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Problems with homemade propane system

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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Problems with homemade propane system

Unread postAuthor: Clutch » Mon Apr 13, 2009 11:19 am

I had a basic combustion launcher with 4" chamber to 4"-2" reducer then a 2" barrel with clean out cap on the end. Used a BBQ sparker for ignition.

This was getting a little "old" so i decided to add a PROPANE system to it :)

I took an old "Mini" camping grill and removed the brass propane fittings and button to release gas. I attached a piece of rubber hose to it and then drilled a hole into the side of my cannon, and sealed with silicone.

I attached the propane bottle (Using 1LB Coleman bottles) by screwing a 4" PVC section to the side of my gun, and sliding the bottle in the extra pipe.

The brass fittings combined with the rubber hose release A LOT of gas. (You can hold a lighter to it and make a 4ft flame thrower)

The only problem is my gun doesn't fire. I have tried everywhere from half a second of gas to 30 seconds+ (It only works if i remove the end cap, and spark it creating a fireball)
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Unread postAuthor: TurboSuper » Mon Apr 13, 2009 11:53 am

You're spraying in too much fuel.

Propane has a "butter zone" ratio in which it will react. By opening up the end cap, you let more air in, and reduced the ratio to that zone, so it worked.
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Unread postAuthor: jimmy101 » Mon Apr 13, 2009 2:47 pm

Turbo is right, too much fuel.

Put the flow regulator and/or needle valve that was on the camping stove back into the system, you need that flow restriction to have a decent chance of getting the right amount of gas when using "one-potato--two-potato--..." counting.

Or make your own flow restrictor. A piece of thin plastic (like a coffee can lid) and the smallest diameter pin you can find. Poke the smallest hole you possibly can in the plastic then install the plastic in your fuel line.

This is how the gas flow is regulated in a Bernzomatic torch head. The hole is so tiny that it is nearly invisible. The torch head hole is considerably smaller than a typical pin hole.
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Unread postAuthor: King_TaTer » Mon Apr 13, 2009 4:05 pm

Invest in a regulator and some fittings to make yourself a proper propane meter. Or you could continue to half ass things. :lol:

No I can't bash you. It's a good first attempt for a fuel meter. You could probably get away with a good one for about $40-50 at your local hardware store. Here you can read about different kinds of fuel meters in the SpudFiles Wiki. If you have anymore questions please ask. Good luck 8)
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Materials links:
<a href="http://www.discounthydraulichose.com/">Discount Hydraulic Hose</a>
<a href="http://www.buyfittingswholesale.com/#">Buy fittings wholesale</a>
<a href="http://www.flexpvc.com/">Flex PVC</a>
<a href="http://www.murrayequipment.com">MEI
</a>
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Unread postAuthor: Clutch » Mon Apr 13, 2009 4:29 pm

Damn, I think i hurt myself on this one. I originally left the flow regulator like normal. With a microscopic hole on it. But i thought it wasn't getting enough fuel, So i drilled out the hole to about 1/4 in.


Stupid me :(
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Unread postAuthor: stewart_1322 » Mon Apr 13, 2009 11:56 pm

I have a similar gun that I made with a 4" combustion chamber that is 2 foot long. It reduces down to a 2" barrel. I want to fuel it with propane and I'm looking into a meter and hook up and everything but one thing is riding my mind.

I bought a pre-cut section of pipe for the chamber, and it happens to be "Not for Pressure" pipe. It looks to have a thin PVC inner and outer layer but in the center is a foam looking material. Is this pipe a major safety issue that needs to be scrapped or am I in the clear?
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Unread postAuthor: Fnord » Tue Apr 14, 2009 7:46 am

If you haven't glued it yet, I'd toss it or save it for some other purpose.
You should avoid cellular core pvc when possible for combustions, and never use it for pneumatics.

DWV (not pressure rated) pipe fittings are generally ok to use for combustions, however, since they are usually solid-walled pvc.

Cellcore ABS pipe is widely used in combustions since is has high impact resistance and good failure characteristics.
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Unread postAuthor: Clutch » Tue Apr 14, 2009 11:04 am

Stewart_1322 please don't thread jack.

But don't use that section of pipe. just buy solid wall white pvc..
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Unread postAuthor: stewart_1322 » Tue Apr 14, 2009 6:29 pm

thread jack, lol. I'm not hi-jacking anything, it fits in to the topic of propane usage and the dimensions of your gun also. I don't want to make another thread just for a simple qeustion.

Thanks for the help guys, I'll leave the thread along now.
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