Isolating The Parts Causing Hydraulic Drift In Work Equipment - Komatsu PC88MR-10 Shop Manual

30 Testing and adjusting
Hydraulic system

Isolating the parts causing hydraulic drift in work equipment

a If the work equipment (cylinder) drifts
hydraulically, perform check to see if the
problem is in the cylinder seal or control valve
according to the following procedure.
Testing
(PC88MR-L410-360-K-00-A)
1. Testing boom cylinder and bucket cylinder
1) Stop the engine with the same posture as the
hydraulic drift measurement.
a Apply rated load to the bucket inside or fill
the bucket with soil or sand.
2) For boom, move the boom control lever to
"RAISE" side. For bucket, move the bucket
control lever to "CURL" side for judgment.
When the lowering speed is increased at
this time, the cylinder packing is
defective.
If the lowering speed does not change at
this time, the control valve is defective.
a The control lever can be operated when
the starting switch is set to ON position.
a If the accumulator pressure is reduced,
run the engine for approximately 10
seconds to accumulate the pressure.
2. Testing arm cylinder
1) Operate the arm control lever to IN, and stop
the engine at the time when the arm cylinder
extends to approximately 100mm front of the
stroke end.
30-58
2) Operate the arm control lever to IN again to
determine the test results.
When the lowering speed is increased at
this time, the cylinder packing is
defective.
If the lowering speed does not change at
this time, the control valve is defective.
a The control lever can be operated when
the starting switch is set to ON position.
a If the accumulator pressure is reduced,
run the engine for approximately 10
seconds to accumulate the pressure.
[Reference] Reasons why the lowering speed is
increased by the above operation when the
cylinder packing causes the hydraulic drift:
1) When the machine is set in the above
posture (where the holding pressure is
applied to the bottom side), the oil leaks from
the bottom side to the head side. Since the
volume on the head side is less than that on
the bottom side by the volume of the rod, the
pressure in the head side is increased by the
oil flowing in from the bottom side.
2) As the internal pressure on the head side
increases, both pressures come to balance
at a certain level of pressure (depending on
leakage), and the lowering speed becomes
slower.
3) If the circuit on the head side is opened to
the drain circuit by the above operation of the
lever (the bottom side is closed by the check
valve at this time), the oil in the head side
flows in the drain circuit. As a result, the
pressure is imbalanced and the lowering
speed is increased.
3. Testing PPC valve
Test the lowering volume of the work equipment
when the work equipment lock lever is set to the
LOCK position and FREE position with the
pressure accumulated in the accumulator.
a The control lever can be operated when the
starting switch is set to ON position.
a If the accumulator pressure is reduced, run
the engine for approximately 10 seconds to
accumulate the pressure.
a In case of a difference of lowering volume
between the LOCK and FREE positions, the
PPC valve is defective (internal defect).
(ALL-L410-001-K-00-A)
PC88MR-10