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High pressure piston valve

Post questions and info about pneumatic (compressed gas) powered cannons here. This includes discussion about valves, pipe types, compressors, alternate gas setups, and anything else relevant.
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Unread postAuthor: DYI » Thu Nov 15, 2007 4:49 pm

Thanks for that advice Solar, I'll make sure to incorporate that on my upcoming launcher.

I would like to personally state that my burst disk cannon is not the future, it is essentially a failure in my mind. I will definitely fix it, as soon as I get the materials, but the firing process is not fun at all, up to the moment that you pull the trigger and see your target disappear. That's the whole reason I'm building a high pressure, high volume BB gun with a piston valve. It will remedy the difficulty of use problems, while being handheld and achieving similar muzzle energies to the SCTBDC.

Keep going with this project Daccel, and it will likely beat mine by several months. High pressure large bore is indeed the future, in my opinion. 3000 psi fittings and pipe will give you all the peace of mind you need, and then some. Ignore all this BS about recoil. People can hold big game rifles with >10000 ft/lbs of muzzle energy and no recoil absorption. With a bit of practice and some pneumatic shocks, firing this shouldn't be any problem. I do agree with the pilot volume worries though. Just attach it to the pressure washer handle with 1/4" hose rather than pipe, and you will significantly reduce the pilot volume without sacrificing ergonomics. Good luck.
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Unread postAuthor: Ragnarok » Thu Nov 15, 2007 5:48 pm

Indeed, I've just looked at the GGDT file properly. There are some inputs that look a bit out of place, I note.

Using my recoil calculations, and making educated guesses as to the launcher weight and temperature drop, I made an estimate for the recoil energy.
The truth is, even with those horrific pressures, the recoil will actually be very low, easily under 10 ft lbs. The low gas volume and large launcher mass, coupled with the fairly low round momentum make the recoil easily handled - that's less than HEAL's recoil (HEAL uses twice the mass of gasses and has a quite high gas velocity leaving the muzzle), which I easily manage.
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Unread postAuthor: daccel » Fri Nov 16, 2007 1:52 am

Ok, a redesign of the pilot is in order, I wasn't thinking there. I'll fill it through the pilot valve. If I can't attach the valve right to the bushing and instead use 1/4" or smaller hose it shouldn't create a restriction right, because the valve opening is obviously a lot smaller than the 3/8 inlet? And if it's vented to the suppressor wouldn't that increase the pressure in front of the projectile lowering performance, or would the volume be small enough not to matter. I could just make a separate small expansion chamber for it. Thanks for saving my hearing, I hadn't thought about the pilot sound. Kind of defeats trying to suppress the muzzle blast if it's not dealt with too.

I still think there are benefits to low volume/high pressure with a larger bore - less bulky, shorter, and easier to silence. There are downsides, like weight, although that's good in that it reduces recoil. It requires a high pressure gas which might be difficult to get/expensive. But I don't have the opportunity to use cannons frequently so the last part wasn't a negative for me, and the other parts sounded good. Agreed, the game quickly changes when you increase chamber volume, but that defeats the easy to silence part, so I don't see it happening on this one.
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