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Piston Face

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: MrCrowley » Wed May 05, 2010 10:07 pm

Go with the second picture. The first one is pointless since the added area is equaled with pressure behind it as well. This could even rip off your sealing face or such too.
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Unread postAuthor: Technician1002 » Wed May 05, 2010 10:18 pm

Leave room behind the piston for a bumper. Without one things will break.

In the Wiki, there is a section on Piston Valves that covers the forces on one that hold it closed and the force and pressure in the pilot required to open it. This force goes down as the piston OD is reduced to nearly the same diameter as the valve seat. As these sizes become close to the same, pressure in the pilot area from blowby (eq pressure) will hold the piston closed to lower pressures and piston friction becomes critical. The upside is they are fast when they do pop open. You don't want these sizes too close to the same as it makes the valve unreliable and subject to not firing.

http://www.spudfiles.com/spud_wiki/index.php?title=Piston_valve
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Unread postAuthor: Crna Legija » Thu May 06, 2010 1:31 am

i made my piston kinda like that i didnt use a washer tho i had a peace of some white plastic i think its nylon it was 2mm bigger than my part it slide in
i drill press lathed it down but not the end so it has a in built washer

it aslo let me use a bigger barrel port
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Attachments
piston.jpg
this it the piston you can see at the rubber end it a bit bigger

bad pic i only have a iphone
piston.jpg (35.44 KiB) Viewed 264 times
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Unread postAuthor: clemsonguy1125 » Thu May 06, 2010 2:47 pm

Ok, I'm going to go with the second picture and the bumpers going to be a couple rubber gaskets
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Unread postAuthor: jhalek90 » Thu May 06, 2010 6:11 pm

Use number 2

Just make sure the piston is a good fit in the bushing, and you will be more than fine.

Pic 1 would probably not work very well.
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POLAND_SPUD wrote:Anything is possible with the proper 3-way valve.
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Unread postAuthor: clemsonguy1125 » Thu May 06, 2010 6:35 pm

Thats what I heard, the pistons cast in a plug so it should fit in the bushing nice, I was just worried there would be no air to push it back
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