CONTROL VALVES
SUB-SECTION 4D
TABLE 4D-1
TROUBLE, CAUSE AND REMEDY CHART
REMEDY
TROUBLE
PROBABLE CAUSE
Replace O-rings.
Oil leaks at either end of spool.
Defective O-rings in valve body.
Spring-centered spools do not
Broken springs.
Replace springs.
return to neutral.
Foreign particles.
Clean system and valve.
Misalignment of operating linkage.
Check linkage for binding condition.
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.
Disassemble, clean and reassemble.
Dirt or foreign particles lodged
between relief valve control pop-
pet and seat.
Check travel.
Spool not moved to full stroke.
No relief valve action (High
Remove relief valve and check
Small particle of dirt plugging
Pressure).
hole. If blocked, clear hole.
orifice in relief valve sub-
assembly.
Load will not hold.
Replace valve.
Oil by-passing between spool
and body.
Repair or replace cylinder.
Oil by-passing piston in cylinder.
Refer to above spool remedies,
Spool not centered.
nect and cap all lines, and disconnect the linkage from the
with the valve and hydraulic system. It indicates the cause
spool. Remove the valve from the machine.
and remedy for each of the troubles listed. It should always
be remembered that pressure and delivery are factors which
2. Remove the screws which secure the end cap, and
are usually dependent upon each other. Adequate pressure
remove the end cap.
gauge equipment and a thorough understanding of the
operation of the complete hydraulic system are essential to
3. Slide the spool out of its bore from the end up, and
diagnosing improper valve operation.
remove the O-rings from the spool bore.
OVERHAUL
4. Screw out the plug which retains the relief valve and
GENERAL. Overhaul of this valve is limited to the replace-
remove the O-ring from the plug. Remove the spring and
ment of the relief valve assembly and seals. Replace the
relief valve.
complete valve when the required overhaul is beyond these
CLEANING, INSPECTION AND REPAIR. After the valve
limitations.
has been disassembled, perform the following:
During disassembly, particular attentions should be given to
identification and orientation of parts for reassembly. The
1. Discard all old O-rings. Wash all parts in a clean mineral
spool is selectively fitted to the valve body and must be
oil solvent and place them on a clean surface for inspection.
returned to the same body from which it was removed.
2. Carefully remove burrs by Iight stoning or lapping. Be
Figure 4D-2 is an exploded view of the valve showing the
certain that there is no paint on the mating surfaces of the
proper relationship of the parts for reassembly. Refer to
valve body. Check all parts for wear. Replace if necessary.
this figure while disassembling and reassembling the valve.
3. Inspect the valve spool and bore for burrs and scoring. If
scoring is not deep enough to cause objectionable Ieakage,
DISASSEMBLY. Disassemble the valve as follows:
the surfaces can be stoned or polished with crocus cloth. If
1. Be sure the valve is not subjected to pressure. Discon-
scoring is excessive the valve body and spool must be re-
4D-2
