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noob question about PVC air pressure.

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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noob question about PVC air pressure.

Unread postAuthor: derrick007 » Wed Oct 18, 2006 9:35 pm

I tried searching, but still haven't found anything, so I figured if any one knows, it's you guys. I have a gun made out of 1 1/2 in. PVC pipe, simple, just a bike tube valve to get air in, and a ball valve to shoot it. but, what is the max air pressure I could put into this thing. air chamber is 1 1/2 in PVC, 27 in. long, with just normal air gowing into it, so how much PSI can go into it. If this has allready been answered, could you pleaes just give me a link. Thanks.
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Unread postAuthor: haulinick » Wed Oct 18, 2006 10:28 pm

Make sure you have pressure rated pvc. It should have writing on along the pipe and somewhere in the writing it will say how much psi. for 1 1/2" its probably something like 300 psi. Now be aware, thats a rating for water pressure. With compressed air its probably best not to go above about 120 psi.
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Unread postAuthor: SquishY » Thu Oct 19, 2006 1:14 am

Haulinick about covered it all, the really thin pipe made for drainage will actually say "NOT FOR PRESSURE" along with the other little bit of information on it. The pipe you are looking for will say something along the lines of SCH-40(can be 80 or 120 also I belive) 280 PSI(just an estimate being that I dont have any 1 1/2") and some other jibberish.
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Unread postAuthor: Recruit » Thu Oct 19, 2006 2:17 am

dig a hole 3ft in the ground cover with board have tank inside pressure gauge on line you are using to pump the tank up with and pump till it blows then divid the peak pressure but three (most pipe only is pressurized to a 1/3 of its burst point) and voila you have the pressure it is safe to work at
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Unread postAuthor: Tyro » Thu Oct 19, 2006 2:37 am

he is right, you can test it that way if you want, But, i wouldn't have made it out of any PVC in the first place. So have a good time feeling un-safe. You shouldn't be making pneumatics outa' stuff you don't know!
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Unread postAuthor: Recruit » Thu Oct 19, 2006 3:37 am

note just remembered this the pump line will most likely be destroyed to help prevent this fill in the hole on top of the pipe ,and you probalbly will want to borrow a compressure from some one.
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Unread postAuthor: derrick007 » Thu Oct 19, 2006 7:36 am

Well, I know it's rated for 330 PSI for water, but I was after air, seeing as I don't use water, lol. So, about 120 is safe? I've been gowing with 80PSI. Thanks.
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Unread postAuthor: joannaardway » Thu Oct 19, 2006 7:47 am

120 should be safe, and 150 would probably also be fine.

As has already been said, most pipe has a 3:1 safety factor, so your pipe would probably blow at about 1000 psi.

Adding a personal 2:1 factor on top of that, and you'll be totally fine.

I personally like a little headroom on ratings (not as much as 2:1 though), and regardless of rating, I would never go above about 300 psi.

I don't see where the problem is with the different ratings for air and water - both are exerting the exact same forces at the same pressures.

Sure, when it blows air will be much nastier, but they'll still go at the same pressure.
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Unread postAuthor: POS » Thu Oct 19, 2006 12:19 pm

if it is rated 330 psi for water, it's rated the same vor air. Pressure is pressure. Water, air, gas, whatever
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Unread postAuthor: haulinick » Thu Oct 19, 2006 7:26 pm

The difference between water and air is what would happen if the pipe does go. At pressure like 100psi air is compressed more than water, so if the pipe does go the air will expand alot more than water causing the pipe to become more bomb-like.
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Unread postAuthor: joannaardway » Fri Oct 20, 2006 4:42 am

Yes, but it will still go at the same pressure, regardless of how nastily it goes.
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Unread postAuthor: Cody0500 » Mon Nov 13, 2006 3:45 pm

yea, pressure is pressure. Doesnt matter the density of whatever is in it. Yea if it blows, the reaction will be different. but it if can hold 300 psi, thats 300 psi, of anything.

Thermodynamics for the win
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Unread postAuthor: POS » Mon Nov 13, 2006 3:52 pm

euh, if you hold a gun that explodes at a pressure of 300 psi, filled with air, you will most likely get killed. If it is pressurized water, you will only get wet.
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Unread postAuthor: drac » Mon Nov 13, 2006 4:07 pm

POS, he just said that.
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Unread postAuthor: mark.f » Mon Nov 13, 2006 11:35 pm

Beautiful the way you treat 300 PSI water pressure as well. Even if it doesn't expand much, if you we're holding a pipe that burst at 300 PSI with water, you still wouldn't be completely safe. Why do you think people who are hydrotesting tanks and such don't stand next to them?
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