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I need help with my Pen Gun

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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I need help with my Pen Gun

Unread postAuthor: PotatoEnemy17 » Wed Apr 11, 2012 5:17 pm

I'm starting my second pneumatic cannon and it is a pen gun type thing. My problem is the piston won't seal onto the barrel. I used wd40 but it didn't help much. The barrel is a piece of an arrow shaft. The chamber is aluminum pipe. and the piston is a little piece of round plastic that fit in the chamber well. It has a bit of red rubber glued on the end of it. I've never posted on spudfiles before, so I might not get the photo attachment thing right.
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Attachments
Cannons 001.jpg
The whole cannon
Cannons 002.jpg
This is all the pieces of the cannon. The top piece is the barrel, the aluminum thing is the chamber and the black and red thing is th piston.
Cannons 003.jpg
Close-up of the piston.

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Unread postAuthor: Fnord » Wed Apr 11, 2012 5:51 pm

Usually a piston will leak if the barrel or sealing face isn't squared up correctly. You could also try using grease on the piston rather than wd40; it usually seals a little better.

How did you make the barrel removable?


<edit: 2k posts. Yeehaw wasted time
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Unread postAuthor: Gun Freak » Wed Apr 11, 2012 7:09 pm

Yeehaw wasted time

:D

As Fnord said, make sure its all square and clean, if the barrel isn't clean where the piston rests it probably won't seal.
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Unread postAuthor: jackssmirkingrevenge » Thu Apr 12, 2012 12:30 am

WD40 and rubber seals are a bad idea, in fact most lubricants tend to make the problem worse. How about a solid rubber piston? Easy to cut with a section of sharpened chamber tubing.

Fnord wrote:<edit: 2k posts. Yeehaw wasted time


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Unread postAuthor: PotatoEnemy17 » Thu Apr 12, 2012 3:53 pm

Fnord wrote:Usually a piston will leak if the barrel or sealing face isn't squared up correctly. You could also try using grease on the piston rather than wd40; it usually seals a little better.

How did you make the barrel removable?


<edit: 2k posts. Yeehaw wasted time


The barrel is not actually removable, I had to un-glue it. I guess I'll try solid rubber.
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Unread postAuthor: jackssmirkingrevenge » Thu Apr 12, 2012 4:23 pm

is the barrel properly centred? some advice on how to guarantee it here: http://www.spudfiles.com/forums/epoxy-c ... t8916.html

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Unread postAuthor: sagthegreat » Thu Apr 12, 2012 6:14 pm

sometimes when you go up to higher pressures, the rubber will compress onto the barrel and make a seal, it has worked for me
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Unread postAuthor: PotatoEnemy17 » Fri Apr 13, 2012 5:31 pm

Thanks for the help. I made a hot glue piston and I have epoxyed evereything together now, I just have to wait for it to dry.
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