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hybrid EXPLOSION!

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: Fnord » Tue Oct 02, 2007 9:26 am

Most nsf-pw PVC is designed to withstand the pressures of a 2x mix, however, being brittle, it cannot withstand the repeated shock loads. It's the same thing with steel and DDT.
Steel pipe can withstand the pressure created by ddt, but not the rate at which it is produced (Or, at least not for very long).

PVC hybrids are basically like using a glass bottle for a combustion gun. It might hold, but the slightest flaw or crack will cause a failure.


Ya' know come to think of it, I bet a solid-wall(unrated) abs hybrid might even last longer than a pvc one. Some one needs to do an experiment.
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Unread postAuthor: spanerman » Tue Oct 02, 2007 9:47 am

^are you volenteering? :lol:
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Unread postAuthor: Fnord » Tue Oct 02, 2007 10:01 am

Well, I was ready to have steel fragment, so I think I could handle abs. I just don't have the materials to build a plastic hybrid right now, nor do I feel like searching the local hardware stores for supplies.
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Unread postAuthor: jimmy101 » Tue Oct 02, 2007 10:31 am

thespeedycicada, glad you are OK.

The pieces of PVC in the second picture look awful thin for Sch40 PVC. Are those PVC frag's that not only broke from the pipe but also peeled apart like the layers of an onion? I don't recall ever seeing PVC fail like that. Or are those pieces of some other part of the cannon?

According to GasEq, a 2x mix of propane in air could generate a peak pressure of ~210 PSIG, getting close to the pressure limits of larger ID pipes and perhaps smaller ID fittings. Is it possible that your burst disk had a problem and for some reason didn't burst?
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Unread postAuthor: DYI » Tue Oct 02, 2007 4:41 pm

I believe it says in my sig that I'm going to do ABS hybrid testing soon, whenever I get the rest of the fittings and the time to hook it all together.
ABS can be used for combustions, so it must be useable for low hybrid mixes.

And I agree with everyone else on the fact that those PVC shards look awfully thin...
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Unread postAuthor: thespeedycicada » Tue Oct 02, 2007 5:55 pm

i just found what those shards belonged to it was the ignitor holder so its not due to the thin pipe.
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