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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: Lockednloaded » Fri Jul 16, 2010 5:14 pm

I am making a small low pressure QEV gun to sell to a friend, but I want it to be aesthetically pleasing as well as functional. when I asked what color he wanted it he said metallic blue. the first thing that came to my mind was those aluminum sigg water bottles. They are lightweight cool and need no modifications to screw into regular fittings.

The only problem is that they aren't pressure rated or pressure tested in any way. So before I slap one on a cannon and sell it away I'd like to pressure test it.

I only have a bike pump, so I will have to be pretty close while the bottle is being pressurized. It will be filled with water, but I still think it is unsafe. I have a pool, so I may even submerge it for safety.

So, any other suggestions or links to people already doing this so that I don't have to waste a good bottle?
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Unread postAuthor: Gun Freak » Fri Jul 16, 2010 5:57 pm

There was a big discussion, as well as a bunch of other small discussions, on the bottles, but I don't recall anybody getting around to testing one. Find a section of PVC that the bottle fits in and cap it, then fill it with water and pressure test it in that. If using a bike pump, I would also pump by a corner of a wall or something and put the bottle around the other side of the corner so you can't be hit by any potential shrapnel.
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Unread postAuthor: Lockednloaded » Fri Jul 16, 2010 6:05 pm

I think I will submerge it then put a small underwater brick barrier around it now. Also the bottle is too large to fit in my largest PVC pipe (3") and I can't get 4".

I've seen these type of bottles used quite often on the french forums, but I can't read french, so no info there...
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Unread postAuthor: blackhawk13 » Fri Jul 16, 2010 6:08 pm

That sounds more dangerous than just pressurizing the bottle as is. PVC has a lower pressure rating than any metal I know of. As for how high the bottle will take, I would guess 300+psi. Probably higher if it is well made but don't blame me if you get hurt. I almost always fire my PVC air cannon at 150ish psi and that is no problem. The PVC says on it 600 PSI. If plastic can take that then the bottle should hold for lower pressure no problem. But testing it around a corner is a good idea. Post the cannon when you finish it.
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Unread postAuthor: Gun Freak » Fri Jul 16, 2010 6:13 pm

Yeah I've seen quite a few french cannons with the bottles as the chamber. I can understand french so if you give me a specific link I can get more info on it if you want.
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Unread postAuthor: Gippeto » Fri Jul 16, 2010 6:14 pm

Air anywhere in the "system" being tested is BAD.

Fill the entire thing (bottle and associated hoses, guage, valves, etc.) with a fluid of some sort...as entirely as is possible. Veg oil is cheap.

Use a hydraulic pump or grease gun to provide the pressure. Grease guns are dirt cheap at Harbor freight.

Do NOT use air as the pressure source...adding air to the system virtually negates the whole point of hydro testing. You're trying to NOT store energy...compressed air = stored energy.
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Unread postAuthor: Lockednloaded » Fri Jul 16, 2010 6:15 pm

this is very thin aluminum, The PVC outer shell would only absorb the shrapnel.

I don't think the bottle will throw out shrapnel, because I am hydro-testing it, but safety first.

EDIT
I've been browsing the french site, and it seems that similar bottles have been taken to 8.5 BAR
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Unread postAuthor: ramses » Fri Jul 16, 2010 7:07 pm

I don't think adding a tiny bit of air to pressurize is too bad. It's less than ideal, but the volume of air is only because of the deformation of hoses, the test vessel, etc. If the air pocket is in something designed for that pressure, I see no problem with it. It will try to propel the water, but water is heavy.

Basically, you're only storing a tiny fraction of the energy you would be storing if you pressurized with air.

Granted, I don't have access to hydro-testing equipment.
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Unread postAuthor: Lockednloaded » Fri Jul 16, 2010 7:30 pm

EDIT
Gipetto wrote:Do NOT use air as the pressure source...adding air to the system virtually negates the whole point of hydro testing. You're trying to NOT store energy...compressed air = stored energy.


hmmm.... I was planning on filling it with water and pumping, dang. Still, filling it with water will leave less room to pump air which equals less energy, which equals smaller explosion
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Last edited by Lockednloaded on Fri Jul 16, 2010 7:33 pm, edited 1 time in total.
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Unread postAuthor: SpudFarm » Fri Jul 16, 2010 7:32 pm

I would just have stood inside a door with the pump and have the bottle burried in loose and wet sand with a carpet over on the other side.
Then just pump as hard as you can and see if anything happends.

If you fill the bottle with water and secure the hose to something so it won't whip around I don't see how it could go wrong.

Remember to set up the all important camera.
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Unread postAuthor: Lockednloaded » Fri Jul 16, 2010 7:36 pm

about the camera: I don't have a proper camera to film this, but if I did I would hope the film would not be very entertaining; i don't want a huge explosion. I don't even want failure.
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Unread postAuthor: urgle the danish cow » Fri Jul 16, 2010 7:37 pm

you may be able to skip this whole situation with the scary bottle by doing a nice paint job or coloring the metal the same way gun barrels are.
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Unread postAuthor: Lockednloaded » Fri Jul 16, 2010 7:44 pm

There are other advantages besides aesthetics. More volume and lighter weight
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Unread postAuthor: SpudFarm » Fri Jul 16, 2010 7:44 pm

Lockednloaded wrote:about the camera: I don't have a proper camera to film this, but if I did I would hope the film would not be very entertaining; i don't want a huge explosion. I don't even want failure.


I would get two more bottles then I need and burst test them to see where their failiure point is. If you get one to 300psi and another only holds 100 you sure have a option less for that cannon.
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Unread postAuthor: Lockednloaded » Fri Jul 16, 2010 7:46 pm

the one I am going to test has minor dents and is about two months old. This is on purpose because I want to test worst case scenario
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