2-26
PTO OPERATION
7)
PTO operation
T1
T2
P3
Arm
P3
To actuator
via A4 port
To B4 port via
actuator
Spool changeover
direction
B4
A4
Travel
P2
P2
PTO
To bridge passage
in PTO comp.
Pa4
R35Z72MCV21
For the PTO operation, both Pa pressurization and Pb pressurization are the same on operation so
that only Pa pressurization is explained as follows.
When the PTO operation (Pa4 pressurization) is carried out, the secondary pressure from the
remote control valve is applied to Pa4 port to change over the PTO spool. Since the P2 side bypass
passage is shut off at the PTO section after the PTO 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 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 A4 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 PTO
section into A4 port via the bridge passage and then into the actuator for PTO.
On the other hand, the oil returned from actuator for PTO flows into B4 port to the tank passage that
has opened after the spool changeover.
