Komatsu ecot3 PC300LC-8 Shop Manual page 395

30 Testing and adjusting
2] If the internal pressure of the head end
increases, the pressure at the bottom end
also rises in proportion to this and
balanced at certain level (this level
depends on the volume of leakage). As
the pressure is balanced, the drifting
speed is decreased.
3] 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 move-
ment becomes faster.
3. Inspection of boom lock valve
1) Set the work equipment at the maximum
reach and the boom top horizontal. Then
stop the engine.
k
Lock the work equipment control le-
vers and release the pressure inside
the hydraulic tank.
k
Do not allow anyone to come under the
work equipment during the work.
2) Disconnect drain hose (1) of the control
valve, and install an oil stopper plug in the
hose.
q Oil stopper plug: 07376-70210
a Leave the control valve end open.
a If oil leaks out the opened port accompa-
nying hydraulic drift of the work equip-
ment, failure on the boom lock valve
should be suspected (loose contact).
PC300, 350-8
4. Inspection of PPC valve
Measure the amount of hydraulic drift of the work
equipment when the accumulator is charged
with pressure and the lock lever is put to the
LOCK and FREE positions.
a Operate the control lever with the engine
starting switch in the ON position.
a If pressure in the accumulator has dropped,
run the engine for approx. 10 seconds to
charge the accumulator again.
a If the lock and free position cause any differ-
ence in the hydraulic drift volume, the PPC
valve is defective (internal failure).
SEN02625-06
55