SUB-SECTlON 4D
CONTROL VALVES
the relief valve setting, there is no flow over the by-pass
3. Install the flat retainer on the spool, if it was removed.
orifice of the relief valve, so full circuit pressure is sensed at
4. Install the spool in the bore from the end cap end.
the spring end of the valve, as well as the opposite end. The
valve is thus hydraulically balanced and the large spring
5. Align the flat retainer by shifting the spool. Spool bind
holds it closed.
is an indication of flat retainer misalignment. Install the end
cap and attaching screws. Tighten the screws to 8 to 10
Maximum circuit pressure is determined by the small spring
foot-pounds (1.1 - 13 m-kg).
inside the relief valve assembly. When circuit pressure is
high enough to overcome this small spring, the poppet
inside the assembly is forced off its seat. Fluid immediately
CONTROL VALVE (36Z727)
flows past the poppet to the tank passage. This flow creates
a pressure drop across the sensing orifice and the relief valve
DESCRIPTION
is no longer hydraulically balanced. When this pressure
differential is great enough to overcome the large spring,
Control valve 36Z727 is used to control the operation of
the valve shifts, permitting flow to the tank passage.
the main winch motor. This is a four-way, spring centered
directional control valve. The valve is a balanced sliding
Anti-cavitation check valves are installed next to the work
spool type with open-center circuitry, which allows free
ports to eliminate cavitation created in the system, and
flow from inlet to outlet when the spool is in the neutral
operates as follows: When the circuit pressure is less than
position. The operation of the valve is illustrated in Figure
tank pressure, a vacuum is created. The anti-cavitation
4D-7.
check valve equalizes the unbalanced pressure condition by
metering fluid from the tank passage back to the pressure
A main relief valve is provided to limit circuit pressure to a
port.
preset maximum. When the circuit is operating at less than
Figure 4D-7. Control Valve Operation (36Z727)
4D-9
