PEX and compressed air

[zxcvbob]

Has anyone used PEX tubing to run compressed air in a shop?

I had copper air lines in my old garage and really liked it. I'm getting tired of tripping over rubber hoses in the new garage. I think one of my coworkers that I've loaned tools to before has a PEX crimper, so if I can borrow a crimper is PEX worth the trouble for an easy 25' run? Or should I just go copper again now that Cu prices are dropping again. (of course with PEX, maybe I could buy a 100' roll and run a line all the way around the garage instead of just down one side...)

Bob

[Ed Pawlowski]

You need pex-al-pex that can handle air

There is another kind of PEX piping that is used in residential and commercial applications and in pressure service on compressed air and compressed gas systems. It is known as crosslinked polyethylene-aluminum-crosslinked polyethylene (PEX-AL-PEX).

[Hipupchuck]

Pressure is pressure, water or air. What's it rated at?

[Ed Pawlowski]

Not that simple. While pressure is pressure, water is not nearly as compressible as air and you don't get the same results with a catastrophic failure. That is why PVC is not allowed for air use. The shards can cause serious injury.

[zxcvbob]

Why would I care about oxygen permeability on a compressed air line? PEX-AL-PEX might be easier to work with tho' because it will take a bend without trying to spring back. And it should tolerate exposure to UV better (fluorescent lighting and occasional indirect sunlight.) Will have to see what the difference in price is...

Thanks, Bob

[Lefty]

Be careful of that one.

The pex-aluminum laminate is the one that had many failures in the early days of PEX.

There was much finger-pointing between contractors and manufacurers. Something about dissimalar materials delaminating...................

[fftt]

Pressure is pressure but air is not water.......its a stored energy thing.

That's why pressure vessels are "hydro-tested" for re- certification... a pressure vessel that fails when pressurized with water, fails with a "spurt" not a "boom".

Most, but not all, plastics are not ok for compressed gas applications ...its a matter of failure mode; ductile vs brittle.

As per Smitty Two's post....a LOT of machine shops / fab shops use PVC for a quick and easy air systems BUT PVC for air is a major no-no. Not just a silly rule...as PVC ages it gets brittle and a brittle gas pressure vessel is a potential fragmentation grenade.

cheers Bob

cheers Bob

[Ralph Mowery]

I did not know for sure, but I was thinking that water would sort of squirt out if the pipe burst,but air would rush out much faster and give a faster release of enegery. That would propel the shards much faster. Where I work we extrude melted plastic under 1500 psi from a hole 3/8 inches in diameter but it is so thick that is just barley gets out of the pipe. Water under that same pressure would go across the room. I sort of think water vers air at 100 psi would act similar.

[fftt]

Gas under high pressure has WAY more stored energy than water under the same pressure.

It's a compressibility issue; gases are compressible, water (for purpose of the this discussion ) is basically incompressible.

cheers Bob

[Ed Pawlowski]

Water cannot be compressed like air, thus it does not hold the energy that air can release. When pressure testing at very high pressure, water is the norm for that reason.