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High Pressure Sealing Faces

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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High Pressure Sealing Faces

Unread postAuthor: VH_man » Mon Jun 30, 2008 8:12 pm

I have consturucted a new cannon for use with my shock pump, and i have been trying for days to make a good sealing face. im asking the people who have sucessfully consructed a high-pressure piston valve what they used as a sealing face?

BTW my piston diameter is 3/4 inch and the barrel is 1/2 inch.

Thanks in Advance im pulling my hair out on this one. ill presusrize it to 200 psi and then ill hear a "pop" followed by a fssssssssttttttt which gets annoying after youve spent 30 minutes on the shock pump to get there.....
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Unread postAuthor: rp181 » Mon Jun 30, 2008 8:50 pm

mabey teflon or viton?
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Unread postAuthor: blind909 » Mon Jun 30, 2008 8:52 pm

some people have used a solid peice of rubber, just go to a craft store and get a small cylindrical peice of rubber the same size as your chamber(if its a coaxail), and just use that as your piston. If not, I have used a cut peice of basketball(works great), other than that, truck tire>
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Unread postAuthor: VH_man » Mon Jun 30, 2008 9:04 pm

they sell cylindrical peices of rubber at miachels? whooooo...... missed that one.

ill have to look into that along with a wooden piston.
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Unread postAuthor: MrCrowley » Mon Jun 30, 2008 11:45 pm

I used a rubber gasket and glued it with neoprene glue which was actually meant for bonding a rubber 'toe guard' to my cricket bat.
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Unread postAuthor: Gippeto » Tue Jul 01, 2008 12:19 am

Wow! :shock: Blowing out at only 200psi?

When you take it apart to repair the seal, what are you finding? ie. How exactly is it failing?

I've been using a single layer of neoprene gasket material. 1/16" thickness simply bolted on. (copper gun) Working trouble free at 400psi.

The co-ax uses teflon.

And by the way,...30 minutes to get to that 200psi? How big is your chamber?
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Unread postAuthor: Pyro Ninja » Tue Jul 01, 2008 2:27 am

VH_man wrote:cylindrical peices of rubber


rubber bung/rubber cork, you may find them in a boating stall.
Just machine it down to the right size.
One rubber cork = piston, sealing face(perfect seal) and bumper.

-edit- -may not have big enough corks for what you want-
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Unread postAuthor: SpudFarm » Tue Jul 01, 2008 2:48 am

the best thing i have ever used is the diphram found in argon regulators, i have fired uncountable shots with it and yesterday it finally gave way.
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Unread postAuthor: Ragnarok » Tue Jul 01, 2008 5:40 am

I just use a 3/4" tap washer - they're made of tougher rubber, because they're designed to be clamped down hard onto that kind of surface.
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Unread postAuthor: jackssmirkingrevenge » Tue Jul 01, 2008 5:46 am

Truck tire inner tube, never failed me :)
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Unread postAuthor: psycix » Tue Jul 01, 2008 6:01 am

Or just the good old bike tire inner tube :)
But neoprene would certainly be the best.

Did you bolt on your sealing face correctly? Glueing is not recommended, use a bolt and washer.
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Unread postAuthor: VH_man » Tue Jul 01, 2008 6:19 am

im using 3 layers of bike inner tube and it simply pops at 200 PSI

and if i use a bolt and a washer it makes that "cone" shape and at 50 PSI the face gets sucked into the barrel.

I need a new piston also, im going to be using a dowel machined down to the proper size. I will try the "tap washers" first, because i have a few of those laying around. if i cant get anything to work i will use a solid rubber rod from McMaster......

And BTW, it takes about 15 minutes..... my pump bore is 1/2 inch copper and my chamber is 5 feet of 3/4 inch pipe, not including the tee valve.

EDIT: WOHOOOOOOOO i got it to seal at 200 PSI. DAMN its loud..... and powerful...... but then on the next shot the sealing face popped again.....
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Last edited by VH_man on Tue Jul 01, 2008 6:27 am, edited 1 time in total.
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Unread postAuthor: MrCrowley » Tue Jul 01, 2008 6:22 am

You need a bigger washer to keep the sealing face down, also glue the back of it to the piston. I had similar issues.
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Unread postAuthor: hyldgaard » Tue Jul 01, 2008 6:45 am

Damn i feel lucky not to have these apparently very normal problems.. i use two layers of bike innertube and it works flawlessly for me at 500psi :) also i dont use any kind of bumper and i have no problems at all :)

EDIT: picture of my piston, back side up (if its to any help)
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Unread postAuthor: Mitchza89 » Tue Jul 01, 2008 7:40 am

Probably the best piston I've come up with was a rubber stopper that I got from a place called "Clark Rubber". They specialise in rubber products but they also deal in pools and what not. I just lathed it down on a timber lathe. You can't go wrong. No sealing face to blow out when you're using one big sealing face :D.
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