Figure 12-8.--Chemical air drier.
air pressure regulator. The relief valve shown in figure
Because the reservoir is pressurized, it can
12-10 is cylindrical in shape and consists of a housing,
normally be installed at any attitude and still maintain a
poppet, spring, and adjusting screw. This valve may be
positive flow of fluid to the pump.
mounted directly to the reservoir or in a line leading
CHEMICAL AIR DRIER.--Chemical air driers
from the reservoir, depending on the aircraft system
are installed in air systems to absorb moisture that may
design.
collect from air entering the system. The main parts of
During operation, air pressure enters the inlet port
the air drier, shown in figure 12-8, are the housing,
and contacts the poppet surface. When system air
desiccant cartridge, filter (porous bronze), and the
pressure increases to 50 psi, the poppet is forced off its
spring. To ensure proper filtering, the air must pass
seat, which allows excessive air pressure to be
through the air drier in the proper direction. The
exhausted to the atmosphere. When system pressure is
correct direction of flow is indicated by an arrow and
lowered to 49 psi, the poppet spring tension overcomes
the word flow printed on the side of the cartridge.
system pressure and reseats the poppet, thus closing
P r eve n t ive m a i n t e n a n c e o f t h i s c o m p o n e n t
the valve.
consists of replacing the cartridge when it becomes
Maintenance of the valve usually includes the
saturated. Maintenance should be accomplished in
replacement of all seals and the adjustment of its
accordance with instructions provided in the
controlling pressures. This valve is designed to relieve
applicable maintenance instruction manual (MIM).
A I R P R E S S U R E R E G U L AT O R S . -- A i r
pressure used in pressurizing hydraulic reservoirs must
be controlled within safe limits. Specific pressure
requirements vary between aircraft. In some aircraft,
the air pressure is controlled by an air pressure
regulator (fig. 12-9). This regulator normally
maintains 40 psi pressure in the reservoir. It also
incorporates a relief valve to relieve excessive pressure
and a differential valve to allow equalization of
pressures between ambient (outside) air and reservoir
air pressures.
AIR RELIEF VALVE.--An air relief valve is
normally incorporated in the air portion of the
hydraulic power system to relieve excessive air
Figure 12-9.--Air pressure regulator.
pressure entering the reservoir due to a malfunctioning
12-10
