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12 GPM......wtf?

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 » Sat Dec 22, 2007 10:02 pm

Well, if it leaks like a sieve, I'm going to go cry. And then throw it at a wall. And then incinerate it.

If that happened, I'd have to make my own trigger style pilot valve (which would obviously be a great challenge, but I'm still going to owe the machinist most of my limbs and organs for the amount of work I need done, and I'd rather not make it any more expensive than it has to be).

I can see where you're going with the whole leaking like a sieve bit. 2400 psi helium is guaranteed to leak a lot worse than 4000 psi water, but it'll only have to hold the pressure for a little while.
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Unread postAuthor: Novacastrian » Sat Dec 22, 2007 10:05 pm

I may be that you just waste some Helium, if thats the case i spose you can live with it!

Edit: Just as a side note the one i pulled apart sealed metal on metal, no washer or o'ring to be seen.
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Unread postAuthor: DYI » Sat Dec 22, 2007 10:15 pm

I may be that you just waste some Helium, if thats the case i spose you can live with it!


Well, either that, or it'll pilot itself with the leak. And we all know how safe tungsten carbide ball bearings headed in random directions at >2000fps are...

Metal sealed on metal isn't necessarily a bad thing, although it may stop the gun from sealing at lower pressures. I know the solid teflon seal on my piston wouldn't work at lower pressures.
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Unread postAuthor: singularity » Sat Dec 22, 2007 10:16 pm

i have used a few pressure washer handles as primary valves on vortex guns they don't have problems sealing at low pressures (at least the ones i have used)
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Unread postAuthor: mopherman » Sat Dec 22, 2007 10:34 pm

@ singularity- hows the flow on those handles? Is it at least as good as a 1/4 ball valve?
@nova- Did you see room to glue a gasket in there? Or would that restrict ball movement.
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Unread postAuthor: Novacastrian » Sat Dec 22, 2007 10:38 pm

No and yes. It had more of a piston with a convex head rather than a ball though, you would have to modify the piston and the travel i think.
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Unread postAuthor: Ragnarok » Sun Dec 23, 2007 12:53 pm

DYI wrote:Assuming 2400 psi helium, can someone do the math and tell me if I just wasted $40?

For that pilot volume, and with high pressure helium, no.

I remember launching a grape a good distance (somewhere about 100 feet, but it was ages ago, so it may well be less) with only 15 psi, two or three feet of barrel, and a valve that was about 6 gpm water (at 30 psi). Totally ghetto, but fun.
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Unread postAuthor: DYI » Sun Dec 23, 2007 4:42 pm

Great. My only real worry now is how badly the pressure washer handle is going to leak. But if it's rated for 4000 psi water, it should be able to take 2400 psi helium without leaking too horribly, right?
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Unread postAuthor: Ragnarok » Mon Dec 24, 2007 6:26 am

DYI wrote:But if it's rated for 4000 psi water, it should be able to take 2400 psi helium without leaking too horribly, right?

Helium is used industrially to find leaks in pressure systems because it has the smallest particle of any gas (because it's monatomic, unlike hydrogen) and a very low viscosity.

In short, if any system has a flaw, helium will leak from it the fastest, which is a little unfortunate. However, if it is mounted the proper way round, it shouldn't leak unreasonably at 2400.
If you should have a problem, it's not hard to get hold of silicon sealant sprays. They aren't that cheap, but I have never found a better solution than silicon greases and sprays to improving moving seals.

I use the grease on HEAL's breech to seal between the back of the copper barrel and the coupler it sits in.
I've been asked why I did it like that rather than putting on an O-ring and sealing into a larger size of pipe instead like most similar breech loaders do. The answer is that the way I've done it, the surface area the air can reach around the back of the barrel is lower, so the forces from the pressure trying to push the barrel forward are more manageable, and I can use more pressure without having to worry about the breech or locking handle bending or breaking.
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