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Coaxial floating diaphragm issues

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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Coaxial floating diaphragm issues

Unread postAuthor: andeh » Sun Jul 06, 2008 9:57 pm

Hello all.. I don't know if anyone remembers me but I've been spudgunning since the old old spudtech forums were up.. got a problem with a new gun I built. Its got a 7' 1" SCH80 barrel and a 5' 2" SCH40 chamber, coaxial. The 2" has a male adaptor hooked up to it and the barrel extends just beyond the end of the adaptor. Got a threaded cap with a 3/8" QEV hooked up to it that I used on a bigger floating diaphragm gun that worked fine. The gun seals up great and has held up to 100 PSI with no issues. I can't get it to actuate though. Is it possible that having the diaphragm operating in the threaded area is allowing too much air around it? The diaphragm isn't a perfect fit but its quite close - not sure if I could do better cutting it by hand. I've tried sanding down the contact area with the diaphragm and the barrel, insuring that there is around 1/4-1/3 of an inch for the diaphragm to travel. I'm not sure what else to do. Seems to me that the valve must be big enough since I used it originally on a 4" chambered coaxial.

This is probably somewhat hard to wrap the old noggin around without pictures and I'll take some tomorrow after work. Just wondered if anyone had any ideas. I've considered using the spare threaded cap I have and filling in the last bit of threads with some kind of epoxy to make for less possible leakage around the diaphragm. Sound like a solid idea?
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Unread postAuthor: brogdenlaxmiddie » Sun Jul 06, 2008 9:58 pm

Try a bigger pilot valve?
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Unread postAuthor: SEAKING9006 » Sun Jul 06, 2008 9:59 pm

Actually, yeah, it does. Go ahead and try it (keep a spare cap on hand) and tell us how it goes.

BTW, do we have a valve troubleshooting section? We oughtta make one.
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Unread postAuthor: brogdenlaxmiddie » Sun Jul 06, 2008 10:00 pm

SEAKING9006 wrote:BTW, do we have a valve troubleshooting section? We oughtta make one.


Thats a damn good idea :!:
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Unread postAuthor: andeh » Sun Jul 06, 2008 10:31 pm

As I mentioned in my OP, the valve was initially used on a gun that used a 4" chamber and the same type of valve and that worked so it should be more than adequate for the 2" chamber. I'll pick up some epoxy and see what I can do with my backup valve. Hopefully that will do it.
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