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psi limit

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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psi limit

Unread postAuthor: tape fist » Sun Dec 21, 2008 4:42 am

I have recently made a compact air cannon and would like to know what the max psi it could hold i have put 150 in it over 500 times and it hasn't had any problems but is this to much or can i put even more?
this are the basic diagram
http://img117.imageshack.us/img117/8190/aaut5.png
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Unread postAuthor: Dgealy » Sun Dec 21, 2008 4:45 am

If it's 3/4 inch SCHEDULE 40 PVC, then you can double the pressure. If not, i have no idea. Shouldn't the pvc have a pressure rating on the pipe itself?
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Unread postAuthor: cheeseboy » Sun Dec 21, 2008 4:58 am

It isn't safe to take SCH40 pressure rated pvc over 200PSI as once you take is near the limit it becomes easy to fracture and then it will shatter, but increasing pressure won't do much while your valve is still :puke: change the valve to a modded sprinkler or add springs to the ball valve to let it open faster, this will give a massive increase in performance.
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Unread postAuthor: ALIHISGREAT » Sun Dec 21, 2008 5:07 am

depends on the pressure rating, if it has no rating, i would decomission your cannon pretty sharpish :wink:
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Unread postAuthor: Dgealy » Sun Dec 21, 2008 5:21 am

Pressurizing it over 200 PSI if it's sch 40 wouldn't be a problem because it's 3/4 inch. That means less energy and less surface area, therefore less tension trying to push the plastic apart. So taking it more than 200 is fine, just keep it under 400.

I didn't comment on the valve cause i thought the schrader was the barrel, and that it was a hp coax.
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Unread postAuthor: noob of noobs » Mon Dec 22, 2008 12:46 am

Cheeseboy, I'd chek out the rating of your sprinkler valve first; my standard Rainbird ones are only rated to 125psi.

Not to be the saftey nerd, but remember that PVC isn't made to handle air pressure; it's built for water. So theoretically, unless you're using water as your pressurizing fluid, you're still running the chance of a fail.

Either way, I'd check the pressure rating on the pipe. But if you want to go higher than 150 psi, I'd go with steel or copper anyways. Overpressurized pvc isn't something you want to be around, but metal's been proven safe up to hundreds of psi. Plus it looks cool. :D
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Unread postAuthor: roboman » Tue Dec 23, 2008 1:37 pm

What's your ball valve made out of? If it's brass, then the whole thing can probably take much more pressure. I think 3/4" Sch. 40 is rated at ~600 psi.
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Unread postAuthor: Hubb » Tue Dec 23, 2008 1:45 pm

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