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How tight should my piston be?

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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Unread postAuthor: iisthemuffin » Sun Jul 20, 2008 12:50 pm

Yes i realize they are out of focus but im using my phone to take them. Takes a little work to focus them.

Also i am not using the mouse pad. I am using the thing from the furniture movers. I posted a picture of them some ways up.
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Unread postAuthor: iisthemuffin » Sun Jul 20, 2008 5:28 pm

Would not having enough pilot room stop it from opening?

Whoops sorry about double post. I thought i had clicked edit...
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Unread postAuthor: Sticky_Tape » Sun Jul 20, 2008 5:40 pm

The minimum lenth you SHOULD have from the back of the piston to the back plug is your barrels I/D divided by 4
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Unread postAuthor: iisthemuffin » Sun Jul 20, 2008 5:42 pm

Oh. Well ive got more than that.

Its still not piloting though. Does it have to be at high pressure to pilot? I have only pumped it to 20 because i havent glued it yet. I just glued it though and im going to try and take it higher and see if it pilots.
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Unread postAuthor: Gippeto » Sun Jul 20, 2008 6:24 pm

It seems to be boiling down to either;

1) A lack of frontal area. (not likely in a co-ax design)

2) Your piston is still too loose.

3) Your pilot is just too small.

I think we can rule out number 1.

JSR has successfully piloted pistons to (I believe) 1" with a schrader. So let's rule out number 3 as well.

That leaves number 2.

And so, I repeat;

When your piston fits so closely that you can't imagine the chamber filling,... then it's just about right.
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Unread postAuthor: iisthemuffin » Sun Jul 20, 2008 6:43 pm

Thats exactly how i feel now. I was actually just thinking that may it wont pilot because no air is getting in front of it because its so tight.
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Unread postAuthor: iisthemuffin » Mon Jul 21, 2008 8:00 pm

Hmmm......
My piston is not piloting. Im sure its tight enough. It cant move on its own. I have to push it for it to move. Im pretty sure air is getting into the rest of the chamber but it just wont pilot....

Im trying to pilot it with the pump attatchment. Im using a regular pump for a shrader. So when you open the clamp it lets air escape. Should that be nough to pilot it? It just wont go. :cry:

I pumped it up to 90 psi with no leaks.
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Unread postAuthor: daberno123 » Mon Jul 21, 2008 8:24 pm

Try pushing the pin of the shrader in with something else after taking the clamp off. Just opening the clamp might not let enough air out.
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Unread postAuthor: iisthemuffin » Mon Jul 21, 2008 8:39 pm

Ok ill go give it a try and ill poist back with results.
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Unread postAuthor: iisthemuffin » Mon Jul 21, 2008 8:49 pm

Bope. Nothing. Is it possible that the air isnt getting into the chamber and just building up behind the piston?

I really dont think that would happen but i honestly dot see why else it would pilot...
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Unread postAuthor: SEAKING9006 » Mon Jul 21, 2008 8:53 pm

Poke a hole through it so the hole would be exposed to the chamber. But, make it like the width of a pin.
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Unread postAuthor: iisthemuffin » Mon Jul 21, 2008 8:56 pm

Im not even sure if the chamber not filling is the problem. Andf if its not i would just make piloting harder by poking a hole though my piston.
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Unread postAuthor: iisthemuffin » Mon Jul 21, 2008 9:10 pm

Ok i know for SURE that air is getting into the chamber. I cut a tiny whole. But its still not piloting.

Is there some secret im missing? Man this is killing me.
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Unread postAuthor: iisthemuffin » Mon Jul 21, 2008 9:59 pm

Now my piston is piloting. But only when im pressurizing. So kind of a misfire. What does this mean? Im pumping too high?
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