Negative Control Valve - Hitachi ZW180 Technical Manual

NEGATIVE CONTROL VALVE

The control valve has a built-in negative control valve.
The negative control valve controls delivery flow of the
main pump by flow rate control pressure (Pc1 and
Pc2).
Operation
•
In Neutral
Pressure oil through the control valve neutral
circuit with the control valve in neutral position is
supplied as pilot pressure for controlling the pump
delivery flow from the front and rear of the orifice
of the negative control valve installed at the outlet
of the control valve.
At this time, spool B moves to the left as the
differential pressure occurs between Pc1 and Pc2.
Therefore, pilot pressure (PS2) enters the large
diameter chamber in the servo piston through
spool B and spool A. Pilot pressure (PS2) also
enters the small diameter chamber in the servo
piston. As the large diameter chamber is larger
than the small diameter chamber, the servo piston
moves to the right and the pump delivery flow is
reduced.
•
In Operation
During operation of the lift arm and the bucket,
pressure oil is not supplied to Pc1 and Pc2.
At this time, as the differential pressure between
Pc1 and Pc2 disappers, the regulator in the main
pump is in neutral and the delivery flow is not
restricted (the pump delivery flow increases).
COMPONENT OPERATION / Control Valve
Pc2
Pc1
Neutral
Circuit
Large Diameter
T3-2-20
Negative
Control Valve
Orifice
Main Pump
Servo Piston
Chamber
Spool A
Spool B
Small Diameter
Chamber
Pilot Pressure
(PS2)
T4GB-03-02-015