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Adding a vent system post-build

Post questions and info about combustion (flammable vapor) powered cannons here. This includes discussion about fuels, ratios, ignition systems, safety, and anything else relevant.
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Unread postAuthor: carlbelcher » Sun Aug 13, 2006 11:58 pm

One: Don't use transitional glue (PVC to ABS) it won't hold.

Two: DWV PVC is ok for combustions as long as its not cellular/foam core

Three: To attach the valve I recommend gluing a PVC 2" male NPT adapter into the valve and a 2" female NPT adapter in the reducing fitting on the cannon. (assuming that you don't have a threaded valve)
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Unread postAuthor: CS » Mon Aug 14, 2006 12:02 am

Jarim, is the transistion occuring on a socket welded joint, or via NPT threads? Just to all you others, its best to make material transition via threads. Ive done it once with a ABS gun and a PVC barrel welding it with ABS cement. No, it hasnt came apart, although I dont reccomend because the glue is simply not designed for such a application.
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Unread postAuthor: frankrede » Mon Aug 14, 2006 12:15 am

What is wrong with cellular core in a combustion?nothing.I have 50+ shots with it and there is no problem.
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Unread postAuthor: MrCrowley » Mon Aug 14, 2006 2:04 am

the pipe is made up of millions of little bubbles to make the pipe lighter and its not safe for pressure,on a combustion i still wouldnt reccomend using it. yet a while back they didnt recomend DWV and now its fine on combustiuons.
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Unread postAuthor: sgort87 » Mon Aug 14, 2006 11:10 pm

2" ball valve ventillation is a godsend. Check out my <a href="http://www.spudfiles.com/forums/viewtopic.php?t=2429&">Blue Flame</a>. It vents faster than you can reload (4 seconds) at the simple turn of a valve.

I'm confused why this isn't standard now because these valves only cost $13...
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Unread postAuthor: MrCrowley » Mon Aug 14, 2006 11:14 pm

cost about $100 here for a 2" one rated to 80psi
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Unread postAuthor: Shrimphead » Mon Aug 14, 2006 11:35 pm

People have had barrels fly off when they tried to glue pvc and abs together.
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Unread postAuthor: flyingspuds2007 » Tue Aug 15, 2006 3:08 am

But if the barrel flys off, it's technicaly not a barrel anymore, so would it be a barrel, or a projectile?

But to get to the point, use only pvc glue, and pvc pipe to join pvc, and abs pipe and abs glue to join abs.
Meet in the middle with threaded connections.
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Unread postAuthor: sgort87 » Tue Aug 15, 2006 8:11 am

McCrowley, are you sure that is a PVC ball valve and not a metal one?
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Unread postAuthor: MrCrowley » Tue Aug 15, 2006 3:13 pm

umm yeah 2"plastic ball valves rated to 90psi in NZ are $100 or close to that price like $90 or something
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Unread postAuthor: Pete Zaria » Tue Aug 15, 2006 3:15 pm

Yep, it's a 2" PVC non-pressure rated (DWV, but not cell core) ball valve. It was less than $15 at home depot or lowes (dont remember which). I'm just going to hope it doesn't blow off. I'm kind of wondering if I should even bother spending more money on this cannon; I really want to build a copper marble gun or a small hybrid.

Thanks for all the info, guys. I appreciate it. I'm also sorry that parts are so expensive over in NZ.

Peace,
Pete Zaria.
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