A Few Advanced Combustion Questions

Boom! The classic potato gun harnesses the combustion of flammable vapor. Show us your combustion spud gun and discuss fuels, ratios, safety, ignition systems, tools, and more.
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Heimo
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Sat Aug 14, 2010 2:08 pm

Gun Freak wrote:Dude, get a stick of it, and pump it up as high as you can with that bike pump of yours, and see if it bursts. Give it like 30 minutes full, and it if passes, then you can't go wrong with it in a combustion.
better Idea: fill it with water before you start pumping, put the pipe into a bucket of water also that should keep you from getting hurt when it bursts...
also putting that bucket around the corner will be a added safety step
Last edited by Heimo on Sat Aug 14, 2010 2:18 pm, edited 1 time in total.
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ramses
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Sat Aug 14, 2010 2:15 pm

Gun Freak wrote:
clemsonguy1125 wrote:Thats the worst idea, Ive heard in a while(No Offense), what if it blows while Im pumping.
Dude I didn't mean stand on top of it while you pump, put it behind a corner and a big thing over it so if it DOES blow, then you're safe and nothing gets damaged except the thing over it.
better yet, fill it with water to drastically reduce the stored energy and time required to pump it up.
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Sat Aug 14, 2010 2:18 pm

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clemsonguy1125
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Sat Aug 14, 2010 2:33 pm

I completly agree SB15, my problem is that in the US where I live it hard if not impossible for me to get Solid Core ABS, I have acess to cellular core ABS which I am leaning towards. I dont trust PVC not to shatter.
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clemsonguy1125
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Sat Aug 14, 2010 3:11 pm

I figure the worst that will happen is it cracks open, Thanks for your help.
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Sun Aug 15, 2010 4:02 pm

clemsonguy1125 wrote:Yeah but i still dont like that idea, the only SAFE way to test it is hydrotest which I dont have acess to the equipment
Fill it with water then pressurize with air. That'll do the same thing as a true hydrotest. The only significant energy in the chamber is in the small compressed air bubble.
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clemsonguy1125
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Sun Aug 15, 2010 4:53 pm

Ok, thanks, right now I am thinking Ill make the chamber from 3 inch cellcore ABS then sleeve it in 4 inch Cell Core ABS, This should have the thickness of a piece of solid core and if the inner one cracks, I wont get burnt. Also I wont ever drill through just one layer.
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Technician1002
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Sun Aug 15, 2010 11:29 pm

I have pressure tested 4 inch cellular core ABS. See my test cannon thread in my sig. I hope that helps. This is with US Cellular Core ABS DWV pipe.
This year's pressure test was 100 PSI.

What pressure are you expecting?
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clemsonguy1125
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Sun Aug 15, 2010 11:41 pm

I'm making an advanced combustion so under 120, which is the max for milli seconds, so with two layers I think I'll be fine
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Last edited by SpudBlaster15 on Thu Jul 15, 2021 1:57 am, edited 1 time in total.
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clemsonguy1125
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Mon Aug 16, 2010 10:21 am

On the subject of fittings, since Im using ABS DWV fittings, I need to put a few bolts through the fittings and pipe, will this weaken the pipe to a point will it would be better to not use bolts at all
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Last edited by SpudBlaster15 on Thu Jul 15, 2021 1:57 am, edited 1 time in total.
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clemsonguy1125
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Mon Aug 16, 2010 11:52 am

Thanks so would a chamber consisting of 5 dwv couplings glued together with abs cement be safer that a chamber of cell core abs? Btw on your advanced combustions was all the pipe solid core with pressure rated fittings?
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Technician1002
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Mon Aug 16, 2010 12:54 pm

For 120 PSI on US 3 inch ABS Cellular Core pipe, a single layer is fine. I have range tested apples with my ABS Cellular Core air cannon next to a propane cannon of the same dimensions.

4 inch ABS holds up to propane combustion launches with a 2 inch barrel just fine.

You biggest hazard is the clean out cap is slightly flexible and tends to blow off.

If you do use couplings, they are solid, not cell core.
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