How to Aftercool a Compressor to Remove Moisture [Easy Project]

First, a little bit of the theory. If you haven't already noticed, compressors accumulate a ton of moisture. It's a good idea to have an electric automatic drain in the bottom of your tank. The moisture comes because the air coming out of the compressor is pretty hot-a couple of hundred degrees isn't unusual. It cools down when it enters the tank and tends to dump the moisture as it cools. If you're using quite a bit of air, it may not have time to dump the moisture, which means it winds up in your air lines, your air tools, your paint sprayers, your CNC machinery, and well, you get the idea. Not good.

The aftercooler is just a simple cooler that goes between the compressor outlet and the tank. It's goal is to cool the air before it gets to the tank, which causes it to drop a bunch of the moisture (not all, you still want a dryer or other moisture reducer if you need really dry air for applications like painting). There are both air-to-air and air-to-water aftercoolers. Heck, you can run a loop of copper pipe through a bucket of water and turn on the hose to run more water through the bucket and that works too. But, it sure is wasteful of the water.

While corresponding with a machinist friend, I learned he was adding a transmission oil cooler to his compressor to help get rid of some of the moisture coming through the system. This is apparently a trick that's been around for some time, and after doing a little research, it's one I'd like to try on my own compressor.

The idea here is to plumb a transmission oil cooler in and let it do the cooling with a fan. You can either piggy back on the fan that cools the compressor or add another fan. Below are some photos from various shopmade aftercoolers:

The aftercooler system is comprised of a B&M model 70266 (11" x 8" x 1½") transmission/engine oil cooler, a 230V AC fan from EBM Pabst model W2E250-HL06-01 (1160 cfm in the open air) that is wired parallel to the motor, activating whenever the motor is in operation, and an auto-drain from Wilkerson model X01-04-M00. One user reported his compressor outlet temperature dropped significantly from 310F to 96F after passing through the aftercooler. He noticed visible water droplets in the plastic drain connected to the Wilkerson unit. Notice his intelligent plumbing setup, directing the moisture downward and allowing the air to rise upwards.

This fellow has made a number of improvements to his compressor, including an aftercooler with muffin fans on the backside...

Another compressor with a B&M transmission cooler and a 230V fan.

Very professional looking guard on this aftercooler. The automatic drain is from below again...

Someday I'll get an aftercooler added to my projects compressor. Doesn't look very hard to do and anything to keep more moisture out of the system has to be a good thing!