SpudFiles

I'm just keeping this short and simple... Here's how to make the meter for my combustion cannon...



Here is a pic of my launcher...



Here's all the info you need on making one.
Wrap 4-5 layers of teflon tape around all the joints.
Click the link below to learn how to thread a propane torch head.

http://www.burntlatke.com/thread.html
http://www.burntlatke.com/lp.html (Read the part on tapping pvc)

More how-to's on my gun coming soon. The meter has a volume of 37 ml. which is a perfect size for the chamber that has a volume of 2675 ml. Each charge that I dump in the chamber is 43 PSI. If anyone has questions i'll be glad to answer them.

I like it-helps me out to build my own for the first time.
But do you happen to know if the meter has a 48cc volume?

Yeah, the volume in the meter is 37 ml.

Err... this is good, but there is a sticky in the combustion cannon section that shows you how to make one. There are probably a half dozen others out there too.
In fact, there are plans in Pete's post, which is directly above yours.

Honestly, I'm beginning to think you're just "advertising" your gun. I've seen your youtube comments, you know.

No actually i'm putting the full plans on here and i'm starting off with the meter first and then i'll just add the rest of the instructions on later this week...I'm not trying to advertise my gun, i'm sure theres a lot of newbs on this site that would like the full plans to a gun like mine, and yeah i'm proud of what it looks like. I'll change the name of the topic to Full Plans For Combustion Launcher after i get all my info gathered, its gonna take me a while but for now im keeping the meter title and edit it all later.

You could omit the pressure regulator and the threading of the propane tourch head and just plumb the fuel supply hose directly from the propane tank valve head to the barb on the meter pipe. That is, omit parts 11, 12 and 13 and don't modify part 14.

He could, but getting the right pressure without a regulator can be tricky sometimes. It's easy to overshoot if your only flow restriction is a ballvalve.

Having a regulator cuts my reloading time in half. I'll never make a gun without a trustworthy regulator again.

_Fnord wrote:He could, but getting the right pressure without a regulator can be tricky sometimes. It's easy to overshoot if your only flow restriction is a ballvalve.

Look closely at the head of a standard Bernzomatic torch.

1. The valve is not a ball valve, it is probably a needle valve.

2. There is a very small orifice in the end of the pipe. Small as in smaller than the diameter of a hair. The orifice is so small that my crappy eyes can't even see the hole without a magnifying glass.

When you crack open the cylinder's valve it'll fill the meter at a pretty leasurly pace. Very easy to shut the cylinders valve when the proper pressure in the meter has been reached.

I just did a quick measurement by water displacement. Using a standard (un-modified) Bernzomatic torch head, with the air diffuser removed, cylinder temperature of 50F, cylinder valve fully opened, the standard orifice delivers about 7cc/second against atmospheric pressure. For a 100in³ chamber (1,640cc) it will take about 9 seconds to pressurize the meter with the correct amount of propane.

If you chop the end of the pipe off, thus removing the orifice, the cylinder probably delivers more like 100's of cc/second.

The cylinder's valve can be easily closed down to the point where it will only deliver ~1cc/second. So it could take a minute or more to fully pressurize the meter pipe using the standard orifice.

The tricky part of this approach is that the pressure in the meter pipe will continue to rise even after the cylinder's valve is closed since there is a fairly large amount of propane, at the cylinder's pressure, between the valve and the orifice. It takes a little trial and error to figure out what pressure the gauge need to read when you close the cylinder's valve so that the pressure rises to the correct final value.

Using two ball valves and a pressure regulator is certainly a good way to build a meter. I'm just saying that you can save a $20 or $30 bucks if you omit the regulator, one valve, and a couple of the fittings, and just use a pressure gauge and the standard Bernzomatic torch head valve and orifice.