View Full Version : soft copper for shop air?

11-02-2003, 11:56 PM
Seeing debequem's post about shop air reminded me of something I wanted to ask my metal friends. My compressor is in the garage and it supplies air to my basement shop via a 3/8 flexible hose with quick disconnect couplers. From there it goes out to my wood shop, again by flexible plastic. With all the quick couplers, the air pressure leaks back to zero over night and my compressor has to start from scratch to build back up to 100 lbs. working pressure.

I am thinking about using soft copper pipe (I would have to fish it thru some 2" plastic conduit, so I can't use hard copper) to replace the flexible plastic to reduce the leaks. May use a ball valve to keep the air in the tank if that doesn't work.

Is the soft copper sufficient for 120 lbs. pressure? Any better ideas? Thanks--Mike.

Forrest Addy
11-03-2003, 12:12 AM
Heck yes. So fas as I'm concerned copper air line is preferred over all other low cost materials for shop air pressure 180 PSI or less.

I suggest 1/2" trade size "L" ("M" is a lighter wall gage and kinks and crushes much easier) residential copper water and solder fittings for all the rigid parts of the system. This size copper tubing is adequate for compressors up to 20 HP having runs of 100 ft or less.

Air line subject to damage and drop fitting should be of 1/2" IPS sch 40 construction to limit actual damage from every day shop hazards.

The design of cost effective and efficient shop air distribution systems is a technical subject worth a little study. Maybe someone can suggest a book or construction guide.

11-03-2003, 12:34 AM
Yes, as Forrest said. Keep the lines above 4' from the floor to avoid damage from movable machines or other stuff.

11-03-2003, 01:35 AM
I have had problems with leaks when compression fittings were used with 3/4" soft copper tubing for compressed air. The replacement was galvanized or black iron pipe. We use hard copper with no problems when we use soldered fittings. We had a compression fitting let go on some soft copper and the loose piece of copper tubing flapped around and knocked a hole in a wall. A lot of noise and one guy strained his back running over stuff to cut off the compressed air. The soft copper tubing will hold average compressed air pressure with a large margin. I would use sweat fittings based on our bad experience with compression fittings. One other comment is to use larger diameter tubing than you think you need as having more flow capacity than you need causes no problem and gives you a nice additional compressed air storage capacity. Too small a flow capacity means you have to replace everything to improve the situation. Use ball valves everywhere as they are much lower pressure drop than globe valves and have fewer problems with leakage.

11-03-2003, 08:17 AM
If it's not exposed to sunlight and you're far enough away from the compressor that heat is not a factor, I'd go with schedule 40 PVC with iron pipe on the drops.

Snaking it through conduit might be a problem, but there are other types of plastic which could be used for that part. Or, you could use the copper there.

I've caught some flak about using plastic for air lines, but my experience with it has been positive.


11-03-2003, 08:37 AM
If you use PVC make sure you use primer before gluing

11-03-2003, 08:45 AM
Unless you have a high quality drying system, not the screw together tube filter/dryer type, I would avoid steel or Iron at all costs. Once the insides start to rust the rust flake can act like shrapnel at 100 psi. And even if you do dry your air sufficiently I would still go with copper.

Without knowledge we stumble blindly through the universe.

11-03-2003, 10:52 AM
Good point about rust in steel pipe. I assume a good drier and the use of so called "point of use" filters to catch pipe scale which can be a problem even with new pipe unless it is chemically cleaned or it is electropolished stainless steel. Probably copper is the best way but I would use the rigid copper and use what ever couplers and fittings necessary to get it through the plastic piping you describe. Don't use PVC, not worth the trouble or the near heart attack you might suffer from the noise when it blows up. People here in Texas try to save some money using it but if the air line is near the ceiling or in the attic above air conditoning it almost always blows in the summer and shuts down the plant at large cost. The pressure capacity of PVC and other plastics drops like a rock with increasing temperature. Look it up. I hope this doesn't start the plastic pipe for compressed air story again. Put in a lot of tee's with plugs in your system plumbing so you can make changes and additions later.

11-03-2003, 11:03 AM
Soft copper is fine for the pressure, as others have said. It is used all the time in the buiding trades. One thing that you could do if you don't like soldering joints is to use flare fittings. It's easy to do and holds much better than compression. Flare fittings are used for ALL copper gas piping and also for burried water service.

Paul Alciatore
11-03-2003, 12:38 PM

Sounds like the soft copper question has been answered but I would add that if you have some long runs you need to think about condensation. I've had to redesign several systems in TV stations where there was quite a lot of moisture accumulating in the lines and finding it's way to the points of use. Filter jars help a litle but are soon overwhelmed in humid climates.

It's best to slope as much of the run as possible to drain back into the tank. Avoid low spots in the lines as water will surely collect there. If they must have a low spot, be sure to add a drain valve. Do put a drain loop with drain valve at the end of the line, just before the filter jar. This should prevent moisture in all but the most critical applications.

