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Piston valve air cannon ratio

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 air cannon ratio

Unread postAuthor: yodabeast14 » Sun Feb 03, 2013 3:16 pm

Hi everybody, i'm building a piston valve air cannon. I was just wondering if there is a certain pilot chamber to air chamber ratio that is perfered when making these. Thanks
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Re: Piston valve air cannon ratio

Unread postAuthor: jackssmirkingrevenge » Mon Feb 04, 2013 2:43 am

yodabeast14 wrote:Hi everybody, i'm building a piston valve air cannon. I was just wondering if there is a certain pilot chamber to air chamber ratio that is perfered when making these. Thanks


The pilot chamber should be as small as possible. The piston doesn't need to travel more than 25% of the barrel diameter to allow full flow, thoughi n practice 50% is a better idea to account for piston bounce - so if you have a 1 inch barrel, the piston only needs to move 1/2". Keeping this distance to a minimum also keeps the piston from accelerating too much and reduces stress on the launcher from the impact.

Valve opening speed is key to performance, and the faster the pilot chamber empties, the faster the piston will open. It stands to reason that for a given pilot valve, a smaller pilot chamber will empty faster. If you drill the same hole in a 1 gallon bucket and a 2 gallon bucket full of water, the first one will empty around twice as fast.
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Unread postAuthor: Technician1002 » Fri Feb 08, 2013 5:05 pm

The 25% applies to a coaxial valve where air can enter the valve seat from 360 degrees to be clear. If the piston is in a T with air entry from just one side, you will want a larger opening for full unrestricted flow.
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Unread postAuthor: jackssmirkingrevenge » Sat Feb 09, 2013 4:19 am

Since they need o-rings, chamber sealing valves tend to be less common than barrel sealing valves so I assumed OP meant to make the latter.
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Unread postAuthor: mobile chernobyl » Sat Feb 09, 2013 11:03 am

Plenty of barrel sealing T and X valves JSR - I've got a arsenal of them! :D

I know you know that just helping the OP
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Unread postAuthor: jackssmirkingrevenge » Sat Feb 09, 2013 11:11 am

mobile chernobyl wrote:Plenty of barrel sealing T and X valves JSR - I've got a arsenal of them!


I think you built your way out of the "typical spudder" category a long time ago ;)
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