Foreign matter could result in binding of the slide,
body, and all four fluid ports connect into this main
bore at intervals along its length. There is also a drilled
scratching the machined surface, and damage to
passageway in the body that runs alongside the main
O-rings. Originally, these valves were provided with
bore. This passageway is used to connect one of the
protective boots on both ends of the slide to prevent dirt
cylinder ports to the return port.
or corrosion from getting on the exposed machined
surface, where it would be carried into the valve when
A hollow steel sleeve (3) fits into the main bore of
the slide was moved. These protective boots usually
the body. Around the outside diameter of the sleeve are
are missing on valves currently issued, leaving the
six O-ring gaskets. As the sleeve is inserted into the
machined surface exposed. As a preventive measure,
main bore, these O-rings form a seal between the
in place of the boots, a light film of hydraulic fluid
sleeve and the body. This creates five chambers around
should be applied to the exposed areas of the slide.
the sleeve, and each chamber is formed by two of the
Primarily, this oil film is to prevent corrosion, but it
O-ring gaskets. Each one of these chambers is lined up
helps to prevent any entry of foreign matter into the
with one of the fluid ports in the body. The drilled
valve. Proper linkage adjustment is necessary because
passageway in the body accounts for the fifth chamber,
linkage that is too long or too short will prevent the
which results in having the two outboard chambers
detent spring from locking the slide in the correct
connected to the return port. The sleeve has a pattern of
position.
holes drilled through it to allow fluid to flow from one
port to another. A series of holes are drilled into the
If it becomes necessary to test this valve under
hollow center of the sleeve between each O-ring
pressure to determine the cause of malfunction, it is
gasket.
important to first check the MIM for the particular
A steel slide (5) or spool is machined so the largest
installation. A slight amount of internal leakage is
diameter portions have a close tolerance fit in the
permitted in the working positions, and this should not
sleeve. Typically, the slide has three raised, machined
be mistaken for faulty operation.
portions known as land areas. These areas usually have
several grooves machined into them around the
Solenoid-Operated Selector Valve
circumference, breaking each area into several lands.
A s o l e n o i d - o p e r a t e d s e l e c t o r va l ve i s a n
T h e l a n d s ( a n d g r o ove s ) , i n c o n c e r t w i t h t h e
electrically controlled valve. Solenoid-operated
close-machined tolerances, provide for easy, smooth
selector valves may be either the slide type or the
operation, long service, and no leakage.
poppet type. They differ from the manually controlled
One end of the slide is connected to the control
valves previously described in that they are electrically
handle in the cockpit through mechanical linkage.
controlled by one or more solenoids contained within
When the control handle is moved, it will then position
the valve.
the slide within the sleeve. The slide lands then line up
different combinations of fluid ports, thereby directing
A solenoid may be defined as a hollow or
a flow of fluid through the valve.
tubular-shaped electric coil, made up of many turns of
fine insulated wire that possesses the same properties
On the end of the slide, next to the eye, are three
as an electromagnet. The hollow core imparts linear
grooves called "detents." These detents are used to
motion to a movable iron core (or plunger) placed
lock the slide in the exact position needed to properly
within the hollow core of the solenoid.
direct the fluid flow.
S o l e n o i d - o p e r a t e d s e l e c t o r va l ve s a r e fa s t
The detent spring (6) is a clothespin-type spring,
becoming the most commonly used valves on naval
secured to the end of the body by a spring retaining bolt
aircraft. Figure 11-11 is a cutaway view of the valve,
(7). The two legs of the spring extend down through
showing all the principal components. The body is
slots in the sleeve and fit into the detents. The slide is
made of cast aluminum alloy and contains four fluid
gripped between the two legs of the spring. To move
ports. These are the pressure port, return port, and the
the slide, enough force must be applied to spread the
two cylinder ports.
two spring legs and allow them to snap back into the
next detent, which is another position.
The body is bored through lengthwise to receive a
slide and sleeve assembly similar to the slide-type
Because of the very close fit between the slide and
valve. All four fluid ports lead into this body bore.
s l e eve , t h e m o s t c o m m o n c a u s e o f fa i l u r e o r
malfunction is the presence of dirt or foreign matter.
Caps or plugs close off the ends.
11-12
