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Piston Valve Design

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 Design

Unread postAuthor: daberno123 » Sun Nov 25, 2007 7:59 pm

This is the design I came up with for a valve on my cannon after getting the basic principals down about a piston valve. The design was based on the idea of a sprinkler valve that has the plastic circle attached to it to make it more efficient. I would probably put it in a 2" tee. Tell me if you think it will work.

I was thinking about using 1/16" sheet pvc
I might use some insulation for a bumper
I might pilot the valve with my 1" sprinkler valve, but I'm not sure if that would help much compared to just a blowgun
The spring would be one that I got out of a rod that holds the toilet paper
I have an old bicycle tube that I would use to help it seal

This is a video of my current cannon at 80 psi with a sprinkler valve

[youtube]http://www.youtube.com/watch?v=HIu4Mjy5R3E[/youtube]
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Description of valve
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A picture of my launcher
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Unread postAuthor: Zen/// » Sun Nov 25, 2007 8:25 pm

Nice, I love the barrel support.

DMW!?!?!?

SCRAP THAT DEATH TRAP!
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Last edited by Zen/// on Sun Nov 25, 2007 8:52 pm, edited 1 time in total.
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Unread postAuthor: VH_man » Sun Nov 25, 2007 8:43 pm

I spy DWV......... Replace the bell reducers on your chamber.......... before they explode.......
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Unread postAuthor: BC Pneumatics » Sun Nov 25, 2007 8:49 pm

VH_man wrote:I spy DWV......... Replace the bell reducers on your chamber.......... before they explode.......


VH_man is right, that cannon is more dangerous than it has to be.
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Unread postAuthor: JDP12 » Sun Nov 25, 2007 8:59 pm

ditto on the DWV.. i was about to mention that
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Unread postAuthor: daberno123 » Sun Nov 25, 2007 9:07 pm

I already know about the dwv and I'm going to replace it
What about the valve design?

I just checked the price of 4x2 bushings and they are $15 a piece!! Any cheaper suggestions?
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Unread postAuthor: Killjoy » Sun Nov 25, 2007 9:19 pm

I like the valve design, looks like an inline-piston valve. It might be hard to build it though (but isn't everything the first time around), but the main problem I see is trying to get the mid-wall and piston to seal since the inside of a tee is round. Its possible, but it would be easier, more reliable (probably), and more durable if you just built a normal piston valve.

But give it a shot, would be pretty awesome if it worked.
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Unread postAuthor: Maniac » Sun Nov 25, 2007 9:27 pm

nice gun scrap than dwv noe also what is up with all the couplers
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Unread postAuthor: BC Pneumatics » Sun Nov 25, 2007 9:34 pm

daberno123 wrote:I already know about the dwv and I'm going to replace it
What about the valve design?

I just checked the price of 4x2 bushings and they are $15 a piece!! Any cheaper suggestions?


No. That is the cost of safety.
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Unread postAuthor: mopherman » Sun Nov 25, 2007 9:37 pm

looks great. loose the reducers and it'l be good for 120 psi. BTW, I love bad religion. props on the music
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Unread postAuthor: daberno123 » Sun Nov 25, 2007 9:43 pm

what is up with all the couplers

I adapted that piece from my first gun to make it level with the barrel support

the main problem I see is trying to get the mid-wall and piston to seal since the inside of a tee is round.

The top part of the piston would be a disk of sheet pvc and the part coming down woud be a rectangular piece of sheet pvc glued to the bottom of the disk
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Unread postAuthor: jackssmirkingrevenge » Mon Nov 26, 2007 12:12 am

I like your launcher, though the length of your hose gave me a mild cardiac arrest and as to the position of the sprinkler valve, see attachment ;)

Your design looks like it would work though not any better than a coaxial piston valve, looks like an excess complication personally but hey, if you want to make something different, go for it :D
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Unread postAuthor: MrCrowley » Mon Nov 26, 2007 12:54 am

Also with JSR's recomendations, having your valve where it is, isn't good for the flow, the air has to do a 180 degree turn before getting to the projectile, it also puts more stress on the joints.
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Unread postAuthor: Pilgrimman » Mon Nov 26, 2007 1:43 am

I second JSR's post. I loaded my gun one time, but forgot to ram it down to the breech. What I got was a flying potato that would have flown further if I had thrown it! This was at 100 psi, mind you! Move the valve to the breech, and you will see an increase in performance.

As to the valve idea, it's certainly interesting, and I'd encourage you to try it, but I think, conceptually, that traditional piston valves will perform better 1. because they don't restrict flow (much), and 2. They don't have bends that cause the gasses to lose energy (Other than the 90 degrees from chamber to barrel, and this is almost infinitesimal). One advantage I do see is that the moving portion is considerably lighter than most pistons, but this advantage is countered by the force of the spring closing the valve, (If, as I assume, it is pressing the valve down), and the weight issue for traditional pistons can be remedied.

Again it's still interesting. Try it! I've been wrong before! (In case you were wondering! :D )
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Unread postAuthor: jackssmirkingrevenge » Mon Nov 26, 2007 2:32 am

The dual chambers are also a little large in comparison to the barrel volume, using just one would make your launcher quieter, easier to pressurise and the performance loss would not be that dramatic.
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