Frequently Asked Questions



  • How much water is in compressed air?
  • How much water can be removed by drying compressed air?

    Actually, nearly two-thirds of the water in compressed air (or 12 of 18 gallons in the answer to question one can be removed with an efficient and clean aftercooler. An aftercooler is a heat exchanger located at or downstream of the air compressor which is either cooled by a fan or can be water cooled. By reducing the compressed air temperature every twenty degrees, half of the water vapor is condensed to a liquid and can be removed with a moisture separator and automatic drain trap. Most aftercoolers reduce the temperature to about 100°F.

    However, this is still not "dry enough" for many uses of compressed air, such as painting, instrumentation, robotics, etc.

    The next step in drying is to install a refrigerated air dryer. This continues to cool the air to just under 40°., which reduces the water left to only 5 % of the total (using the example in question one, of the 18 gallons per day total, less than one gallon of water is left). This is adequate drying for 90% of the compressed air systems.

    If the compressed air lines are not exposed to temperatures below 40°F. then the remaining water will stay in a vapor or gas form and will not condense or liquefy.

    If there are air lines exposed to freezing temperatures or additional dryness is required due to the critical use of the compressed air, then a desiccant dryer would be required.

    Desiccant dryers remove over 99% of the water in compressed air and are usually rated with pressure dew points of minus 40 or minus 100°F. A membrane dryer could also be used downstream of a refrigerated dryer for point-of-use/ critical applications.

  • What's the best type of dryer?
  • What type of filters are recommended for dryers?
  • I have a refrigerated air dryer installed and it had been working fine, but suddenly I'm finding water
    in my compressed air, what's going on?

  • How do I write a specification to ensure I get the air dryer features I need?