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piston valve trouble

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 valve trouble

Unread postAuthor: yodabeast14 » Tue Apr 23, 2013 7:06 am

Hi, i built a barrel sealing piston valve cannon everything went smoothly until filling. I have air sneaking around the piston.

The piston is made from a coupler filled with some epoxy and hot glue, then topped of with a rubber washer. The piston moves freely inside the 2" T housing.

I was thinking of puting in a spring behind the piston to hold it up against the barrel. Or should I just make a new piston?
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Unread postAuthor: jackssmirkingrevenge » Tue Apr 23, 2013 7:22 am

If air pressure isn't enough to keep it shut, then a spring isn't really going to help.

How are you filling it? It could be that you are filling too slowly, do you have a large chamber volume?
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Unread postAuthor: RBurke83 » Tue Apr 23, 2013 8:11 am

How is the rubber sealing surface attached? Could be air coming through the threads of a screw.
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Unread postAuthor: jackssmirkingrevenge » Tue Apr 23, 2013 8:16 am

Some pictures of your setup would help us help you ;)
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Unread postAuthor: mattyzip77 » Tue Apr 23, 2013 5:19 pm

You need to epoxy the bolt and washer holding the sealing face on..
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Unread postAuthor: yodabeast14 » Tue Apr 23, 2013 7:44 pm

alright so i cant figure out why i cant post a picture, I even read the stickies.

Any how, i made a new piston today with less travel. I still have the leaking problem. Could it be that my fill port is on my chamber and not behind my piston with my pilot valve?

Once I fill the gun past 40 psi it fires but still has the same herendous leak out the barrel. The new piston is 1/2" rod With washers Neoprene Ruber and nuts secure the sandwich together little washer holding rubber in front to seal against the barrel of course.
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Unread postAuthor: mattyzip77 » Tue Apr 23, 2013 8:26 pm

That is why!!!! You must fill through your pilot!!! Did you epoxy together the nuts onto the rod????
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Unread postAuthor: yodabeast14 » Tue Apr 23, 2013 8:41 pm

no not yet. there just force tightened on right know

Can i use loctite?
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Last edited by yodabeast14 on Tue Apr 23, 2013 8:56 pm, edited 1 time in total.

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Unread postAuthor: yodabeast14 » Tue Apr 23, 2013 8:43 pm

How do fill through my pilot if its a sprinkler valve?
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Unread postAuthor: jackssmirkingrevenge » Wed Apr 24, 2013 1:15 am

You have to fill through the sprinkler valve pilot.

alright so i cant figure out why i cant post a picture, I even read the stickies.


Come on, this is 2013... could it be that your picture is too big? I believe the size limit is 350kb.
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Unread postAuthor: yodabeast14 » Wed Apr 24, 2013 7:04 am

I know how its just to big. but can i post more than one at a time

Why can't i fill through my chamber and add a spring behind the piston? has anyone ever tried this before?
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Unread postAuthor: RBurke83 » Wed Apr 24, 2013 7:42 am

Am I missing something here..? He has a sprinkler valve and a homemade piston? I have heard of qev's triggering qev's but this seems overkill. We need a picture.
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Unread postAuthor: Crna Legija » Wed Apr 24, 2013 7:43 am

to post more then one press the add attachment button
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Unread postAuthor: jackssmirkingrevenge » Wed Apr 24, 2013 8:18 am

if it was destined to seal, you wouldn't need a spring.

http://www.spudfiles.com/forums/new-jsr ... 20075.html
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Unread postAuthor: mattyzip77 » Wed Apr 24, 2013 1:36 pm

RBurke83 wrote:Am I missing something here..? He has a sprinkler valve and a homemade piston? I have heard of qev's triggering qev's but this seems overkill. We need a picture.


You obviously havnt been around here that long... There is no such thing as overkill, and a piston valve needs something to pilot it. And actually a qev is a better pilot than a sprinkler valve..

Try wrapiing a layer or 2 of duct tape around your piston. It may be a little to small. If its not the perfect size it will not seal. I have made a coupler piston before and I had to do this for the right fit. No locktite... you need to epoxy it so air wont escape through it. As for chamber filling do some research and you will know why you cant do it.Do a search of superna with gun freak as the author and look at this cannon.
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Last edited by mattyzip77 on Wed Apr 24, 2013 4:55 pm, edited 1 time in total.
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