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2" Galvanized Fittings

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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2" Galvanized Fittings

Unread postAuthor: Lentamentalisk » Sat Apr 12, 2008 2:51 am

I went to the local ACE Hardware to check out parts for the high pressure helium cannon I am going to make. I saw galvanized steel pipe and fittings of the perfect size and all, for fairly cheap (I'm gona go to a plumbing supply place to buy the stuff though cuz they are bound to have better deals,) so I asked the guy how high they were rated. He said he would check, and when he came back he said that they were rated for at least 200psi.
I can't believe that the fittings would be rated at 200psi when the pipe is rated at 3000 or so. Do any of you have counter evidence as to what galvanized steel fittings are rated at?

Also as a side note, does anyone know what the vapor pressure of helium is at room temp? I haven't been able to find it anywere.
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Unread postAuthor: bigbob12345 » Sat Apr 12, 2008 8:50 am

Well they are wrong
They are actually rated to 150psi and made of malleble iron
But they are good up to 400-500psi
If you plan on going higher than that I would suggest you just buy some high pressure fittings off mcmaster
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Unread postAuthor: POLAND_SPUD » Sat Apr 12, 2008 8:50 am

DYI claims that galvanized malleable iron fittings are rated by manufacturers to 150 psi. However they have been used by many people (including me) at pressures in the range of 400 - 500 psi.
QEVs are rated to 150 psi but there are people who use them at 400 psi (al-xg is said to have tested them at 800)

I hope you get the idea - manufacturers lower the pressure rating of their stuff for some unknown reason but you can use them at higher pressures - but it's your fault if something goes wrong :wink:

sometimes I do come across some reasonable info about pressure ratings of malleable iron fittings given in PN numbers - for example a standard galvanized 1/2" nipple has PN 25 (so it is rated to 25 bar)

could you tell us what kind of fittings you are going to use ? (steel or malleable iron ?)
at what pressures are going to use that gun ?
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Unread postAuthor: Lentamentalisk » Sat Apr 12, 2008 11:26 am

well I was going to use it at what ever pressure the helium comes out of the tank (I still haven't been able to figure out how high that is, anyone know?) I am looking for as much power as possible.
I guess I will use what ever fittings will do the job well...
To McMasters!!!
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Unread postAuthor: DYI » Sat Apr 12, 2008 11:31 am

The helium that comes out of the tank ranges from a minimum of 2200 psi for the larger tanks, up to 2600 for some tanks, and as high as 6000 for the expensive high pressure tanks.

Galvanised malleable iron fittings are almost always rated for 150 psi, although I have no problems with using them at 500 or so, and I did put 2000 in a 1/4" galvanised iron fitting.

I wouldn't be suprised at all if 2.2kpsi helium caused failure in the 2" fittings. The only way to know for sure without risking life and limb is to do some hydrostatic testing with a grease gun to find out their actual burst pressure.

3kpsi forged steel fittings from McMaster will handle it no problem.
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