How to Select the Right Compressed Air Dryer

Moisture in compressed air used in a manufacturing plant causes problems in the operation of pneumatic systems, solenoid valves and air motors and can adversely affect the process or product being manufactured. For many years, problems from moisture in compressed air lines were simply tolerated as unavoidable. Moisture:

  • Causes rust and increased wear of moving parts in production equipment as it washes away lubrication
  • Can adversely affect the color, adherence, and finish of paint applied by compressed air
  • Can jeopardize process industries where many operations are dependent upon the proper functioning of pneumatic controls. The malfunctioning of these controls due to rust, scale, and clogged orifices can result in damage to product or in costly shutdowns
  • Can freeze in control lines in cold weather, which may cause faulty operation of controls
  • Causes corrosion of air or gas-operated instruments, giving false readings, interrupting or shutting down plant processes

In almost every operation, clean, dry compressed air will result in lower operating costs. Dirt, water and oil entrained in the air will be deposited on the inner surfaces of pipes and fittings, causing an increase in pressure drop in the line which results in a loss of performance efficiency.

Liquid water accelerates corrosion and shortens the useful life of equipment and carryover of corrosion particles can plug valves, fittings and instrument control lines. When water freezes in these components, similar plugging will occur.

 

Know the Specific Uses of the Compressed Air

 

The selection of a compressed air dryer is done best by the professional who knows or learns the particular end uses, the amount of moisture which each use can tolerate and the amount of moisture which needs to be removed to achieve this level. Air, which may be considered dry for one application, may not be dry enough for another.


Know the Temperatures

To determine whether or not the compressed air will remain sufficiently dry, we must know the end use of the air and the temperature at which it must work. In an industrial plant where the ambient temperature is in the range of 70ᵒF or higher, a dryer capable of delivering a pressure dew point 20ᵒF lower than ambient, or 50ᵒF, may be quite satisfactory. A dryer which may be satisfactory for high daytime temperatures, may not be satisfactory for lower nighttime temperatures. In areas where freezing temperatures are encountered, a lower pressure dew point may be required. In general, the dew point should be specified 20ᵒF lower than the lowest ambient temperature encountered in order to avoid potential condensation and freezing.

 

Know the Actual Performance

While many compressed air dryers have a standard rating of 100ᵒF saturated inlet air temperature and 100 PSIG operating pressure, it is important to check on the actual performance of the units obtained in actual plant operating conditions.

 

Know Each Use

There are many other uses requiring moisture removal to a low dew point. For example, railroad tank cars, which carry liquid chlorine, are padded (charged) with compressed air to enable pneumatic unloading. Chlorine will combine with water vapor to form hydrochloric acid; therefore, the compressed air must have minimum moisture content to prevent severe corrosion. Droplets of moisture in wind tunnel air at high- testing velocities may have the effect of machine gun bullets, tearing up the test models. Air used for low temperature processing (for example, liquefaction of nitrogen or oxygen) can form ice on cooling coils, thus requiring defrosting. The lower the moisture content of the air, the longer the periods between defrosting shutdowns.

For these and similar temperature applications, compressed air must not only be free of liquid phase water but must also have a minimum content of vapor phase water. Usually specified for these requirements are dew points in the range of -40ᵒF to -100ᵒF at pressure.

 

If you have questions or need assistance selecting a compressed air dryer, please contact us.