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Small coaxial

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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Unread postAuthor: Novacastrian » Sat Oct 27, 2007 5:14 am

Seems a bit short to me, however not having completed a pneumo it may work fine. I just tend to think it *might* have troubles sliding freely.
Meh, what do i know!? Best wait for the experts to reply :wink:
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Unread postAuthor: rixth » Sat Oct 27, 2007 5:24 am

May have found something even better.

See image. b is 52.9mm, c is 55mm

Perfect width, and length!

http://www.hansenproducts.co.nz/product ... s/SMHT.jpg
I'd have to chop the thread off though
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Unread postAuthor: Novacastrian » Sat Oct 27, 2007 5:40 am

Now that sounds like the go :wink:
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Unread postAuthor: rixth » Sun Oct 28, 2007 11:54 pm

I swear to God I'm going to kill someone....

I'm going MENTAL. I can't get the barrel to seal (yes this is my first piston valve)...

I've tried a couple different pistons, as well as trying putting fabric or a disk of hot glue behind it (as in http://www.spudfiles.com/forums/files/untitled2_531.jpg). Whenever I pump, air just escapes out the barrel. I've tried manually pressing the piston up against the barrel, then filling it but it still escapes.

The sealing face is a disc cut out of a neoprene gumboot (for you yanks, this is what a gumboot is: http://en.wikipedia.org/wiki/Image:Wellies.jpg ). It's maybe 2mm (0.07in) thick.
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Unread postAuthor: Mitchza89 » Mon Oct 29, 2007 12:04 am

Hmm thats a tough one mate but I reckon the face on the barrel might be abit wonky. That was the problem I had. Just place some fine wet n dry sandpaper down on a table and rub the face against it. That should smooth out any irregularities.
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Unread postAuthor: rixth » Mon Oct 29, 2007 12:13 am

I checked the face, I think the rubber might be a bit hard. What is typically used as a sealing face? I know it's neoprene, but I don't think it's what I have.
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Unread postAuthor: Novacastrian » Mon Oct 29, 2007 12:13 am

It may be that the gumboot material is too hard. Try a different kind of rubber.
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Unread postAuthor: jackssmirkingrevenge » Mon Oct 29, 2007 12:18 am

One of the best sources of rubber is a car or bicycle inner tube, I'm sure you can easily get your hands on one.

Also, make sure that the sealing end of your barrel is 100% flat, smooth and parallel to the sealing face of your piston.
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Unread postAuthor: rixth » Mon Oct 29, 2007 1:21 am

Well, all the air escaping was my fault, but lets not go into that.

Now I've fixed that, but when I take the pressure past 20, it lets anything more out the barrel. Is this another sign of a poor seal?
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Unread postAuthor: jackssmirkingrevenge » Mon Oct 29, 2007 1:36 am

How is the sealing face attached to the piston?
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Unread postAuthor: rixth » Mon Oct 29, 2007 1:44 am

A bolt in the middle
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Unread postAuthor: Novacastrian » Mon Oct 29, 2007 1:48 am

Is the piston filled with anything? If not the rubber might be getting pushed into the piston under pressure.
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Unread postAuthor: MrCrowley » Mon Oct 29, 2007 1:53 am

The bolt could be leaking, chuck some epoxy on covering up the bolt and the test it.
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Unread postAuthor: rixth » Mon Oct 29, 2007 1:56 am

The piston isn't filled at this stage.

I'll go epoxy the bolt now though
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Unread postAuthor: jackssmirkingrevenge » Mon Oct 29, 2007 1:58 am

is there a washer between the bolt and the rubber?
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