Air Dryers The purpose of an air dryer is to remove water vapor from the air. The higher the pressure, the higher the dew point. Dew point is the temperature at which water vapor will condense out of the air and turn into liquid. When air is compressed to 100 PSI, the water vapor is concentrated up to 8 times! 0 PSI = -4°F 180 PSI = 57°F

Air Dryers There are 3 main types of air dryers: Deliquescent Regenerative Desiccant Refrigeration

Deliquescent Dryers Use chemicals to absorb the water vapor. Sodium Chloride (Salt) or Calcium Chloride are commonly used. The resulting solution must be drained. Lower in initial cost, but the chemical must be continually replaced. Recommended chemical level should be maintained. Inlet air temperature should not exceed 100°F.

Deliquescent Dryers Can normally produce outlet air with a dew point °F below the inlet temperature. Can prevent freeze-ups down to 12 – 15°F.

Regenerative Desiccant Dryers Remove water by adsorbing it with an inert desiccant material. Silica gel, activated alumina or molecular sieve are commonly used. The desiccant must be dried or “regenerated” periodically. There are two methods of drying the desiccant: The heated regenerative dryer The heatless regenerative dryer Silica gel and activated alumina will produce a -40°F dewpoint. Molecular sieve will produce a -100°F dewpoint.

Blower Purge Dryer BlowerImmersion Heater

Refrigeration Dryers Remove moisture from the air by condensation. Three major designs: Tube-In-Tube Direct Expansion Water Chilled Can produce dew points of 35° to 50°F at system operating pressure.

Tube-In-Tube Refrigeration Dryer

Direct Expansion Refrigeration Dryer

Water Chilled Refrigeration Dryer

Dryer Failures and Maintenance The #1 cause of air dryer failure is overheating! Dirty condenser fins High ambient temperature Hot gas bypass valve failure (direct expansion design) Cold temperatures (ice formation)