CONTROL VALVES
SUB-SECTION 4D
Figure 4D-2. Control Valve (36Z724)
placed. Check the valve spool for freedom of movement in
centered directional control valve. The valve is a balanced
the bore.
sliding spool type with open-center circuitry, which allows
free flow from inlet to outlet when the spool is in the
4. Check the relief valve for smooth movement in its bore.
neutral position. The operation of the valve is illustrated in
The valve should mow by its own weight.
Figure 4D-3.
ASSEMBLY. To assemble the valve, proceed as follows:
A main relief valve is provided to limit circuit pressure to a
preset maximum. When the circuit is operating at less than
NOTE
the relief valve setting, there is no flow over the by-pass
orifice of the relief valve, so full circuit pressure is sensed at
Coat all parts with clean hydraulic oil to facilitate
the spring end of the valve, as well as the opposite end. The
reassembly and provide initial lubrication. Petroleum
valve is thus hydraulically balanced end the large spring
jelly can be used to hold O-rings in place during reas-
holds it closed.
sembly.
Maximum circuit pressure is determined by the small spring
inside the relief valve assembly. When circuit Pressure is
1. Install the O-ring on the relief valve plug. Install the
high enough to overcome this small spring. the poppet
spring in the relief valve bore, then install the relief valve
inside the assembly is forced off its seat. Fluid immediately
on the spring. Install and tighten the relief valve plug.
flows past the poppet to the tank passage. This flow creates
Do not over-tighten the plug.
a pressure drop across the sensing orifice and the relief valve
2. Install new O-rings at each end of the spool bore.
is no longer hydraulically balanced. When this pressure
differential is great enough to overcome the large spring,
3. Install the flat retainer on the spool, if it was removed.
the valve shifts, permitting flow to the tank passage.
4. Install the spool in the bore from the end cap end.
RELIEF VALVE ADJUSTMENT
5. Align the flat retainer by shifting the spool. Spool bind
The setting of the main relief valve is determined by a
is an indication of flat retainer misalignment. Install the end
spring installed in the relief valve at the factory, and no
cap and attaching screws. Tighten the screws to 8 to 10
provisions have been made to adjust this relief valve.
foot-pounds (1.1 - 1.3 m-kg).
CONTROL VALVE (36Z725)
TROUBLESHOOTING
Table 4D-2 lists the difficulties which may be experienced
DESCRIPTION
with the valve and hydraulic system. It indicates the cause
Control valve 36Z725 is used to control the operation of
and remedy for each of the troubles listed. It should always
the boom teIescope cylinders. This is a four-way, spring
be remembered that pressure and delivery are factors which
4D-3
