« Back To Motion Control & Motors Case Studies
Fluid-Aire Dynamics Logo

Member Since 2022


Content Filed Under:



How Do I Know If I Need a Desiccant Type Compressed Air Dryer?

POSTED 05/12/2022

It’s a common belief that refrigerated type compressed air dryers are a great piece of equipment that will remove all the moisture from compressed air keeping your distribution system dry. While this is true when the dryer in good working order, condensate can still develop if the temperature of the compressed air drops below the dew point it was originally dried at.

Refrigerated compressed air dryers are designed to reduce the dew point of compressed air to a normal range between 33 and 42 degrees depending on the application and operating condition. This means that all the raw liquid and water vapor has been condensed from the compressed air at this dew point but the real question is: what is the relative humidity? How much cooler does the air have to get before liquid condensation to begins to develop inside the air distribution system?

In many North American regions, the outdoor temperature can get below 32 degrees F. Many manufacturing facilities have compressed air piping that is exposed to this temperature. Some food packaging facilities have compressed air requirements for automation in refrigerated environments. Orifices installed on equipment where the compressed air rapidly expands such as a venturi device, will create a cooling known as the Joule Thomson Effect. Condensation will form at this point if the cooling effect reaches the dew point of the compressed air. If only a refrigerated type dryer is installed in these environments, moisture will become a problem! Here’s why…..

When compressed air (or any gas for that matter – compressed or not) is exposed to a temperature cooler than what it has been condensed to, condensation (liquid) will form. So, what’s important is to know is the relative humidity of your compressed air which is a simple relationship between ambient temperature and the dew point of the compressed air measured with a hydrometer. For example; if your dew point is 42 degrees F and the ambient temperature is 42 degrees F, the relative humidity is 100% you are going to see water! If your air distribution system is exposed to 32 degrees F or less, that water is going to turn to ice. The only way to cure this is to further reduce the dew point of the compressed air. Check out this website for a cool relative humidity calculator: http://www.dpcalc.org/

To answer the original question, have you experienced one or more of the following scenarios:

  • Frozen pipes which could completely stop the flow of compressed air
  • Frozen and damaged solenoid valves on equipment (Dust collectors, automation equipment, custom applications with compressed air cylinders and solenoid valves, ect.)
  • Low system pressure resulting from a stuck valve allowing compressed air to constantly flow
  • Loss of production
  • Costly emergency service call from your service provider

If you answered yes to any of these, a desiccant air dryer will help solve these issues.

Desiccant type compressed air dryers remove all water vapor down to a negative 100 degree dew point. Instead of refrigerating the compressed air, the dryer adsorbs the moisture with the use of Activated Alumina and Molecular Sieve type desiccants. Desiccant dryers are made up of two towers that hold the desiccant beads. The system alternates between the two allowing one to dry the compressed air while the other is self regenerating the desiccant material. These types of dryers typically consume between 5 and 18% of your compressed air supply depending on the type of controls. Dryers with optional purge controllers regenerate only when absolutely needed, thus offering energy savings that may be worth the additional capital cost.

Do you have to install these dryers by the compressors and maintain -40 to -100 dew point air for the whole plant? Not at all. These dryers are best installed at the point in which it needs to apply. If you have piping outdoors,  going into a refrigerated area, or into a critical application area, you can install the dryer at the point of use. This will allow sizing only for that application. This can greatly reduce the cost of your compressed air and the initial capital expense in the size of the dryer needed. The balance of your plant should still have a refrigerated dryer installed in the compressor area.

Desiccant Dryers also greatly enhance the quality of compressed air required for critical applications that involve painting, high accuracy machining that are sensitive to oils and contaminants, pharmaceutical applications, powder coating, and other applications where the requirement for the quality of compressed air is high.