CONTROL VALVES
SUB-SECTION 4D
Figure 4D-8. Control Valve (36Z727)
1. Install the O-ring and beck up ring on the. relief valve
5. Screw out the plug which retains the relief valve, and
plug, with the O-ring nearest the relief valve. Install the
remove the O-ring and back up ring from the plug. Remove
relief valve in its bore, then install the spring on the relief
the spring and poppet. Do not lose the pin in the relief
valve. Install and tighten the relief valve plug. Do not over-
valve.
tighten the plug.
CLEANING, INSPECTION AND REPAIR. After the valve
2. Install new O-ring in each end of the spool bore.
has bean disassembled, perform the following:
3. Install the spool in the bore from the end cap end.
1. Discard all old O-rings and back up rings. Wash all parts
in a clean mineral oil solvent and place them on a clean
4. Install the end up end attaching screws. Tighten the
surface for inspection.
screws to 8 to 10 foot-pounds (1.1 - 1.3 m-kg).
2. Carefully remove burrs by light stoning of lapping. Be
5. Install the retainer plate, wiper, and wiper retainer over
certain that there is no paint on mating surfaces of valve
the spool, and secure with screws.
body. Check all parts for wear. Replace if necessary.
CONTROL VALVE (36Z986)
3. Inspect the valve spool and bore for burrs and scoring. If
DESCRIPTION
scoring is not deep enough to cause objectionable Ieakage,
the surfaces can be stoned or polished with crocus cloth. If
Control valve 36Z986 is used to control the operation of
scoring is excessive the valve body and spool must be
the boom hoist cylinders. This is a four-way, spring cen-
replaced. Check the valve spool for freedom of movement
tered directional control valve. The valve is a balanced
in 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
This should move by its own weight.
Figure 4D-9.
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 then
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 and the large spring
jelly can be used to hold the O-rings in place during
holds it closed.
reassembly.
4D-11
