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Quick Question on Combustion design...

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: gwoloshyn » Mon Dec 03, 2007 10:22 pm

Hey octane, are you sure the first one isn't NSF-PW? I'm a little worried, and disappointed because im near done contructing the basics of my propane/mapp powered cannon and I used DWV parts. I don't shoot my cannons all that much so maybe I should be ok?
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Unread postAuthor: SpudBlaster15 » Mon Dec 03, 2007 10:30 pm

DWV ABS is possibly the best combustion cannon building material available to the average spudder. It is inexpensive, easy to join, very shock resistant, and lightweight. It is superior to even pressure rated PVC due to the fact that it's higher shock resistance means it is less likely to fail when subjected to the (relatively) high shock loading caused by the combustion of the air/fuel mixture inside the chamber.

ABS also tends to fail by splitting along its length, rather than fragmenting as PVC does.

I have used DWV ABS to construct 7 combustion cannons, and have experienced only one failure (which was my fault, and should I have made the same mistake when building a pressure rated PVC cannon, I might not have lived to post this message).
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Unread postAuthor: octane89 » Mon Dec 03, 2007 10:51 pm

I don't think all of it is pressure rated. I can tell the two small elbows are, but I haven't seen rated 3"x2" bushing in any stores...(only 3" pressure fittings i seen in stores were tee's actually)

What store may carry ABS? Or online store at least....I never seen any at home depot or lowes so Im gonna assume a plumbing store (maybe ace) has it.

And do I join ABS just as I would any other pvc? Primer and solvent? Seems like a dumb question but I never used it before.
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Unread postAuthor: SpudBlaster15 » Mon Dec 03, 2007 11:11 pm

ABS should be available at most any hardware store in North America.

ABS requires a one step cementing procedure due to its greater solubility in ketone solvents. No priming is required, just the cement.
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Unread postAuthor: MrCrowley » Mon Dec 03, 2007 11:19 pm

SpudBlaster15 wrote:should I have made the same mistake when building a pressure rated PVC cannon, I might not have lived to post this message).


You wouldn't die, 110psi pressure rated PVC shrapnel wasn't enough to pierce me and two other people's skin at close range (1m).

You'd have to go a lot higher then that, which a MAPP/Propane combustion can't generate.

Though you could be blinded, you wont die...
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Unread postAuthor: SpudBlaster15 » Mon Dec 03, 2007 11:31 pm

That depends entirely on the mass, geometry, and flight characteristics of the shrapnel. A small, relatively blunt piece of PVC that impacted a human's skin with it's flat face as the leading edge would not likely do much damage. However, a large, sharp piece of PVC could have sufficient impact force to piece the skin, and potentially lacerate a vital blood vessel.

I have used PVC as confinement for black powder, and though the pipe experiences a much greater pressure spike, the shrapnel has on occasion managed to imbed itself fairly deeply into tree trunks. It certainly has the potential to cause significant damage to human tissue.
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Unread postAuthor: MrCrowley » Tue Dec 04, 2007 1:32 am

SpudBlaster15 wrote:I have used PVC as confinement for black powder, and though the pipe experiences a much greater pressure spike, the shrapnel has on occasion managed to imbed itself fairly deeply into tree trunks. It certainly has the potential to cause significant damage to human tissue.


I'm sure PVC could kill someone, but unless like you said from cutting an artery, at 110psi you're not dying any time soon. Yes there are some variables you could change to make it kill you, but sch 40/80 wont at such little pressure.

The largest piece I found that had gone somewhere was a mere 2m away, the furthest piece only travelled about 15 feet. Not enough to kill you, and the piece was about the size of the tip of my finger.
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Unread postAuthor: octane89 » Tue Dec 04, 2007 10:53 am

Thanks for the input Spudblaster15, I liked your advanced cannon quite a bit.
gwoloshyn-You should be fine from what everyone says. Some prefer dwv over abs and vice cersa. Just be safe and think things thru.
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