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Buried air line

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k9fletch
Join Date: Jul 2003
Posts: 52 Whittemore, MI
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2005-02-16          106233

I am in the process of planing my shop and would like to have a large air compressor in the back shop and then run buried air line up to the the garage, which is attached to my house. There is about 100' between the back garage and the front garage, I have an old 20 gallon air tank which I would mount in the rafters of the front garage as a reservoir or surge tank.

I have to dig the trench for the electrical once it thaws, and would put the buried air line in the same trench.

Has anyone ever tried this? I had considered using PVC pipe but was told that I can't because it can fail, so now I am thinking about using 3/4" copper, gal. steel would be my last choice.

I am open to your thoughts on this, I am just tired of dragging around air hose.


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HuckMeat
Join Date: Jan 2004
Posts: 121 Colorado
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2005-02-16          106235

I'm doing something similar - I wanted 50psi air down in the barn from my garage, for blowing out plumbing, etc.

I buried a pex line alongside my water line. I bought it in a 500' roll, so I didn't have any joints buried.

I crimped on connectors to convert it to 1/4" NPT, and so far things seem great.

The problem with pex is that you really shouldn't pressureize it too high, but as I recall it was good to 120psi at 180 degrees for water.

I put a regulator inline between the compressor and the pex supply, so that the pex line is always at 50 psi.

You can buy the crimp tools, pex, and fittings on flea-bay. ....

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denwood
Join Date: Jul 2004
Posts: 542 Quarryville PA
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2005-02-16          106236

I have never seen air run in copper, is it strong enough. Galv. steel is common. We have even used the stronger rated black coil of tubing used for wells. I can't remember but I thought it was rated for 160 psi at 74 degrees F.? As long as you are not going over that and it is isolated a little from the hot compressor, it should be fine. I think I would just use it at the bottom of the trench. ....

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hardwood
Join Date: Dec 2002
Posts: 3583 iowa
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2005-02-16          106239

I've never seen copper used for air either, there may be a reason, pressure limits, corrosion, maybe some other reason? Surely there is a plastic product that will replace galanized, I would'nt want all the buried joints either. My only concern would be water that will collect in the line over time, so maybe a blow off valve at the low end of the line. Good luck. Frank. ....

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Murf
Join Date: Dec 1999
Posts: 7249 Toronto Area, Ontario, Canada
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2005-02-16          106242

I have my whole shop plumbed in regular 1/2" copper water pipe.

The misunderstood thing about ratings is that there is in reality two ratings, what something is designed to handle (read what the lawyers said was OK to say) and the point at which something breaks. Usually the 'rating' is about 1/3 of the 'burst point', so if something is 'rated' at 50 psi, it will burst at 150+ psi, sometimes burst is MANY times working pressures, not just 3 or 4 times.

I didn't build my shop so the buried utilities were done by the previous owner, a house builder. I wanted air at the house for tires and odd jobs, but that is so infrequently that I just picked up a small 120v compressor and leave it in the garage.

The other problem wiould be to run an air line any distance, the losses and reduced pressure would be a PITA anyway.

Best of luck. ....

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k9fletch
Join Date: Jul 2003
Posts: 52 Whittemore, MI
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2005-02-16          106244

I currently have copper branch lines in my front garage for air and while trying to conduct some research I found that its an ok material to use for air but for most situations its cost prohibitive because of the labor used in sweating joints. I have access to copper and I don't mind in sweating on fittings.I haven't found any plastic pipe that is readily available yet but the search continues, I have got to believe that there is some type out there. As I stated before I would have liked to use PVC but I have it can burst and create a shrapnel effect upon bursting.

Thanks for your opinions and keep them coming.

....

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hardwood
Join Date: Dec 2002
Posts: 3583 iowa
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2005-02-16          106245

Just another thought. When we wired the shop the electrican somehow wired the compressor so that it will only run when the shop lights are on. He had just replaced a compresor for his brother that somehow developed a bad leak over a weekend, it just ran till it melted down. Frank. ....

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yooperpete
Join Date: Jan 2004
Posts: 1413 Northern Michigan
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2005-02-16          106252

We had our machine shop plumbed with special thick walled PVC pipe for air lines. It was suspended about 10' off the floor height. After about 5 years some of the joints began to let loose and some areas sagged from the suspension points being too far apart and collected moisture. When they let loose, the lines flung around. A couple of guys got slapped from it and we said enough with that. We replaced it with steel pipe. Frank make a good point about moisture and the need to have some way to collect and separate it. I'd stay away from buried plastic and would think that you may want to slightly separate other underground utilities from it in case you need to go back in someday to perform maintenance. ....

