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safe for propane?

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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safe for propane?

Unread postAuthor: FishBoy » Tue Aug 19, 2008 9:33 pm

hey, I am considering setting up my spray 'n pray for propane; my question is, will it be safe. All the parts are pressure rated but the ignition screws only go through 1 layer of pvc (epoxy maybe?) Also, can you get fans for 3" pvc?

link to cannon- http://www.spudfiles.com/forums/my-firs ... 14638.html

Also, to anyone in the US, how much would it cost for the necessary materials?
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Unread postAuthor: starman » Tue Aug 19, 2008 9:42 pm

Propane is an ideal fuel for combustion spud guns. You can use a metering system like this:

Image

Install a female quick release on your chamber and you're good to go. Not counting the propane canister, this is roughly a $30 metering system counting the regulator and very reliable.

Yes, safe....
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Unread postAuthor: FishBoy » Wed Aug 20, 2008 5:54 am

where can i get the 1/2" sched. 80 & the meter?
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Unread postAuthor: jimmy101 » Wed Aug 20, 2008 12:17 pm

Yes, it'll be safe as long as you glue it properly and fire it in a safe manner.

An even cheaper meter (disposable butane lighter, piece of wire insulation, syringe needle);
Image
plus a plastic animal syringe
Image
from here.

Putting the spark electrodes through a single layer of PVC is fine. I recommend fine thread drywall screws.

Attached is an alternative layout for your gun. The handle setup is much nicer and more ergonomic than the one in the OP. Easy enough to convert the barrel to chamber junction to a breech loader with replaceable barrels.

Total cost? Perhaps $20 to $30 for the PVC parts plus a can of PVC primer and a can of PVC glue. About $15 for the BBQ piezo. It is possible to use the piezo from a long handled butane lighter (about $5) but it's a bit more work to come up with a decent mounting system.

If you use a disposable butane lighter as the fuel source and a syringe + needle for the meter, the meter system will cost about $6.
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Unread postAuthor: blind909 » Wed Aug 20, 2008 12:40 pm

FishBoy wrote:where can i get the 1/2" sched. 80 & the meter?


Home depot by the sprinkler section. They are called Sch. 80 PVC Risers.
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Unread postAuthor: starman » Thu Aug 21, 2008 12:38 am

blind909 wrote:
FishBoy wrote:where can i get the 1/2" sched. 80 & the meter?


Home depot by the sprinkler section. They are called Sch. 80 PVC Risers.


Regulator and quick connect parts in the air compressor dept.
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Unread postAuthor: BigGrib » Thu Aug 21, 2008 2:55 am

I made just about the same meter Starman posted. It's a badass system. I unfortunately don't have a regulator on mine, but i did install the gauge on the meter pipe so all I have to do is open the valve and shut it off when my desired pressure is reached. It takes a little more time to meter than having a regulator, but it does the job fine. I have also used the meter still hooked up with the fill valve open to gauge the pressure of the combustion chamber during firing.
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Unread postAuthor: SEAKING9006 » Thu Aug 21, 2008 11:26 am

Unfortunately, I don't trust the accuracy of Husky gauges and regulators anymore. The gauges seem to be off by as much as 10psi or more from the gauges on my compressor. Now, I get my gauges and regulators from Fastenal by having them ship them from the distribution centers. But if you're doing it on the cheap, go for it.
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