How They Work
Compressed air dryers are used to remove water and other contaminants from compressed air. Compressed air dryers use technologies such as refrigeration, desiccant adsorption, and membrane filtration to remove contaminants, particularly water, from the air.
Major groupings include refrigerant (which removes the water by cooling the air) force condensation, and desiccant (which adsorbs the water in the air with granular material such as activated alumina, silica gel and molecular sieves).
Other technologies include membrane and in-line compressed air dryers. The air can be dried in single or multiple stages to prevent tool corrosion and other problems associated with water.
Important specifications to consider when searching for compressed air dryers include drying capacity, maximum pressure, minimum output Dewpoint, motor power, and operating temperature.
Drying capacity is the maximum volume of air through dryer; typically given at 100 psig.
The maximum pressure refers to the maximum rated inlet pressure of dryer.
Dew point is a measure of dryness; it describes how much water vapor is present and tells us how cold the compressed air can get before liquid water will form.
Motor horsepower is a reference value often used to approximate dryer size; pressure and capacity are the differentiating specifications.
The operating temperature is the full-required range of ambient operating temperature.
If the compressed air dryer is a desiccant dryer important specifications to consider include stages and regeneration method.
Video Credit: Parker Balston
Stages include single stage and double stage.
Choices for regeneration method include heatless regeneration, internally heated regeneration, and externally heated regeneration.
In heatless regeneration by means of expanding cold dry air to near atmospheric pressure inside the regeneration tower, the dryer air picks up moisture from the saturated desiccant bed and is then purged to atmosphere.
In an internally heated regeneration dryer the process air enters the dryer through the inlet piping, is then dried as it passes through the desiccant bed, and discharges through the outlet piping as dry air. Regeneration of the desiccant is accomplished at atmospheric pressure, using steam or electric heaters, embedded in the desiccant bed.
In an externally heated regeneration dryer process air enters the dryer through the inlet piping, is then dried as it passes through the desiccant bed, and discharges through the outlet piping as dry air. Reactivation is accomplished using a reactivation blower or a cooler.
Choices for power sources for compressed air dryers include:
No power source
AC single phase
AC three phase
Common features include pressure gauges, integral filters, and automatic condensate drain.
Pressure gauges monitor pressure; includes dial or digital readout.
Integral filters are used for the mechanical trapping of moisture, oil, smoke, etc.
An automatic condensate drain automatically senses the level or amount of removed moisture and automatically drains it off.
BS ISO 7183 - Specifications and testing of compressed air dryers
ANSI B93.45M - Pneumatic fluid power compressed air dryers - methods for rating and testing
BS 6754 - Specifications and testing of compressed air dryers
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