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Compression 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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Compression Fittings

Unread postAuthor: thedeathofall » Tue Feb 17, 2009 2:58 pm

Okay guys, stupid question time.

Before I try to blow myself up, are compression fittings pressure rated? I haven't seen much about them, and the fittings themselves don't say anything. I'm working on a couple projects at once and they both may need to use copper.
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Re: Compression Fittings

Unread postAuthor: Ragnarok » Tue Feb 17, 2009 3:22 pm

You'll probably not find one that is specifically rated, as their strength depends on how well they are made, so they can't really be rated - indeed, not many joints specifically are rated, unless they have a "done well" attached as a disclaimer.

Still, that does not mean that they're not pressure capable, not in the slightest. The important questions here are how far do you want to use them, and in what size?
Like I said, the pressure they will take also depends on how exactly you assemble them - just like any other joint, if it's done badly, they'll not be as good as if done well.
In other words, I recommend the use of a bloody huge wrench (or, more ideally, two wrenches). If you're not concerned about dropping it on your foot, that means it's not big enough yet.

Now, I use them occasionally (both compression fittings and weaponised wrenches). I did the whole of Behemoth in them, and there are... five, I think, compression joints on HEAL - one to allow the piston to be serviceable, two as part of the pilot line, and one on each end of the ball valve safety, if I'm not missing any. Everything else is threaded or soldered.

I should note however, that as the one for the piston servicing is also where the piston hits on firing, the Olive was also soldered on for an extra measure of security (in addition to a big bumper). Doing this requires the soldering to be done neatly, or the fitting will leak, but it's a viable trick.

If they're not being hit by heavy pistons, if done properly and depending on exact size, larger sizes (1" or so) should be good for 300 psi at a minimum, even if not soldered in place.
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Unread postAuthor: Brian the brain » Tue Feb 17, 2009 3:29 pm

I've had 1" compression fittings at 26 bar lost of times.That's quite a lot..
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Unread postAuthor: thedeathofall » Tue Feb 17, 2009 3:30 pm

I'm simply talking about small sizes. 5/16 inch-3/8 inch. I am using them to connect a small piece of copper tube between the chamber and the valve of a small caliber gun. If they can be pressurized to over 300psi then I'm good. I don't have anything that will reach that pressure anyway.
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Unread postAuthor: Ragnarok » Tue Feb 17, 2009 3:40 pm

thedeathofall wrote:I'm simply talking about small sizes. If they can be pressurized to over 300psi then I'm good.

Yes - as long as they're not done sloppily, then those sizes should be fine to potentially thousands of psi.
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Unread postAuthor: thedeathofall » Tue Feb 17, 2009 3:44 pm

those sizes should be fine to potentially thousands of psi.


Wow, thats a lot...

Thanks for your help. I feel quite a bit safer now.
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Unread postAuthor: Brian the brain » Tue Feb 17, 2009 4:03 pm

Copper pipe isn't, though...
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Unread postAuthor: thedeathofall » Tue Feb 17, 2009 4:11 pm

i'm not gonna pressurize it past 120 psi anyway..
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