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no burst disc hybrid revisited

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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Unread postAuthor: Deceiver » Fri Apr 27, 2007 4:46 pm

Yeah, I noticed that after I uploaded it, it works fine though when I open it in its own window(ie double click the animation itself) or try downloading it.
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Unread postAuthor: frankrede » Fri Apr 27, 2007 6:03 pm

The pressure created from combustion would make your barrel collapse in on itself.
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Unread postAuthor: Deceiver » Fri Apr 27, 2007 8:59 pm

Who says it has to be a PVC barrel? or that it is impossible to find crush rated pipe? Or that schd 40/80/120 won't stand up to the stresses of a 1-2x mix?

If anyone has the data I'd like to see some figures, for future designs.
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Unread postAuthor: frankrede » Fri Apr 27, 2007 10:43 pm

Well If I am not mistaken, sch-80 pvc is more vulnerable to outside forces.

as for steel or other exotic materials, it should work fine.
But I can't imagine how you could use steel without custom machining and welds.
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Unread postAuthor: Cool » Wed May 16, 2007 12:40 am

You could make a system that locks the piston when it goes back, then the flow of gas would be maximum. Make it spring loaded, and something that locks/catches the piston in the back position.
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Unread postAuthor: Pete Zaria » Wed May 16, 2007 12:53 am

I know this thread is old, and normally I wouldn't post, but I have to point something out -

The piston HAS to be 100% air-tight. If any fuel gets behind the piston, the results could be disastrous. A combustion behind the piston in this design could (and probably would) prevent the barrel from opening. As we all know on this forum, a sealed chamber of pressurized fuel/air mixture with nowhere to go is called a "pipe bomb".

Using two or even three O-rings on the piston and keeping it properly lubricated would be critical. So making the chamber accessible for maintenance is necessary. I'd also devise a way to test it for leaks, and do so frequently (say every 5 shots).

A 250psi pop-off safety valve and pipe rated to well over 250psi would make this design much safer.

Your concept is great - using compressed air behind the piston to allow a variable opening pressure should work wonderfully. Just make sure the rear piston surface area is at least 2x that of the front piston (barrel seal) surface area, just for safety factor and quick opening time. I wouldn't attempt this in anything weaker than sch80 pvc, and I'd really consider making a small-ish scale metal model first if possible. If time and funds allow, I might consider making a small scale model of this design. It's intriguing.

Peace,
Pete Zaria.
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