Steering Main Relief Valve - Hitachi ZW180 Technical Manual

STEERING MAIN RELIEF VALVE

The main pump has a built-in steering main relief valve.
When the steering circuit pressure exceeds the set
pressure, pressure oil is returned to the hydarulic oil
tank through the main pump casing.
Operation
When the steering circuit pressure exceeds the set
pressure, the poppet is pushed toward the spring and
pressure oil is returned to the hydraulic oil tank
through the main pump casing.
NOTE: When the steering relief valve is operated,
the spool of the priority valve moves toward
port LS and the majority pressure oil from
the main pump flows to the control valve
through port EF. (Refer to T3-1-18.)
COMPONENT OPERATION / Pump Device
Before Operation
During Operation
To Main Pump
Casing
T3-1-20
Steering Circuit Pressure
Below Set Pressure
T4GB-03-01-020
Steering Circuit Pressure
Beyond Set Pressure
T4GB-03-01-021