On Draining Air Compressors

I’ve probably told this story before, but where I used to work, we bought a humidity chamber for calibrating the humidity sensor on one of my products. Right in the operations manual it specified that the 5 gallon tank on the integral air compressor needed to be drained every X hours of use. To make it simple on the techs, I just specified to drain it every week. They must not have thought it was very important because only a few drops would ever come out of the tank.

One day, I got called down because the chamber wasn’t stabilizing at certain humidities. I started up the chamber and watched the pressure gauges, I noticed that the air compressor couldn’t maintain enough pressure to drive the humidity chamber. So I shut it down and bled off the pressure.  When I twisted the drain valve, water started poring out. I quickly closed it and went to find a bucket. When all the water had finally drained I was left with over a gallon of water. When I fired up the humidity chamber again, it was working perfectly. I showed the techs the bucket full of water and told them there was a reason I specified that the tank be drained. After that dramatic event, I never was called down again — at least for that problem.

After that experience, I set a reminder for myself to drain my air compressor every few months.

So today I bled my air compressor,  opened the drain valve, and only a few drops leaked out. I was expecting a lot more since I’ve been leaving it on so that it runs every 8-12 hours to maintain pressure in the tank and push the moisture out of the heads. So I turned the compressor on with the valve still open, figuring that there was some gunk in the valve and a little pressure would blow it out. Well, I got the tank pressured to 50 PSI and there was no air leaking from the open drain valve.

I bled the tank again and removed the drain valve. I must not have bled it completely because water shot all over the place as soon as I got removed the valve. It was packed tight with gunk. I thought about getting my camera at this point to take a picture, but I really didn’t want to track the rusty, oily water into the house. I cleaned the gunk out of the valve and replaced it, after about a pint of water drained.

It really made me wonder how many people actually drain their air compressor tanks and how many gallons of water are sitting in the tank of the average air compressor. I’m also seriously thinking about buying an automatic drain valve, but I’m wondering if I’ll have the same problem with it filling up with gunk.