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Supersonic Aluminum Cannon- Piston Valve Help

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: Killjoy » Sun Jul 10, 2011 3:01 am

Different topic, same project,
Have you accounted for the impact force of the valve against the end plate? I'm looking at you tie rods for holding the end plate on to the pressure chamber, and taking into account operating pressure, piston size, and travel my gut tells me to be concerned the tie rods could fail or suffer permanent deformation when the valve opens.

I recently finished a 4" steel piston valve similar in design to you cannon, and my calculated averaged force on the end plate due to the impact of the piston was over 14,500 lbs of force with a 5" diameter, 11lb piston and 2 inches of travel. I doubt your piston weighs as much, but this exemplifies the importance of considering impact forces as well as static forces.
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Last edited by Killjoy on Mon Jul 11, 2011 8:51 pm, edited 1 time in total.
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Unread postAuthor: MrCrowley » Sun Jul 10, 2011 3:44 am

Im using a very tough rubber to withstand the 11000 pounds of pressure pushing it against the barrel

What rubber are you using by the way? I need to replace a sealing face on a piston hybrid and so far haven't found anything that will last 20+ shots.
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Unread postAuthor: POLAND_SPUD » Sun Jul 10, 2011 4:41 am

What rubber are you using by the way? I need to replace a sealing face on a piston hybrid and so far haven't found anything that will last 20+ shots
why not experiment with metal-metal seals ??
I guess that it might be tricky with a steel piston + steel barrel but what about steel barrel and piston made of more malleable material - like copper
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Unread postAuthor: Crna Legija » Sun Jul 10, 2011 5:03 am

POLAND_SPUD wrote:
What rubber are you using by the way? I need to replace a sealing face on a piston hybrid and so far haven't found anything that will last 20+ shots
why not experiment with metal-metal seals ??
I guess that it might be tricky with a steel piston + steel barrel but what about steel barrel and piston made of more malleable material - like copper



i think teflon would be better, ether way the piston and valve seat would have to be perfectly level probably impossible with out a lathe.

you might wanna try car/truck tire, you should be able to get a peace for free from a tire junk yard
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