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lorraine · Member

There is some tanks Ive seen with helium for parties that look about the size of a 20lb LP tank. Can these be regged down to 90-100 psi and feed into a shoebox to get a charge of 3000-3200 psi?. I don't have to purge things right?. Does anyone know what about theses clown can's hold for working PSI? or can I let it rip into my F8 shoebox?. These silly tanks have a gauge that has only a green, yellow,red , NO numbers!

Robw · Veteran Member

I doubt if an AIR compressor will pump helium.

rsterne · Moderator

I don't know what the pressure is in the specific tanks you are talking about.... but typically Helium for party balloons is sold in tanks filled to about 2000 psi.... They come in several sizes.... Chris Alls does exactly what you are suggesting, he regulates the He down to the appropriate input pressure for his ShoeBox, and then uses it to fill a Great White to 4500 psi with Helium.... then fills his guns from that, as per normal....

Since Helium is inert, there is no special danger in this procedure.... If you don't start from an empty tank or gun, you won't get 100% He on the first fill, and the percentage will increase each time you fill.... If you drain the gun to start, by the time you fill it to 3000 psi with Helium, it will be 99.5% pure, relative to what was in the tank you started with....

Bob

AirGunEric · Site Admin

Why not ignore the compressor and just fill the gun straight from a nitrogen tank at 6000psi regulated to -whatever- ?

rsterne · Moderator

She wants to use Helium, and the commonly available tanks are only about 2000 psi when full.... so you have to boost the pressure for most PCPs.... You can do that with a compressor, or a pressure booster (which generally cost more than a ShoeBox)....

Bob

AirGunEric · Site Admin

I got that- by why helium and then boosting things? Seems like extra effort for nothing. The only reason I can see off-the-top would be if someone has access to free helium or something similar.

rsterne · Moderator

Helium will produce a 40-80% increase in FPE.... The lower mass of the Helium, plus its higher speed of sound and atomic velocities are the reason.... It allowed the guys from Virginia to push my 200 gr. .308 cal bullet at ~1100 fps when getting ready for the EBR last October.... using 4500 psi and a 33" barrel.... that's over 500 FPE in .30 cal....

Bob