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The Dangers of a PVC 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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The Dangers of a PVC hybrid

Unread postAuthor: noname » Sun Aug 26, 2007 10:19 pm

In my opinion, PVC hybrids are pretty much time bombs, just waiting to go off. This was about the 30th shot, and only at a 2x mixture, but apparently it was too much for the pipe. My friend and I believe that from the stress of the PVC expanding and contracting just a tiny bit, the pipe couldn't take it after a while and blew up. I will never make a PVC hybrid again, and I don't encourage anyone else to either. If you really want the massive power of a hybrid, spend a couple more (literally, not much more) bucks and make from steel, so you can go to extreme mixes without worrying about explosion of the cannon.

http://www.spudfiles.com/spudtech_archi ... php?t=6095

FuzzyScorpion's hybrid blew up at a low mixture, for no apparent reason. It was all Sch 80 PVC.

Lucky13's hybrid blew up as well. It had a couple of Sch 40 fittings, but the pressure generated still should have been under the failure pressure of the parts.


It's just an added safety measure. Use steel or iron for a chamber, and you don't have to worry about any kind of explosion (except the one inside the chamber, duh). It's about the same price as Sch 80 PVC anyway, if not cheaper. You also don't have to worry about faulty solvent welds; just use about 1 foot of teflon tape for every fitting 1/2" or smaller, and silicone sealant for anything larger.
If you do make a PVC hybrid, I wouldn't advise using it at more than a 1.5x mixture for it's whole life span.
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Attachments
hybridblownup1.jpg
Pieces of my hybrid.
hybridblownup1.jpg (34.17 KiB) Viewed 1333 times
hybridblownup2.jpg
Pieces of my hybrid.
hybridblownup2.jpg (21.3 KiB) Viewed 1333 times
lucky13hybridblownup1.jpg
Shrapnel from Lucky13's hybrid.
lucky13hybridblownup1.jpg (19.12 KiB) Viewed 1333 times
lucky13hybridblownup2.jpg
Thickness of failed parts.
lucky13hybridblownup2.jpg (15.6 KiB) Viewed 1333 times
hybridblownup3.jpg
Thickness of failed parts.
hybridblownup3.jpg (19.31 KiB) Viewed 1333 times
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Unread postAuthor: iPaintball » Sun Aug 26, 2007 10:22 pm

Oh no! Is that the DevilStick?
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Unread postAuthor: noname » Sun Aug 26, 2007 10:24 pm

What I could find of it, yes.
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Unread postAuthor: hi » Sun Aug 26, 2007 10:35 pm

ill bet that was pretty spectacular! you werent hurt were you?

i had the same thing happen to a piston valve of mine, but it obviously wasnt a hybrid, it was a valve.

i think we just have to learn that pvc simply isnt made for making cannons... sure its ok for combustions and low pressure pneumatics, but once you take it over about 150 psi then you need a steel or copper chamber. it is only plastic...
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Unread postAuthor: frankrede » Sun Aug 26, 2007 11:08 pm

ahhh scary crap right there.

So should I trash my non-remote fire- 4" all sch-80 pvc hybrid?
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Unread postAuthor: noname » Sun Aug 26, 2007 11:15 pm

Either that or switch to remote firing, from at least 20 feet away. I'd say limit your mixture to 1.5x, or 2x occasionally. Or just use it as a 150-or-so psi burst disc gun; you'll get insane performance as it is.
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Unread postAuthor: Hotwired » Mon Aug 27, 2007 7:42 am

Guess PVC isn't elastic enough to take the shock load of the hybrid combustion then.

Bring on the metal piping.
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Unread postAuthor: jackssmirkingrevenge » Mon Aug 27, 2007 7:53 am

fork in hell :shock:
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Unread postAuthor: Hailfire753 » Mon Aug 27, 2007 8:16 am

Geez, I guess my PVC hybrid plans are a no-no then... :cry: .... NOW WHADO I DO!?
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Unread postAuthor: noname » Mon Aug 27, 2007 10:20 am

You make it out of steel so you have have fun with 6x + mixtures. :P
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Unread postAuthor: paaiyan » Mon Aug 27, 2007 10:28 am

Oh, man, that sucks. How far away were you when it blew?
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Unread postAuthor: noname » Mon Aug 27, 2007 10:37 am

Around 3 feet. I was standing next to the barrel though, just in front of the union. I was wondering why nothing left the barrel, and when I looked behind me the back had blown off and there were pieces all over.
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Unread postAuthor: paaiyan » Mon Aug 27, 2007 10:53 am

So you weren't hurt then, that's good. Good thing you weren't holding it, lol.
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Unread postAuthor: noname » Mon Aug 27, 2007 10:55 am

The damn thing had a 10 foot 1 1/2" barrel! How was I supposed to hold it?!?!
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Unread postAuthor: paaiyan » Mon Aug 27, 2007 12:55 pm

Well... Telekinesis?
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