Priority Valve - Hitachi ZW180 Technical Manual

PRIORITY VALVE

(Refer to the Main Curcuit in the SYSTEM /
Hydraulic System group.)
The main pump has a built-in priority valve.
The priority valve is installed for effectively distributing
the main pump delivery oil to the steering valve and
the control valve.
Operation
1. Before Steering Operation
Pressure oil from the main pump flows to the
steering valve through port CF. Pressure oil flows
to the both ends of the priority valve spool as port
CF is blocked.
As pressure oil on one end of the spool flows from
port LS to the hydraulic oil tank through the
steering valve, pressure is lowered. The spool to
both ends of which different pressures are applied
overcomes spring force and moves toward port
LS, Therefore, the majority of the main pump
pressure oil flows to the control valve through port
EF.
2. During Steering Operation
If the steering is operated and the steering valve
spool moves, pressure at port LS rise in response
to the movement of the steering valve spool. The
spool is pushed up by pressure at port LS and the
spring force. Therefore, the main pump pressure
oil flows to both port EF and port CF. When the
steering valve spool moves to the maximum
stroke, the majority of the main pump pressure oil
flows to the steering valve through port CF.
COMPONENT OPERATION / Pump Device
Before Steering Operation
To Steering Valve
To Control Valve
During Steering Operation
To Steering Valve
To Control Valve
T3-1-18
Port
CF
Port
EF
Port LS
To Hydraulic
Oil Tank
Port
CF
Port
EF
Port LS
From Main Pump
Spool
Spring
T4GB-03-01-018
From Main Pump
Spool
Spring
T4GB-03-01-019