Testing Parts Which Cause Hydraulic Drift Of Work Equipment - Komatsu PC130-7 Shop Manual

TESTING AND ADJUSTING
TESTING PARTS WHICH
CAUSE HYDRAULIC DRIFT OF
WORK EQUIPMENT
a If the work equipment (cylinder) drifts hydrauli-
cally, check to see if the cause is on the cylinder
packing side or control valve side or hydraulic
drift prevention valve side (if equipped) accord-
ing to the following procedure.
1. Testing boom cylinder and bucket cylinder
1) Set the machine in the position of measuring
hydraulic drift and stop the engine.
a Fill the bucket with a rated load or with
dirt and sand.
2) When testing the boom cylinder, set the
boom control lever in the RAISE position.
When testing the bucket cylinder, set the
bucket control lever in the CURL position.
• If 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 or hydraulic
drift prevention valve (if equipped) is
defective.
a Operate the control lever while the start-
ing switch is in the ON position.
a If the pressure in the accumulator is lost,
run the engine for about 10 seconds to
heighten the pressure in the accumula-
tor.
2. Testing arm cylinder
1) Stop the arm cylinder about 100 mm before
the IN stroke end and stop the engine.
PC130-7
TESTING PARTS WHICH CAUSE HYDRAULIC DRIFT OF
2) Operate the arm control lever in the IN posi-
tion.
• If 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 Operate the control lever while the start-
ing switch is in the ON position.
a If the pressure in the accumulator is lost,
run the engine for about 10 seconds to
heighten the pressure in the accumula-
tor.
[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 low-
ered.
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 unbal-
anced and the lowering speed is increased.
WORK EQUIPMENT
20-137
(1)