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Thread: Pex pipe for air lines

  1. #1
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    Pex pipe for air lines

    I have a bunch of left over pex pipe. Do you think it would be ok to use as my main air lines in my shop? Minimum quick burst capacity of 475 psi long term presure rating of 165 psi sustained pressure test of 1000 hours at 190 psi at 180 degrees. Anyone have experience using it as air line?

  2. #2
    Is it rated for carrying gasses? If so then it would be fine for air, if not then don't. There are some plastic materials suitable for air use, PVC is not one of them. I don't know if the Pex you have is. Do you know who made it, if so call them

  3. #3
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    I have wondered about using PEX for compressed air as well. All the PEX I have is marked: 80PSI @ 200F, 100PSI @ 180F 160PSI @ 73F. With a 175PSI max compressor I didn’t feel like the pressure rating was high enough. It looks to me like the pressure rating goes down rapidly with temperature rise. What would happen in the summertime?

    Any flexible pipe/tubing/hose used for permanent air piping would have to be installed in some way to prevent any sags between attachment points. Otherwise moisture will collect in the sags until it fills the pipe, and then be forced out to the tool by the moving air stream. If you could prevent the sags, or install it with enough slope that they wouldn't trap moisture then this negative could be overcome.

    Also, one of the concerns with any plastic pipe is the effect the oil in the air has on the plastic over long-term exposure.

    I know I am not answering your question, just adding to it. But my answer to myself, so far, has been: Not a high enough pressure rating, and uncertainty of long-term life because of exposure to oils.

    It has crossed my mind to use rubber air hose to plumb for shop air. It meets the pressure rating test; it is designed for compressed air, so oil shouldn't be a problem. The only drawback would be installing it so that there were no water traps. It sure would eliminate a lot of fittings. I haven't gone so far as to do a cost comparison to copper or black iron. Has anybody used hose to plumb their shop, or even thought about it?

  4. #4
    The problem (aside from those you mentioned) with plumbing with rubber hose is that if it fails or is accidently cut it could whip around your shop until fully discharged.

  5. #5
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    I have never used "Pex Pipe". I have however ran miles of Poly-Flo tubing for use in compressed gas systems and instrument air systems. Poly tubing works just fine when installed properly, and gives a level of flexibility un- matched by rigid applications( I've run miles of copper pipe also).
    One thing to consider. Are thr manufacturers stated ratings applicable to the size tubing you will use. 1/4" OD tubing has a higher working/ burst pressure rating than 1/2" OD. Pascals Law states that pressure is equal to force times area, ergo the wall thickness for 1/2" poly has to be thicker than the 1/4" poly to have the same ratings. You will want your main header to be at least 1/2"-3/4" to give you enough volume at the end of the branches
    In all honesty I have never checked into the cost for a poly tubing installations. It used to be that the compression fitting and cost of the tubing itself were significantly higher than an ASTM B66/ B68 copper installation.
    It's hard to beat a properly installed rigid copper installation. Done right it will be working long after you have used your last tool.
    I don't recommend Black pipe. It will work, and work well but I'm certain that it is not coded for compressed gas installations, and PVC should also be avoided. The failure mechanism for PVC and Black pipe is "catastrophic, in other words. If copper fails it is usually a gradual wall thinning that develops pinhole leaks, at worst it is a burst tear along the long grain of the material. Black Pipe and PVC fail in a manner that fragments the pipe.
    Didn't mean to be so long winded, this is what I do for a living.

  6. #6
    Quote Originally Posted by Mike Cutler
    Pascals Law states that pressure is equal to force times area, ergo the wall thickness for 1/2" poly has to be thicker than the 1/4" poly to have the same ratings.
    Didn't mean to be so long winded, this is what I do for a living.
    An excellent point, Mike! Don't worry about being long winded, this is exactly the kind of answers we need, and makes excellent reference material in the archives. Thanks!!!

  7. #7
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    Quote Originally Posted by Mike Cutler
    I have never used "Pex Pipe". I have however ran miles of Poly-Flo tubing for use in compressed gas systems and instrument air systems. Poly tubing works just fine when installed properly, and gives a level of flexibility un- matched by rigid applications( I've run miles of copper pipe also).
    Overall great info and well stated.

    But, what is "Poly-Flo" tubing? The only reference I could find on-line was for Poly-Flo fittings, but no specific reference to what tubing to use with them.

    I keep thinking there is an eaiser/better way or material to use to plumb for compressed air, but it seems all roads (advice) lead back to copper.

  8. #8
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    Quote Originally Posted by John P. Smith
    I keep thinking there is an eaiser/better way or material to use to plumb for compressed air, but it seems all roads (advice) lead back to copper.
    John,
    I have never understood why there is such an aversion to running copper air lines. Copper solders easily, there’s a large selection of fittings available, it doesn’t leak, it doesn’t have catastrophic failures and it is relatively cheap. I installed it in my garage shop last year, replacing my old PVC lines, for less than $35.
    They look cool too.
    Please help support the Creek.

    When everything is coming your way, you're in the wrong lane.

    - Steven Wright

  9. #9
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    I used left over and recycled copper from home projects for the garage and shop. I regulate my preasure at the compressor so it never excedes the rating of the pipe.

