Hitachi ZW180, Technical Manual

Page: 132 / 374

SYSTEM / Hydraulic System
T2-3-16
•
When the service brake accumulators are
pressurized to a certain amount, the relief valve
opens. As port A of the priority valve is connected
to the hydraulic oil tank, pressure is lost.
•
As pressure at port B of the priority valve is larger
force than the spring force, the priority valve spool
moves leftward. Therefore, all pressure oil from
the pilot pump is supplied to the priority valve and
the circuit downstream.
•
Pressure oil from the priority valve is supplied to
the respective pilot circuits through each port.
•
When pressure in the pilot circuit rises higher than
a certain amount, the pilot relief valve opens and
prevents components of the pilot circuit from
being damaged.
•
Pressure oil from port PS1 passes the steering
pilot valve and is supplied for actuation of the
steering valve spool. (Refer to Steering Circuit.)
•
Pressure oil from port X changes its flow in
response to the stroke of the pump torque
control solenoid valve which is controlled by the
signal from MC, and is used to control the main
pump regulator.
(Refer to Pump Control Circuit.)
•
Pressure oil from port BR3 is supplied for parking
brake release pressure by operation of the
parking brake solenoid valve. (Refer to Parking
Brake Circuit)
•
Pressure oil from port PS2 is supplied to control
the servo piston of the main pump (Refer to Pump
Control Circuit.), and the spool of the ride control
valve (Refer to Ride Control Circuit.).
•
Pressure oil from port PP enters each pilot valve
through the pilot shut-off valve, and is supplied to
the control valve for actuation of the spool. (Refer
to Front Attachment Operation Circuit.)