2-17
BOOM OPERATION
Boom up operation
When the boom up operation is carried out, the secondary pressure from the remote control valve is
applied to Pa8 port to change over the boom spool. Since Pa8 port is connected to boom up port
through the piping, the pressure oil supplied to boom up port changes over the connecting spool
through the connecting piston in the P3 supply section
Also, since the P1 side bypass passage is shut off at the boom section after the boom spool
changeover, 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.
On the other side, after the connecting spool changeover the oil flowed into P3 port.
Η
Flows through the internal passage in connecting spool and the check valve in the P3 supply
section into the P1 side parallel passage.
Θ
The oil flows through the P3 side parallel passage and P3 side bypass passage and then:
Flows through the check valve in the P3 supply section into the P1 side parallel passage.
Some oil flows through the orifice passage provided in the connecting spool and the check valve
in the P3 supply section into the P2 side parallel passage.
The oil flowed into the P1 side parallel passage is connected with the oil from P1 pump.
The oil flowed into the P2 side parallel passage flows through the bypass passages in the arm
section and PTO section to the tank passage.
Since the passage connected to the boom lock valve and the bridge passage are opened after the
boom spool changeover, the oil flowed into the P1 side parallel passage flows through the load
check valve in the boom section and the bridge passage into the boom lock valve section
The oil flowed into the boom lock valve section opens the lock valve (free flow condition), flows into
A9 port, and the to the head side of the boom cylinder.
On the other hand, the oil returned from the rod side of the boom cylinder flows into B8 port to the
tank passage that has opened with the spool's notch after the spool changeover. Then, the boom
cylinder extends to raise the boom.
3
3
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a.
b.
