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 TM 55-1905-219-14-6
3-137.9. DIRECTIONAL CONTROL VALVE - MAINTENANCE INSTRUCTIONS (Continued).
a.
GENERAL
The directional control valve is comprised of a rectangular valve body containing a precision fitted
sliding spool in a central, longitudinal bore. Spool lands serve to divide the bore into a series of separate
chambers, and ports in valve body lead into these chambers. The position of the spool determines which ports
are open to each other and which are sealed off from the others. Thus, oil flow is directed from one port to
another within the valve body.
b.
PRINCIPLES OF OPERATION
(1)
VALVE TYPE:
SPRING CENTERED - Spring centered valves are provided with a spring and centering washer at
each end of the spool. The springs and washers center the spool within the valve body, when solenoids are de-
energized.
(2) FUNCTION
(a)
Three cross section views of a valve are shown. The cross sections show locations of the spool lands
and the basic valve block machining. Each cross section is-provided to show porting of the valve as the spool
is moved within the valve block. Assume the spool is moved to the left within the valve body. The "P"
pressure port will connect to the "A" cylinder port and the "B" cylinder port will open to the "T" tank port.
(b)
If the spool is moved to the right as shown, the "P" pressure port will connect to the "B" cylinder port
and the "A" cylinder port will connect to the "T" tank. When the spool returns to center, (solenoids de-
energized), flow is blocked in all ports. It can be seen that the function of a valve is to direct the flow of system
fluid within a circuit. The valve is actually used to direct flow from the pump to the actuator and from the
actuator to the tank or reservoir.
3-2290
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