16.4 Ounce Containers for a Combustion Cannon

[lbfergus]

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:



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?

[Technician1002]

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.

[spudtyrrant]

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 )

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,

[kjjohn]

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.

[lbfergus]

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.

[kjjohn]

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.

[SpudBlaster15]

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[clemsonguy1125]

Thats been done before its just not as exact, by the way, wgere did you find that fitting.

[lbfergus]

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.

[lbfergus]

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.

[clemsonguy1125]

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?

[lbfergus]

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.

[lbfergus]

And I have another question, how does the computer fan not get toasted going through that many explosions?

[Gun Freak]

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.

[theBOOM]

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