PEX for compressed air line
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dawgee
Well-known member
and it wont rust. mcmaster-carr sells air line thats like pex and fittings for compressed air
e-rockin-it
Well-known member
The only reason I see not to use PEX for compressed air line is that it is UV sensitive. That being said what I ended up doing is running hard line on any exposed area (black pipe along wall and into ceiling) once in the attic I switched to PEX to continue the run, then back to black pipe when I can down and out. Been working with that for a year now at 120psi without issue. Ran PEX in the attic for the same reasons you stated (easier to work with, cheap, etc. )
rlitman
Well-known member
Water pressure ratings assume very little safety factor because water is a non-compressible fluid, so the stored energy of a hydraulic system is very low.
Air pressure ratings have a safety overhead calculated in to account for the fact that compressed air stored energy like a spring, and releasing it can be very dangerous.
Here's my thoughts on pex for an air line:
Right off the compressor. No. The air is very hot, and that's not good for the pex.
Also, vibrations passed along from the compressor can make the pipe rub through where it contacts things (this is also an issue with steel clips on copper pipe, but not really an issue on black pipe). That's one reason I have a few feet of steel pipe off my tank, followed by a rubber hose whip to my piping system.
Exposed to any light. No. UV breaks it down. In sunlight, that could be in as little as a matter of weeks. In fluorescent light, more like years, but it still hurts it.
Hidden away. Maybe. But I'm still not that trusting of pex fittings to bury them.
Air pressure ratings have a safety overhead calculated in to account for the fact that compressed air stored energy like a spring, and releasing it can be very dangerous.
Here's my thoughts on pex for an air line:
Right off the compressor. No. The air is very hot, and that's not good for the pex.
Also, vibrations passed along from the compressor can make the pipe rub through where it contacts things (this is also an issue with steel clips on copper pipe, but not really an issue on black pipe). That's one reason I have a few feet of steel pipe off my tank, followed by a rubber hose whip to my piping system.
Exposed to any light. No. UV breaks it down. In sunlight, that could be in as little as a matter of weeks. In fluorescent light, more like years, but it still hurts it.
Hidden away. Maybe. But I'm still not that trusting of pex fittings to bury them.
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soapii
Well-known member
How did you go back and forth between the two? Did you use NPT to barb fittings?
--Joe
2ridgebacks
Member
- Joined
- Oct 12, 2009
- Messages
- 8
I work in the auto industry. We have miles of flexible plastic line in the plant. I've never seen one rupture. Failure is caused by a kink or an errant spark 99% of the time. Fwiw, we run 90psi.
e-rockin-it
Well-known member
Pretty much, there are fittings that you can buy at the hardware store to do this. Just make sure that you get the right barb for PEX (rounded barbs) or it will cut through when you crimp on the fitting. Also something I noticed was that PEX is sized by outside diameter while black pipe is sized by inside diameter. So in my case I was running 1/2" black pipe, then had to go to 3/4" PEX to maintain the same internal diameter through my run. Was something I noticed at the hardware store when I was buying fittings, so just a heads up.
I work in the food industry and we have Pex installed thoughout the plant for air lines supplying all sorts of equpment from a large central compressed air plant, all of it under florsesent lights it has all be there for many year without any failures.
I also have it installed in my own shop and it has been there for quite some time without issues. I installed it on uni-strut with vibration reducing clamps Where I have point of use I switched to schedule 40 stainless with drip legs so that I had more ridigity to hook up air hoses etc. I see no reason, other than hard piping looks nicer installed, not to use pex.
I also have it installed in my own shop and it has been there for quite some time without issues. I installed it on uni-strut with vibration reducing clamps Where I have point of use I switched to schedule 40 stainless with drip legs so that I had more ridigity to hook up air hoses etc. I see no reason, other than hard piping looks nicer installed, not to use pex.
I have had PEX in my shop for about 5 years now at 150ish psi and no problems. I went from a carport shed where the aircompressor is into PVC (I know no one likes PCV for air) into the ground to my shop. I then converted to PEX inside the wall up to the attic space to two fitting in the ceiling and one on the wall. I have had no leaks and was easy to work with. If the PVC ever blows it is in an area that no one is around so no danger.
