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Pressure testing

Post questions and info about pneumatic (compressed gas) powered cannons here. This includes discussion about valves, pipe types, compressors, alternate gas setups, and anything else relevant.
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Pressure testing

Unread postAuthor: skyjive » Fri Mar 20, 2009 5:16 pm

Hi all, I have a copper gun which I have been using at up to 200 psi without trouble but want to take higher. I was thinking of pressure testing it first, since at such high pressures there is no margin for error. I don't have any specialized pressure testing equipment, but I was thinking I could use my CO2 hookup. The plan is to hook up the gun to the tank and regulator and put it around the corner of my garage at the end of a 3-foot hose rated to 2750 psi. I then turn up the pressure to I'm thinking 500 psi and run for cover. I let it sit for however long, then come back, turn off the pressure, and wait for the gas to leak out. Under this plan, the corner of the garage would always be between me and the gun. I should say at this point that my garage is from the early days of motor vehicles when they thought they could explode at any second and it has foot thick stone walls. Is this plan, while maybe not ideal, practical? Or am I going to kill myself?
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Unread postAuthor: D_Hall » Fri Mar 20, 2009 7:49 pm

A much safer, easier to control method....

Hydrostatic testing.

The tool of choice used by professionals in the field? A garden variety pressure washer (available at any Lowe's, Home Depot, etc.).

Just fill your gun with water, hook it up to the pressure washer, and fill to your desired pressure. It really is that easy.
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Unread postAuthor: inonickname » Fri Mar 20, 2009 8:17 pm

I'll elaborate on the hydrostatic testing. As water is (under such low pressures) incompressible it will store little to no energy. The only thing that can store (reasonable) amounts of energy will be the air in there, so the less air, the less danger.

So that means with a pressure washer you will have basically no air, plus they will go to several thousand psi.
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Unread postAuthor: Gippeto » Fri Mar 20, 2009 9:47 pm

Skyjive;

If it does fail, your posted testing method will be highly dangerous.

I recommend that you NOT do that.

Perhaps you could link to your launcher and tell us which part/s are causing you concern? You might be worrying about nothing.

Drawn copper tube has a much higher rated working pressure than 200psi. (Not to mention the burst pressure.)

Even 50/50 lead/tin joints will handle more pressure than the pipe.

Threaded fittings? Not to worry.

What's bothering you?
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Unread postAuthor: skyjive » Fri Mar 20, 2009 10:15 pm

I have great theoretical confidence in my gun. I just don't think I can bring myself to hold my head next to an object pressurized to several hundred psi without testing it first. Specifically I'm worried about the McMaster 3/4" QEV and the blowgun pilot, they aren't rated to even 200 psi I don't think. I bet they can take a lot of pressure but I can't be sure. Also, while I think I soldered all the joints properly, I can't be 100% certain until something explodes under pressure. The pipe itself and threaded joints I have no worries about.

Is there any way to do hydro testing without using a pressure washer? I can't spare the money for one right now.
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Unread postAuthor: Gippeto » Fri Mar 20, 2009 10:21 pm

Have access to anything like this?

http://www.germes-online.com/direct/dbi ... r_Kit_.jpg

Might find one at a rental shop too. Rent for a day?
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Unread postAuthor: jimmy101 » Sat Mar 21, 2009 2:32 pm

If you don't have a high pressure system like a pressure washer you can slightly mod your original plan and get reasonable safety.

Just fill the gun with water then pressurize with the CO2 setup. Since most of what is in the chamber is water, which doesn't really compress, only the small air volume will actually store much energy. Get that volume down to a couple cubic inches and there won't be all that much energy in the chamber. If your air volume is 1% of the chamber volume then you've only got about 1% the energy in the chamber if it should fail.
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Unread postAuthor: clide » Sat Mar 21, 2009 9:37 pm

A grease gun can also be used as a low cost high pressure fluid pump, but you'll need a thick fluid like corn syrup. http://home.mchsi.com/~hanson49/air_can ... r_test.htm

But if you already have a CO2 setup then jimmy's suggestion would probably be easiest.
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Unread postAuthor: skyjive » Sat Mar 21, 2009 11:09 pm

Yeah, I think I will go with the water/CO2 idea, as I already have all the necessary stuff.
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Unread postAuthor: jimmy101 » Sun Mar 22, 2009 12:23 pm

When doing the pressure test, make sure the air hose is restrained by something. Don't want the hose wipping about at high speed if something fails. Since most of the energy in the system is going to be in the supply hose that is where you'll need to contain any possible movement.
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