Air lines - Under Ground

Red Sleeper

Red Sleeper

Active member
I need to relocate my air compressor to a new area, about 130' behind my shop where I have a shipping container. For running air lines under ground, the only material I know to use is schedule 80 pvc.

A customer of mine used the 3/4" Rapid air pipe with aluminum core to run air line 300' from his compressor to a new shop, all under ground. I like the idea of using this product, but unsure of the longevity to being buried under ground.

Thoughts?
 
I'd just run a 3/4" ID rapid air line inside a 1-1/4 schedule 40 pvc. If it ever leaked, at least you could pull it and replace it easily. Actually, just some thin wall poly pipe would be better and it would have no couplers or seams to come loose. Just like sleeving a pex pipe in a slab. Hell, you could honestly just use 3/4" or 1" pex for all that matter. Most of it is rated to 200psi.
 
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I ran 3/4 pex 95 foot underground, left my air compressor in the garage and wanted the extra space/no noise in the shop. Been that way for two years now and no leaks. I ran the air and also a 3/4 water line inside 4" corrugated along with a pull string so if I ever wanted to add or replace anything I can just pull it through without digging everything back up. I also ran a remote switch out to the shop with a starter on the compressor because 9x out of 10 I forgot to turn on the compressor otw out to the shop.
 
thatguy69 said:
I also ran a remote switch out to the shop with a starter on the compressor because 9x out of 10 I forgot to turn on the compressor otw out to the shop.
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I wired an external on/off switch to disable the coil on the motor starter on mine. Before I leave for multiple days I'll switch it off in case my lines develop a leak while I'm gone. I hope that keeps from burning up a compressor someday. I shut the ball valve mounted to the outlet pipe and flip the switch off.
 
I have thought about the pex route. Have plenty of 3/4". Though the fittings have me worried. Can they handle 175psi of air pressure? What method of connection did you use?

Last fall I buried two electrical runs from the new pole. 2" non metallic pipe, one to the house, another to the shop. Also buried a 1 1/4" for possible 3ph to the shop one day. And two 1/2" PVC sch 40 lines for water and air. All 36" in the ground and covered.
Well, I have learned the sch 40 pvc will handle 175psi, but the fittings will fail.

So now I'm at the point of digging a 12" deep trench for my air line. I'd like to only dig it once.
 
High quality garden hose works great as a budget air hose as long as you don't need it to be super flexible.

Might not want to freeze it though. Not sure.
 
Red Sleeper said:
I have thought about the pex route. Have plenty of 3/4". Though the fittings have me worried. Can they handle 175psi of air pressure?
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Are you honestly going to run your regulator at 175 PSI? That sure makes a compressor work hard.

Begle1 said:
High quality garden hose works great as a budget air hose as long as you don't need it to be super flexible.
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Is there such thing as a high quality garden hose? I'd never trust that setup.
 
I didn't use any shark bites, I use the brass pex barb with crimp rings to 3/4 npt. Plumbed my regulator/drier all in 3/4 along with my main trunk, then branched off with 1/2 to the rest of the shop.
 
4x4dually said:
Are you honestly going to run your regulator at 175 PSI? That sure makes a compressor work hard.
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I have an IR2475N5 in my work trailer and it runs up to about 165 psi at the tank, and then regulated down to about 120 at the water separator. I understand it's probably "hard on it" to work like that but...it's a tool.

I've had it like that for over 3 years now, if it craps out on me I'll just buy another and do it again. Cost of doing business.
 
thatguy69 said:
I didn't use any shark bites, I use the brass pex barb with crimp rings to 3/4 npt. Plumbed my regulator/drier all in 3/4 along with my main trunk, then branched off with 1/2 to the rest of the shop.
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I like this idea. Already have everything to run and crimp pex with. The 3/4" rapid air is just too big for what I honestly need.
3/4" pex = 1/2" ID
1/2" pex = 3/8" ID
Largest air line I will use is 3/8". But what is the longevity of pex? What is your regulator/pressure switch set at?
 
4x4dually said:
Is there such thing as a high quality garden hose? I'd never trust that setup.
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Industrial suppliers will just sell "hose" at a point, rated for fluid pressure, be it liquid or air. You can get "garden hoses" rated for 500 or 600 psi at a hardware store. The garden hose-style fittings are definitely more flow-minded than leak-tight, but the hose itself is plenty robust. Probably not as robust as a rigid line, but nobody has shown me why it's less trustworthy than any ~200 psi-rated "air hose" product.
 
Red Sleeper said:
I like this idea. Already have everything to run and crimp pex with. The 3/4" rapid air is just too big for what I honestly need.
3/4" pex = 1/2" ID
1/2" pex = 3/8" ID
Largest air line I will use is 3/8". But what is the longevity of pex? What is your regulator/pressure switch set at?
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Pressure switch comes on at 100 and shuts off at 140. I have the regulator wide open on the compressor and regulate it down at the shop. So the pex is always under pressure from 100-140.longeviity idk, but it was cheap enough and easy enough. If it fails I can pull another one through so I'm not worried about it
 
thatguy69 said:
Pound is a pound right?
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I want to say no. Now I never got into the particulars, but when I was working with building and inspecting pressure vessels, the highest I ever seen an air test was 100psi. Hydro tests went into the thousands of psi on certain vessels. Most did not get both, but one that did was hydro tested at 425psi, and air tested at 100psi.

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thatguy69 said:
Pound is a pound right?
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No

J-Pipes said:
I want to say no. Now I never got into the particulars, but when I was working with building and inspecting pressure vessels, the highest I ever seen an air test was 100psi. Hydro tests went into the thousands of psi on certain vessels. Most did not get both, but one that did was hydro tested at 425psi, and air tested at 100psi.

Sent from my SM-G991U using Tapatalk
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Air is compressible, liquid is not. Liquid is an incompressible fluid — its density is almost constant as the pressure changes — while air is a compressible fluid — its density changes with pressure.
 
Pressure is pressure as long as nothing is moving. The compressibility and viscosity of the fluid becomes relevant when there is flow within the vessel or if the vessel fails suddenly.

Vessel failures under high water pressure are less catastrophic than failures under high air pressure, which is why they hydrotest vessels above working pressures.

You also have "water hammer" type effects in a working liquid system that won't be nearly as pronounced in an air system. Water hoses will have 600 psi pressure ratings despite the working pressure never exceeding 120 psi, because there are pressure spikes when the hose is full and a tractor drives over it, which aren't as violent in a hose full of air.
 
4x4dually said:
Are you honestly going to run your regulator at 175 PSI? That sure makes a compressor work hard.
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Mine has been at 180psi for I bet 50yrs (and it was ancient when we got it) and it's only had the oil changed once every 10yrs and belts when it needed it and she still chugs along. Ran PVC to another building under ground and it handles it like a champ. If i wasn't scared of the tank I would crank it higher for maximum ugga dugga's to keep from having to torch bolts off.
 
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