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Piston not actuating

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 not actuating

Unread postAuthor: Counterstriker » Sun Jul 27, 2008 3:53 pm

I need help.. I made my mini coaxial, I made it so it's actuated by the shrader but every time i push the shrader pin in all the air goes out the back.. not the front.. This is pissing me off so freaking much.. I did every possible thing.. I made the piston a real good fit and still didn't work.. it's a 1/2 piston btw.. any help.. :?:
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Unread postAuthor: iisthemuffin » Sun Jul 27, 2008 4:37 pm

You should have searched. I made the exact same thread about a week ago. Im making a mini coaxial as well. The shrader wont pilot. Its too small so all of the air slowly comes out of it instead of one large gust that actuates the piston.

Just slap a 1/2 inch ball valve on there and you should be golden.
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Unread postAuthor: starman » Sun Jul 27, 2008 4:38 pm

Hey man, good to see you back. This can almost always be attributed to the piston letting too much air slip around it...especially in small guns where everything is smallish....piston face, small air quantity, pilot, etc.

It's going to have to fit really well...without catching any of course.
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Last edited by starman on Sun Jul 27, 2008 4:42 pm, edited 1 time in total.
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Unread postAuthor: Mr.Sandman » Sun Jul 27, 2008 4:39 pm

you cant make a piston fit too tight or it will not pilot. is the piston serviceble if so put some plumbers grease or vaseline on it if that doesnt help you need to make a slightly smaller piston. but the smaller piston still needs to fit tight.
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Unread postAuthor: Sticky_Tape » Sun Jul 27, 2008 5:47 pm

iisthemuffin wrote:You should have searched. I made the exact same thread about a week ago. Im making a mini coaxial as well. The shrader wont pilot. Its too small so all of the air slowly comes out of it instead of one large gust that actuates the piston.

Just slap a 1/2 inch ball valve on there and you should be golden.

Don't listen to that I used a shrader works fine. you just need the pilot volume to be small and have a good fitting piston also do what
Mr. Sandman said.
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You can tell how awesome a cannon is by the pressure used.
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Unread postAuthor: jr » Sun Jul 27, 2008 9:49 pm

So you guys are saying that :

If a piston is to tight it will not work and if the piston is to loose it will not work. A little confused!

Is there a perfect gap number? If you could build a perfect assembly what would the tolerance (distance between piston and housing) be? .030, .069, .008, ect.... I ask because I now have a 7x10 mini lathe :D
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Unread postAuthor: MrCrowley » Sun Jul 27, 2008 11:01 pm

I had to put three o-rings on a 1/2" dowel rod to get it to pilot of a schrader, just use a blow gun if you can't minimize the pilot volume much more.
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Unread postAuthor: jrrdw » Mon Jul 28, 2008 5:45 am

You know you built a nicely fitted piston when you can move it with lung power, but it doesn't slide when you tilt the cannon one way or the other. Whan you have built that good of a fit and it doesn't accuate, piloting is mostly allways the buzz kill.
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Unread postAuthor: Sticky_Tape » Mon Jul 28, 2008 8:37 am

Use the shrader it will work if you can trobleshoot the piston use vaseline and make it fit pretty good what is the piston material? You can use electrical tape to make the piston fit better. Also what pressures are you useing? The piston might not fit loose enough for the pressure to easily push it just letting the air pass around it. How far does the piston move back if it was actuating?
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You can tell how awesome a cannon is by the pressure used.
http://www.spudfiles.com/forums/high-pr ... 12803.html
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Unread postAuthor: Counterstriker » Mon Jul 28, 2008 11:16 am

The piston material is a crayola marker, very ice fit with a good sealing face. I'll try vaseline again. Thanks.
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Unread postAuthor: Mr.Sandman » Mon Jul 28, 2008 11:17 am

kinda funny because on all of my mini coaxials i use either an part of axe bullet or a crayola marker
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Unread postAuthor: Counterstriker » Mon Jul 28, 2008 11:20 am

Oh yeah, that axe bullet.. Those are so tiny, that's a good idea.
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Unread postAuthor: Mr.Sandman » Mon Jul 28, 2008 11:23 am

yeah i get a pipe cutter and cut about 1 cm of the end and fill it with epoxy wrap it in a little electrical tape and it is a perfect fit for 1/2 inch pipe
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Unread postAuthor: Sticky_Tape » Mon Jul 28, 2008 11:50 am

Yeah that might work fpr a piston I suggest glueing a disk of leather between the rubber and metal to give the rubber a little bit more of give to seal on the barrel and use vaseline.
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http://www.spudfiles.com/forums/high-pr ... 12803.html
xnt rnm ne z ahtbg
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