air line run - whats the correct rate of fall for draining

[Mike Heidrick]

I am about to run some airline (max line). Is there a correct rate of fall back to the compressor the lines should run at?

[Jim Becker]

Like any pipe that involves liquids, you don't need much of a slope at all to get static drainage in a given direction...

[Paul F Franklin]

You might find this drawing useful: http://www.sharpe1.com/sharpe/sharpe.nsf/Page/Air+Piping+Layout

They recommend 4 inches in 50 feet slope.

You will note that they recommend sloping piping *away* from the compressor, to a drain leg, and I have seen this recommendation elsewhere as well.

Although that site doesn't explain the rationale, I've been told it is to avoid having the water collect in the compressor where some of it will just be reabsorbed into the flowing air. By sloping the piping away to a drain leg, the water quickly moves out of the flowing air stream, minimizing the amount that get reabsorbed.

You can get an automatic drain valve to attach to the drain leg, provided you have a drain nearby to drain to. They eliminate the need to remember to empty the water from time to time.

You still need to empty the tank from time to time as some water will still collect there, but not nearly as much as if you slope the pipes toward the compressor.

[Wayne Lomman]

Yes, slope it away from the compressor and have a drain at the lowest point. Also have a final water trap and regulator at each outlet. There are two schools of thought about automatic drains. They are good while they work but they train you to forget about water and oil in the system. I do it manually or if I need to be sure I crack the valve so it just hisses and that keeps things clear. Cheers

[peter gagliardi]

1/8" per foot is plenty, but 1/4" per foot is better.

[Mike Heidrick]

I put it up wrong then. Ran south wall draining towards compressor. Should have read this before starting today. Will check into changing it tomorrow.

Every drop will have drain as well.

I do have auto drain as well. You can get them cheap on ebay from China.

[John K Jordan]

I suspect the reverse slope might work if the air line is large and the air flow not enough to blow condensate up the slope and into the rest of the plumbing. If for some reason you can't change the slope you might still put a trap at the end to try to catch what gets blown forward and put a second trap right at the compressor to catch water before it drains back into the tank. Also, a long enough line of any material should cool enough (mine is the plastic RapidAir but plan to someday replace the condensing section with about 24' of copper line.

I put a gravity trap just before the water separator and dryer. I made it from a fairly large diameter brass nipple with a valve on the bottom to drain. The air comes in the top, goes straight down, then sideways near the top of the trap, at the left here.

370531

If that looks like a lot of fittings it is. Some are unions so I can easily take the whole thing off the wall if needed. My compressor is 5hp/60gal. If moving a lot of air in humid conditions a trap with more volume might be useful. My air is drawn from an conditioned space so it is fairly dry to start with. Very little moisture in the traps. (One small trap/drain at each outlet as well.)

JKJ

[Bill Adamsen]

Mike: I ran 3/4" copper type "L" with the 1/8" per foot pitch away from the compressor. My compressor has an automatic condensation discharge at the end of each run ... though I still get some condensation in the tank that I remove every day if I remember. Interestingly, I have never had any appreciable amount of condensation in the copper runs. Just checked the runs this morning and nothing.