Hitachi ZW180 Technical Manual page 138

Brake Circuit
Service Brake Circuit
(Refer to the COMPONENT
Charging Block group.)
(Refer to the COMPONENT OPERATION / Brake
Valve group.)
•
Pressure oil from the pilot pump flows through the
charging block, and is accumulated in the service
brake accumulators.
•
By stepping the brake pedal, pressure in the
service brake accumulators is applied to the front
brake and the rear brake through the brake valve,
and actuates the service brake.
•
When the brake pedal is stepped several times,
pressure inside the service brake accumulators is
lowered, and the relief valve is closed.
•
The priority valve spool moves rightward, and
pressure in the service brake accumulators is
kept constant by preferentially supplying pressure
oil from the pilot pump to the service brake circuit,
and firmly brakes the vihicle.
NOTE: The spring of the priority valve is adjusted
so that the priority valve is not completely
closed. Although the priority valve is closed
completely, a certain amount of pressure oil
is being
downstream.
NOTE: Although the engine is stopped, the service
brake circuit pressure is retained for a while
due to the functions of the service brake
accumulators and the check valve.
SYSTEM / Hydraulic System
OPERATION
supplied to the
Parking Brake Circuit
•
/ Pressure oil from the pilot pump is applied to the
parking brake solenoid valve in the charging
block.
•
When the parking brake is turned OFF, the
parking brake solenoid valve is excited, and
pressure oil entering the parking brake cylinder
releases the parking brake.
•
If the parking barke is turned ON, the parking
brake solenoid valve is unexcited, and pressure
oil stops supplying to the parking brake. Therefore
the parking brake is applied.
•
Although pressure is lowered caused by damage
of hose or something in the upstream of the
parking brake solenoid valve, pressure for parking
brake circuit is maintained for a while by the pilot
accumulator.
NOTE: The parking brake is released when the
circuits
T2-3-22
solenoid valve is excited.