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Mapp gas + Oxygen

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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Mapp gas + Oxygen

Unread postAuthor: Spudgun on Crack » Sat Jun 23, 2007 5:13 pm

I have this mapp gas/oxygen blow torch that i got from sears for $50 and i don't have a use for it really, but it does have a map gas and oxygen regulator w/ hoses attached so i cut the torch off and i am left with 2 hoses and 2 regulators that i believe i can drill 2 holes in as the hoses are small into a regular potato gun and mapp gas burns hotter than propane and combined with oxygen i think that i will boost its bang considerably but is this safe as i believe the pressure may explode the damn thing.

If this does work i can install some of my potato gun things like glowing 40mm chamber fans to mix it more evenly, grips, scopes, lasers you name it i have it.

I will post some pics of my first potato gun w/ chamber fans and if i can find the video than i can post that to.

My first potato gun was very VERY LOUD! lol i had the whole neighborhood asking what the explosion was but it was loud for some odd reason lol i only used chamber fans and hairspray, 8 inch combustion chamber, 4in diameter, and an 8 inch barrel, 2in diameter and it pack a loud bang.

This is only an idea i had, and a test model would be required on the size of like a 4 inch long chamber, 1in in diameter, and a 12in long, 1/2in diameter barrel
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Unread postAuthor: Pete Zaria » Sat Jun 23, 2007 6:02 pm

Welcome to the forums.

Although it has been done before, burning oxygen mixtures (regardless of the fuel) in plastic pipe (PVC or ABS, regardless of schedule or pressure rating) is generally regarded as a BAD IDEA. The pressure spike is unsafe for plastic pipe.

In metal, it's absolutely awesome. Burning hybrid oxy/mapp mixtures can get objects supersonic pretty easily.

If you're going to attempt this with PVC (which I do NOT recommend whatsoever), use sch80 EVERYTHING (and keep it small, 2" chamber, 1" barrel, small pipe holds pressure better) and FIRE IT REMOTELY. 50 ft or more away.

Better idea: Use metal, or just burn mapp with no oxygen.

By the way, if you read around (i.e., the Wiki at the top of the page, etc...) you'll find out that the reason your last cannon was so loud is because of it's very bad C:B (chamber to barrel) ratio. C:B ratios are measured by volume (not in inches, etc...).

For a hairspray gun, a 1:1 - 1.5:1 ratio is acceptable.
For metered propane/mapp, .8:1 is considered ideal.
For hybrids, depending on the mixture, between .3:1 and .8:1 are acceptable.

For your example, 8" of 4" pipe is roughly 100 cubic inches (ci). 8" of 2" pipe is roughly 25 ci, giving you a 4:1 C:B ratio, which is very inefficient. Most of that excess energy is dissipated as sound and muzzle flash, because the barrel isn't long enough to "harness" the extra energy coming out of the chamber. Make sense?

Peace,
Pete Zaria.
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Unread postAuthor: Spudgun on Crack » Sat Jun 23, 2007 7:53 pm

Yea i need to do my homework on this, but thanks.

I hope to engineer a very very powerful cannon but i don't have welding equipment to put metal together so i will stick with pvc and parts from mcmaster and the hardware store and drop the oxygen and use mapp gas or propane as the fuel.

And if i get the ratio just right will the cannon be super loud or be like a woosh sound because i don't want to have the cops come to my house and ask where my artillery piece is lol!

I am going to make a potato gun with single shot fuel canister's that are filled with an oxidizer and fuel in one tiny package so you can shoot, take one out, insert into the quick disconnect valve, recharge and shoot again if there is a magazine or shell in the barrel.

Anything that i make will have a 3d model made on the pc that you look at and see any design flaws that it has.

Thankyou
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