IV-54
HYDRAULIC UNITS
CONTROL VALVE
TROUBLESHOOTING
The following items are a list of all the problems
that might occur individually, but in actual practice,
2 or 3 of these problems might occur simultaneously
Symptom Probable Causes Remedy
Oil leaks from spool
seal.
• Seal is scratched or the seal lip is worn
due to long use.
• Spool·s seal sliding portion was dam
-
aged by some external cause (bruise,
scratch, etc.).
• Seal bulged out and the cover was in
-
stalled in a warped state.
• Paint adhered to the sliding portion of
the spool·s seal portion during painting.
• Tank circuit·s pressure became high and
exceeded the pressure level that the seal
was capable of withstanding.
• Replace with a new part.
• Repair or replace the spool.
• Return to the correct shape and check
for eccentric wear of the seal lip.
• Remove paint with paint thinner or re
-
move it mechanically. However, at this
time, be careful not to damage the spool
surface or the seal lip.
• Eliminate the factors causing excessive
flow resistance.
Spool·s sliding is not
smooth.
• Foreign matter is biting into the spool·s
sliding surface.
• Oil film between the spool and body
disappears due to abnormally high oil
temperature.
• Lubrication is improper due to deterio-
rating oil.
• Spool is worn from long use or due to
pressure bearing on one side only.
• Spool is bent from externally applied
pressure.
• Entire valve is strained due to strain in
the installation face.
• Valve was used at a pressure or a flow
volume which was out of specification.
• Bolts used to assemble the valve were
tightened excessively.
• Oil is accumulating in the cover (the
side with a spring or a detent) opposite
the side where the spool operates.
• Overhaul and repair or replace.
• Use some method to lower the oil tem-
perature or if the relief valve is operat-
ing frequently, investigate the cause and
reduce the frequency.
• This could be alleviated by simply
replacing the hydraulic oil, or it could
require an overhaul of the circuit.
• Check the spool·s diameter and consider
the necessity of replacement.
• Check the spool·s straightness and other
factors, then repair or replace.
• Loosen the installation bolts, then cut the
installation face and edge and check.
• In the case of pressure, check with a
pressure gauge. In the case of flow vol-
ume, check by the actuator·s speed of
movement and the capacity.
• Check if the assembly bolts are tight
-
ened to the specified torque. If the torque
deviates markedly from the specified
torque, tighten them again.
• The spool is leaking oil, so when the
spool moves, oil leaks from the cover.
After confi
rming this, replace the seal.
Cylinder drops while
shifting to a lift opera-
tion.
• Foreign matter is biting into the load
check valve seat or lar
ge scratches were
made by foreign matter biting into the
valve·s seat previously.
• Disassemble and check, then overhaul
or replace.
to compound the trouble. It is therefore desirable to
proceed so that the causes can be eliminated one at
a time.
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