MM-34
Revised 11-02
Page 25
Appendix I
Glossary
Basic Air System/Air Dryer Terms
Air Compressor
A device that pumps air to and builds air pressure in an air system.
Air Dryer
A device that cools, filters, and dries the air delivered by an air
compressor.
Air Governor
A device that controls the operation of the air compressor by constantly
monitoring air pressure in the supply tank of the air system. The air
governor initiates the compressor load cycle when “cut-in” pressure is
realized, and initiates the compressor unload cycle when the “cut-out”
pressure is reached. The air governor also controls the air dryer by
sending an air signal (at the beginning of the compressor unload cycle)
to the control port of the air dryer, initiating the purge cycle. When this
air signal is removed by the governor (at the beginning of the
compressor load cycle), the purge valve closes and the drying cycle
begins.
Compressor Load Cycle
The time during which the air compressor is building air pressure in an
air system.
Compressor Unload Cycle
The time during which the air compressor is idling and is not building air
pressure in an air system.
Cut-In Pressure
The pressure level in the air system supply tank which triggers the
compressor load cycle.
Cut-Out Pressure
The pressure level in the air system supply tank which triggers the
compressor unload cycle.
Dedicated Purge Tank
A separate air tank used exclusively for holding air used in an air drying
cycle. This tank eliminates the need for a regeneration valve. Optimum
mounting location for the dedicated purge tank is ABOVE the air dryer.
Desiccant
A granular substance that has a high affinity for water and is used to
retain moisture from the air stream flowing through the air dryer
cartridge.
Discharge Line —
An unloader or air discharge line used to dump unused air to
Unloaded Compressor
atmosphere once system has reached cut-out pressure.
Drying Cycle
The time during which the air dryer cools, filters, and removes moisture
from the air delivered by the air compressor. The drying cycle begins
and ends the same as the compressor load cycle.
Purge
The initial blast of air (decompression) from the air dryer purge valve at
the beginning of the unload cycle of the air compressor.
Purge Cycle
The time during which the air dryer is undergoing purge and
regeneration. This cycle starts at the beginning of the compressor
unload cycle and normally ends well before the beginning of the
compressor load cycle.
Regeneration
The mild backflow of air through the air dryer and out the purge valve
that begins immediately after the purge and lasts normally 10 to
25 seconds. This backflow of air from the air system and through the air
dryer removes moisture from the desiccant cartridge and readies the air
dryer for the next compressor load cycle.
