Underground Compressed Air

[zuiko]

I want to run a compressed air line in a trench, about 100 feet with three 90 degree bends (one in the trench and two to come out of the ground).

I am leaning towards copper since I am pretty confident of the solder joints not leaking... I'm much less confident in pasted up PVC joints. Do buried copper lines last or does it corrode when buried? I would be probably want to use the thinwall stuff because of cost.

Polyethelene pipe would also be an option and is very cheap but I don't know how good those barbed connections on the ends would be at holding air. They do make it in a 150psi version that would probably work.

Any suggestions?

 

[EddieWalker]

There was a big discusion on this topic not too long ago if you do a search. The concesus was stay away from plastic, it will shatter and could be very dangerous. Underground wont be as dangerous, but if it breaks, you still have to redo it.

Another concern for me wasn't so much for my saftey, but what if it explodes and somebody else is hurt. It's just not worth the risk of for saving a couple bucks.

Copper is the best and probably only way to do it correctly. I couldn't tell you if thin wall will work or not, but for a little extra, I'd buy the best I could find. Do a preasure test before you bury with soapy water and you'll find you leaks if you have any.

Good luck,
Eddie

 

[Inspector507]

Why not use the flexible copper in rolls? No joints except at either end, heavier wall may hold up under more pressure. Just a guess on that one though.

 

[chim]

I'm not a plumber, but I often pay attention to how they do things. For copper underground installations (at least for domestic water) they use flared fittings and not soldered. A plumber told me it was against the code to solder water lines for underground use.......................chim

 

[RonL]

zuiko

I'm also planning on running underground air lines. My intent is to run oversize PVC conduit and then run an air hose through it. If the air hose gives out I'll pull it out and pull a new one. The conduit will be vented by leaving the ends open.

RonL

 

[JacknCoke]

Another problem that I ran into with an underground line was that moisture collected in it. And after a year or two the line was full of water and we could never purge it all out. We ended up abandoning it and going with an over head line but this was only about a distance of about 25 feet. So overhead is probably not an option for you 100 feet distance. I would recommend biulding an underground box at the lowest end of the line and install a valve that you could open to drain any moisture out.

J.D.

 

[K_Daulby]

here is what i did about 5 years ago and i have had no problem.
I used black pipe and did about 150 feet of piping to do my whole 40x60 barn.
Then I wanted air to my house for many reasons. My house is 150 feet from my barn and i was runing electrical to my barn from house so i just went to a wholesaler and bought a length of high pressure air line, just like u would use if you conected a tool to your compressor. i just direct buried it. in the electrical line trench. i think i bought 200feet for $75 or $80 then i just put quick conects on the end of the high pressure hose and i have had no problems since. hope this helps
kevin /forums/images/graemlins/grin.gif

 

[Bird]

Ron, I think I'd pay heed to JacknCoke's advice myself. I think it's a safe bet that sooner or later you'll have moisture in that line that you want to get rid of.

 

[BobReeves]

Just had a thought, I understand how trying to blow water out of a line wouldn't completly clear it, but what about hooking a shop vac to one end and sucking it out. Anyone tried it?

 

[RonL]

Bird

The PVC will be just a conduit to carry the air hose to the shop and garage. The air hose will connect to permanently mounted piping with a drop for collecting and draining moisture. I want to isolate my air compressor in the shipping container that I have on sight, along with an electrically powered hydraulic pump to run the log splitter. The shipping container will evolve into my machinery building.

RonL

 

[zuiko]

Interesting, I hadn't even thought about moisture but I can see that being a big problem since the line would be the lowest part of the system. I suppose I could figure out where the low end is and put a valve in there.

 

[CTyler]

If this was a hose then connect a shop vac to one end and drop a ball bearing in the other. Should get most it. If this was a conduit then run a hose thru and suck it out. Or dig a manhole and put in a valve.

 

[ns_in_tex]

I think the moisture falls out of the air as it cools and if possible, you should try to accomplish this before the air enters the distribution line.

 

[sfcsarge]

As far as moisture is concerned, you can get yourself a water trap to use right off your compressor. Just open a valve on the bottom and drain the water. You can even get an automatic one to blow water out at regular intervals. As a matter of fact, it's not a bad idea to get one for the drain valve on the compressor itself to keep water from building up in the tank. We use them all the time at work and unless you have an extreme problem with water, they work pretty good.

 

[fractal]

I looked into running air line around my shop a while back. Interesting the gyrations people have to go through to keep water and corrosion out of the lines.

I would use black pipe and put a water trap at each end. It seems conventional to run the pipe at full tank pressure with only a filter between the compressor and the pipe and to put filter-regulators or filter-regulator-lube units at each point of use. A water trap is nothing more than a stub of pipe going straight down with a valve at the end. It does mean running the pipe at a slope and having a 6-12 inch pit at either end for the water trap.

 

[BIGUN]

</font><font color="blue" class="small">( I think the moisture falls out of the air as it cools and if possible, you should try to accomplish this before the air enters the distribution line. )</font>

Yes it does and you should, but it would be difficult for the home user to accomplish this since the air will continue to cool as it enters the buried line outside, especially in the winter.

At the plant we run our air through a refrigeration unit to condense the majority of the moisture from the air, then to reduce the dew point to a value much lower than the lowest anticipated ambient temp we run the air through desiccant driers. This will lower the dew point to somewhere around -50 deg F. This prevents water (ice in the winter) from forming in the air lines which supply air to operate controls within the plant. Without all this expensive equipment, water will form in your underground line. /forums/images/graemlins/frown.gif

You can run whatever type of pipe you decide on with a slope away from the source of air with a "low point" drain coming off the bottom of the pipe close to where it comes back up out of the ground. The valve on this drain doesn’t need to be below the pipe. The drain line can be routed to come up above ground level with the valve installed in a convenient location. Use a smaller line (1/4") for the drain than the main pipe. I like the ball valves for air lines. The line can be blown down daily or as needed.