Spud Gun Combustion

[crazyfreak0075]

Havent yet built a lagre spud gun (only those of smaller size). And today i sprayed probly too much WD-40 into the chamber and it exploded. Luckily I wasent hurt. But the plastic was very thick (2mm to 2.5mm) and felt like it could take a beating. The potato gun was no bigger than my arm.

So heres the question. When I do build a spud gun out of pvc and of substantial size, is there a limit on how much fuel i can put into it. Or in other terms can there be such a thing as too much fuel. Thanks.

[Bluetooth]

Yes i think there is a limit ive burst one of my combustions before you should use the combustion calculator.

[carlbelcher]

You probably used "DWV Cellular Core PVC" instead of SCH 40 PW Pressure rated PVC. Next time use pressure rated PVC and if you use too much fuel the cannon just won't fire instead of blowing up. (unless you're using acetylene or some other "death wish" fuel)

You are VERY lucky that you weren't injured or killed. NEVER use cellular core pipe.

[crazyfreak0075]

Thanks for the info carlbelcher.

Yes i think there is a limit ive burst one of my combustions before you should use the combustion calculator.

But what is this calculator.

[carlbelcher]

I don't think you or Bluetooth understand...

Even most non-pressure rated (not cellular core) can withstand the full pressure created by any reasonable fuel (hair spray, starter fluid, even propane, or mapp gas) the simple fact is that you can only use so much fuel, because there has to be a minimum air:fuel ratio for the fuel to ignite. So you can't just put "too much" fuel in your cannon and have it explode. If you put "too much" fuel there won't be enough air for the fuel to ignite and your cannon simply won't fire.

[crazyfreak0075]

Okay now I understand.

[MrCrowley]

you said the plastic was thick(2mm-2.5mm)umm thats not thick at all,
ive got some 4" dia pipe and the wall thickness is 1.5cm.
Did you use spouting pipe or something?Thats the only pipe i know of that thin.if you used DWV you would be fine on a combustion but spouting is way to thin its designed to carry water from your roofs gutter to the ground.

[Mihlrad]

Cellular core should not even burst from combustion especially if it isnt even using propane... There is no way in hell you used pvc pipe you used some kind of low grade stuff for just running water with 0 pressure. Also, regardless of the pipe you use, if you put in too much fuel, it will not fire. There is no way you put in too much wd-40 it would have just not ignited from lack of oxygen. Unless there is something you arent telling us, like you added air to the mix or something, than theres no way you used PVC, pressure rated or not.

[Dom]

My ABS combustion as Schedule 40 written all over it.

Should never blow in my hands, right? (I know I'm redundant, I just prefer being annoying than being dead)

[Mihlrad]

ABS is fine for combustion for the most part. Its always better to use pressure rated if you can get it, but combustion only generates 30-60 psi of pressure.

[crazyfreak0075]

Sorry I haven't been very clear. The gun wasent made from pvc instead a heavy duty pill bottle of substantial size (im guessing 30-40cc). Now I understand, I can't build spud guns out of that crap any more. It was way too thin.

[Mihlrad]

Yea, that would be your problem... A pill bottle is not really able to withstand more than a drop of like purel or something combustion wise... Stay away from ghetto parts as often as you can, they are unsafe.

[schmanman]

go with all schedule 40 and you will not be sorry

[MrCrowley]

i thought he was talking about a full scale combustion not some mini pill bottle crap lol

[drac]

You can't have "too much" fuel in the chamber. There is a combustibility limit in air, and once you exceed that the fuel won't ignite.

It was most likely due to improper construction practices, or in your case, improper construction materials (not that it's ever stopped me ).