just a few questions

Post questions and info about combustion (flammable vapor) powered launchers here. This includes discussion about fuels, ratios, ignition systems and anything else relevant to launchers powered by igniting things like hairspray or propane.

Postby cheeseclip » Fri Feb 09, 2007 4:51 pm

when i make my spud gun how thick does the wall of the tube have to be for the combustion chamber? 2mm? what about the barrel, does it have to be so thick?

thanks
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Postby Arborman495 » Fri Feb 09, 2007 6:39 pm

Just use PRESSURE RATED sch 40 PVC. It is cheap, it works well, it won't blow up on you unless you do something incredibly stupid.
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Postby cheeseclip » Fri Feb 09, 2007 7:38 pm

cool thanks.
what psi does a basic spud gun get to before firing?
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Postby Paulstrealer » Fri Feb 09, 2007 8:46 pm

It depends on the fuel used
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Postby Arborman495 » Fri Feb 09, 2007 8:55 pm

The psi before firing is 14.7 psi at sea level. The psi during firing depends on the tightness of you wadding or projectile in the barrel and the fuel that you use.
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Postby cheeseclip » Sat Feb 10, 2007 1:41 am

cool thanks.
do you think this ignitor would work well?
http://www.trademe.co.nz/Browse/Listing ... d=87532528
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Postby Zorrowannabe9 » Sat Feb 10, 2007 2:13 am

it'll work
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Postby MrCrowley » Sat Feb 10, 2007 5:41 am

Hey cheeseclip looks like your from NZ as well. I've bought 2 of those. Work great. If you need help determining pressure pipe and what not, anything to do with spudguns my msn is shifty_0@hotmail.com
NZ pipe is a pain in the butt, Don't cut corners by using downpipe, pressure pipe is expensive but its worth it.

oh and guys don't tell him to use sch40. Not every country uses it. He'll end up spending a few weeks searching for it. cheeseclip pressure pipe in New Zealand is labled 'PNXX' the xx is the pressure rating in BAR. e.g 'PN18' on the pipe means 'Pressure Number 18 BAR' which is about 260psi.
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Postby Arborman495 » Sat Feb 10, 2007 10:58 am

That will do it.
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Postby jimmy » Sat Feb 10, 2007 3:00 pm

Cheezeclip:

Worse case senario for a combustion spudgun would be a projectile jammed in the barrel. Under that condition the pressure peaks out at about 120 PSIG (135 PSIA) for propane. So, get pipe and fittings that are rated higher than that.
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