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havoctec
Join Date: Sep 2004
Posts: 56 Minnesota
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2005-02-16          106253

Just talked to a plumber friend of mine this weekend about the air lines he has in his shed. I noticed they were pex and asked him about it. He said a lot of the guys he works with use it for thier air lines and that is waht is run in the company shop. I bielive he said it was rated for 300 psi but not to sure about that number. I think that is the way I would go. No worry about corrosion with that stuff.


....

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AnnBrush
Join Date: Mar 2004
Posts: 463 Troy OH
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2005-02-17          106276

As Murf pointed out your biggest problem will be drop in pressure over the long length of line. You will have to oversize the line considerably. If I understood you correctly I would also have reservations adding a second "reserve tank", you might generate air flow in two directions, from the reserve back to the original compressor tank especially if you are drawing air from two locations on the line at the same time. This may affect the compressors ability to regulate the compressor tank pressure. I am not sure if this is problematic or not. ....

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beagle
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2005-02-17          106277

Good point about the back pressure, but I think an in-line check valve would solve that problem. The pressure (head) drop in the line is propotional to the flow vlume or velocity. For low flows, around 4cfm, the pressure drop over 100' isn't too much of a problem, especially with 3/4" lines. If you need over 10cfm, for running high consuption tools like impacts or sandblasting equipment, the losses could be high. Elbows, valves, strainers, etc. are high contributors to losses in a flow system, and should be kept to a minimum.

I think the condensation problem could be the biggest challenge, especially underground where the air will cool in the line. You will need a way to continuously remove the condensation. ....

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shortmagnum
Join Date: Nov 2003
Posts: 848 Wisconsin
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2005-02-17          106282

I think all of these responses have been beneficial. It seems that the ability of this system to work depends on what your needs for pressure are at the remote site. If you just need it to pump up a tire, most likely no problem. If you want to run air tools, it might just be an expensive mistake.

I have also thought of the same project but I only have about 8' to run underground. Condensation was also my biggest concern. You'll need to be able to blow the line out regularly so you'll need a high flow valve at the low pressure end.
Dave ....

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earthwrks
Join Date: Dec 2003
Posts: 3853 Home Office in Flat Rock, Michigan
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2005-02-19          106448

I'm not a plumber but I did have to fix some 2" sprinkler lines that I hit. Maybe this is common knowledge...but there is a different PVC (or CPVC??) cement used for underground. Above-ground cement used below ground is easily attacked by moisture. The supplier said "universal cement" isn't intended for underground. I got some "universal cement" on my clothing and hands and sure enough after a little coaxing it turned milky-white and flaked off indicating it did disolve in or absorb water. Super Glue falls into this category--in fact the main ingredient for the curing accelerator is water. ....

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denwood
Join Date: Jul 2004
Posts: 542 Quarryville PA
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2005-02-19          106450

If water attacks the glue on pvc water lines, a lot of us are in trouble. I was under the impression that the glue used (Normal glue) softened the pipe some and let it almost weld a little and after cure time it is ok to use. Are you sure that underground glue isn't just something that cures better underground? I have never used pvc underground so maybe I just haven't heard of this potential problem. ....

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earthwrks
Join Date: Dec 2003
Posts: 3853 Home Office in Flat Rock, Michigan
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2005-02-19          106452

I'm 100% positive it is special glue (not really a cement which is a solvent a.k.a. "welding") for underground. Constant moisture on the outside of the pipe attacks the glue, and that it's under pressure (sprinkler system) doesn't help. Is your underground piping under pressure? If not then I wouldn't worry. I was working next to a plumbing supply house and they knew what I was working on so they gave me the heads-up. As I recall, the glue was green-colored probably for inspection purposes (the primer was clear), not clear like aboveground (purple color is also for inspection but it's for the primer). I use the term "glue" because the fittings weren't "welded" together becoming one material. I found that the pipe fittings were not made of the same, identical material (pipe has small airbubbles in it from the foaming process when it's extruded the fitting are molded and have no detectable air bubbles). I found this out when I mis-fitted some pipe to the existing fittings; I used a propane torch to CAREFULLY burn or melt the old pipe and the fitting was ok!--it didn't melt as fast. So the joint was "glued" together rather than "welded". ....

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