Hyundai r35z-7 Workshop Manual page 64

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COMBINED CONTROL OPERATION
Boom up + Arm in + bucket
When the above combined control is carried out, the secondary pressure from the remote control
valve is applied to each spool to change over them. Since the secondary pressure for arm in
operation is also applied to the pilot chamber on the connecting section spring chamber side
according to the piping, the connecting spool operates against the secondary pressure developed
from boom up operation and arm in operation.
(Boom up operation secondary pressure - Arm in operation secondary pressure =
connecting spool changeover pressure)
When all the above combined operations are carried out in full lever operation (full changeover), the
oil supplied from P1 pump is supplied to the boom and bucket and the oil from P2 pump to the arm.
Since the connecting spool changeover pressure becomes "0" as mentioned above, the connecting
spool cannot change over and the oil from P3 pump flows to the P1 and P2 side parallel passages
through the connecting section. Accordingly, much oil flows to the arm side normally because of its
low working load.
In this condition, since gradually restricting the arm in operation (returning the lever) causes the
secondary pressure for arm in operation to decrease, the connecting spool changeover pressure to
increase, the connecting spool to start changing over, and the passage to the arm side to be
narrowed, the oil supplied from P3 pump flows abundantly into the P1 side (Boom, bucket).
As mentioned above, the oil supplied from P3 pump flows suitably into each attachment according
to the control input during the above combined control, resulting in a well-balanced and efficient
working speed.
Besides, since the oil flow to the bucket whose working load is less than the boom is restricted with
an orifice (the orifice of boom priority) provided before the bucket section in the P1 side parallel
passage, much oil flows into the boom section. As a result, the working speed balance between
both attachments is maintained during the combined operation of boom and bucket.
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