TROUBLESHOOTING
CONTROL VALVE
1
5
CONTROL VALVE 5J0AQ00
CONTROL VALVE
“4. Disassembly and assembly, Control valve”
The problems are listed individually in the table below, but in reality, many problems have multiple causes. Therefore,
try to check and eliminate each possible cause one at a time.
Symptoms Major causes Remedies
Oil leak from the spool
seal
• Flaw is on the sealing part or the seal lip
is worn out due to prolonged use.
• Replace with a new one.
• Flaw (e.g., dents or scratches) on the
sliding part of the spool seal is caused
by an external factor.
• Repair or replace the spool.
• The lid that is pushing the sealing parts
in place is installed improperly (lid is
distorted)
• Correct the lid, and determine the partial
wear degree of the seal.
• Old paint remains on the seal sliding
part of the spool.
• Remove it by using thinner or mechanical
force. When removing, take care not to
damage the spool surface or the seal lip.
• Tank pressure becomes too high for the
performance of the sealing material.
• Remove the cause of the flow resistance.
Sliding part of the spool is
not smooth
• Foreign matter is caught in the sliding
part of the spool.
• Overhaul and repair or replace.
• Oil film between the spool and the body
becomes too thin due to the increased
oil temperature.
• Try to decrease the oil temperature. If the
relief valve is started often, find the cause
and correct it.
• Lubrication is disabled due to deterio-
rated oil.
• Oil should be replaced. The circuit also
should be overhauled in some cases.
• Spool is worn out because of prolonged
use or of the unbalanced force applied.
• Replace the spool and the valve block as-
sembly.
• Spool is bent by the external force. • Check for the straightness of the spool, and
repair or replace.
• Whole valve is distorted due to the dis-
tortion of the installation surface.
• Check the distortion, independent of the in-
stallation surface (loosening the bolts will
help).
• Valve is operated with the pressure or
the flow rate of out-of-spec.
• For pressure, measure it with a pressure
gauge. For flow rate, determine it by finding
out the movement speed and capacity of
the actuator.
• Fixing bolts are over-tightened. • Check if the fixing bolts are tightened with
the specified torque. If not, tighten them
again with the specified torque.
• Oil stays in the lid (spring or detent) op-
posite to the spool operation.
• Oil may come out from the lid, if it is leaking
in the seal of the spool. If that is the case,
replace the seal.
When the actuator is be-
ing raised, it drops once
• Foreign matter is caught in the seat on
the load check valve, or the seat is
damaged by large foreign matter.
• Disassemble the valve and overhaul or re-
place the faulty part(s).
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