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Highbeam
Well-known member
I would actually tend to think that water pressure ratings demand a higher factor of safety. Water is non-compressible, true, and this means that any hammer or pressure waves will beat up on the pex vs. air pressure which will absorb the energy. So a pex pipe rated for 180 psi water would be able to take a higher air pressure. Safety factors are not based on damage incurred from rupture but on confidence in the variables.
This is the opposite of what rlitman thought so I thought it odd.
This is the opposite of what rlitman thought so I thought it odd.
rlitman
Well-known member
Safety factors in the case of hydraulic pressure ratings are there only for the safety of the plumbing assembly. You're protecting it from leaks. That's it.
Safety factors in a pneumatic case are there to protect you from injury.
A rope may be rated to pull 5000 lbs, but nobody is going to say that it is safe to use that same rope to lift an elevator car.
Safety factors in a pneumatic case are there to protect you from injury.
A rope may be rated to pull 5000 lbs, but nobody is going to say that it is safe to use that same rope to lift an elevator car.
icenfire01
Well-known member
I too have been wondering why more people don't use pex for air systems? I see the issues with pcv, but even considering the vu exposure how much line is exposed to sunlight if you run it up high, behind benches and shelving ect? Can pex be painted to prevent exposure?
dbabicky
Well-known member
120 psi is 120 psi, whether it's an air cylinder or a hydraulic cylinder. Yes you can compress air and not fluids, but pressure is pressure if they're both the same psi.
I love how people say you can't do something and have all the magical answer's but no proof.
If you want to use PEX, go for it. If you want to use PVC, go for it. All the know-it all Nazi's on forum's just kill me.
Fishplate
Well-known member
Stored energy.
rlitman
Well-known member
120 psi is 120 psi, whether it's an air cylinder or a hydraulic cylinder. Yes you can compress air and not fluids, but pressure is pressure if they're both the same psi.
I love how people say you can't do something and have all the magical answer's but no proof.
If you want to use PEX, go for it. If you want to use PVC, go for it. All the know-it all Nazi's on forum's just kill me.
I never said anything about you can't use PEX.
If you want to go calling me a "know-it all Nazi", you can go F yourself.
There's nothing magical about physics. Maybe evolution is magical to your world of thinking, but those of us who've evolved past eating nits off our relatives do know better.
When it comes to breaking a pipe 120 PSI in a hydraulic system is indeed more likely to cause a burst than 120 PSI in a pneumatic system because of the shock loads mentioned above. BUT in a hydraulic system the pressure will also drop precipitously as soon as it leaks and the failure will be pretty uneventful.
Tell me this. How hard is it to hurt yourself jumping on a cinder block?
Now how hard is it to hurt yourself on a pogo stick?
Torque1st
MEMBER EMERITUS
Plastic pipe and tubing have poor thermal conductivity which is necessary to cool the air and drop the moisture out quickly.
Hard piping is easy to run so that there are no low spots to collect water in the main lines.
Most plastic tubing used in modern industrial plants is carrying dry air that has been mechanically dehumidified or otherwise conditioned to remove water.
Hard piping is easy to run so that there are no low spots to collect water in the main lines.
Most plastic tubing used in modern industrial plants is carrying dry air that has been mechanically dehumidified or otherwise conditioned to remove water.
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55bigblockcid
Well-known member
- Joined
- Jun 17, 2011
- Messages
- 250
These pex airline threads never fail to deliver.
6768rogues
Banned
The pipe full of pressurized water has one pipe capacity of water under pressure. When it bursts, less than one pipe capacity of water comes out then the pressure is relieved. The pipe full of air can have dozens or hundreds of pipe capacities of air inside. When it bursts, it can be explosive as all that air volume escapes until the pressure drops.
Fill a balloon with water and pop it with a pin. Pretty non-eventful, hardly a pop. Fill a balloon with air and pop it and POW.
