port would have to be to the left of the valve, in line with the barrel.... and like the Condor, it will have a lot of volume downstream of the valve seat.... Better, more unrestricted flow (after all, the valve can be made larger than boresize with no penalty).... but a slight pressure drop depending on the relationship between the reservoir and the downstream volume....
This has made me wonder.... What, other than higher opening force (which the balanced design eliminates).... is the downside of running larger than boresize valving and porting in a conventional PCP?....
Bob
The dead air space between the valve and the bullet can be pretty much eliminated by a falling block/sliding block arrangement immediately downstream of the valve. The block slides out to the side, the bullet is loaded into the block, and it is then slid back in. Some tapered surfaces are usually required to seal the HPA. This is similar in application to I think what is called a tap loader.
re: bore-size valving: in general, I have found that the larger the valve, the more difficult it can be to meter very small amounts of air repeatably. If the application is not in that range, it ought to work fine.
Lloyd-ss
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Yes, if the valve is larger than the bore, then sonic choking would occur (in the barrel) only when the airflow reaches Mach 1 at whatever pressure is present at the time.... which means not until the pellet exceeds Mach 1 at the muzzle.... If you don't shoot beyond 950-1000 fps, it would never be an issue.... As examined in the thread on Sonic Choking, it isn't a hard limit anyway, sonic choking causes a reduction in pressure downstream of the choke point, which reduces (but doesn't stop) acceleration after it occurs....
I wasn't thinking of using a .50 cal valve in a quarterbore.... but on the other hand if the flow rate is adjustable, it might mean one valve body for any caliber.... A muzzle loader could eliminate the dead air space as well.... *grin*.... or a break-action like a shotgun.... Would have been a good solution for my .410....
Bob
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My idea was to have a sleeve that move forward to open a space for air flow through, then have a cone shaped plug follow that and close the port. My idea would have been limited by struts going back to the closing mechanism and spring, but that can be done far enough from the port to not limit flow. The other way would be to come from below like in your design. The timing would be adjusted with the distance between the sleeve and the plug and however you slow down the plug. I had thought of using lugs to force it to twist and slow down or make a suction behind the plug as it closes. The suction idea might even allow some self regulation depending on pressure. Pardon the bad drawings. I couldn't get any software to draw it in.
Edit: My idea does have more dead space behind the bullet but maybe you can see a fix for that.
Edit 2: just to be clear, my idea was to have this all screw into a small tank then have that tank filled from a regulated cf tank.
Chris
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Have you looked at the details of the valves in the Airforce bottles? Similarities and very good performance.
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Have you looked at the details of the valves in the Airforce bottles? Similarities and very good performance.
I've never had access to one of those or design details.
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Have you looked at the details of the valves in the Airforce bottles? Similarities and very good performance.
I've never had access to one of those or design details.
Try here:
http://www.talonairgun.com/forum/ (http://www.talonairgun.com/forum/)
A search will turn up diagrams and photos of the valves.
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Those are nice designs. Lloyd, where does the switching pulse come from on that patent? It could be done by solenoid i suppose but the air coming off the reservoir would have to be regulated down to 150 psi. The design that I've been working on works more like a dump valve. It is fed from a regulated reservoir and recharges the dump chamber once the firing cycle is complete. piston movements are very small. I find that I can use smaller porting since I have no dwell to contend with. I do have a small amount of dead volume. The dead volume consists of the head thickness of the dump chamber, so it is very small. The con is, that you have to decide on how large of a dump volume that you want. Bob referred to 50% of barrel volume in a post some time ago and that works out in the model. 50% happens to be the volume used at the minimal psi to get most power with highest shot count. There is some change in the model as you go to smaller calibers. Big bore seems to follow the 50% rule to the tee. Efficiency looks like it will be improved greatly according to my model. Lloyd, your balanced valve for your big bore project is what got me on this design. My building issues are the same as Bobs. The force of the piston moving rearward is big and dangerous. In fact, I won't even show pics because I feel it would be irresponsible. It wont take long to have a failure at this point. Yea, I tried it at only 1500 psi and it is spooky. Evidence of onset of failure after only 60 cycles. Learned a bunch though and I'm currently pondering how to overcome this issue. The new design looks promising but more complicated. Unfortunately, complicated = time.
Bill
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Solving the inefficiency of dump valves compared to timed valves which close before the pellet has travelled less than half the length of the barrel is the greatest problem.... With a valve of 50% of the barrel volume, if you dump it you use all the air in the valve.... If you close it when the pellet reaches the muzzle, you conserve 1/3rd of the air in the valve with NO loss of power.... If you close it when the pellet is only half way down the bore, you save 1/2 the air in the valve and lose only a few fps in velocity.... Close it even sooner, you save even more air.... but the velocity will start to drop off....
