SUB-SECTION 4D
CONTROL VALVES
Figure 4D-10. Control Valve (36Z986)
1. Install the O-ring on the relief valve plug. Install the
orifice of the relief valve, so full circuit pressure is sensed at
the spring end of the valve, as welt as the opposite end. The
spring in the relief valve bore, then install the relief valve on
valve is thus hydraulically balanced and the large spring
the spring. Install and tighten the relief valve plug. Do not
holds it closed.
over-tighten the plug.
Maximum circuit pressure is determined by the small spring
2. Install new O-rings at each end of the spool bore.
inside the relief valve assembly. When circuit pressure is
3. Install the flat retainer on the spool, if it was removed.
high enough to overcome this small spring, the poppet
inside the assembly is forced off its seat. Fluid immediately
4. Install the spool in the bore from the end cap end.
flows past the poppet to the tank passage. This flow creates
a pressure drop across the sensing orifice and the relief valve
5. Align the flat retainer by shifting the spool. Spool bind
is no longer hydraulically balanced. When this pressure
IS an indication of flat retainer misalignment. Install the end
differential is great enough to overcome the large spring,
cap and attaching screws. Tighten the screws to 8 to 10
the valve shifts, permitting flow to the tank passage.
foot-pounds (1.1 - 1.3 m-kg).
6. Install a new O-ring on the check valve plug. Place the
Anti-cavitation check valves are installed next to the work
poppet and spring in the valve body and install the plug.
ports to eliminate cavitation created in the system, and
operates as follows: When the circuit pressure is less than
tank pressure, a vacuum is created. The anti-cavitation
CONTROL VALVE (36Q70)
check valve equalizes the unbalanced pressure condition by
metering fluid from the tank passage back to the pressure
DESCRIPTION
port.
Control valve 36Q70 is used to control the operation of the
RELIEF VALVE ADJUSTMENT
main winch motor. This is a four-way, spring centered
directional control valve. The valve is a balanced sliding
The setting of the main relief valve is determined by a
spool type with open-center circuitry, which allows free
spring installed in the relief valve at the factory, and no
flow from inlet to outlet when the spool is in the neutral
provisions have been made to adjust this relief valve.
position. The operation of the valve is illustrated in Figure
4D-11.
TROUBLESHOOTING
A main relief valve is provided to limit circuit pressure to a
preset maximum. When the circuit is operating at less than
Table 4D-6 lists the difficulties which may be experienced
the relief valve setting, there is no flow over the by-pass
with the valve and hydraulic system. It indicates the cause
4D-14
