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New piston gun

Built a pneumatic cannon? Then post it here! This section is for completed, finished cannons that you have built. Please include pictures and information.
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New piston gun

Unread postAuthor: charizzardd » Sun Apr 12, 2009 11:56 pm

This is my first piston gun!!!! welcome to the big leagues lol... well not yet because its not done but close enough.

Well i got the parts and put this together this weekend... still cant get the piston to seal quite right yet... Although i haven't glued it together yet and actually tried it at higher pressures. Perhaps you guys have some suggestions.

check pics for more details...

o yea the pipe size...

the barrel is 3/4'' - to shoot paintballs... i have cpvc pipe on there... i know not that great of an idea but i wrapped it in some GORILLA duct tape and i used it on an older gun for a while that just used a ball valve and had no problems. So this new gun is kinda an upgrade for the old ball valve one...

-the chamber is 1''
-the tee connected to the blow gun is 1''
-the 1'' tee is connected to the 1'' coupling... which holds a washer and the bumper for the piston.
-The piston is housed in 1'' pipe and is supposed to seal against 3/4'' inside the tee.

The rubber washer is just about the size of the sealing face, a little bigger... but that's why its not screwed all the way into the piston, so that the area of piston is still exposed to allow air to blow it back once the pilot pressure is dumped via blowgun.

hope this all makes sense, im still working to fix the sealing problem so opinions are welcomed and hoped for!!! otherwise enjoy the cannon... Ill post more pics and damage ones too once its completed.


-charizzard
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Attachments
0413090011.jpg
Full gun...
0413090011a.jpg
back part of the gun. The tee on the left is just to branch off to my schrader valve which is in a threaded plug at the far left. Also goes to the blow gun which i assume is plenty to pilot this sized valve... The coupling has a big washer in it so that the piston cant slide back and will eventually have some kind of bumper in it...
0413090012.jpg
This is the tee with the valve... piston is not seated...
0413090012a.jpg
valve is seated... it seems to be sealing with minimal air leaking... i cant hear any hissing but just from blowing and sucking on the pilot side i can feel suction on the barrel side...
0413090013.jpg
finally the piston... hot glue cast in the pipe its housed in. a simple bolt screwed into it with a nut a metal washer a nicely sized neoprene rubber washer... i have the exact measurement somewhere... i think its 7/16... then another washer and the top of the bolt. I tightened it up pretty good. It really seems like i just need a little more of something to get it to seal perfectly... its barely leaking, but i want to not leak when i finally glue it together and test it at higher pressures than just me blowing in it.

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Valve sealing

Unread postAuthor: Technician1002 » Mon Apr 13, 2009 12:19 am

If the end of the barrel is not smooth, the piston may have trouble sealing it. In one of my piston cannons, I used a dowell with a piece of sand paper glued on the end and used it to "polish" the valve seat nice and flat. It fixed my leak.
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Unread postAuthor: jackssmirkingrevenge » Mon Apr 13, 2009 12:56 am

Why the enormous pilot chamber?
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Unread postAuthor: Pilgrimman » Mon Apr 13, 2009 1:26 am

Why the enormous pilot chamber?


To annoy you :D
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Unread postAuthor: charizzardd » Mon Apr 13, 2009 3:02 pm

I kept thinking about how big the pilot was. That's really the shortest I could make it. I mean I guess I coulda just put an elbow on there and threaded the shrader through it but a tee seemed like the best idea. And thanks Im gonna try sanding it down when I get home from college. Hopefully that works.


-charizzardd
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Unread postAuthor: LCTChamp » Mon Apr 13, 2009 4:14 pm

The valve not sealing is probably because the barrel isn't smooth or the sealing face isn't lined up with it straight.

The huge pilot volume will decrease performance. You could just put a plug in the piston valve tee. Then tap a hole to put a 1/8" or 1/4" tee in the back.
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Unread postAuthor: twizi » Mon Apr 13, 2009 8:02 pm

nice gun but why is it in the bbmg show case, congrats on the step up from ballvalves
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Unread postAuthor: jackssmirkingrevenge » Mon Apr 13, 2009 10:38 pm

Pilgrimman wrote:To annoy you :D


Mission accomplished :roll: :D

charizzardd wrote:I kept thinking about how big the pilot was. That's really the shortest I could make it.


No it isn't, it's at least 10 times bigger than it needs to be and you will see the difference when it comes to power, which is a shame.
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Unread postAuthor: Carlman » Mon Apr 13, 2009 11:01 pm

pilot volume fail :roll:

nice work if you cut down the pilot volume, if nt then you will know to do it next time!
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