A baffle-type separator is illustrated in figure
11-15. In this unit the air is subjected to a series of
sudden changes in direction that result in the
heavier moisture particles striking the baffles and
walls, then draining to the bottom.
Some compressed air supplies require dryers
that ensure removal of all moisture that might
otherwise condense in air lines, air-powered tools,
or pneumatic instruments. Small amounts of
moisture can cause damage to equipment from
corrosion, freezing, and water hammer and can
result in malfunctions of instruments and con-
trols. The cost of dryers is often justified by the
reduction in maintenance costs, production time
lost in blowing down piping, and compressed air
lost during blowdown.
There are three basic designs of dryers: two
absorption types and a condensation type. One
type of absorption unit consists of two towers, each
containing an absorbent material. Reactivation is
accomplished by means of electric or steam heaters
embedded in the absorbent or by passing dried-
process air through it.
Another type of absorption unit consists of a
single tank or tower containing a desiccant (dry-
ing agent) that dissolves as it absorbs moisture
from the air and drains from the unit with the con-
densate. The drying agent must be replenished
The third type removes moisture from the air
by condensation through the use of a mechanical
refrigeration unit, or where available, cold water.
Inlet air passes over cold coils where moisture is
condensed out of the air and is drained from the
unit by a trap. This process is illustrated in figure
Air receiver tanks in compressed air plants act
as surge tanks to smooth the flow of air from the
action of the compressor to discharge; they collect
excessive moisture that may condense from the
cooled air and provide a volume of air necessary to
operate the pressure control system. A typical air
receiver is shown in figure 11-17. Related
components include a relief valve, pressure gauge,
drain valve, service valve, and inspection opening.
Figure 11-17.Air receiver.
Compressors must receive adequate lubrica-
tion using clean oil of characteristics recom-
mended by the compressor manufacturer. The
manufacturer will usually specify oil requirements