Komatsu PC500LC-10R Shop Manual page 217

10 STRUCTURE AND FUNCTION
Pump discharged volume is increasing.
11. As servo piston (9) moves, the springs (4) and (6) expand, and the reaction force decreases.
12. When the reaction forces of the springs decrease, spool (3) moves to the right, port (C) is disconnected
from port (D), and pump discharged pressure port (B) is connected to port (C).
13. Since the pressure in port (C) and the pressure at the large diameter side of the piston increase, the servo
piston (9) stops moving to the left.
14. The stop position (= pump discharged volume) of servo piston (9) is determined by the position where the
thrust caused by pressures (PP1) and (PP2) applied to spool (3) is balanced with the thrust of PC-EPC
valve solenoid and forces of springs (4) and (6).
When the pump controller is normal, the actuator load is large, and the pump
pressures (PP1) and (PP2) are high
1.
When the load is high and pump discharged pressures (PP1) and (PP2) are high, the force pushing spool
(3) to the right increases and spool (3) is positioned as shown in the previous figure.
2.
The pressure which flows from the port (C) to the LS valve becomes a half of the pump pressure (PP2)
since a part of the pressure from the port (B) flows from the port (C) through the LS valve and the port (D)
as shown in the previous figure.
3.
When spool (3) moves to the left, the opening of ports (C) and (D) expands.
4.
The pressure (= J) in port (C) decreases and the servo piston (9) stops moving to the right.
PC500LC-10R
COMPONENT PARTS OF HYDRAULIC SYSTEM
AEP19359
10-123