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Pressure rating for schedule 40 aluminum

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 rating for schedule 40 aluminum

Unread postAuthor: grumpyoldman » Sun Apr 29, 2012 10:07 pm

I was looking on McMaster's web site at schedule 40 aluminum nipples. It says to use 150 class fittings which are only rated to 150 psi operating pressure.

They don't have a pressure rating on the nipples but I'm assuming it would be the same as pipe. I went to the following web page to calculate the pressure rating of the size nipple or pipe I want to use.
http://www.ajdesigner.com/phpaluminumpipe/pressure_rating_equation.php


According to the calculations the 2 inch pipe is pressure rated at about 972 psi.

I'm guessing the nipple can take 300 psi easily but I'm limited to 150 psi because of the fittings. Is this correct?
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Unread postAuthor: jackssmirkingrevenge » Mon Apr 30, 2012 12:40 am

150 psi rated fittings will not suddenly explode at 151 psi, you're likely to be ok at twice the pressure given the safety factors thrown in by the manufacturers. This isn't of course recommended, but hey, neither are most fun things :)
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Unread postAuthor: grumpyoldman » Mon Apr 30, 2012 1:03 am

150 psi rated fittings will not suddenly explode at 151 psi

:D LOL JSR's impeccable sense of humor.

I'm just a bit worried because I plan on selling the cannons.
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Unread postAuthor: jackssmirkingrevenge » Mon Apr 30, 2012 1:21 am

Not humour, just fact ;)

If you're planning on selling, aim for the best possible performance with lower pressures. If you're worried people will try to turn it up, put a pop-off safety valve on the chamber. If you're even more worried, put a nice "warranty void if tampered with" sticker next to the valve.

Ultimately, in terms of liability it's several orders of magnitude more likely that someone will injure themselves or others by using the thing incorrectly (aiming at stuff or people they shouldn't, at rangest they shouldn't, with unsafe projectiles etc.) as opposed to mechanical failure of the launcher itself.
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Unread postAuthor: grumpyoldman » Mon Apr 30, 2012 1:29 am

Thanks Jack! (I had to put in more words because a pop-up said my message was too short. :) )
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Unread postAuthor: Moonbogg » Tue May 01, 2012 2:16 am

Keep in mind that Mc masters pipe is almost certainly not seamless. Its hard to see with aluminum pipe visually, but there is seamed and seamless versions of extruded pipe. Check the ASTM spec.
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Unread postAuthor: grumpyoldman » Tue May 01, 2012 2:57 am

Thanks moonbogg. I thought all aluminum pipe was seamless.

I just checked and McMaster's says it's seamless ASTM B241 so it looks like it's truly seamless. I was going to buy some aluminum pipe from SpeedyMetals and thread it myself. Their pipe is about 1/2 the price of McMaster. If it's that much cheaper it might not be seamless. Their web site doesn't say if it's seamless or what standards it meets. I'll have to email them to find out. Thanks again for the heads up.

BTW. Very impressive cannons on your site. Must take a while to build them and also some expensive tools. I think I fell in love with the Striker. Sleek, tight and beautiful. If I had an old lady right now, I'd trade you. :)
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