Compressed Air Moisture Control

Last issue, I covered some easily-accomplished maintenance procedures on air compressors. This month I’ll discuss components in the compressed air system that remove water from the compressed air stream.

First, a quick note about air and temperature: The hotter the air the more water vapor it can hold. As air cools, the water vapor condenses out in the form of liquid water. Liquid water in compressed air systems is a contaminant stripping away helpful lubricants, degrading rubber and plastic parts as well as corroding and rusting metal components. It has been my experience that liquid water is the leading cause of failure for air-operated machinery. Several devices which are applicable to the drycleaning industry can be used to reduce the amount of water that gets to the compressed air components of machinery. Often compressors are located in boiler rooms where there is a high level of humidity. If possible, locate the air intake of a compressor as close to an outside vent as possible. Usually, it is fairly simple to provide the compressor air intake area with a vent line to the outside of the boiler room providing cooler, drier air at the compressor air intake.

  1. Drains and Auto-Drains – Somewhere, usually at the bottom of the tank on which the compressor pump is mounted, there is a drain valve of some sort. Water which has condensed out of the hot compressed air as well as fugitive oil from the compressor pump collects in the tank. When this drain valve is opened, the water-oil mixture is blown out of the tank removing it from the compressed air system. THIS WATER AND OIL MAY BE CONSIDERED A HAZARDOUS WASTE. Opening the drain valve and draining the compressor tank should be done on a regular basis, at least once a day. Effective, inexpensive, and easily-installed automatic drain valves are widely available. These auto-drains contain an adjustable timer which regularly opens an electric solenoid valve allowing the tank to drain. Besides the obvious advantage of knowing your compressor is being drained regularly without you having to squat down in a hot boiler room to open, wait, and then close a greasy valve you’re also spared the maintenance on this hard-to-reach area. Even a small leak in the compressor drain valve will have a big effect on your compressor by cycling more often, thus incurring greater wear as well as higher electric bills.
  2. 2. Aftercoolers and Refrigerated Dryers – Compressed air exiting the compressor pump is extremely hot and therefore capable of holding lots of water vapor. As this air cools, some of the water vapor condenses out as liquid water in the compressor tank requiring the draining procedure discussed in paragraph one. However, the air is still hot and lots of water vapor remains in the air stream which will later condense in the cooler air lines and equipment. In the drycleaning plant the most effective way to reduce the remaining water vapor before it condenses and travels into the machinery is to further cool the airflow. The simplest method of achieving this is using what is termed an aftercooler. An aftercooler is usually a finned coil with a fan mounted on it. Compressed air leaving the compressor pump enters the tubing with the fins attached while the fan blows air across the coil cooling the compressed air. This condenses out much of the remaining water vapor. A variant of this method uses a water-cooled heat exchanger instead of a finned air-cooled coil. Refrigerated dryers are the most effective device to remove troublesome liquid water from the compressed air stream. They apply the same principal as the aftercooler but a refrigeration system is used instead of using air or water for cooling the compressed air. This provides a much lower condensing temperature, hence lower levels of water vapor in the compressed air stream to later condense into liquid water in the air lines and machinery. Keep in mind you still are going to need some type of drain on any system you use. Aftercoolers and refrigerated dryers need to be properly sized to the air compressor.

Well that’s it for this issue, I’ll continue discussing compressed air systems and more easily-accomplished maintenance tasks to help save you big bucks in next quarter’s issue.



I will be presenting webinars on boiler and general dry cleaning machinery troubleshooting, maintenance and repair. These webinars will have great charts and illustrations with live real time question and answer sessions. They will be free; the only requirement will be for you to register so I can set up the broadcasts. Just email me at bruce@eztimers.com and request to be added to the webinar list. I’ll acknowledge your email and send you a schedule and sign-on code. Thanks, I know these webinars will be a valuable addition to your knowledge base as well as an opportunity to discuss your current machine problems.


Bruce Grossman is the Chief of R&D for EZtimers Manufacturing. EZtimers is the manufacturer of the new EZ DOSE boiler compound manager and return tank level control which replaces that troublesome ball float valve in the condensate return tank. SAHARA and DROP IN THE BUCKET line of high purity separator water mister/evaporators provide a thrifty, legal method to get rid of the separator water generated by your dry-cleaning machine. See our Ad in this issue and for further information on EZtimers products visit  www.eztimers.com   Please address any questions or comments for Bruce to  bruce@eztimers.com  or call 702-376-6693.


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