Hitachi ZW180 Technical Manual page 202

Increasing Flow
1. When the pump load is reduced, own pump
pressure Pd1 lowers. (Pump control pressure (Pi1
- Pi2) remains lowered during an operation.)
2. Load piston (5) and spool 2 (6) are pushed by
inner spring (8) and outer spring (9), and spool 2
(6) moves toward the arrow.
3. Therefore, the circuit of servo piston 1 (10) is
connected to the hydraulic oil tank.
4. As primary pilot pressure Pg is always applied to
servo piston 2 (12), swash plate (11) tilts toward
the flow rate increasing 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. When sleeve 2 (7) has moved the same distance
as spool 2 (6), the openings of spool 2 (6) and
sleeve 2 (7) close, servo piston 1 (10) is not
connected to the hydraulic oil tank. Therefore,
servo piston 1 (10) stops and the flow increase is
completed.
COMPONENT OPERATION / Pump Device
Flow (Q)
0
Pi1
ST
Pd1
7
5
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
T3-1-14
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