"boxer" piston spring airgun and balanced valve

[wyz2285]

I was wondering around piston airguns to see about effects of piston weight and spring length and I found this very interesting build log: https://www.gatewaytoairguns.org/GTA/in ... ic=25115.0. The guy attempted to build a dual piston airgun, in which the two pistons are positioned in opposite side so when it fires, the recoil cancels out. So no matter how hard is the spring (the guy is using gas spring) nor how heavy is the piston, the gun is theoretically vibration free. (Kinda like one of these AKs with a counter weight to cancel the bolt).
Then I visited the builders website: www.americanairarms.com in which I found he uses an "air assisted valve". after further reading I'm fairly certain he is using a counter balanced hammer valve.

[jackssmirkingrevenge]

The Diana Model 6 used dual pistons:



Only one of them did the actual pellet firing though, the other one was just there to balance the spring recoil.

The real powerhouse was the Whiscombe series of rifles however that used dual opposed pistons.



Very rare and expensive but they were shooting in the region of 30 ft/lbs muzzle energy with almost no recoil

Then I visited the builders website: http://www.americanairarms.com in which I found he uses an "air assisted valve". after further reading I'm fairly certain he is using a counter balanced hammer valve.

Yup, very common topic of discussion on the GTA forum and commercial manufacturers have caught on.

Megathread

[wyz2285]

Nice. Now I need to look into Cobra and SS valves...

[jackssmirkingrevenge]

Cobra valve

Balanced valve with the poppet that sleeves over a spigot



Same concept as the balanced valve we are familiar with but differently configured.

SS valve

A "stepped" variation of the balanced valve in an attempt to make it more tunable:



By controlling the flow through the equalization port that air can go through once the valve is open, then you have some control over how fast it will close and therefore you can tune the dwell time to some extent.

[wyz2285]

So the holy grail is to have the valve close as the pellet extis (or whenevr it's optimal) by adjusting the air flow through the equalization port (pressure raises on barrel side, air flows into the balance chamber at X rate and forces the valve close at Y moment)

[jackssmirkingrevenge]

So the holy grail is to have the valve close as the pellet extis (or whenevr it's optimal) by adjusting the air flow through the equalization port (pressure raises on barrel side, air flows into the balance chamber at X rate and forces the valve close at Y moment)

Precisely.

as the pellet extis (or whenevr it's optimal)

The rule of thumb is to have the valve close when the pellet is approximately half-way down the barrel, any more than this wastes significantly more air for little benefit in velocity.

[wyz2285]

So if you make the valve stem length adjustable so the bleed port is half covered, then it's only exposed after the valve has open to a certain depth (AKA the needed dwell), closing the vavle in the right time.

[jackssmirkingrevenge]

Yes that looks like it would work.