Komatsu PC88MR-10 Shop Manual page 960

40 Troubleshooting
Troubleshooting of hydraulic and mechanical system (H-
mode)
No. Cause
Malfunction of boom
control valve (pressure
7
compensation valve)
(boom LOWER side)
Malfunction of boom
control valve (safety
8
valve for lock valve)
Malfunction of boom
control valve (lock
9
valve)
Malfunction of boom
control valve (suction
10
valve) (boom RAISE
side)
Malfunction of boom
control valve (suction-
11
safety valve) (boom
LOWER side)
40-472
Procedure, measuring location, criteria, and remarks
a Be ready with engine stopped, then perform troubleshooting with engine at
high idle.
Boom relief pressure
a Check hydraulic drift of boom cylinder with engine stopped.
Hydraulic oil temperature: Within
operating range, arm cylinder fully
Hydraulic drift
a Check whether boom cylinder moves slowly when performing hydraulic
relief of other work equipment. (If boom cylinder moves, it is abnormal.)
a If any failure is found in either of above check items, interchange pressure
compensation valves on RAISE and LOWER sides, and check whether
failure symptom changes.
(Pressure compensation valves have different area ratio, so be sure to
return them to their original positions after test.)
a Be ready with engine stopped, then perform troubleshooting with engine at
high idle.
Boom RAISE hydraulic relief, arm
Boom relief pressure
and arm relief IN hydraulic relief, or arm OUT
pressure
a Among above relief pressures, if arm IN relief pressure and boom RAISE
relief pressure are low, safety valve may be defective. Check safety valve
for damaged sealing material.
a When disassembling the safety valve, replace the safety valve assembly
with a new one since its relief pressure cannot be adjusted on the
machine.
Check that pilot piston and poppet are seated on body in position (they are
not stuck halfway).
Check for stuck or seized pilot piston and poppet in lock valve body (pilot
piston and poppet must move smoothly).
Remove pilot piston and poppet from valve body and check them for
defects and dirt.
Check poppet spring for fatigue and deformation.
Take care not to let foreign matter enter valve when re-installing spool.
a Be ready with engine stopped, then perform troubleshooting with engine at
high idle.
Boom relief pressure
a Among above relief pressures, if only boom RAISE relief pressure is low,
suction valve may be defective. Check it.
Check that check valve is seated on valve body in position (it is not stuck
halfway).
Remove check valve from valve body and check it for defects and dirt.
Check spring for fatigue and deformation.
Take care not to let foreign matter enter valve when re-installing spool.
a Be ready with engine stopped, then perform troubleshooting with engine at
high idle.
Boom relief pressure
a If boom LOWER relief pressure is low, suction-safety valve may be
defective.
Boom LOWER hydraulic relief
extended, machine raised off
ground
hydraulic relief
Boom RAISE hydraulic relief
Boom LOWER hydraulic relief
26.5 ± 1.5 MPa
{270 ± 15 kg/cm 2 }
If visible hydraulic
drift is observed, it is
abnormal.
26.5 ± 1.5 MPa
{270 ± 15 kg/cm
2 }
26.5 ± 1.5 MPa
{270 ± 15 kg/cm 2 }
26.5 ± 1.5 MPa
{270 ± 15 kg/cm 2 }
PC88MR-10