Figure 7-8.Chemical air drier.
shows a hydraulic power system with an
air-pressurized reservoir incorporated. This system is
similar to the one found on many aircraft; however,
for clarification in the discussion of the operation of
the system, we have deleted some components
between the reservoir and the pump.
The reservoir is cylindrical in shape and has a
piston installed internally to separate the air and fluid
chambers. The piston rod end protrudes through the
reservoir end cap and indicates the fluid quantity. The
quantity indication may be seen by inspecting the
distance the piston rod protrudes from the reservoir
end cap. The reservoir has threaded openings for the
connection of fittings and components. The
schematic shown in figure 7-7 shows several
components installed in lines leading to and from the
reservoir; however, this may not be the case in the
actual installation. The air relief valve, bleeder valve,
etc., may be installed directly on the reservoir.
Because the reservoir is pressurized, it can
normally be installed at any attitude and still maintain
a positive flow of fluid to the pump.
CHEMICAL AIR DRIER.Chemical air driers
are installed in air systems to absorb moisture that
may collect from air entering the system. The main
parts of the air drier, shown in figure 7-8, are the
housing, desiccant cartridge, filter (porous bronze),
and the spring.
To ensure proper filtering, the air
must pass through the air drier in the proper direction.
The correct direction of flow is indicated by an arrow
and the wordflow printed on the side of the cartridge.
Preventive maintenance of this component
consists of replacing the cartridge when it becomes
saturated. Maintenance should be accomplished in
accordance with instructions provided in the
applicable maintenance instruction manual (MIM).
pressure used in pressurizing hydraulic reservoirs
must be controlled within safe limits.
pressure requirements vary between aircraft. In some
aircraft, the air pressure is controlled by an air
pressure regulator (fig. 7-9). 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
Figure 7-9.Air pressure regulator.