Solenoid-operated selector valves are fast
becoming the most commonly used vaIves on naval
aircraft. Figure 8-11 is a cutaway view of the valve,
showing all the principal components. The body is
made of cast aluminum alloy and contains four fluid
ports. These are the pressure port, return port, and the
two cylinder ports.
The body is bored through lengthwise to receive a
slide and sleeve assembly similar to the slide-type
valve previously described. All four fluid ports lead
into this body bore. The ends are closed off by caps
A hollow steel sleeve is pressed into the body
bore. There are no flanges or grooves machined on
the sleeve, but a pattern of holes has been drilled all
around it. These holes are arranged in five rings,
along the length of the sleeve, drilled through to the
hollow center. When the sleeve is installed in the
body, each ring of holes will line up with a fluid port.
The return port connects to the two outboard rings of
holes. To separate each ring of holes around the
outside of the sleeve, six O-ring gaskets are installed
in the body bore at intervals along its length. The
sleeve is then inserted through the centers of the
A steel slide is fitted inside the hollow sleeve.
The slide has three lands, which form a lapped fit to
the inside of the sleeve. Fluid will not flow past them.
By properly positioning the slide inside the sleeve, the
slide lands will connect different fluid ports by
opening or closing the rings of holes in the sleeve.
The flow of fluid to and from the actuator is directed
by the slide. When the valve is in neutral, the slide is
held in the exact center of the sleeve by two coil
springs. These springs, working through spring
guides, apply equal pressure to each end of the slide.
Variation in slide design will determine the valve
To position the slide, apply hydraulic pressure to
the working surfaces at each end of it. This pressure
is obtained from the pressure port, and is called bleed
pressure. Body passageways direct this pressure to
the ends of the slide. Two solenoid assemblies are
used to control the flow of bleed pressure.
A solenoid is installed in each side of the valve,
pointing toward the center of the body. The solenoids
are tubular in shape, with coil wires wound around a
hollow center. Hydraulic fluid can enter the center
portion, but cannot reach the coil wires. The
solenoids are held in place by threaded caps that
screw into the body. The function of these solenoids
is to control bleed pressure.
A metal core, called a plunger, is placed in the
hollow center of the solenoids. This plunger reacts to
the magnetic field created when the solenoid coil is
energized. The plunger sits above the level of the coil
wires, so that when the solenoid is energized, the
plunger is pulled down into the magnetic field. When
the plunger is pulled down by the magnetic field, it
drives the plunger pin ahead of it. When this happens,
the pin opens a passage and relieves bleed pressure
from one end of the slide.
During all periodic inspections, selector valves
are inspected for security of installation and external
If a malfunction occurs, it must be
determined whether the cause is electrical, hydraulic,
or material failure. If the aircrafts hydraulic pressure
and electrical current are both normal, remove the
selector valve and send it to the supporting AIMD.
Use the proper 03 series maintenance publication as a
guide to clean, inspect, repair, and test the selector
Testing procedures are thoroughly outlined in the
MIMs and 03 series manuals. In general, these
procedures will consist of checking for internal and
external leakage, and on electrically controlled
valves, testing the operation of the solenoids. Before
applying pressure, make sure all air is bled out of the
valve; otherwise, a leak may exist but go undetected.
As the testing procedure begins and after the air has
been bled, the selector valve shouId be subjected to a
low pressure for a short period of time to allow all
parts to be lubricated and all O-rings to seat. If the
valve is to be stored prior to use, it must be filled with
preservative hydraulic fluid, then drip drained before
The purpose of a check valve is to allow the fluid
to flow in only one direction. In some installations,
such as brake systems, the check valve confines fluid
under pressure within the desired section of the
hydraulic system. The valve prevents the fluid from
reversing its normal direction of flow. The valve
prevents pressure from escaping into adjacent
sections of the system.