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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: MrCrowley » Fri Jul 20, 2007 5:40 pm

Alright quick question here...

When pressure testing a pneumatic cannon is it better to leave it pressurized for a period of time or fill the gun up and fire the gun rapidly so the fittings are under constant pressure change and stress?
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Unread postAuthor: Gepard » Fri Jul 20, 2007 5:44 pm

Well - pressurised nearly 100% with water is the first point.

I can't see a fitting failing during/after a firing....

I'd say it's most likely to fail on a rapid increase in pressure - but leaving it pressurised would certianly be a good test....

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Unread postAuthor: DYI » Fri Jul 20, 2007 5:49 pm

Pressurising with water is definately a good idea and, if you have the resources, testing it both under constant pressure and rapid filling/firing cycles would certainly be helpful. What would this pneumatic cannon be made of? And yes, rapid filling would be the easiest way to make it fail (just look at DDT in hybrids)
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Unread postAuthor: MrCrowley » Fri Jul 20, 2007 5:50 pm

Yeah I will do that today then, its just weird how after about 50 shots of the gun, part of the chamber decides to explode about five seconds after filling of the chamber to 100psi.

Image

That third handle you see there at the front with the 45* elbow is what exploded.

DYI wrote:Pressurising with water is definately a good idea and, if you have the resources, testing it both under constant pressure and rapid filling/firing cycles would certainly be helpful. What would this pneumatic cannon be made of? And yes, rapid filling would be the easiest way to make it fail (just look at DDT in hybrids)


Yeah I figured rapid filling is the best way to go to make it go boom. Last time I filled my barrel with water it leaked a bit into the piston and for some reason the piston stopped firing and I had to open the back up which is annoying to do so filling the gun with water is not something I want to do.

Cannon is made from 50mm PN18(260psi) PVC pipe.
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Unread postAuthor: mopherman » Fri Jul 20, 2007 6:21 pm

wow, pvc cannons are starting to really scare me. do you think it would be safe to test it under water? it would slow the fragments down emmediatly.
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Unread postAuthor: Gepard » Fri Jul 20, 2007 6:30 pm

Yes - go read the Big Bang thread currently active

But if you do a hydrostatic test its very safe anyway....

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Unread postAuthor: noname » Fri Jul 20, 2007 7:00 pm

Why does everyone believe you when you say PVC blew up at relatively low pressures, but no one believed me? Maybe people will start listening....

Any way to get the broken pipe out and make a new handle?
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Unread postAuthor: jrrdw » Fri Jul 20, 2007 7:21 pm

If i was going to worry about failure of the pipe i would buy all sch80. I would do a stadic test over night and see how much you loose overnight. If you do rapid fills and fires, each one is one less shot you get to take!
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Unread postAuthor: Acdcmonkey1991 » Fri Jul 20, 2007 7:31 pm

This is a little off topic but do you think that the foam pipe cover stuff they sell at home depot, when slid over pipe could contain the pieces of pipe if it explodes?
And I'd say your best bet is to pressurize it then back off for about 30 seconds, then come back and fire.
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Unread postAuthor: MrCrowley » Fri Jul 20, 2007 7:41 pm

noname wrote:Why does everyone believe you when you say PVC blew up at relatively low pressures, but no one believed me? Maybe people will start listening....

Any way to get the broken pipe out and make a new handle?


Yeah the pipe fragments still glued inside the fitting came out with some brute force, i've replaced the handle but couldn't get a 45* elbow so I just stuck an end cap on instead.

Yeah I hope they do, because I think its just a fault in the fitting which anyone can get, but like I said there were three of us within 2feet of it when it blew at 100psi, no one got hurt, I think the handle blew downwards into the ground instead of blowing out sideways, so im not saying if your gun blows up your fine we were just lucky it blew downwards.
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