Anybody see any reason why I can’t use 3/4″ PEX to carry compressed air in my workshop (max 150 psi)? Seems like it will handle the pressure, and doesn’t have the explosion/shrapnel hazards that PVC does. Also a whole bunch easier than installing copper or black iron pipe.
Any thoughts appreciated.
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Replies
One of the functions of metal pipe is to cool down the hot air as it comes from the tank, and draw mositure out of the air. That's why the horizontal runs are all supposed to be sloped toward a drainage point, all vertical runs have drainage valves at the bottom, and all horizontal-to-vertical tees (and vice versa) have 8" vertical risers.
Pex wouldn't conduct heat nearly as well, so probably does not perform the moisture-condensation function as well.
One of the functions of metal pipe is to cool down the hot air as it comes from the tank, and draw mositure out of the air. That's why the horizontal runs are all supposed to be sloped toward a drainage point, all vertical runs have drainage valves at the bottom, and all horizontal-to-vertical tees ...*Barry
Barry pretty much sums it up, 'cept for that ALL take-offs should be vertical And all slope should be downstream. IMO galvanized is the only way to go, copper???? a second choice.
WSJ
'cept for that ALL take-offs should be vertical
That's what I was trying to say: even when taking off from a vertical drop, you should go vertical for a few inches before turning horizontal, like this:
http://www.tptools.com/statictext/airline-piping-diagram.pdf
Yes, metal conducts heat better, but most of the resistence (to heat exchange) is in the outer air film. Followed by the inner air film (it moves more and it is denser air). Lastly, the solid wall - the smallest factor in the total heat exchange. Materials of construction does make a difference but much less then you'd think. And less difference than you feel when you touch metal versus plastic.
Moving air over the ouside would make more difference than metal versus plastic.
David Thomas Overlooking Cook Inlet in Kenai, Alaska
We've had this discussion before. Many people have said that only black metal pipe should be used.You get out of life what you put into it......minus taxes.
Marv
Go ahead, should work fine, we use nylon tubing all the time at work for 250 psi N2 systems. I would guess that unless you are and extremely major consumer of air, the tank will drop out most of the moisture.
I would have thought that with the softer, flexible nature of PEX, it would bubble somewhere ?
"Criticism without instruction is little more than abuse." D.Sweet
It seems to me that all the old discussions about plastic air supply had the greatest negative factor being fire hazzard.
If fire burns through a charged plastic supply line you have a large volume of air to feed / fan the flames.
On a hill by the harbour
That sounds like the argument over "should plastic be used for dust collector lines"?, which came down to the fact that plastic cannot prevent an internal dust fire from spreading.
For most shops, the lines will be pressurized only when someone is around. The argument against rigid PVC are: 1.) is loses strength quickly when heated, such as by hot air; 2.) a potentially catastrophic failure mode would send shrapnel flying.
"That sounds like the argument over "should plastic be used for dust collector lines"?, which came down to the fact that plastic cannot prevent an internal dust fire from spreading.
For most shops, the lines will be pressurized only when someone is around. The argument against rigid PVC are: 1.) is loses strength quickly when heated, such as by hot air; 2.) a potentially catastrophic failure mode would send shrapnel flying."
Barry,
I probably should have qualified my post as food for thought ......
Dust collection is another subject.
I think alot of larger shops leave their systems pressurized most of the time ( I do IE Compressor is shut down at the end of the day but we don't drain the system everyday) except for sheduled maintenance.
I totally agree with rigid PVC / shrapnel potential.
On a hill by the harbour
The argument against rigid PVC are: 1.) is loses strength quickly when heated, such as by hot air; 2.) a potentially catastrophic failure mode would send shrapnel flying."
Barry,
Fatigue and cold temperatures are also factors against it. It gets very cold at outputs making that portion of the pipe brittle, and hot (which you mentioned) where air enters making it soft. PVC has NO place in an air distribution system other than when used for very low pressures and volumes.
With metal pipe, when a joint fails, it just starts to leak, with PVC...BOOM!!! Seen it happen many a time.
WSJ
Edited 8/24/2004 8:39 pm ET by WorkshopJon
Edited 8/24/2004 8:40 pm ET by WorkshopJon
SB,
Here is an interesting alternative. A little expensive but it looks easy to install and change as needed. I am thinking of doing our shop with it.
http://www.garagepak.com/
Bill Koustenis
Advanced Automotive Machine
Waldorf Md
I am thinking of doing our shop with it.
Bill,
Shaking my head in disbelief. You notice how the guy's site was half "under construction" and claimed copper had to be welded. Not to mention, no mention of sloping lines and vertical take-offs.
Barry's link had a graphic of the right way to do it. Period.
WSJ
Jon,
I have not really looked at his entire web site. I saw the actual material at a trade show and it is very nice. Used by a lot of Nascar teams and bunches of industrial applications. As far as correct installation goes, that is the responsibility of the installer, not the material supplier. Bill Koustenis
Advanced Automotive Machine
Waldorf Md
Some pex needs to be protected from UV exposure.
The only plastic I would use is the stuff designed and certified for compressed air.....Topring has a nice line, I think it may be nylon, but would have to check.cabinetmaker/college woodworking instructor. Cape Breton, N.S
Certainly there is flexible plastic tubing (generally of the reenforced variety) that is designed for compressed air use. You'd need to make sure that you got a sufficiently large diameter, and that you could field-terminate the ends with appropriately rated fittings. And you'd want to support/protect it somehow (possibly by running it inside rigid plastic water pipe or conduit).
Look at the Topring stuff.....it's all designed for compressed air, the fittings are easy to use, and work like a dream....installation is easy.....sleep easy at night. And if you have to move anything around tomorrow....no problem. Disassemble, and reassemble in minutes.cabinetmaker/college woodworking instructor. Cape Breton, N.S
Well, the reenforced air line is really only one step back from hydraulic hose -- pretty tough stuff. You'd probably be in more danger of snapping off a black iron fitting.
Though I see that the Topring stuff is a rigid nylon, apparently unreenforced:
http://www.topring.ca/english/topring.html