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16.4 Ounce Containers for a Combustion Cannon

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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16.4 Ounce Containers for a Combustion Cannon

Unread postAuthor: lbfergus » Mon Jul 19, 2010 12:53 pm

Hey everyone. I am getting ready to make my first combustion cannon (have made a bunch of pneumatics), and I want to go the metered propane route. I have read around a lot, but I have a question.

All of the sites I have read from have the blue cannisters with a torch you have to cut off, etc.- as well as a pressure regulator.

Why can't I use the 16.4 ounce propane canisters like you would use for a Coleman camp stove? Those are everywhere and cheap, I already have half a dozen anyway.

And, why would I need a regulator for those? Why couldn't I plumb it directly to a metering tube with the correct dimensions to meet the correct pressure, etc. I could connect it with a fitting like this one:

Image

Wouldn't that be the cheapest? I have tried finding the pressure on those, and I keep seeing 15 come up. But I could just use Burnt Latke's fuel tool and figure it out, right?
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Unread postAuthor: Technician1002 » Mon Jul 19, 2010 1:05 pm

That way of metering would work fine, if your temperature never changed.

Using the short fat tank instead of the tall skinny one makes little difference. The skinny one is easier to hold while using a torch. The fat one holds more fuel. The fitting and fuel pressure is the same for both.

Below is a graph showing the pressure you get from unregulated propane at various temperatures. As you can see, there is a wide variation in pressure with changes in temperature. A regulator or pressure gauge is highly recommended for an accurate mix every time.
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Re: 16.4 Ounce Containers for a Combustion Cannon

Unread postAuthor: spudtyrrant » Mon Jul 19, 2010 1:06 pm

lbfergus wrote: Why can't I use the 16.4 ounce propane canisters like you would use for a Coleman camp stove? Those are everywhere and cheap, I already have half a dozen anyway.
you can, most people just prefer the long slender look (don't go there jack :roll:)

lbfergus wrote:And, why would I need a regulator for those? Why couldn't I plumb it directly to a metering tube with the correct dimensions to meet the correct pressure, etc.
You can do this also, people usually use regulators to keep the pressure constant , so instead of raising the meter to the correct pressure ever time all they need to do is fill their meter and release it into the chamber,
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Unread postAuthor: kjjohn » Mon Jul 19, 2010 1:08 pm

Welcome to Spudfiles!

I believe Coleman canisters have the same threads as the blue propane tanks, so you could use those. However, I'm not sure, but I think they are a slightly different mixture of fuel. If you just calculate for propane, the Coleman canisters should work.

And yes, you could run a propane tank unregulated, but I wouldn't. Propane tanks put out a pressure of about 90psi throughout their usable life, which is a little high for my taste, and it varies with temperature. I would go with a regulator. This one screws directly on to the propane tank, no adapter needed.

Good luck, looking forward to seeing your cannon.
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Last edited by kjjohn on Mon Jul 19, 2010 1:10 pm, edited 1 time in total.
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Unread postAuthor: lbfergus » Mon Jul 19, 2010 1:09 pm

So, could I put a pressure gauge in my metering tube, and crack my 1st valve until I have the desired pressure on my gauge and then shut it and open it into the combustion chamber? And if that worked it wouldn't really matter what the pressure coming out of the can was as long as i metered it the same.

Thanks so much for the help.
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Unread postAuthor: kjjohn » Mon Jul 19, 2010 1:12 pm

Yes, that should work, but still, I would use a regulator for better precision, plus you would just have to open the valve and the meter would fill with the correct pressure immediately.
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Unread postAuthor: SpudBlaster15 » Mon Jul 19, 2010 1:32 pm

The 16.4oz camp stove tanks work just fine. They use the same fuel composition, and an identical threaded fitting/outlet valve design. The only difference is the shape and volume of the tank, which depending on your launcher design, may or may not be beneficial.

Is the threaded output on that fitting NPT? If so, it would be simple to connect it to a ball valve and your fueling system.

spudtyrrant wrote:you can, most people just prefer the long slender look


:lol: :D
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Last edited by SpudBlaster15 on Mon Jul 19, 2010 1:36 pm, edited 1 time in total.
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Unread postAuthor: clemsonguy1125 » Mon Jul 19, 2010 1:33 pm

Thats been done before its just not as exact, by the way, wgere did you find that fitting.
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Unread postAuthor: lbfergus » Mon Jul 19, 2010 1:37 pm

Alright, that sounds good. Would you recommend putting in a chamber fan then?

Which leads me to my next question. I was thinking to power the electrical I would make some leads to hook to my car battery with alligator clips. Could I use a chamber short with the battery like that? Just placing a narrow gap for the spark to jump, + on one side and - on the other?

You guys are the best, I love the forums.
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Unread postAuthor: lbfergus » Mon Jul 19, 2010 1:40 pm

SpudBlaster15, I was thinking the same thing, it is 16.4 oz cannister female out and 1/4" npt in, which would be really perfect.

And clemsonguy1125, I am a hardware purchasing agent for my company, and one of our hardware vendors had that available.
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Unread postAuthor: clemsonguy1125 » Mon Jul 19, 2010 1:40 pm

Yeah you defianatly want a chamber fan, I dont know about the car battery but that is bulky why not just use a BBQ ignitor?
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Unread postAuthor: lbfergus » Mon Jul 19, 2010 1:42 pm

Well a BBQ ignitor can't run my chamber fan, and the battery will stay in the car, I will have my car close whenever I am shooting the thing so why not.
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Unread postAuthor: lbfergus » Mon Jul 19, 2010 1:46 pm

And I have another question, how does the computer fan not get toasted going through that many explosions?
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Unread postAuthor: Gun Freak » Mon Jul 19, 2010 1:48 pm

Most people put the fan on a different circuit than the ignitor with a 9 volt battery. Also... chill with the double posts... the mods hate that.
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Unread postAuthor: theBOOM » Mon Jul 19, 2010 1:51 pm

The combustion last's too little for it to affect the fan in any way, its over in less than a second.
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