Maeda MK0003, Service Manual, Page: 109 / 348

2-81
8.5 FAILURE CAUSE AND COUNTERMEASURE
Abnormal Phenomenon Cause Remedy
Pressure cannot be raised to
the specified pressure.
･ Mounting bolts are not tightened with
the specified torque.
･ Unloaded without reaching the full
stroke.
･ Checking torque value
･ Refer to the description on “Does not
switch the magnetic switching valve
when excited”.
Does not switch the magnetic
switching valve when excited
･
Excitation voltage is excessively low, or
the circuit is open.
･
Pilot valve catches foreign matters.
･
Spool catches foreign matters.
･
Reducing valve set value has dropped.
･
Sequence valve set value has dropped.
･
Check the electrical system and repair as
required.
If the coil is broken, replace it.
･
Disassemble and repair or replace as
required.
･
Disassemble and repair or replace as
required.
･
Disassemble and repair or replace as
required.
･
Disassemble and repair or replace as
required.
Demagnetizing the magnetic
switching valve does not
return it to neutral.
･ Pilot valve catches foreign matters.
･
Spool catches foreign matters.
･ Disassemble and repair or replace as
required.
･
Disassemble and repair or replace as
required.
Although the magnetic
switching valve is not excited,
the valve is switched.
･
Failure in seat due to the pilot valve
catching foreign matters, or deformation
of the seat
･
Disassemble and repair or replace as
required.
Oil leakage from a spool seal
area
･
Damage of sealing part, or abrasion of
seal lip
･
Impact dents or scratch blemishes
found on the spool seal sliding area
･
Defective mounting of sealing part fitting
lid
･
The paint applied on the spool seal
sliding area is still sticking
･
Replacement
･
Repair or replace spool as required
･
Correction, or examination of uneven
abrasion degree of the seal lip
･
Remove the paint with a diluent
Spool sliding is not smooth.
･ Spool catches foreign matters.
･ Loss of oil film between the spool and
body due to an abnormal oil
temperature rise
･ Spool is unevenly abraded.
･ Failure in lubrication due to degradation
of hydraulic oil
･ The spool is bent.
･ Distortion of the entire valve body due to
defective mounting face.
･ Defects in external or operating area
･ Oil deposition on the lid on the other
side of spool
･ Disassemble and repair or replace as
required.
･ Lower the oil temperature, or replace it.
･ Replacement
･ Oil replacement (overhaul of the circuit)
･ After examining the straightness of spool,
repair or replace it as required.
･ Loosen the mounting bolts and check
and repair as required
･ Check links and levers followed by repair
as required
･ Leaking oil from spool seal is oozing out
from the air vent hole in the lid as the
spool is moved. After checking it, replace
the seal.
Flow rate cannot be
controlled smoothly.
･
Spool and piston catch foreign matters.
･
Orifice in the spool is clogged with
foreign matters.
･
Reducing valve catches foreign matters
and the set value has dropped.
･
The negative proportional reducing
valve catches foreign matters and
malfunctions.
･
Orifice in the spool is clogged with
foreign matters.
･
Disassemble and repair or replace as
required.
･
Disassemble and repair or replace as
required.
･
Disassemble and repair or replace as
required.
･
Disassemble and repair or replace as
required.
･
Disassemble and repair or replace as
required.
Acceleration control cannot
be performed smoothly.
･ Spool and piston catch foreign matters.
･ The proportional reducing valve catches
foreign matters and malfunctions.
･
Reducing valve catches foreign matters
and the set value has dropped.
･ Defects in external or operating area
･ Disassemble and repair or replace as
required.
･ Disassemble and repair or replace as
required.
･
Disassemble and repair or replace as
required.
･ Check links and levers followed by repair
as required