SUB-SECTION 4D
CONTROL VALVES
During disassembly, particular attentions should be given to
RELIEF VALVE ADJUSTMENT
identification and orientation of parts for reassembly. The
The setting of the main relief valve is determined by a
spool is selectively fitted to the valve body and must be
spring installed in the relief valve at the factory, and no
returned to the same body from which it was removed.
provisions have been made to adjust this relief valve.
Figure 4D-8 is an exploded view of the valve showing the
proper relationship of the parts for reassembly. Refer to
TROUBLESHOOTING
this figure while disassembling and reassembling the valve.
Table 4D-4 lists the difficulties which may be experienced
with the valve and hydraulic system. It indicates the cause
DISASSEMBLY. Disassemble the valve as follows:
and remedy for each of the troubles listed. It should always
1. Be sure the valve is not subjected to pressure. Discon-
be remembered that pressure and delivery are factors which
nect and cap all lines, and disconnect the linkage from the
are usually dependent upon each other. Adequate pressure
spool. Remove the valve from the machine.
gauge equipment and a thorough understanding of the
operation of the complete hydraulic system are essential to
2. Remove the screws which secure the wiper retainer, and
diagnosing improper valve operation.
remove the wiper retainer, wiper, retainer plate, and O-ring
from the valve body.
OVERHAUL
3. Remove the screws which secure the end cap, and
GENERAL. Overhaul of this valve is limited to the replace-
remove the end cap.
ment of the relief valve assembly and seals. Replace the
complete valve when the required overhaul is beyond these
4. Slide the spool out of its bore from the end cap end, and
remove the O-ring from the spool bore.
limitations.
TABLE 4D-4
TROUBLE, CAUSE AND REMEDY CHART
TROUBLE
PROBABLE CAUSE
REMEDY
Replace O-rings.
Oil leaks at either end of spool.
Defective O-rings in valve body.
Broken springs.
Replace springs.
Spring-centered spools do not
return to neutral.
Clean system and valve.
Foreign particles.
Check linkage for binding condition.
Misalignment of operating linkage.
No motion, slow or jerky action of
Relief valve not properly set, or
Repair, clean and readjust.
hydraulic system.
stuck in base and/or worn.
Dirt or foreign particles lodged
Disassemble, clean and reassemble.
between relief valve control pop
pet and seat.
Spool not moved to full stroke.
Check travel.
Remove relief valve and check
No relief valve action (High
Small particle of dirt plugging
hole. If blocked, clear hole.
Pressure).
orifice in relief valve sub-
assembly.
Replace valve.
Load will not hold.
Oil by-passing between spool
and body.
Oil by-passing piston in cylinder.
Repair or replace cylinder.
Refer to above spool remedies.
Spool not centered.
4D-10
