SUB-SECTION 4D
CONTROL VALVES
SUB-SECTION 4D
CONTROL VALVES
Maximum circuit pressure is determined by the small spring
CONTROL VALVE (36Z724)
inside the relief valve assembly. When circuit pressure is
high enough to overcome this small spring, the poppet
DESCRIPTION
inside the assembly is forced off its seat. Fluid immediately
Control valve 36Z724 is used to control the operation of
flows past the poppet to the tank passage. This flow creates
the swing and auxiliary winch motors. This is a four-way,
a pressure drop across the sensing orifice and the relief valve
spring centered directional control valve. The valve is a
is no longer hydraulically balanced. When this pressure
balanced sliding spool type with open-center circuitry,
differential is great enough to overcome the large spring,
which allows free flow from inlet to outlet when the spool
the valve shifts, permitting flow to the tank passage.
is in the neutral position. The operation of the valve is
RELIEF VALVE ADJUSTMENT
illustrated in Figure 4D-1.
The setting of the main relief valve is determined by a
A main relief valve is provided to limit circuit pressure to a
spring installed in the relief valve at the factory, and no
preset maximum. When the circuit is operating at less than
provisions have been made to adjust this relief valve.
the relief valve setting, there is no flow over the by-pass
orifice of the relief valve, so full circuit pressure is sensed at
TROUBLESHOOTING
the spring end of the valve, as well as the opposite end. The
valve is thus hydraulically balanced end the large spring
Table 4D-1 lists the difficulties which may be experienced
holds it closed.
Figure 4D-1. Control Valve Operation (36Z724)
4D-1
