TESTING AND ADJUSTING
TESTING LOCATIONS CAUSING HYDRAULIC DRIFT OF WORK EQUIPMENT
TESTING LOCATIONS CAUSING
HYDRAULIC DRIFT OF WORK
EQUIPMENT
*
If there is any hydraulic drift in the work equipment
(cylinders), check as follows to determine if the cause
is in the cylinder packing or in the control valve.
1. Checking for defective cylinder packing
1) Checking boom and bucket cylinders
i) Set in the same posture as when measuring
hydraulic drift, and stop the engine.
ii) Operate the boom control lever to RAISE or
the bucket control lever to CURL.
l If the lowering speed increases, the pack-
ing is defective.
l If there is no change, the boom holding
valve (boom) or the control valve (bucket)
is defective.
2) Checking arm cylinder
0
ii)
Operate the arm cylinder to move the arm in
fully, then stop the engine.
Operate the control lever to arm IN.
l If the lowering speed increases, the pack-
ing is defective.
l If there is no change, the control valve is
defective.
* If the pressure in the accumulator has
dropped, run the engine for approx. IO
seconds to charge the accumulator again
before operating.
[Reference]
If the cause of the hydraulic drift is in the
packing, and the above operation is carried
out, the downward movement becomes
faster for the following reasons.
1) If the work equipment is set to the above posture
(holding pressure applied to the bottom end), the oil
at the bottom end leaks to the head end. However,
the volume at the head end is smaller that the volume
at the bottom end by the volume of the rod, so the
internal pressure at the head end increases because
of the oil flowing in from the bottom end.
2) When the internal pressure at the head end increases,
the pressure at the bottom end also rises in proportion
to this. The balance is maintained at a certain pres-
sure (this differs according to the amount of leakage)
by repeating this procedure.
3) When the pressure is balanced, the downward move-
ment becomes slower. If the lever is then operated
according to the procedure given above, the circuit at
the head end is opened to the drain circuit (the bottom
end is closed by the check valve), so the oil at the
head end flows to the drain circuit and the downward
movement becomes faster.
Boom, bucket checking posture
Y1?FRO26
Arm checking posture
20-56
a
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