2-25
Arm out operation
T1
T2
P3
Arm
P3
To cylinder rod
side via A5 port
To B5 port via
cylinder head side
Spool changeover
direction
B5
A5
Travel
P2
P2
PTO
To bridge
passage
Pa5
R35Z72MCV20
Arm out operation
When the arm out operation is carried out, the secondary pressure from the remote control valve is
applied to Pa5 port to change over the arm spool.
Since the P2 side bypass passage is shut off at the arm section after the arm spool changeover, the
oil flowed from P2 port flows through the travel section and a passage between travel section and
arm section into the P2 side parallel passage.
Also, since the oil flowed from P3 port flows through the direction of dozer
Ą
boom swing
Ą
swing
section and then into the P2 side parallel passage via the check valve in the P3 supply section, the
connecting flow of P2 pump and P3 pump is supplied to the P2 side parallel passage. [Although the
P3 side bypass passage is also connected to the P1 side parallel passage through the check valve
in the P3 section, there is no oil flow into the P1 side as long as the P1 side sections (boom ,
bucket) are not operated.]
Since a passage between A5 port and the bridge passage is opened after the spool changeover,
the oil flowed into the P2 side parallel passage flows through the load check valve in the arm section
into A5 port via the bridge passage and then into the rod side of the arm cylinder.
On the other hand, the oil returned from the head side of the arm cylinder flows into B5 port to the
tank passage that has opened after the spool changeover. Then, the arm cylinder retracts to make
the arm out.