Bob
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Excellent summarization Bob. Your graph really brought it home for me. Above 50% barrel volume cant really be justified by power gains IMO.
Bill
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Balanced chamber quick exhaust valve that uses a spring to upest the ballance. pressur released fom backside of piston allows piston to move rearward thus removing poppet from flow path. this allows contained pressure to evacuate bore obstruction violently. work s like a dump valve and will require a shut off from reservoir during the cycle.
Bingo. Certainly the most elegant of available solutions in my mind. Simple is always easier to make.
Airgun Designs Auto Mag Painball pistol worked on this concept. I saw a household drain cleaner that was a pump up that worked that way as well. The Shimel Air Pistol used that concept as well with manual charging to eliminate flow during the firing cycle. You could also control the flow during firing cycle with a small restrictor.
TimmyMac1
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Tim, I'm trying to get the shut off to be part of the cycle. I think I have a concept that will work. The system requires pressure regulation for consistancy, but Ive realized that the system doesn't care if the piston is smaller. It only requires a dump plenum at needed pressure, that is adiquate for the desired power output. A smaller piston only increases efficiency and reduces applied forces. This will make it a safe build by reducing component stress. This concept when applied to Big Bore will allow hammer spring and hammer to be tiny in comparison to traditional valve works.
Bill
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IMO, if you can't get the valve to close before the pellet is half way down the barrel (ie in about 1 mSec.) you are just wasting air.... or are doomed to operate with a very small valve to barrel ratio, and hence low power....
Bob
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Napier Sabre, Bristol Centaurus and a few others ran sleeve valves. By the End of WWII the big poppet valve radials were giving them a run for their money and jets were about to deliver a knock-out. No way to get anything resembling a reasonable seal at the pressures you'd need for a PCP. While the Sabre was capable of significantly better breathing at high rpm, their 'junk box' would no way stand the effective rpm as defined by a PCP firing event...lol
cheers,
Douglas
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I may be posting in this thread incorrectly. Just dawned on me that the concept initiated was for a ROTATING cylindrical valve and Im thinking in a balance piston type.
I see your point Bob. The theory is to find the combination of psi and volme to produce desired energy output. For the most shot count with highest energy, I have found that my model matches what you had published about dump valves. 50% of barrel volume is the reasonable maximum. Yes we can get more fpe with highe ration of barrel volume, but the gains arereally small for the losses in efficiency. I have modeled a .45cal 230gr at 900fps using a dump chamber of 3.125ci at 2400psi. with a 22ci reservoir, this gives 5 shots at 906 -889 fps. 1.8% spread at 400+fpe for 1.59 efficiency. FPS and shot count aren't exceptional but the efficiency seems to be a tad better than when I modle the traditional valve. with a dump valve the valve is open the entire time, so my thought was to use as little as possible, at as low psi as possible, as long as it achieved the desired fpe range. Then of course, we can change bullet mass, barrle legth ect and every thing else changes. :o
Bill
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Interesting model results, I ran those numbers in Lloyd's spreadsheet, using a barrel volume of 6.25 CI, which in .45 cal works out to 39.3".... and it requires 75% efficiency to get to 400 FPE when dumping 3.125 CI at 2400 psi.... That's high, but not impossible, although I can't imagine using a rifle with a 39.3" barrel.... and going shorter will require higher efficiency to reach 400 FPE, which is unlikely to be achieved.... Also, I don't see how you can get 5 shots of 3.125 CI with a setpoint of 2400 psi, as that works out to 5 x 3.125 = 15.6 CI x 166 bar = 2590 CI, and for a 22 CI reservoir to deliver that much air without dropping below 2400 psi (at which point it still contains 22 x 166 = 3650 CI), it would have to contain 3650 + 2590 = 6240 CI when filled, which means filling to about 300 bar, but perhaps that is what you are considering....
You are dumping 3.125 CI of air at 2400/14.5 = 166 bar x 3.125 CI = 517 CI of air per shot, producing 400 FPE, so the efficiency is 400/517 = 0.77 FPE/CI.... so you need to take a look at your efficiency number.... If you used a timed valve, closing it when the bullet left the muzzle, you get the same power and the efficiency jumps to 1.16 FPE/CI.... Closing it at 50% of the barrel travel, then you would still get ~ 385 FPE of energy and the efficiency would increase to 1.49 FPE/CI with no other changes.... You can see how inefficient a dump valve is compared to a timed one....
