1. Housing
6.
Oil seal assembly
11.
Universal link retainer pin
16.
Retaining ring
2. Drive shaft bearing
7.
Bearing spacer
12.
Cylinder block
17.
Cap
3. Bearing spacer
8.
Shaft and piston subassembly
13.
Spring retaining washer
18.
Cylinder bearing ring
4. Thrust bearing
9.
Retaining ring
14.
Spring
19.
Valve plate
5. Drive shaft bearing
10.
Bearing and oil seal retainer
15.
Cap retaining ring
20.
Valve plate mounting plate
Figure 11-6.--Typical hydraulic motor.
similar, the design and construction may be very
The typical four-way selector valve has four
different.
ports--a pressure port, a return port, and two cylinder
(or working) ports. The pressure port is connected to
SELECTOR VALVES
the main pressure line from the power pump, the return
port is connected to the reservoir return line, and the
Selector valves are used in a hydraulic system to
two cylinder ports are connected to opposite working
direct the flow of fluid. A selector valve directs fluid
ports of the actuating unit.
under system pressure to the desired working port of an
actuating unit (double-acting), and, at the same time,
Three general types of selector valves are
directs return fluid from the opposite working port of
discussed in this course. They are the poppet, slide,
the actuating unit to the reservoir.
and solenoid-operated valves. Practically all selector
Some aircraft maintenance instruction manuals
valves currently in use come under one of these three
(MIMs) refer to selector valves as control valves. It is
general types.
true that selector valves may be placed in this
classification, but you should understand that all
Poppet-Type Selector Valve
control valves are not selector valves. In the strict
sense of the term, a selector valve is one that is engaged
Poppet-type selector valves are manufactured in
at the will of the pilot or copilot for the purpose of
both the balanced and unbalanced design. An
directing fluid to the desired actuating unit. This is not
unbalanced poppet selector valve offers unequal
true of all control valves.
working areas on the poppets. The larger area of the
poppet is in contact with the working lines of the
Selector valves may be located in the pilot's
system; consequently, when excessive pressure exists
compartment and be directly engaged manually
within the working lines due to thermal expansion, the
through mechanical linkage, or they may be located in
poppet will open. This action allows the excessive
some part of the aircraft and be engaged by remote
pressurized fluid to flow into the pressure line, where it
control. Remote-controlled selector valves are
is relieved by the main system relief valve.
generally solenoid operated.
11-8
