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8" PVC combustion chamber

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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8" PVC combustion chamber

Unread postAuthor: shiftyguy » Tue Dec 11, 2007 11:56 am

Has anyone tried an 8" combustion chamber, and reduced it down to 4" and then down to 2" for the barrel?

It sounds like fun. probably could get a hell of a blast.

How long would the barrel need to be with a 8" x 12" chamber
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Unread postAuthor: psycix » Tue Dec 11, 2007 2:08 pm

pi*r*r*h=V
8"diameter @ 12" length = 603 square inch
V/(pi*r*r)=h
So 191" for a 2" barrel

Have you got 8" then??
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Unread postAuthor: MikeNice » Tue Dec 11, 2007 3:05 pm

I'm really thinking 8" chamber is just too big to burn effectively without already being under pressure. So maybe an 8" hybrid? That would be awesome. Fuel it with diesel and a glow plug ignition and you'd have a some serious bragging rights to the first diesel powered potato cannon.
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Unread postAuthor: octane89 » Tue Dec 11, 2007 3:30 pm

Short-stubby chambers burn better from what Ive heard. But it would be very costly for the 8" reducer and pipe.
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Unread postAuthor: shiftyguy » Tue Dec 11, 2007 3:52 pm

Yes I have about 10' of 8" and about 10' of 5". I dont want to just make a big gun just to make a big gun, i want to make a big gun that i can have some serious fun with....
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Unread postAuthor: MikeNice » Tue Dec 11, 2007 4:05 pm

You're going to have a tough time getting it to fire consistently. With chamber and barrel that size you might think of building a pneumatic instead. That there is punkin' chunkin' parts.
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Unread postAuthor: Velocity » Tue Dec 11, 2007 11:35 pm

psycix wrote:pi*r*r*h=V
8"diameter @ 12" length = 603 square inch
V/(pi*r*r)=h
So 191" for a 2" barrel

Have you got 8" then??


More like 240" for the 2" barrel

Volume of an 8"x12" chamber = (8/2)^2(12)(pi) = 192pi
Ideal C:B ratio is 0.8; 192pi/0.8 = 240pi, meaning the volume of the barrel should be 240pi cubic inches

Therefore, Barrel Volume = (diameter/2)^2(Length)

Length = (Barrel Volume)/(diameter/2)^2; Length = (240pi)/(1); Length = 240 inches
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Unread postAuthor: jimmy101 » Wed Dec 12, 2007 11:54 am

Yes, you can make a gun with very large diameter pipe.

With a chamber fan you should have no problems getting it to ignite. (And it'll be real easy to get the fan to fit in the chamber. :D )

Here is DR's basketball cannon; no reducers, barrel etc., just a big-ass piece of pipe with a home made breech plug.
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Unread postAuthor: bigbob12345 » Wed Dec 12, 2007 12:03 pm

where did that guy get pipe so big
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Unread postAuthor: psycix » Wed Dec 12, 2007 12:27 pm

bigbob12345 wrote:where did that guy get pipe so big


Not at a normal hardware store thats for sure.
Maybe he or a friend of him works in a company that uses those pipes and this was a cutoff section.
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Unread postAuthor: jimmy101 » Wed Dec 12, 2007 2:23 pm

You can get large diameter PVC pipe at a PVC pipe supplier. Most cities in the US have one since the larger pipes are used for major construction projects.

Expect to spend $$$ for the pipe and $$$$$$ for fittings :(
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Unread postAuthor: octane89 » Wed Dec 12, 2007 3:10 pm

He said he has the pipe already, but the fittings would be over $25 I would think.
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Unread postAuthor: BigGrib » Wed Dec 12, 2007 3:45 pm

MikeNice wrote: Fuel it with diesel and a glow plug ignition and you'd have a some serious bragging rights to the first diesel powered potato cannon.


Sorry, but I'm gonna be an ass. You are Tarded my friend. I'm an ASE Certed Diesel Mechanic and I seriously laughed so hard when I seen that. Ok here are the problems with your idea. First there are three things that diesel needs to run, Fuel, Air, and Heat from Compression. Therefore your glowplug idea wont work because they just dont get hot enough to do it. Second, Diesel needs to be atomized to burn. To get diesel to atomize you need to have a high pressure pump of somesort. Third, Atomized Diesel still needs to be really hot to ignite, so hot that you will melt your chamber before it ignites. Anyway there you go.
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Unread postAuthor: DR » Thu Dec 13, 2007 3:57 pm

BigGrib wrote:
MikeNice wrote: Fuel it with diesel and a glow plug ignition and you'd have a some serious bragging rights to the first diesel powered potato cannon.


Sorry, but I'm gonna be an ass. You are Tarded my friend. I'm an ASE Certed Diesel Mechanic and I seriously laughed so hard when I seen that. Ok here are the problems with your idea. First there are three things that diesel needs to run, Fuel, Air, and Heat from Compression. Therefore your glowplug idea wont work because they just dont get hot enough to do it. Second, Diesel needs to be atomized to burn. To get diesel to atomize you need to have a high pressure pump of somesort. Third, Atomized Diesel still needs to be really hot to ignite, so hot that you will melt your chamber before it ignites. Anyway there you go.


BigGrig,
I'm not sorry for being an ass, for correcting you're assumption that MikeNice is "Tarded". He specifically stated:

I'm really thinking 8" chamber is just too big to burn effectively without already being under pressure. So maybe an 8" hybrid?

A hybrid is a pressurized fuel/air cannon and although DIESEL fuel would have to be compressed beyond the limits of the PVC pipe to ignite, his idea made (at least) some sense.

As an aside, for everyone else; The large diameter pipe I used for all of my previous basketball cannons was found at local plumbing supply outlets. - Contractors dump off used sewer pipe after a repair... probably because they're too lazy/cheap to bring it to the dump.

I currently scored some white 10" PVC pipe, lying in a ditch in an adjacent lot where I work. Its inside diameter is much closer to the diameter of a basketball than any of my other 10" cannons and I plan on buiilding a new one, after Christmas.

Good Luck to the author of this topic! I would only suggest finding a projectile to fit the bore of your 8" pipe, as fittings ARE extremely expensive.
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Unread postAuthor: jimmy101 » Thu Dec 13, 2007 5:46 pm

I currently scored some white 10" PVC pipe, lying in a ditch in an adjacent lot where I work. Its inside diameter is much closer to the diameter of a basketball than any of my other 10" cannons and I plan on buiilding a new one, after Christmas.

Hey DR, any ratings on the found pipe? Solid or cell core?

BTW, you lucky bastard
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