Hitachi ZW180 Technical Manual page 200

Control by Own Pump Pressure
Decreasing Flow
1. When load is applied to the pump due to any
operation, own pump pressure Pd1 rises. (Pump
control pressure (Pi1 - Pi2) remains lowered
during an operation.)
2. Load piston (5) pushes spool 2 (6), inner spring
(8) and outer spring (9), and spool 2 (6) 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 2 (7) through feedback lever link (13).
Sleeve 2 (7) moves toward the movement of
spool 2 (6).
6. Primary pilot pressure Pg to servo piston 1 (10) is
blocked when sleeve 2 (7) has moved the same
distance as spool 2 (6). Therefore, servo piston 1
(10) stops and the flow decrease is completed.
COMPONENT OPERATION / Pump Device
Flow (Q)
0
Pi1
ST
Pd1
5 7
5 - Load Piston
6 - Spool 2
7 - Sleeve 2
8 - Inner Spring
9 - Outer Spring
Pd1 - Own Pump Pressure
ST - Pump Torque Control
Pressure
T - Returning to Hydraulic Oil
Tank
T3-1-12
Air
T Bleeding
T
6
10
Increase Decrease
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)
Pressure (P)
Pi2
Pg
T
8, 9
12
13
T4GB-03-01-006