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Piston probloms

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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Piston probloms

Unread postAuthor: turbohacker » Sun Apr 08, 2007 6:09 pm

this is my firt piston gun. I have been building pnumatics for quite a while but i cant seem to get this dang piston to work :evil:
the pison seals well but when i exaust it only air from behind the pison leaves, the piston will not slam back. when te pressure is relived then the pison will slide back. any suggestions?[/img]
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air guns 002.jpg
full gun
air guns 005.jpg
gun opened
air guns 006.jpg
close up of piston
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Unread postAuthor: A-98 » Sun Apr 08, 2007 6:11 pm

ive had that happen to me, and i couldnt fix it. other people will probably answer your question tho. and ide like to know the answer
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Unread postAuthor: benstern » Sun Apr 08, 2007 6:12 pm

Is the piston lubricated? If not it may not move because of friction.
How big is the chamber?
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Unread postAuthor: spudthug » Sun Apr 08, 2007 6:17 pm

yes rubber is very tricky to get to move....lube it up wtih gun oil......alot of gun oil if it doesnt work...maybe the inside of ur chamber is rough/bumpy??sand it a bit just to be sure...fine grit sandpaper 250 grit+ only u will rough it more if u use any less grit..
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Unread postAuthor: jrrdw » Sun Apr 08, 2007 6:17 pm

Can't really see how much pilot volume you have. Do you get a little amount of air out of the sprinkler valve, or does the whole main chamber empty out of the sprinkler valve?
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Unread postAuthor: turbohacker » Sun Apr 08, 2007 6:18 pm

chainber is around the barrel
3 inch outer pipe for resivior and two inch inner pipe for barrel
ps. it is lubed extremly well
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Last edited by turbohacker on Sun Apr 08, 2007 6:25 pm, edited 1 time in total.
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Unread postAuthor: keep_it_real » Sun Apr 08, 2007 6:21 pm

I would make a lot more chamber volume. I doesn't look like you have very much. Make sure the piston slides pretty easily but it should also seal pretty well against the pipe.
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Unread postAuthor: jrrdw » Sun Apr 08, 2007 6:22 pm

Do you have enough of a pilot chamber for piston to retreat into?
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Unread postAuthor: experament-u2 » Sun Apr 08, 2007 8:47 pm

this is the exact problem i had a few days ago
i fixed it by adding a oring and cutting the size of my piston down but im not sure how u could do that to urs
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Unread postAuthor: hi » Sun Apr 08, 2007 9:44 pm

i had that exact same problem with my first coaxial. the solution is simple, your piston is too loose int the chamber. you need to make it fit better and put a little oil on it and it ill work fine. your piston isnt exactly round, it close, but not quite. it need to be perfecly round and fit in the chamber just right.
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Unread postAuthor: Matheusilla » Mon Apr 09, 2007 10:17 am

I agree with "hi". Your piston is probably too loose. There are many ways to make it fit better, it just depends on what you have to use/work with.
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Unread postAuthor: deusXmachina » Tue Apr 10, 2007 12:44 pm

It's too thin to put o-rings around easily, but Ive heard a few layers of duct tape/painters tape work, just make sure they don't come loose and get lodged in the pilot assembly.
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Unread postAuthor: Freefall » Tue Apr 10, 2007 12:52 pm

When you try to fire, does the chamber completely depressurize? At first glance, I'd guess that you're leaking too much air past the piston, which prevents the force imbalance needed to drive the piston open.
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Unread postAuthor: tater36 » Tue Apr 10, 2007 4:15 pm

if i use an end cap for my piston on my first would multiple wraps of duct tape work to let air get past but still work?
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Unread postAuthor: Blitz » Tue Apr 10, 2007 4:26 pm

tater36 wrote:if i use an end cap for my piston on my first would multiple wraps of duct tape work to let air get past but still work?


Dude, start your own thread to ask that.

What exactly is that piston made of? What kind of rubber?
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