If dryer air is needed a refrigeration type dryer is best (but expensive).

Brian Gale
11-03-2003, 01:13 PM
Rule #1 in compressed air piping...

NO PVC - it IS NOT safe under high pressure. It is cheap and used for vent pipes where it passes 2 PSI and that's it...

Slope your lines back to a drain, use a drip loop at the top of your take off before running your connection line down the wall, put your line dryer/collection glass as far away or as close to your take off as possible. This gives the water vapor time to condense in the cool pipe and get collected in the dryer. Use 1" rigid copper pipe if you can as it will increase your tank capacity for minimal expense...pressure is pressure wether its a 10 gallon tank or 1000 gallons in pipe, it doesn't matter. You could also try 5/8" ID Goodyear Gorilla hose available at any decent compressed air supply shop...sounds like you are having more trouble with fittings as opposed to pipe.

Good luck- hope this helps...


11-03-2003, 02:45 PM
Just for kicks one time I tested some 1/4 inch copper tubing just to see how much pressure it would take. It split at 7000 psi. I wouldn't worry about 150 psi.

11-03-2003, 03:07 PM
Just remember if you are running the air line underground (outside) there may be a chance of the condensation in the air line freezing and splitting the copper somewhere in the conduit. We only used type "L" for our air lines where I used to work, all inside lines. We soldered the joints using regular plumbing solder, the same stuff we used for the water lines. We never had an air leak unless the end of the line was not secured properly. I've put in copper air lines from 1/4" to 6" dia using type "L". We were always satisfied with the results.

11-03-2003, 04:57 PM
"NO PVC - it IS NOT safe under high pressure. It is cheap and used for vent pipes where it passes 2 PSI and that's it..."

1" schedule 40 PVC is marked 450 PSI @23*C (75* F) Smaller sizes have even higher ratings.

PVC is easier to install, and will cost a small fraction of what copper will. Making changes later will be easy and inexpensive. Put it where it won't get hot and it won't get smashed, and it'll do just fine.


11-03-2003, 05:28 PM
Brian Gale is correct in stating that PVC is UNSAFE to use in the transportation of compressed gases. Check out this web site.


Peter S
11-03-2003, 05:57 PM
Quick release couplers don't have to leak, why not fix that problem first? Flexible hoses are fine for home use.

In reply to the PVC debate....
There are several plastic systems sold locally here specifically for compressed air, some with glued connections, others with hand-tight fittings. However, the plastic used is PE not PVC...

I have used the PE systems several times on machinery where we needed a quick, neat job, combined it with standard nylon air pipe and push-on fittings - great result.

However, steel has advantages for workshops, not least it is rigid (plastic isn't and needs lots of supports), it is cheap too. Make sure all joints are really tight, it is difficult to tighten once assembled and installed.

No experience with copper.

11-03-2003, 06:41 PM
Thank you, rangerod, for the reference to the safety problems associated with PVC. That's certainly a source I won't argue with.


11-03-2003, 07:44 PM
PVC sucks period,I don't even use it for tap water,I was almost blinded in one eye when a fitting blew off a 3/4 pvc line,it wizzed by mt head and left a 3" long cut over my timple.

One other option is a cheap roll of surplus hydraulic hose,lots of it on ebay,you can get it and have a npt fitting crimped on each end.

11-03-2003, 09:00 PM
Thanks for all the ideas. Peter S says that quick couplers don't have to leak. Are you suggesting fixing the ones that I have or buying new ones of better design? I have some American ones and some Chinese ones that I got at Menard's Home Center. They all leak slowly and my air is depleted by morning. I have never tried to take one apart--is this something anyone here has tried? Thanks--Mike.

11-03-2003, 09:23 PM
We always used black iron pipe and never had a problem. Of course we always had drains at each end and blew down the tank every night.

11-03-2003, 09:24 PM
Mike, it comes to mind that a valve on the tank before air goes out to the system would be a good safety feature, as well as stopping air loss during idle times. I'll shut off the valve on my compressor before leaving the shop for the night, even when there's no leaks. Some of my attachments do leak, and I don't want to take the time to fix that, doessn't seem worth it. If I forget and leave the valve open, I hear the pump run a couple of times during the night. Bugs me, but not enough to get up to shut it off.
Interesting experiment with the 1/4 in copper tubing. I wonder what wall thickness that is, since I've seen a difference there of nearly 2 to 1. I'd like to see the test results on say, 3/4 in tubing.

11-03-2003, 10:17 PM
WOW! i just want to give a big THANKS to you folks for posting the PVC warnings. i have a small run (about 12 feet) of PVC that takes the air line from my compressor in the corner of the garage to a connector in the center. i will switch it over to copper the next time i have a chance.

on a similar note, how many of you drain your compressor tank daily? or do most folks leave the system under pressure and check the drain once a week or so to let out any condensation?

andy b.

