Komatsu Galeo PC138US-8, Руководство по ремонту, Страница: 370 / 946

SEN02458-01 30 Testing and adjusting
42
PC138US, USLC-8
Checking parts which cause
hydraulic drift of work equipment 1
a
If the work equipment (cylinder) drifts hydrauli-
cally, check to see if the cause is on the cylin-
d er pac k i ng s i d e or c on tr ol v al v e s id e
according to the following procedure.
1. Checking boom cylinder and bucket cylinder
1) Set the machine in the position for testing
hydraulic drift and stop the engine.
a
Fill the bucket with a rated load or
with dirt and sand.
2) When checking the boom cylinder, set the
boom control lever in the RAISE position.
When checking the bucket cylinder, set the
bucket control lever in the CURL position.
q
If the lowering speed is increased at this
time, the cylinder packing is defective.
q
If the lowering speed does not change at
this time, the control valve is defective.
a
Operate the control lever while the
starting switch is in the ON position.
a
If the pressure in the accumulator is
lost, run the engine for about 5 sec-
onds to heighten the pressure in the
accumulator.
2. Checking arm cylinder
1) Stop the arm cylinder about 100 mm before
the IN stroke end and stop the engine.
2) Operate the arm control lever in the IN
position.
q
If the lowering speed is increased at
this time, the cylinder packing is
defective.
q
If the lowering speed does not change
at this time, the control valve is defec-
tive.
a
Operate the control lever while the
starting switch is in the ON position.
a
If the pressure in the accumulator is
lost, run the engine for about 5 sec-
onds to heighten the pressure in the
accumulator.
[ Reference ]
Reason why the lowering speed is increased
by the above operation when the cylinder
packing is the cause of the hydraulic drift:
1) If the machine is set in the above position
(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 pressure in the head side is
increased, it is balanced at a certain level
(which depends on the leakage), and then
the lowering speed is lowered.
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 on the
head side flows in the drain circuit. As a
result, the pressure is unbalanced and the
lowering speed is increased.