Fill a balloon with water and pop it with a pin. Pretty non-eventful, hardly a pop. Fill a balloon with air and pop it and POW.
rburke65
Well-known member
Right now, my compressor is in the pole barn and in order to feed my new shop, I ran 3/4" black pipe overhead then ran pex under groung inside a 2" PVC conduit to the new shop. In the new shop, all pex tubing. Happy so far.
icenfire01
Well-known member
Agreed. That makes perfect sense, however the question still stands what's the difference between 100' of coiled rubber hose bursting or 100' of pex attached to your wall?
same goes for the cooling factor, or has no one hooked an impact right to the end of a rubber coil before 
Just asking 
djjsr
Well-known member
In your garage you can use whatever you want. It's your decision and your risk. The horse was beaten to death long ago.
But if you're in a business that's subject to OSHA regulations, using a material that's not approved for compressed air may bite you in the *** someday.
But if you're in a business that's subject to OSHA regulations, using a material that's not approved for compressed air may bite you in the *** someday.
Torque1st
MEMBER EMERITUS
Yup, but even in your own garage the risk to others is present. You will never forgive yourself if your wife, sibling, neighbor, child, etc walks into your garage and a line bursts at that moment throwing a piece of shrapnel into them or worse. Businesses get fined, sometimes criminal charges are made. Your neighbor may press charges and the insurance company may not pay out leaving you holding the bag.
Besides-
PEX is easy to use but that is about the only good thing about it. Same as a rubber hose. A pair of ***** hose can be used as a fan belt. It is also easy! -No tools required. It even WORKS! The only time it is a good choice is when someone is stuck out in the middle off nowhere with no other choice.
BD1
Well-known member
There is tubing designed for air. The manufacture states it is for ''AIR.'' If what you choose to use does not say for air, you are on your own. 
Osha states, '' Plastic pipe used for compressed air service must be designed for such service by the manufacturer.''
http://www.orosha.org/pdf/pubs/fact_sheets/fs44.pdf
Tubing for air.
http://www.rapidairproducts.com/choose.asp
Osha states, '' Plastic pipe used for compressed air service must be designed for such service by the manufacturer.''http://www.orosha.org/pdf/pubs/fact_sheets/fs44.pdf
Tubing for air.
http://www.rapidairproducts.com/choose.asp
e-rockin-it
Well-known member
I looked at Rapidair as well when I was setting up my garage. It is very nice stuff, but harder to get in my neck of the woods. An alternative to Rapidair tube (although I think it's the same thing) is air brake hose for trucks. Was readily available with all the fittings at the local truck dealer around the corner and was slightly cheaper than the Rapidair kit once you factor in shipping etc.
icenfire01
Well-known member
Yup, but even in your own garage the risk to others is present. You will never forgive yourself if your wife, sibling, neighbor, child, etc walks into your garage and a line bursts at that moment throwing a piece of shrapnel into them or worse. Businesses get fined, sometimes criminal charges are made. Your neighbor may press charges and the insurance company may not pay out leaving you holding the bag.
What shrapnel? That's what I'm getting at. If a pex line bursts it should be no more dangerous than if the rubber drop hose or reel at the end of the line fails, correct? Or am I missing something? We all know that rubber hose is "designed" for air, and it bursts all the time. I replace a hose once a week in our shop because it got run over, punctured, or just failed.
Higgins
Well-known member
It's not the damage to the PEX it's self, it's all the collateral damage that will occur when the pipe ruptures!
AL
AL
Highbeam
Well-known member
We know how pvc can create shrapnel when it blows up. That shrapnel is what causes damage. Fine. What happens when PEX bursts? I don't suspect that it causes shrapnel and if that is the case then the only thing to worry about it the end of the pipe whipping around or dust being blown onto the wet paint.
Oh and a hydraulic leak can be quite disasterous. Haven't you ever been told not to check for leaks with your hand?
Hydrostatic testing includes no air.
Oh and a hydraulic leak can be quite disasterous. Haven't you ever been told not to check for leaks with your hand?
Hydrostatic testing includes no air.
I will agree with plant air being conditioned, filtered, dried, etc. and you are right that what causes failures in most piping systems is moisture, or hydraulic shock. If you have ever worked on high pressure steam systems this is very important, supply only dry steam to the headers and there will be no issues, fail to drain the headers and send a water slug down the header and it will reach velocities that will blow the backs out of elbows, or explode condensate traps etc, at pressures lower than you would believe.
bldgengineer
Active member
Know about this all too well.