Bob
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I'm going to have to look into this. My model was originally done for timed valves and I have made a copy that is SUPPOSED to take the inputs and convert them to regulated out puts. I think that I may be missing some element. The idea is to have a known dump volume, that is adequate to propel the desired bullet, at desired velocity and try to maintain that condition with a reg. Same as a timed valve. But, as you know, a timed valve has to have a plenum that is sufficient to keep psi drop across the valve acceptable to produce the power desired. As i see it, timed valve uses ever changing volume under ever changing psi, unless reg is employed. Then you use same volume at the same psi until equilibrium is met between the reg and the reservoir. under this condition, the dose of air from the plenum is modulated by poppet duration. What I want to do is do away with the valve duration aspect of the shot. I want to take 50% or less of the barrel volume and have it filled to the required psi for desired performance. when the valve actuates, I want the reservoir feed to be interrupted until the dump volume(50% or less of barrel vol) is expended. once dump is expended, valve returns to home position allowing regulated flow to return and fill dump volume. This should result in a drastic and sudden plummet of velocity once equilibrium is reached. The now, lower psi, isn't adequate to produce the energy level desired and volume is static. Flow can't change to make up for the lack of psi, like a unregulated timed valve.
The issue may be in converting the losses from the reservoir accurately. Every shot at the known volume and psi of the dump chamber, degrades volume in the reservoir. Perhaps this is where i'm failing. Another possible point of contention is the break away friction of a lead bullet of that size, I have no real world measurement of this. I simply used 20lbs, If it is more, then obviously it will require either more psi or more volume and maybe both. That will shrink thing quite a bit.
Thanks for the input Bob
Bill
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The first half of your post is a perfect description of what I think of as a dump valve.... filled after the shot cycle from a regulated chamber.... The air used is very simple, it is the volume of the chamber times the pressure, in the example you gave 3.125 x 166 = 517 CI.... I understand the desire to stay away from the duration aspect of the shot, but it is that which leads us to wasting a lot of the air.... With a valve having 50% of barrel volume, at the instant the pellet leaves the muzzle the air contained in the valve has expanded to fill the barrel (ie threefold), so your 2400 psi is at that moment 800.... The valve still contains 517 / 3 = 172 CI of air, which ends up exiting the barrel after the pellet has gone, contributing nothing to the shot.... If you closed the valve at that instant, capturing that 172 CI of air, instead of using the entire 517 CI for the shot, you would only use 345 CI.... without changing the muzzle velocity 1 fps.... However, your efficiency would go up from 400 / 517 = 0.77 FPE/CI to 400 / 345 = 1.16 FPE/CI.... THAT is the problem with dump valves.... Incidently, I was using a much lower breakaway and sliding force, increasing that to 20 lbs. would require even higher efficiencies to balance Lloyd's spreadsheet....
Bob
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So...... if I were to reduce the volume of the dump chamber, there would still be the issue of 1/3 that volume still being in the chamber when the bullet exits the bore. This results in lower fps. I see. To get the velocity I would have to have a 517 plenum so to speak and close it when 172 was still in the chamber. The question is then, how do i close the valve right before the bullet exits? Well that doesn't get away from duration at all does it? ;D Thanks again Bob.
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If you made the dump valve smaller, relative to the bore, you waste less air, but have less power.... If it was 25% of the barrel volume, at the moment the bullet exits the air would have expanded 5 times and you would be wasting only 20%.... but the pressure drops faster during the shot, so you have less power (but you are only using half the air).... I don't see any way to get the kind of efficiency we expect/desire with a dump valve.... and once you close it at the moment the pellet exits, why not close it when the pellet has only gone 50% of the way down the barrel, lose only a few fps and get a big jump in efficiency....
Bob
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Agreed. Originally when I started working on this valve design my intent was to make a valve for big bore guns that could be opened with the same force as is used to operate a .177 pcp valve. My oversight lead me down a false path of efficiency and my attention was diverted. I now see that i can probably get the desired low energy opening of the valve but at the price of efficiency. After some serious mods to this dump model, I see that mid .7 to mid .8 range is likely the best that could be achieved with this valve design. It is possible to get a tad closer to 1.0 if the range of motion and timing were right. WAIT!!!! :o thats the original conundrum! ;D. It may be worth the effort, if opening the valve is reduced to a more reasonable cocking effort, as long as the efficiency can be closer to 1.0
Bill