Hitachi ZW180 Technical Manual page 196

Control by Pump Control Pressure
Decreasing Flow
1. When the control lever stroke is reduced,
pressure difference (difference between pressure
Pi1 and Pi2) arising at the flow control valve in the
control valve is larger.
2. Pump control pressure Pi1 pushes spool 1 (3)
and spool 1 (3) moves toward the arrow.
3. Therefore, primary pilot pressure Pg is led to
servo piston 1 (10).
4. As there are two servo pistons 1 (10), swash plate
(11) tilts toward the flow decreasing direction.
5. Movement of swash plate (11) is transmitted to
sleeve 1 (2) through feedback lever link (13).
Sleeve 1 (2) moves toward the movement of
spool 1 (3).
6. Pilot primary pressure Pg to servo piston 1 (10) is
blocked when sleeve 1 (2) has moved the same
distance as spool 1 (3). Therefore, servo piston 1
(10) stops and the flow decrease is completed.
COMPONENT OPERATION / Pump Device
Flow (Q)
0
3
Pi1
ST
Pd1
10
1 - Spring
2 - Sleeve 1
3 - Spool 1
4 - Piston
Pd1 - Own Pump Pressure
ST - Torque Control
Pressure
T - Returning to Hydraulic
Oil Tank
T3-1-8
Pump Control Pressure (Pi1-Pi2)
2
Air
T
Vent
T
Decrease
Increase
Displacement Angle
10 - Servo Piston 1
11 - Swash Plate
12 - Servo Piston 2
13 - Feedback Lever Link
Pi1 - Pump Control
Pressure 1
Pi2 - Pump Control
Pressure 2
Pg - Primary Pilot Pressure
(From Pilot Pump)
1
4
Pi2
Pg
T
13
12
T4GB-03-01-006