Figure 12-11.--Air bleeder valve.
pressure regulator. The regulator decreases engine
bleed air pressure to a desired working pressure.
As air pressure leaves the regulator, it enters the
reservoir and acts on its piston, which, in turn,
transmits force to the fluid. If malfunction of the
Figure 12-10.--Air relief valve.
regulator causes excessive reservoir air pressure, an air
at a cracking (just open) pressure of 50 psi; the
relief valve will open at a preset pressure and exhaust
reseating pressure is 49 psi. The valve will operate at
excessive air overboard. Fluid under pressure in the
full flow when the pressure reaches 60 psi.
reservoir provides a positive flow of fluid through a
one-way check valve to the suction port of the
All pressure adjustments of relief valves must be
hydraulic pump, thus preventing pump cavitation or
performed on a test bench. You can control valve
pressures by adjusting the adjusting screw on the valve
until the proper settings are obtained.
AIR BLEEDER VALVE.--During hydraulic
Some aircraft hydraulic systems use fluid pressure
system maintenance, it is necessary to relieve reservoir
for pressurizing the reservoir. The reservoir shown in
air pressure to assist in the installation and removal of
figure 12-12 is a fluid-pressurized reservoir. This
components, lines, etc. An air bleeder valve is
reservoir is divided into two chambers by a floating
incorporated within the reservoir air system to avoid
piston. The floating piston is forced downward in the
disassembly of lines or units. A similar valve may be
r e s e r vo i r b y a c o m p r e s s i o n s p r i n g w i t h i n t h e
incorporated in reservoir return lines to provide a
pressurizing cylinder and by system pressure entering
means for bleeding air from returning fluid.
the pressurizing port of the cylinder.
This type of valve is small in size and has a push
The pressurizing port is connected directly to the
button installed in the outer case. Figure 12-11 shows a
pressure line. When the system is pressurized,
full view schematic drawing of a bleeder valve. The
pressure enters the pressure port, thus pressurizing the
valve is made up of a body, spring, poppet, and push
reservoir. This pressurizes the pump suction line and
button. When the bleeder valve push button is
the reservoir return line to the same pressure. Positive
depressed, pressurized air from the reservoir flows
pressure prevents pump starvation.
through the valve to an overboard vent, until the air
pressure is depleted or the button is released. When the
The reservoir shown in figure 12-12 has five
button is released, the internal spring causes the poppet
ports--pump suction, return, pressurizing, overboard
to return to its seat. In case of malfunction, this type of
drain, and bleed port. Fluid is supplied to the pump
valve is replaced with a new valve.
through the pump suction port. Fluid returns to the
reservoir from the system through the return port.
S Y S T E M O P E R AT I O N . -- D u r i n g n o r m a l
Pressure from the pump enters the pressurizing
operation, the pressurizing air source comes from
cylinder in the top of the reservoir through the
engine bleed air. See figure 12-7. This bleed air is
pressurizing port. The overboard drain port is for the
routed through a poppet-type, one-way check valve to
purpose of draining the reservoir, when necessary,
the chemical drier. The chemical drier conditions the
while performing maintenance. The bleed port is used
air by absorbing its moisture. Conditioned air is then
routed through a poppet check valve to the system air
as an aid in servicing the reservoir.