remove any moisture caused by the compressor. A
STORAGE CYLINDERS.--Pneumatic storage
cylinders (bottles) are made of steel and may be either
complete moisture separator consists of a reservoir, a
cylindrical or spherical in shape. Both types of
pressure switch, a dump valve, and a check valve, and it
cylinders are made up of two main parts--the
may include a regulator and a relief valve. The dump
container itself and a manifold assembly. The
valve is energized and de-energized by the pressure
container serves as a trap for moisture, as well as an air
switch. When de-energized, it completely purges the
storage space. The manifold assembly is made up of
separator reservoir and lines up to the compressor. The
the "in" and "outlet" ports and a moisture drain fitting.
check valve protects the system against pressure loss
See figure 12-44.
during the dumping cycle and prevents reverse flow
Cooling of the high-pressure air in the storage
through the separator.
cylinders will cause some condensation to collect in
R E L I E F VA LV E S . -- A r e l i e f v a l v e i s
them. To ensure positive operation of systems, storage
incorporated in a pneumatic system to protect the
cylinders must be purged of moisture periodically.
system from overpressurization. Overpressurization is
This is accomplished by slightly cracking the moisture
generally caused by thermal expansion (heat). Relief
drain fitting, located on the cylinder manifold.
valves are generally adjusted to open and close at
Some aircraft have a pneumatic system that will
pressures slightly above normal system operating
maintain the required pressure in these bottles in flight.
pressure. For example, in a system designed to operate
However, most of these pneumatic systems require
at 3,000 psi, the relief valve might be set to open at
servicing on the ground with an external source of
3,750 psi and reseat at 3,250 psi.
high-pressure air or nitrogen prior to each flight.
CHEMICAL DRIERS.--Chemical driers are
Air storage bottles are serviced in the same manner
incorporated at various locations in a pneumatic
as accumulators. Most air bottles have an air filler
system. Their purpose is to absorb any moisture that
valve and a pressure gauge. These systems generally
may collect in the lines and other parts of the system.
require higher servicing pressure than accumulators
do.
Each drier contains a cartridge, which should be
blue in color. If otherwise noted, the cartridge is to be
Since gases expand with heat and contract when
considered contaminated with moisture and should be
cooled, air storage bottles are usually filled to a given
pressure at ambient temperature. A graph similar to
replaced.
Figure 12-44.--Air cylinder.
12-42