    3/4 " for the garage with impact wrenchs, hand grinder and sander.
    1/2" for the shop with blow and nail guns.
    TJH
    Live Like You Mean It.



    http://www.northhouse.org/

  10. #10
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    'Poly Flo" is a trademark name for softline flexible tubing from the Swaglock line of compression tubing and fittings.
    There are easier ways to run compressed airlines than copper, but they will be quite a bit more expensive. The compression fittings used in softline and hardline installations can be pretty expensive when compared to sweated copper pipe joints.
    I know that alot of folks are intimidated by sweating copper pipe, but there really is no need, it's a very straight forward procedure. Attention to detail and setup are the prerequisites for success. Everyone messes up their first 1/2 dozen joints and has to redo them. Proper cleaning,proper fluxing, and applying heat correctly are the keys to succces, just takes a little practice. One of the nice things about copper is that if you make a bad joint, you just reheat it, take it apart, clean it up, and redo it.
    In reviewing my previous post, my brain got ahead of my fingers. "Pascals Law states that force is equal to pressure times area, but the intent of the sentence is correct. Although Pascal's law is more attributed to non compressible fluids, it is applicable for compressed gases also. The larger the ID of the tubing the greater the surface area, and the greater the total force. Pressure is pressure. Sorry for the misfire.
    Last edited by Mike Cutler; 02-13-2005 at 8:05 AM.

  11. #11
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    Quote Originally Posted by Bruce Page
    John,
    I have never understood why there is such an aversion to running copper air lines. Copper solders easily, there’s a large selection of fittings available, it doesn’t leak, it doesn’t have catastrophic failures and it is relatively cheap. I installed it in my garage shop last year, replacing my old PVC lines, for less than $35.
    They look cool too.
    I agree. I was initially wary of doing copper (since I hate plumbing). I researched all the options and finally decided to bite the bullet as it really seems to be the best solution. A few hrs. later it was done. I probably spent twice as much time trying to find an alternative.
    I did buy an inexpensive auto-start MAPP gas torch. That's the way to go. I hate plumbing a little less now

    Jay
    Jay St. Peter

  12. #12
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    And, if you really want the flexibility of hose but still want copper, why couldn't you use refridgerator tubing?

    Greg

  13. #13
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    Quote Originally Posted by Mike Cutler
    I don't recommend Black pipe. It will work, and work well but I'm certain that it is not coded for compressed gas installations, and PVC should also be avoided. The failure mechanism for PVC and Black pipe is "catastrophic, in other words. If copper fails it is usually a gradual wall thinning that develops pinhole leaks, at worst it is a burst tear along the long grain of the material. Black Pipe and PVC fail in a manner that fragments the pipe.
    Didn't mean to be so long winded, this is what I do for a living.
    Mike, Put Me in the rigid copper group, as the best selection for these systems. However, I will add, (and I don't know where to go to get the rating specs for black pipe), but.... the Natural gas industry has used black pipe for transmission and distribution systems for compressed gas, since before I was born, and I'm 66 now. My Dad worked for a gas co for 31 years, and I even worked for them for a year and a half, and that's all we used, and they are still using it in my area today. Some places, however, have now gone to some type of plastic pipe for this purpose for underground applications, in low pressure systems, as it is designed to be impervious to the different types of corrosion caused by several different elements in the different soils.

    In the late 50's, we were using either mill coated pipe, (an asphalt coating wrapped in heavy paper) on the larger and higher pressure lines, and a wide, black, heavy plastic tape similar to electrical tape. We also used anodes and synthetic insulators between certain connections, but this was ONLY for underground applications. Even if the black pipe leaks or blows out, it does not SHATTER like pvc, except in RARE cases in extremely high pressure applications.

    In general, for above ground applications, as long as you stay within the working pressure of the pipe being used, I would consider it very safe for this application, but this is JUST My Opinion for what it's worth.

  14. #14
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    Norman. We may not be talking about the "same black pipe". I am referring to the black pipe found at home improvment centers. I'm fairly certain that the piping used by the Gas Co. is spec'd for them, and is of the proper WOG rating. The plastic pipe is most likely a spun resin impregnated fibercast. We use it in some of the lower pressure higher velocity process systems.
    The key sentence in your post, at least to me, is your final statement about adhering to the proper ratings of the materials in any process system. All to many times we fall into the "bigger is better, and even bigger must be really better" mindset, and an unforseen application down the road can lead to problems, even though the initial installation was fine and well within the safety parameters of the initial choice of materials.
    Do I think that every installation of PVC and Black pipe fail. No I do not. I just believe that copper is the "most correct" choice.
    Imho, copper pipe is the easiest, most conservative installation for the average person, and is well within the skills of any woodworker to install. It also works out to be the cheapest.
    More than another .02 worth.

  15. #15
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    Quote Originally Posted by Mike Cutler
    Norman. We may not be talking about the "same black pipe". I am referring to the black pipe found at home improvment centers.

    The key sentence in your post, at least to me, is your final statement about adhering to the proper ratings of the materials in any process system. All to many times we fall into the "bigger is better, and even bigger must be really better" mindset, and an unforseen application down the road can lead to problems, even though the initial installation was fine and well within the safety parameters of the initial choice of materials.

    I just believe that copper is the "most correct" choice.
    Imho, copper pipe is the easiest, most conservative installation for the average person, and is well within the skills of any woodworker to install. It also works out to be the cheapest.
    More than another .02 worth.
    Mike I agree with you 100% that the Rigid Copper is the most correct to use, and my preference, (With the Proper letter designations--there are two, and I always have to check whether it is K, L, or M that are the correct ones to use). I also always like to see a short Rubber Hose used to connect the compressor to the pipe system, to eliminate vibration/noise transfer, and that of dissimilar metals corrosion.

    I don't know the specs of the black pipe at the home centers, as I only buy from pipe companies or plumbing suppliers and ask for the pipe that meets all the parameters for it's intended use, ie; use code, working pressure, etc., and I leave plenty of room between the intended use pressure and the working pressure as a safety/longevity buffer.

    Hopefully, these posts will help those that don't already have an understanding of these piping systems so they can install good safe systems that will work well for them for a long time without further attention to them.

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