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Improving performance on my Piston valve air cannon?

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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Improving performance on my Piston valve air cannon?

Unread postAuthor: Metalcookie » Mon Mar 15, 2010 4:40 pm

I recently built a 2 inch piston valve with 1 inch porting. The tank is screwed on via a 1 inch slip to thread adapter. I use a 1 inch srinkler valve as a pilot valve (This one's an Orbit Watermaster). I used a 1 1/4 inch coupler as the piston and filled it with epoxy. When I fill the gun with air, everything is airtight, but when I release the pilot volume, the gun's performance is less than impressive. It can still shoot a spud, but right now I'm getting better performance out of a cannon using a 1 inch sprinkler valve :oops: I'd post pics of it, but I'm way out of state for the moment. What should I do to improve performance? I was thinking that having air flow through a 1 inch hole twice(once to get out of the main tank on the gun, and again to get out of the cannon) was messing with performance, but since this is one of my first kind of successful piston valve air cannons I'm not really sure.
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Unread postAuthor: jackssmirkingrevenge » Mon Mar 15, 2010 4:48 pm

A diagram of the internals would be helpful. How tight is the piston in the tube it travels in?
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Unread postAuthor: Metalcookie » Mon Mar 15, 2010 4:51 pm

It's a pretty good fit. Probably not the best, but it's pretty good. I'll try to make a diagram of it ASAP
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Unread postAuthor: jackssmirkingrevenge » Mon Mar 15, 2010 4:58 pm

Try wrapping it in tape until it's tight enough that you can barely move it with one finger.
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Unread postAuthor: Metalcookie » Mon Mar 15, 2010 5:11 pm

Hmm. I'l have to try that.

Anyways here's a very rough drawing of the gun. I used the design Klugeboy demonstrated in one of his videos on youtube. It's in part 2 of his piston valve videos.

on the diagram I have a 1 inch slip - thread adapter at the end of the 1 inch pipe so I can screw on barrels.
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Unread postAuthor: FighterAce » Mon Mar 15, 2010 5:21 pm

If its hard to move then it wont open at lower pressures... right?
If you could make the piston move easily but seal 100% with O rings you'd have a real winner :D Unfortunately if the piston moves easily it starts to leak air around itself.
You really got to balance adequate seal and ease of movement the hard way... Or a floating O ring design maybe?
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Unread postAuthor: c11man » Mon Mar 15, 2010 5:25 pm

is the entire piston full of epoxy? that will hurt preformace. also how long is your piston travel?
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Unread postAuthor: jackssmirkingrevenge » Mon Mar 15, 2010 5:25 pm

Unless your piston is ridiculously heavy, the only reason I can see for poor performance is a loose piston fit.

c11man wrote:how long is your piston travel?


He's already done his homework ;)
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Unread postAuthor: Metalcookie » Mon Mar 15, 2010 5:52 pm

The piston isn't very heavy, and it travels about an inch. Like jackssmirkingrevenge said, I've already done mah math. :D


The piston has a far from airtight fit, and when I exhaust the pilot volume, there is quite a gust of air coming out of the sprinkler valve.
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Unread postAuthor: Gun Freak » Mon Mar 15, 2010 5:54 pm

Try rebuilding the piston with a lighter material. Thats what I would do...
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Unread postAuthor: Metalcookie » Mon Mar 15, 2010 5:57 pm

How light should the piston be? It's not heavier than a wooden piston of the same size.
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Unread postAuthor: jackssmirkingrevenge » Mon Mar 15, 2010 6:08 pm

Metalcookie wrote:The piston has a far from airtight fit, and when I exhaust the pilot volume, there is quite a gust of air coming out of the sprinkler valve.


Wrap it in duct or masking tape as suggested earlier and see if it makes a difference
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Unread postAuthor: Gun Freak » Mon Mar 15, 2010 6:29 pm

Jack it might just be too heavy, ya know?
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Unread postAuthor: Metalcookie » Mon Mar 15, 2010 6:47 pm

I wish I could work on it, but I'm stuck in Omaha for the moment :cry:
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Unread postAuthor: jackssmirkingrevenge » Tue Mar 16, 2010 1:04 am

Gun Freak wrote:Jack it might just be too heavy, ya know?


True, but in that case a loose fit isn't helping.

I wish I could work on it, but I'm stuck in Omaha for the moment


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