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2 X Spring Piston Hybrid

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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2 X Spring Piston Hybrid

Unread postAuthor: Rocketmanstu » Thu Jan 14, 2010 1:02 pm

Hi from Canada , I am mulling around an idea here goes ,
I am building this into a 3" T , a piston valve held against the combustion chamber outlet with a compression spring behind it to hold the chamber @ 28 PSIG
in theory the subsequent pressure rise on ignition will overcome the spring and dump the chamber then slam shut again any thoughts ???
Stu
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Unread postAuthor: jeepkahn » Thu Jan 14, 2010 1:29 pm

Are you gonna be able to dial that up??? Really you should shoot for the spring holds whatever your LAUNCH pressure is intended for, otherwise it will be surely underpowered... Is that a schedule 80 tee?
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Unread postAuthor: Rocketmanstu » Thu Jan 14, 2010 1:34 pm

Yes can change spring pressure , just want it to hold back the 28 psig mix until the boom- the chamber is sked 80 the rest will be wrapped in fibreglass
epoxy for reinforcement have you seen this done yet ? and does it work ?
Stu
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Unread postAuthor: jackssmirkingrevenge » Thu Jan 14, 2010 1:40 pm

Piston hybrid have certainly been done, something like this:

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The idea works, but your parts appear to be made of plastic...
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Unread postAuthor: jeepkahn » Thu Jan 14, 2010 1:43 pm

A couple have done it, I'm sure someone will be by shortly with links...Or you can check the wikipage and look under cannon designs or such... The point of doing a piston hybrid is to raise the launch pressure(the psi that hits the projectile) without having to use burst discs, so you'll want your spring to hold back more than just yoour mix pressure, you'll want it to hold combustion pressure untill it reaches a given psi and then opens...
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Unread postAuthor: Rocketmanstu » Thu Jan 14, 2010 1:46 pm

Thats an interesting design and yes the parts are plastic for now , have a metal lathe and milling machine its just easer machining plastic LOL
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Unread postAuthor: Rocketmanstu » Thu Jan 14, 2010 1:50 pm

Thanks Grumpy Old Fart
Sounds like were getting into the 400-600 psi range will switch to metal parts if thats the case
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Unread postAuthor: jackssmirkingrevenge » Thu Jan 14, 2010 2:19 pm

Rocketmanstu wrote:Sounds like were getting into the 400-600 psi range will switch to metal parts if thats the case


That was my point, with higher mixes it's best to err on the side of caution when it comes to construction, especially with large diameter fittings.
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Unread postAuthor: Moonbogg » Thu Jan 14, 2010 5:47 pm

4-600psi from a 2x cannon? How do you figure?
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Unread postAuthor: Rocketmanstu » Thu Jan 14, 2010 5:51 pm

Just a guess momentary peak pressure
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Unread postAuthor: psycix » Thu Jan 14, 2010 7:12 pm

Pressure is not the only thing. With hybrids, the shockwave from the sudden pressure increase may cause the PVC to develop micro cracks.
IIRC, so far, all PVC hybrids known to spudfiles have eventually failed.
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Unread postAuthor: Rocketmanstu » Thu Jan 14, 2010 7:30 pm

PVC not good for hybrids ,thanks for the input.Safty first I guess within reason of course LOL
Stu 8)
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