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Firing Blanks

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: Jumpin Jehosaphat » Tue Jul 03, 2007 6:26 pm

I want to fire my combustion cannon without loading it so it is safe to use in a small area.
I was wondering if anyone who has done something similar recommends that I use wadding (paper towels or something) to ensure it works properly. Is there any risk of paper wading catching fire?
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Unread postAuthor: paaiyan » Tue Jul 03, 2007 6:37 pm

Well if you want to try a dry-fire I suggest you use some kind of wadding, otherwise the fuel tends to flow out the barrel and just go pfft. Paper wadding not reccomended, but that just depends on what your fuel is. I suggest using on old dishrag or somethign similar. It's less likely to catch fire and if it gets scorched it's no big deal.
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Unread postAuthor: sandman » Tue Jul 03, 2007 7:53 pm

i use wood plugs with a plastic bag to slow it down when i fire in my backyard
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Unread postAuthor: noname » Tue Jul 03, 2007 8:15 pm

You can use a burst disc to hold the fuel in...
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Unread postAuthor: paaiyan » Tue Jul 03, 2007 8:23 pm

noname wrote:You can use a burst disc to hold the fuel in...


That's not really an option for some cannons.
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Unread postAuthor: Big-mac » Tue Jul 03, 2007 8:26 pm

wet toilet paper makes a nice seal
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Unread postAuthor: Jumpin Jehosaphat » Tue Jul 03, 2007 8:27 pm

I'm too lazy to use a burst dist right now, but that is a great idea because my cannon's barrel just so happens to have one of those sch 80 unions on it.
I ran my cannons specifications through a calculator, and the estimated propane combustion pressure peaks around 120-130 psi. I don't need a very strong burst disk at all, I would actually prefer it to fail at a low pressure since all I need it for is holding fuel.
Does anyone out there have recommendations for burst disk materials that will give out between 10-30 psi
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Unread postAuthor: sandman » Tue Jul 03, 2007 8:30 pm

lol, um, i dont want to do math now, but i calculated for my combustion there will be like .578 psi of propane in the chamber, so i would use like a piece of computer paper, or wax paper
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Unread postAuthor: Jumpin Jehosaphat » Tue Jul 03, 2007 8:41 pm

Wax paper seems like it should work great.
Burst disks in a combustion launcher, the thought never occurred to me even when I have the correct type of union for mounting one. Thanks for all the suggestions guys.
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Unread postAuthor: sandman » Tue Jul 03, 2007 8:50 pm

just wondering, why is there a union on your combustion launcher?
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Unread postAuthor: Jumpin Jehosaphat » Tue Jul 03, 2007 8:52 pm

So I can remove/exchange the barrel.
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Unread postAuthor: noname » Wed Jul 04, 2007 11:07 am

A burst disc can go in the male/female threaded joint of a detachable barrel, that's what I use. It won't get a perfect seal, but it's enough to hold in the fuel.
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Unread postAuthor: Jumpin Jehosaphat » Wed Jul 04, 2007 11:31 am

I didn't use a male adapter/ female adapter combo like normal. I used an actual union, the three piece kind made out of SCH 80 PVC.
I tested use of a burst disk made of wax paper about a half hour ago, and it worked great! It was loud. All this burst disk talk has made me want to make a hybrid, but I've put too much money into cannons in the past few weeks. I gotta stop myself. :lol:
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Unread postAuthor: sandman » Wed Jul 04, 2007 11:50 am

glad to hear it worked
um, im in the same predicament, i need a job :!:
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Unread postAuthor: frankrede » Wed Jul 04, 2007 1:43 pm

If you still want to use a wadding a moist hand towel works great, or one of those foam water ball toy do too.
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