End-Around Pneumatic Cannon

Step 6 Pressure Test

Before firing anything, I carefully and slowly filled my pressure chamber. I started at 10 psi, and gradually increased the pressure with short bursts from my compressor. I charged the chamber to about 65 psi, and left it alone for a while. When I returned 15 minutes later and took this picture, the pressure has dropped to about 50 psi. Since I almost never wait 15 minutes between pressurizing and firing, this shouldn't be too much of a problem. I think the largest leakage is from the junction between the pressure gauge and the dark-gray nipple. I'm not too sure that they have compatible threads. During the pressure test, I laid a heavy coat over the pressure chamber, just in case. Be careful.

Comments

[nugget659]

The safest way to pressure test this is to fill the pressure chamber as completely as possible with water and then pressurize. Water will not expand with a sudden pressure drop and send PVC shrapnel everywhere. DO NOT PRESSURE TEST WITH AIR. Remember that PVC shrapnel is bad for your eyes...

[TheMadScientist]

pvc shrapnel is bad for you period

[Ledmik]

The "Orbit" pressure valve you used is made for a hose-bib. Garden hose threads or more course than pipe threads. The smaller threads however should be either 3/8" or 1/4" pipe thread. I would use a tee with a 1/2" thread and a brass bushing down to the size of the smaller thread on the pressure gauge. You could probably also fit your fill valve between the bushing and pressure gauge. That would eliminate the problem of weekening the cap by drilling a hole in it.

[greybeard]

If you want to pinpoint leaks in any pressurized gas system, apply soapy water around your joints and fittings with a sponge, or foam brush after you've pressurized the vessle. The escaping gas will produce bubbles. Cheap, quick and easy. I use this technique when I change hoses or tanks on my oxy/acetylene and oxy/propane torch setups.

[matthewbeckler]

Wow, that is an awesome idea. Why didn't I think of that. I'll have to try that soon on my cannon. Thanks again!