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Propane meter

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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Propane meter

Unread postAuthor: SpudBlaster15 » Tue Dec 12, 2006 12:18 am

After finding a propane/Mapp tank valve in my shed, I have decided to build a propane meter for my over/under gun. I need to keep the costs low, so a $30 pressure regulator is out of the question. I am wondering what the experienced individuals here think of this setup.

Image

Because the tank valve has a hose barb end, I plan to attach a hose, and clamp it in place with a hose clamp. To use the meter, I would open the first ball valve, and then open the tank valve until the pressure guage in the meter pipe read a set pressure (on the order of 40 - 50psi, depends on how long I want to make the meter pipe), then I would close the first ball valve, and open the 2nd to fuel the chamber. Basically, it would use the tank valve as a regulator.

Sound good? Any comments? Thanks.
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Unread postAuthor: frankrede » Tue Dec 12, 2006 12:25 am

Sounds fine, have you check burntlatke.com?
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Unread postAuthor: Pete Zaria » Tue Dec 12, 2006 3:45 am

I use a meter setup almost identical to this on my combustion gun.

You can find some spreadsheets to help you find the right psi. Since you don't have a regulator, you just have to be quick on closing the first (propane tank side) ball valve when the gauge hits the right pressure. It works fine.

Make sure you use the right kind of hose (the clear flexible stuff bursts at ~70psi, and is DAMN loud when it does), and clamp down the hose clamps *really* tight. I recommend using 2 hose clamps on each connection, they tend to leak a bit.

Make sure you Teflon tape all the threaded connections and crank them down tight with a wrench. Also, its best to leak test the entire setup underwater in your bath tub before you install it on the gun. The whole thing should be waterproof, so no worries there.

Where you install it onto your gun, make sure you tap the elbow through to the chamber where a fitting and the pipe overlap (thus two layers of plastic), and use some epoxy on the threads to hold it in tight.

Just FYI, on my gun, it's easier to do two "shots" at 40psi than one at 80psi (for a 4% mix). Play around with the psi, sometimes what the spreadsheets tell you doesn't provide the best "boom" and distance in practice.

Just my input.

Whats your ignition source? How many spark gaps? Chamber fan?

Peace,
Pete Zaria.
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Unread postAuthor: mark.f » Tue Dec 12, 2006 6:21 am

This is also mostly the same setup I used on my first propane meter, (well, my second. First one was a syringe). It works good for a modified torch head, but I'm betting you'd have to install a flow regulator after one of those little tank x 1/4" MNPT adapter things. Too much flow.
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Unread postAuthor: SpudBlaster15 » Tue Dec 12, 2006 10:28 am

Thanks for the input guys. Pete, that was vey helpful.

Pete Zaria wrote:Whats your ignition source? How many spark gaps? Chamber fan?


BBQ igniter, 2, yes.
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Unread postAuthor: Pete Zaria » Tue Dec 12, 2006 1:38 pm

You probably know this already, one spark gap near the back (just in front of the fan) and one gap near the middle of the chamber seems to work best. With a BBQ sparker, you have to use pretty small gaps - around 1/8th" or so. Using a chamber short (burntlatke) is easiest, and reduces holes in the chamber.

Just FYI, my current big combustion gun has a 250ci chamber and interchangeable barrels. The chamber has onboard propane just like you've setup above.
According to the math (fueltool, other spreadsheets) I should be using something like 60psi in my meter pipe. I've found that 80 (or two shots of 40) produces a bigger boom and better distance. This could be because of residual meter pipe volume, or incomplete fuel/air mixing (though I run the fan for a count of 5 before firing to mix fuel). But anyway, as I was saying, play with the amount of fuel you use. Sometimes the spreadsheets aren't quite right.

BTW, rather than trying to use the needle valve on the propane tank as a regulator, just open it all the way up. The pressure in the meter will slowly build. Shut the tank-side ball valve when the gauge hits your correct PSI.
I intentionally put a TEENY (smallest needle I could find) hole in the tubing between the propane tank and the meter pipe, so the unused propane after injecting a "shot" could escape. If you don't do that, then you need to vent the meter when you're done firing.

Anyway... sounds like a fun one. Post some pics when you're done?

Peace,
Pete Zaria.
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