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HELP!! question about a coaxial piston

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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HELP!! question about a coaxial piston

Unread postAuthor: whatthehellamidoing » Thu Aug 31, 2006 5:57 pm

so i am making a coaxial piston gun, and for some reason, i cant get a good seal on the barrell. i squared off the end of the barrel to the best of my ability, and i have no idea what else could be going wrong! could someone please help me! any tips, or even if you have plans for a piston gun, will help me out immensely. i will post pictures of my piston and design if that will help anyone figure out this problem.


thanks
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Unread postAuthor: DonTheLegend » Thu Aug 31, 2006 6:16 pm

Pictures would help, along with more details (sealing material, thickness, pipe size, etc.
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Unread postAuthor: schmanman » Thu Aug 31, 2006 6:53 pm

use a end cap as the piston, and put a rubber coupler on the end of the barrel inside of the valve o use as the sealing surface.
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Unread postAuthor: noname » Thu Aug 31, 2006 9:32 pm

Don't tell him to use an end cap until you know what sizes he's working with. End caps only work well in 4" guns and 1.25" guns with a somewhat good fit. And like donthelegend said, give us details.
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Unread postAuthor: whatthehellamidoing » Thu Aug 31, 2006 11:10 pm

i am using a custom made piston out of a peice of 2" pvc with 3" washers screwed onto it, with neoprene on one end of the piston to seal the barrel. i am using a 3" I.D peice of PVC. i will get some pictures up in the morning of my piston, and any other pictures that might help.
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Unread postAuthor: whatthehellamidoing » Fri Sep 01, 2006 4:23 pm

pic of piston
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Unread postAuthor: whatthehellamidoing » Fri Sep 01, 2006 4:23 pm

here is the part of the barrel that is recessed inside the chamber.
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Unread postAuthor: whatthehellamidoing » Fri Sep 01, 2006 4:25 pm

here is the end cap, its a little burnt up, but it still functions.
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Unread postAuthor: whatthehellamidoing » Fri Sep 01, 2006 4:27 pm

i was thinking about using a bouncy ball to seal the 1.5" barrel. i saw this on some one elses spud gun, and thought it would work well. also, how big of a spring should i use?

thanks
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Unread postAuthor: richardbridges » Fri Sep 01, 2006 4:32 pm

Look here and see if it helps at all.http://www.spudfiles.com/forums/viewtopic.php?t=3331&
:twisted: Happy cannoning!!! :twisted:
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Unread postAuthor: whatthehellamidoing » Fri Sep 01, 2006 4:58 pm

any ideas on if the piston i built will work, or should i just start over?
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Unread postAuthor: noname » Fri Sep 01, 2006 7:34 pm

Why wouldn't it work?
And you can use any spring that fits between the cap and the piston really. How big is that ball valve? I'm pretty sure it's 1/2", but it could be 3/4". If it's 1/2" it might not release that much air that fast.
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Unread postAuthor: schmanman » Fri Sep 01, 2006 9:19 pm

you could still use a rubber coupler on the barrel, because rubber and rubber will seal better than rubber and PVC

EDIT: I like your username, whatthehellamidoing. :D
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Unread postAuthor: whatthehellamidoing » Fri Sep 01, 2006 9:37 pm

i think i have it working. i just added a little bouncy ball thing to the end of the piston, and it seals really nicely. i got a 3lb resistance spring, and it seems to be holding fine. just inside waiting for the glue to set up. going to go pressure it up, and see what it does
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Unread postAuthor: dinsdale » Fri Sep 01, 2006 9:38 pm

is that a mousepad you used for a seal?
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