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Why wont my piston work!!!!?!?!??/!!!!!!

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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Why wont my piston work!!!!?!?!??/!!!!!!

Unread postAuthor: THEMOST » Sun Nov 19, 2006 5:04 pm

I made a coaxle piston valve with a 2" chamber and a piston that slides through a 3/4" pipe. The piston will seal but when I let out the exaust the piston doesnt move until it is completely depressurized! I used a neoprene washer on the end of a 1/2" pipe with a cap for the piston. I sanded the pipe down so that is would slide through the 3/4"pvc. Why the hell wont is work?!?!! :evil:


Do you think I might need O rings in it because I didnt put those in...? :?
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Unread postAuthor: jrrdw » Sun Nov 19, 2006 6:31 pm

What do you have for a vent on the pilot chamber? Mine didn't work at all untill i went with a modded sprinkler valve, now it's a bad ass piston valve!
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Unread postAuthor: schmanman » Sun Nov 19, 2006 6:46 pm

how well does it slide? spray in some wd-40, or pam (just an idea), or put a glob of Teflon/silicon paste inside of there, and I almost guarantee it will work. oh, put the stuff in first, then slide in the piston, so It does not get scraped off as it's being inserted. lithium grease works too. get the stuff in the grease gun tube, then pop open the metal tab/cut off the top, scoop some out with your finger, and put it on that way.
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Unread postAuthor: noname » Sun Nov 19, 2006 7:35 pm

2" chamber, and your piston slides in 3/4" pipe. Why? It might be the thing that's wrong.
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Unread postAuthor: THEMOST » Sun Nov 19, 2006 9:46 pm

jrrdw: I am using a blow gun for the exaust I think that should work because that seems to be the most :lol: popular thing to do.

schmanman: I did loob it with oil but I think that there is too much space around the piston where it slides. That would result in not having enough sucktion on the piston and the air goes around. It could also be because I used sizzors to shave down the pvc and mabey it should be completely round...idk. I should get some of the glopy grease though.

noname: It's not that. What I did was essentially ran the barrel tube all the way down the chamber, sliced it in the middle, and stuck a piston in it. The piston is located in the center of the coaxle chamber. It's only about 7" long and that includes the reducers. It's a very small chamber for a bb gun.
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Unread postAuthor: SpudStuff » Sun Nov 19, 2006 10:02 pm

A picture would be really helpful. You need to have a surface area on the sealing face so that the air can push it when you vent.
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Unread postAuthor: THEMOST » Mon Nov 20, 2006 6:53 am

I could take a pic of the chamber but it's already sealed off with the piston inside.(I'll have to saw it in halve to fix it)
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Unread postAuthor: joannaardway » Mon Nov 20, 2006 7:45 am

*grits teeth*

Never ever seal a piston valve permantly.

Why do you think that Joel uses screws to fit the end piece on to the Supah valve? In case he needs to fix it - he's built hundreds of the things and he still takes the precaution.

Gort does the same thing with the Mauler. So does my twin when he builds a piston valve.

Whatever happens, that valve is not going to work until it's been altered, so you'll need to cut it open anyway.
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Unread postAuthor: POS » Mon Nov 20, 2006 1:53 pm

What's the diamete of your barrel ? In this setup, it should me smaller than 3/4". The piston always needs to be bigger than the barrel diameter.
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Unread postAuthor: schmanman » Mon Nov 20, 2006 5:01 pm

wrap the piston in electrical tape, so it fits perfect. It should work then.
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Unread postAuthor: jrrdw » Mon Nov 20, 2006 7:24 pm

I tryed to use just a blow gun, it didn't work. I discovered the problem when i filled my chambers and then unscrewed the blow gun untill it flew off makeing my cannon fire. Basicly i found my problem by accident. And there it was, the blow gun just didn't vent the pilot chamber fast enough, try it, it mite work for you to. Then you will know for sure!
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Unread postAuthor: POS » Tue Nov 21, 2006 11:42 am

I had that same blowgun problem with my first. Use a as big as possible pilot valve, and a as small as possible pilot volume
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Unread postAuthor: THEMOST » Wed Nov 22, 2006 5:38 pm

I'll try the electric tape.

My barrel is reduced down a to bb size from the 3/4.
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