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help with first piston valve

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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help with first piston valve

Unread postAuthor: BoxOfSpuds » Sun Nov 25, 2007 11:26 pm

I have been working on my first piston valve.its been an on and off project for a couple of months. i cant seem to get it to work. its a Barrel sealing tee valve housed in a 2" tee with 1 1/2" porting. until i get it working im just piloting it by disconnecting the quick connect i use to fill it.
i have tried many different things for pistons but i always have the same problem, all the air leaks out of the back, i Just made a hot glue piston today, i put it all together and the same thing happened. the piston wont slide back, its well lubricated and i can slide it with my finger just fine. it seams like the air is leaking around the piston faster than out the back. i added some duct tape to make it a bit more snug fit but it did the same thing.

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Pic of valve, note quick connect on left
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inside of valve
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hot glue piston
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valve in front of chamber
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Unread postAuthor: jackssmirkingrevenge » Mon Nov 26, 2007 12:05 am

Have you tried using a longer piston? That seems to be the problem.
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Unread postAuthor: Killjoy » Mon Nov 26, 2007 12:20 am

Yeah the piston looks to short, also the lip in the tee may be catching on the piston.

By the way I had the same problem, the piston slid well with my finger but I just couldn't get it to actuate, so I sanded a piece of 2" pvc pipe down and glued it in to the tee (so that the end of the pipe extended about a 1/2" past the inside hole of the tee (not sure if that makes sense)) to act as a guide and to provide a relatively smooth surface for the piston to slide in and it worked perfectly.
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Unread postAuthor: MrCrowley » Mon Nov 26, 2007 12:52 am

2" barrel sealing piston valve you say....

<A HREF="http://www.spudfiles.com/forums/how-to-make-a-pneumatic-cannon-with-a-2-piston-valve-t10381.html"> My How-To</a>

You could either use my how-to to troubleshoot your design, or scrap your piston and make one similar to mine, it's up to you.
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Unread postAuthor: BoxOfSpuds » Mon Nov 26, 2007 9:41 pm

today i made a new piston that was longer and put some 2" pipe on the inside of my valve. it did the same thing. the air is leaking around the piston instead of pushing it back. its a snug fit but still slides well. any ideas
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Unread postAuthor: MrCrowley » Mon Nov 26, 2007 9:50 pm

You need a way better pilot valve. There is no way a QC will cut it.

You NEED a 1/2" ball valve, even bigger would be better, don't worry it wont waste any power, it will give you a lot better performance though.
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Unread postAuthor: jackssmirkingrevenge » Mon Nov 26, 2007 11:37 pm

seconded, basically the flow out of your QC is less than the flow around the diameter of the piston.
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Unread postAuthor: BoxOfSpuds » Tue Nov 27, 2007 8:11 am

ok thanks il try that today
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Unread postAuthor: BoxOfSpuds » Wed Nov 28, 2007 9:04 pm

thanks verry much guy's i tried a 1/2" ball valve today and it worked great i will be finishing the cannon as soon as i can. i will post some pics when i'm done
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Unread postAuthor: jackssmirkingrevenge » Wed Nov 28, 2007 11:31 pm

Good to hear :) don't forget some damage pics ;)
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Unread postAuthor: MrCrowley » Thu Nov 29, 2007 12:33 am

BoxOfSpuds wrote:thanks verry much guy's i tried a 1/2" ball valve today and it worked great i will be finishing the cannon as soon as i can. i will post some pics when i'm done


Glad to hear. It's a great feeling when it finally works isn't it.
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Unread postAuthor: spudgunnerwryyyyy » Thu Nov 29, 2007 12:44 am

Just a comment mr crowley is the god of teaching noobs how to make a piston valve. he helped me and countless others.

listen to him, most of his advice is comonplace but other is great
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