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

Compressor aftercooler

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:

Aftercooler system consisting of a B&M model 70266 (11″ x 8″ x 1½”) tranmission/engine oil cooler, an EBM Pabst model W2E250-HL06-01 230V AC fan (1160 cfm in open air) wired in parallell with the motor so when the motor runs, the fan runs and a Wilkerson model X01-04-M00 automatic drain. This fellow measured his compressor outlet temperature at 310F going into the aftercooler and 96F coming out. That’s a big drop! He says there are visible droplets of water in the plastic drain going to the Wilkerson. Note how he organized his plumbing to take the moisture down low and the air rising above.

Compressor with aftercooler

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

Aftercooled compressor

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

Guarded Aftercooler

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!


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Recently updated on August 25th, 2023 at 03:58 pm