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Piston valve problem

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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Piston valve problem

Unread postAuthor: bigbob12345 » Sat Dec 01, 2007 11:14 am

Right now Im working on barrel sealing piston valve
and I just cant get the sealing face to seal against the barrel.
I have been using tire rubber as a sealing face.
what would you recomend as a sealing face other than neophrene(I have no acsess to the stuff)
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Unread postAuthor: BigJon » Sat Dec 01, 2007 11:36 am

It might not be the rubber, it could be that you didn't cut the pipe straight and that there's not an even sealing face.
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Unread postAuthor: bigbob12345 » Sat Dec 01, 2007 11:44 am

The piston is molded out of hot glue and I know it is a flat sealing face
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Unread postAuthor: LikimysCrotchus5 » Sat Dec 01, 2007 2:07 pm

yea but what bigjon said is legitamit, that can be a problem.

There are several factors that can be the reason why your piston isnt sealing. You need to be more specific about what the problem may be. remember to list all of these specifications so that we can diagnose your problem.

Your piston may not be sliding, so use litihium grease. What is your setup that could be the reason its not working. So tell us more info so that we can help.
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Unread postAuthor: MrCrowley » Sat Dec 01, 2007 3:42 pm

Few things,

1. Piston isn't a good enough fit
2. Not enough flow from your air source(compressor, bike pump etc)
3. Sealing face isn't a good material
4. The seat(barrel) is uneven
5. Sealing face could be leaking if you attached it with a bolt(leaks through the bolt)
6. Piston too tight and you need lube.


That's just some of the problems you could have.
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Unread postAuthor: bigbob12345 » Sat Dec 01, 2007 9:11 pm

The barrel possibly could be uneven Ill go check right now.And today I found another possible sealing face that seems like it could be better
It is one of those flex pipe end caps It seems to be perfect for my needs
Ill check to see if it works tomorrow.Ill also lube it.Ill also go buy a precut stock of pvc pipe tomorro.
1.is probably too tight
2.mabey I am using a bike pump(will soon get compresser)
3.just found better matierial
4.probably is
5.no bolt
6.Ill lube it tomorro
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Unread postAuthor: Hubb » Sat Dec 01, 2007 10:04 pm

Be sure to lube it with a water based lubricant and not a petroleum based. Also, This may can be utilized to help seal it better.

As far as using a bike pump, it may be that there is not enough air flow to make the seal. You could make a small secondary chamber (see diagram for more detail). This chamber should be able to seat the piston, if that is the problem.
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Unread postAuthor: bigbob12345 » Sun Dec 02, 2007 9:12 am

Ill try that and see if that helps
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Unread postAuthor: explsvcookie257 » Sun Dec 02, 2007 1:50 pm

How much psi can a hot glue piston take before it busts? because Im thinking of making one out of epoxy but hot glue is cheaper.
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Unread postAuthor: bigbob12345 » Mon Dec 03, 2007 8:37 am

I dont know But Id guess quite alot I only plan to take it to 100psi so Im not worried about that happening
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Unread postAuthor: iknowmy3tables » Mon Dec 03, 2007 10:36 am

you are using tire tube and not the actual tire material right,
you aren't at risk if the piston breaks because it will just fly out the barrel, which should be in a safe direction as it is
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Unread postAuthor: battlemonkey » Tue Dec 04, 2007 1:56 am

The best lube that i found was power-up grease. It is very expensive though
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Unread postAuthor: bigbob12345 » Wed Dec 05, 2007 9:09 pm

After fiddeling with it for a hour or two I got it to work now all I have to do is put a chamber and a barrel on it and I should have a powerful peice of machienery.And thanks hubb017 for sugesting the secondary chamber idea it worked
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