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piston hybrid, relief valve?

Post questions and info about hybrid (compressed gas with fuel) powered cannons here. This includes discussion about fuels, ratios, ignition systems, build types, safety, and anything else relevant.
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piston hybrid, relief valve?

Unread postAuthor: pat123 » Thu Apr 03, 2008 3:07 pm

I have been trying to design a piston for my hybrid. I was wondering if I could use a relief valve. it would hold in the pressure until combustion then let it vent. do you think it will work. It may not be able to hod the suddent spike of the combustion.
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Unread postAuthor: SpudFarm » Thu Apr 03, 2008 3:09 pm

no valve is needed..
the air behind the piston act as a bumper..
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Unread postAuthor: pat123 » Thu Apr 03, 2008 3:11 pm

I mean instead of a piston. the air would flow through the valve into the barrel.
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Unread postAuthor: SpudFarm » Thu Apr 03, 2008 3:54 pm

you get BAD flow and BAD power:)
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Unread postAuthor: psycix » Thu Apr 03, 2008 4:09 pm

Yes, it will block your flow so much, that an normal combustion would be better.
Also on top of that, it closes again when it reaches the lower limit and thus limits the pressure in your barrel.
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Unread postAuthor: pat123 » Thu Apr 03, 2008 4:20 pm

would you reccomend a spring design like fnords old one or a barrel sealer.
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Unread postAuthor: SpudFarm » Thu Apr 03, 2008 4:22 pm

try to be the first to make a coaxial hybrid :)
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Unread postAuthor: pat123 » Thu Apr 03, 2008 4:23 pm

I already made the gun i am working on just adding a poston to it.
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Unread postAuthor: SpudFarm » Thu Apr 03, 2008 4:26 pm

ok then make a barrel sealer housed in a TEE.

BTW you get less performance..
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Unread postAuthor: pat123 » Thu Apr 03, 2008 4:55 pm

how much less performance. it is driving me crazy changing the foil every time.
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Unread postAuthor: SpudFarm » Thu Apr 03, 2008 5:01 pm

if you have a piston open at 30psi you can find out by using a disk that blows right after ignition..
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Unread postAuthor: pat123 » Thu Apr 03, 2008 5:05 pm

http://www.lowes.com/lowes/lkn?action=productDetail&productId=48570-15649-PPRV50&lpage=none
how bad would performance be with like a 1.5 in valve like this on on a .5 in barrel.

if you have a piston open at 30psi you can find out by using a disk that blows right after ignition..

I am a little confused?
edit: I think I get it now. a normal burst disk is set at a higher pressure to burst but the piston would move at the minimum change in pressure.
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Unread postAuthor: Jeeperforlife » Thu Apr 03, 2008 10:29 pm

I am almost done with my coaxial hybrid. What I did is the piston has a 1/8" brass pipe off the back of it going through the end cap. I have a shrader valve on that witch fills the chamber behind the piston with compressed air and lets all the air out once the gun fires. I designed it this way so I can adjust the "burst rate" and get full power with the piston staying in the back letting all the power out the barrel.

I will post pictures when it is done.
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Unread postAuthor: sniperjosh » Fri Apr 04, 2008 6:12 am

I'm also getting infected with piston valve hybrid designs, its only a matter of time :P

I imagine power loss compared to burst discs would be significant, but I'm sure different piston valve designs would produce varying power. I'm looking at it for small bore applications, just the ease/speed of pressurizing a small chamber and getting power gains over a larger chambered / longer barreled pneumatic seems attractive.
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Unread postAuthor: SpudFarm » Fri Apr 04, 2008 9:59 am

if i got money to spare i will make a piston valve to my full sized hybrid so if i want to shoot fast and easy with lower power i just screw it in the union and there i have a piston hybrid :)

also i am going to use a really tight spring behind the piston to hold it there until the pressure is at about 400psi.
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