CONTROL VALVES
SUB-SECTION 4D
TABLE 4D-2
TROUBLE, CAUSE AND REMEDY CHART (CONTINUED)
REMEDY
TROUBLE
PROBABLE CAUSE
Replace valve.
Load will not hold.
Oil by-passing between spool
and body.
Repair or replace cylinder.
Oil by-passing piston in cylinder.
Spool not centered.
Refer to above spool remedies.
Load drops when spool is moved
Dirt or foreign particles lodged
Disassemble, clean and reassemble.
from neutral to a power position.
between check valve poppet and
seat.
Replace poppet.
Scored or sticking check valve
poppet.
oil solvent and place them on a clean surface for inspection.
are usually dependent upon each other. Adequate pressure
gauge equipment and a thorough understanding of the
2. Carefully remove burrs by light stoning or lapping. Be
operation of the complete hydraulic system are essential to
certain that there is no paint on the mating surfaces of the
diagnosing improper valve operation.
valve body. Check all parts for wear. Replace if necessary.
OVERHAUL
3. Inspect the valve spool and bore for burrs and scoring. If
scoring is not deep enough to cause objectionable leakage,
GENERAL. Overhaul of this valve is limited to the replace-
the surfaces can be stoned or polished with crocus cloth. If
ment of the relief valve assembly and seals. Replace the
scoring is excessive the valve body and spool must be
complete valve when the required overhaul is beyond these
limitations.
replaced. Check the valve spool for freedom of movement
in the bore.
During disassembly, particular attention should be given to
4. Check the relief valve for smooth movement in its bore.
identification and orientation of parts for reassembly. The
The valve should mow by its own weight.
spool is selectively fitted to the valve body and must be
returned to the same body from which it was removed.
ASSEMBLY. To assemble the valve, proceed as follows:
Figure 4D-4 is an exploded view of the valve showing the
proper relationship of the parts for reassembly. Refer to
NOTE
this figure while disassembling and reassembling the valve.
Coat all parts with clean hydraulic oil to facilitate
DISASSEMBLY. Disassemble the valve as follows:
reassembly and provide initial lubrication. Petroleum
1. Be sure the valve is not subjected to pressure. Discon-
jelly can be used to hold O-rings in place during reas-
nect and cap all lines, and disconnect the linkage from the
sembly.
spool. Remove the valve from the machine.
1. Install the O-ring on the relief vavle plug. Install the
2. Remove the screws which the the end up, ad
spring in the relief valve bore, then install the relief valve on
remove the end cap.
the spring. Install and tighten the relief valve plug. Do not
over-tighten the plug.
3. Slide out of its bore from the end cap end, and
remove the O-ring from the spool bore.
2. Install new O-rings at each end of the spool bore.
4. Screw out the plug which retains the relief valve and
3. lnstall the flat retainer on the spool, if it was removed.
remove the O-ring from the plug. Remove the spring and
4. Install the spool in the bore from the end cap end.
relief valve.
5. Align the flat retainer by shifting the spool. Spool bind
CLEANING, INSPECTION AND REPAIR. After the valve
is an indication of flat retainer misalignment. Install the end
has been disassembled, Perform the following:
cap and attaching screws. Tighten the screws to 8 to 10
foot-pounds (1.1 - 1.3 m-kg).
1. Discard all the O-rings. Wash all parts in a clean mineral
4D-5
