Compressed Air Moisture Content
Another major element in assuring a
successful compressed air rental program lies in addressing
the moisture content of the compressed air.
Most manufacturing plants today already use
compressed air aftercoolers and air dryers to remove liquid
water and/or water vapor from their compressed air systems.
This same care and concern should be extended to the rental
air system, to insure consistent high quality compressed air
being delivered to critical manufacturing systems.
With most permanently installed compressors
in use today, aftercoolers are an integral part of the
The two most common air dryer designs are the
refrigerated air dryer and the twin tower desiccant air
dryer. As the name suggests, refrigerated dryers use a
refrigeration system to physically reduce the temperature of
the air, condensing water vapor, which is then separated and
removed from the compressed air system. There are several
control variations used, such as direct expansion, thermal
mass, etc. Refrigerated dryers usually achieve a Pressure
Dew Point (PDP) of 35° to 39° F.
Twin tower desiccant dryers use an entirely
different principle of operation – desiccant materials
(usually Activated Alumina) to adsorb water vapor
directly out of the compressed air. Once the desiccant bed
has adsorbed sufficient water vapor, the two towers switch,
and while the second tower is actively drying the compressed
air stream, the first tower is being "regenerated," meaning
the vapor is dried out of the desiccant material. The towers
then switch again, and this process is repeated over and
over. Desiccant dryers can reduce moisture to a much lower
level than refrigerated dryers, typically producing a PDP of
-40° F to -100° F.
How does one handle compressed air moisture
in a rental scenario? In one of two ways – the rental
compressors can be connected to the plant air system
UPSTREAM of the permanently installed cooling/drying
equipment, or aftercoolers and either refrigerated or
desiccant air dryers can be rented along with the
compressors, to supply dry air directly to the system.