11-03-2003, 10:50 PM
Seems I saw where the WWII subs used soft copper as a charging line for torpedos. Annealed it whenever it got too stiff.

IIRC that would have been 2500psi or so, way below the 7000 mentioned by Mac1

The larger the line diameter though, the worse the pressure. The copper at 1/4 inch only had to withstand about 1800 lb per inch length in MAc1s test. Depending on wall thickness, that could be exceeded strengthwise.

Go up to 1" line, and the thickness of wall comes down as the total bursting force goes up. At 1" ID, it is "psi" lb per inch.....

[This message has been edited by Oso (edited 11-04-2003).]

11-03-2003, 10:52 PM
Andy - You should drain your tank at least weekly, depending on use. If the compressor only cycles once a day and you live in a desert, you aren't likely to get much condensation. If your compressor cycles once a day and you live in a high humidty area, drain it daily. I have seen tanks that would not blow water, or very little, drain several cups when the drain valve was removed. This was due to the rust buildup around the drain valve, or the valve being clogged. I drain mine every time I think about it. The other option would be an automatic drain, but they tend to be expensive....

11-04-2003, 01:34 AM

"Thank you, rangerod, for the reference to the safety problems associated with PVC. That's certainly a source I won't argue with."

No problem just trying to keep it safe. Have a good one.

[This message has been edited by rangerod (edited 11-04-2003).]

11-04-2003, 03:17 AM
For quick disconnect couplings try Aeroquip or $$$Swagelock products. The US industrial grade couplings don't leak but they are expensive. If you only need one or two you might want to spend the money. The $wagelock are the best and for $100 or so you can get a couple of quick disconnects and a "free" ballpoint pen and a diamond coated nail file from your friendly dealer. It is probably the best plumbing on this planet though.

11-04-2003, 10:10 AM
FWIW. The shop, in the cargo containers at the ranch, is plumbed with galvanized pipe, sloped for drainage control with ball valves throughout. It is divided into sections with one 400' long out to the 1000 gal water storage tank. The added pipe makes for nice additional storage. The city house is done with soldered copper with one branch to a Q/D under the kitchen sink for in house use. Again ball valves are used for branch control.

Neil Peters

11-04-2003, 10:12 AM
Wow, There is a quite a lot of input on this subject, so I may as well pipe in one more time. Copper, Copper and more copper. If you are just plumbing up a small home shop the cost will not be so great that you will have to take out a 2nd mortgage. Invest a little extra for a low maintenance system that will last years, not to mention safety.

Without knowledge we stumble blindly through the universe.

Brian Gale
11-04-2003, 11:43 AM
For reference, I have a 26 gallon compressor in one corner of the garage, and 3' piece of Gorilla hose connects it to 1" hard line on the wall. The hard line runs up the wall 6', then to a 40' that runs clear across the garage, down the wall 6' splits into 2 horizontal pipes about 3' long each. I have 2 ball valves, a handful of hangers and bushings, and quick connects...I spent no more than $100 on the whole thing. One of the best things ever put in my garage as it keeps all the stupid hoses off the floor...

Good luck!

Treven Baker
11-04-2003, 12:00 PM
I'd like to read prior discution of PVC for air line use. I could not locate it yet from the search function. Anybody know where to look or what the thread name was?

11-04-2003, 12:03 PM

11-04-2003, 09:18 PM
Our 10hp pump at work during the summer will produce 4gallons of condensate per 10 hour shift!
I have a seperate ball valve and hose connection in place of the petcock drain on the tank,it goes through the wall and outside,at 5:00I use it to blow the tank down for the night keeps the thing dried out.

I also would like to mention that it is a good idea to run as large a pipe as will fit in the tank threads for the main line to the shop,they you can branch off the workstation drops in smaller stuff,this greatly improves the effecincy of the setup.You can lose a lot to friction in a small pipe or hose.

11-04-2003, 10:13 PM
<font face="Verdana, Arial" size="2">Originally posted by andy_b:
WOW! i just want to give a big THANKS to you folks for posting the PVC warnings. i have a small run (about 12 feet) of PVC that takes the air line from my compressor in the corner of the garage to a connector in the center. i will switch it over to copper the next time i have a chance.

on a similar note, how many of you drain your compressor tank daily? or do most folks leave the system under pressure and check the drain once a week or so to let out any condensation?

andy b.</font>

One day I had a call from a shop to service their moog hydropoint. It wasn't reading the tape. A moog uses hydraulics to position in XYZ, it uses electrics to program and punch tapes, but it uses air to read the tapes.
I got there and opened the door to the console to access the tape and water flooded all around my feet. They hadn't drained their system in months and seemed genuinely supprised that there was a valve in the bottom of the tank for just that purpose.