SUB-SECTION 4D
CONTROL VALVES
TABLE 4D-5
TROUBLE, CAUSE AND REMEDY CHART
REMEDY
PROBABLE CAUSE
TROUBLE
Replace O-rings.
Defective O-rings in valve body.
Oil leaks at either end of spool.
Replace springs.
Broken springs.
Spring-centered spools do not re-
turn to neutral.
Clean system and valve.
Foreign particles.
Check linkage for binding condition.
Misalignment of operating linkage.
Repair, clean and readjust.
Relief valve not properly set, or
No motion, slow or jerky action of
stuck in base and/or worn.
hydraulic system.
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.
Remove relief valve and check
Smell particle of dirt plugging
No relief valve action (High
hole. If blocked, clear hole.
orifice in relief valve sub-
Pressure).
assembly.
Replace valve.
Oil by-passing between spool
Load will not hold.
and body.
Repair or replace cylinder.
Oil by-passing piston in cylinder.
Refer to above spool remedies.
Spool not centered.
Disassemble, clean and reassemble.
Dirt or foreign particles lodged
Load drops when spool is moved
between check valve poppet and
from neutral to a power position.
seat.
Replace poppet.
Scored or sticking check valve
poppet.
certain that there is no paint on mating surfaces of valve
2. Remove the screws which secure the end cap, and
body. Check all parts for wear. Replace if necessary.
remove the end cap.
3. Inspect the valve spool and bore for burrs and scoring. If
3. Slide the spool out of its bore from the end cap end, and
scoring is not deep enough to cause objectionable leakage,
remove the O-ring from the spool bore.
the surfaces can be stoned or polished with crocus cloth. If
4. Screw out the plug which retains the relief valve and
scoring is excessive the valve body and spool must be
remove the O-ring from the plug. Remove the spring and
replaced. Check the valve spool for freedom of movement
relief valve.
in the bore.
5. Remove the check valve plug, and remove the O-ring
4. Check the relief valve for smooth movement in its bore.
from the plug, Remove the spring and poppet from the
The valve should move by its own weight.
valve body.
ASSEMBLY. To assemble the valve, proceed as follows:
CLEANING, INSPECTION AND REPAIR. After the valve
NOTE
has been disassembled, perform the following:
Coat all parts with clean hydraulic oil to facilitate
1. Discard all oil O-rings. Wash all parts in a clean mineral
reassembly and provide initial lubrication. Petroleum
oil solvent and place them on a clean surface for inspection.
jelly can be used to hold O-rings in place during reas-
2. Carefully remove burrs by light stoning or lapping. Be
sembly.
4D-13
