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Need Help with All Metal Barrel Sealing 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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Need Help with All Metal Barrel Sealing Valve

Unread postAuthor: MaxuS the 2nd » Tue Apr 08, 2008 2:06 pm

Hi everyone,

I've already searched my face off trying to find information on one particular question I have. This is for the people who have made barrel sealing all metal cannons made from threaded iron/steel fittings.
I was wondering what the piston would seal against inside the threaded tee since you can't put a piece of pipe randomly through a threaded fitting without it leaking like a bugger. The piston can't rest against the thickness of the threaded reducer either because then there would be no force acting upon the front of the piston.

I know I probably explained that very badly, but if someone could enlighten me?

Thanks
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Unread postAuthor: potatoflinger » Tue Apr 08, 2008 2:20 pm

I think that your best bet is making the gun pretty much the same way as you would make a coaxial cannon, except with a tee coming off from the chamber, but the barrel going completely through the tee. (I did a terrible job of explaining that) I think that Schmanman did something similar to this when he made the S.W.A.T. (Notice how the tee is farther forward than where the piston is seated)
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Unread postAuthor: Jared Haehnel » Tue Apr 08, 2008 2:36 pm

I don't know as though its been done before...I can't think of a way to do it...

@ potatoeflinger The only problem with that is the thread on cast iron pipe is not long enough...but thats the way I designed my piston on my large cannon
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Unread postAuthor: MaxuS the 2nd » Tue Apr 08, 2008 3:03 pm

Hmm, I've looked around at almost all of the other all metal cannons and would really like to know how to do it.
The only thing is that it can't be a bodge job because this launcher is designed for very high pressures. If there is no way for this to work, then I will just weld the barrel into the tee.
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Unread postAuthor: Ceppu » Tue Apr 08, 2008 3:34 pm

This is how I did it with my gun:

Image
Not on scale of course :roll:

I soldered 35mm copper pipe into 1,5" brass nipple. It was quite loose fit but when I added 35mm copper coupling inside the brass nipple, it was perfect.
Works like a charm.

Piston is red thing inside 1,5" iron nipple and can be piloted through that hole on top of the iron cap.

Hopefully this helps even a little.
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Unread postAuthor: POLAND_SPUD » Tue Apr 08, 2008 3:43 pm

it isn't difficult at all...
first of all, cut more threads than you would normaly need - so that the pipe can be screwed all the way into the threaded reducer and stick out on the other side...
now all you have to do is to join the reduced with the tee

I hope you can understand what I mean... it really easy if you have a thread cutter or you can get someone to do it for you
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Unread postAuthor: SpudFarm » Tue Apr 08, 2008 3:45 pm

like ceppu drawed.
when i thought of a piston hybrid i was going to do that.
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Unread postAuthor: MaxuS the 2nd » Tue Apr 08, 2008 4:07 pm

Ahhh!

Thankyou very much guys. :D
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Unread postAuthor: pizlo » Tue Apr 08, 2008 4:17 pm

I'm my barrel sealer I had a 3/4 inch T and dremeled out a 3/4 threaded converter and solvent welded some half inch PVC through. half inch PVC is rated quite high.
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