Hyundai r35z-7 Workshop Manual page 51

Boom down operation
When the boom down operation is carried out, the secondary pressure from the remote control
valve is applied to Pb8 port to change over the boom spool.
Since Pb8 port is connected to Pb8' port through the piping, the pressure is also applied to pb8' port
(Boom lock valve release port) to release the boom lock valve.
(For the explanation of boom lock valve operation, see pages 2-20, 21)
Since the bypass passage is shut off at the boom section after the spool changeover (some oil
flows through the orifice passage provided in the boom spool's bypass passage to the downstream
side of the bypass passage), the oil flowed from P1 port flows through the check valve provided
above the bypass passage in the travel section into the P1 side parallel passage.
Also, since a passage between B8 port and bridge passage is opened with the spool's notch after
the spool changeover, the oil flowed into the P1 side parallel passage flows through the load check
valve in the boom section into B8 port via the bridge passage and then into the rod side of the boom
cylinder.
On the other side, the oil returned from the head side of the boom cylinder flows into A9 port to the
tank passage that has been opened with the spool's notch after the spool changeover through the
boom lock valve that has been released by Pb8' port pressure. Then, the boom cylinder retracts to
lower the boom.
T1
T2
To bridge passage
in boom comp.
Oil flows from A9 port into
boom comp. via lock valve
P1
Boom
Boom lock
valve comp
To A9 port via
cylinder head side
Pb8'
Lock valve
release signal
Boom down operation
T2
B8
Some oil flows to downstream side
Some oil flows to downstream side
2-19
Spool changeover
direction
Dr1
P1
To cylinder rod side
via B8 port
R35Z72MCV14
Pb8