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All Springer/NP/PCP Air Gun Discussion General > Engineering- Research & Development

regulated PCP design with "pre-chamber" and "dump all valve"

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^^artin:
Currently I did a little research on regulated pcp air rifle designs.
I'm thinking about an more or less "ideal" regulated pcp rifle design with a closed "pre-chamber" that get filled with regulated pressure from the air-reservoir after each shoot.
The exhaust valve then dumps all the air out of this pre-chamber into the barrel with each shoot. If it's well made this design should be pretty constant.

Can someone tell if such design allready exists ?
I couldn't find something like that by know - possibly I just don't have the proper term to search.

Greetings Martin       

Motorhead:
Can't give the math behind it .. but can offer some insight.

When you have a smaller volume "DUMP" chamber you start out with high pressure there, but soon as valve is open and the contained HPA starts filling valves throat & transfer area the pressure is collapsing before the pellet is even launched.  Once the pellet is in motion the volume gained between the dump chamber and pellet exponentially increases with the pressure pulse driving it crashing lower & lower.
While one can control lower to modest power guns in this manor it is really inefficient when weighted against a more conventional design that just takes sips of HPA off a larger volume plenum.
In a conventional set up the increased volume within containment ( much bigger Pot if you will ) as poppet opens and valve throat / transfer spaces get filled before pellet launches the average pressure available to launch said pellet is much higher & remains much higher as pellet gets underway.  Then generally within 1/2 or less the barrels length the valve gets closed and no more air is sent down the barrel. * Which FWIW adds NOTHING to increasing the pellets speed !

So ... a small dump valve wastes or simply can not utilize the energy of the pressure it starts out at because it collapses so quickly.  Adding a bigger pot will help average pressure and power will become higher, but at a cost of extreme air use.  *Much like a pneumatic pump up gun where muzzle blast is a LOT due to so much air leaving barrel that really contributed little to the actual pellet speed achieved.

JMO ...
Scott

^^artin:
If I get you right a common regulated pcp gun is much more efficient in terms of shoot count then my design would be (if both have had the same per shoot energy output).
Of course, if the more or less constant pressure from the large air-reservoir is put behind the pellet and then gets cut off if it no longer contributes to further acceleration of the pellet, that should be more efficient. Needs a good valve timing though.

rsterne:
Dump valve guns are notoriously inefficient, unless they are very low FPE.... Pumpers (MPSs) are the classic example.... This chart is for .22 cal. with a 24" barrel...



The key relationship is valve volume as a percent of barrel volume.... Since ALL of the air that is in the valve / prechamber is going to be expelled out the muzzle, some of it, by definition, will be wasted, because the pellet will have already left.... If the valve volume equals the barrel volume (ie 100% in the chart above) then HALF the air is wasted, resulting in horrible efficiency.... If the valve is 50% of the barrel volume, then 1/3 of the air inside is wasted.... This is because at the moment the pellet exits, the pressure has dropped to 1/3 what you started with.... It has been determined by many people that 50% is the largest valve volume that makes ANY sense in a MSP, and most of them are more in 25% range (about 1/5 - 1/3 being common values).... Note that you have to get down to about 10% valve volume before the efficiency gets up to what we expect as a minimum in PCPs (1.0 FPE/CI).... and by that time you are at very low power levels....

Dump valves can be very consistent.... but they are not very efficient....

Bob

Bill G:
I have a design for this.  Bob is correct though.  You would have to run really high psi with no more than 1/3 barrel volume to get a chance at power and efficiency.  How would you segregate your plenum from your reservoir during the shot cycle?  if you don't, you end up with a more complicated version of what already exists.  If you do, you end up with a really complicated valve with more moving parts.  Something I would refer to as a balance plenum valve perhaps?  Check out balance valves, you may find them more effective for what you might be desiring. Unless you just want to tinker, explore and discover.  More power to you if that is your desire.  That is by far the best education a man can buy in my opinion. 


Bill   

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