Komatsu PC600LC-7 Manual page 87

STRUCTURE, FUNCTION AND MAINTENANCE STANDARD
4. NC valve
Function
• The NC valve controls the main pump discharge
amount to reduce the neutral loss and fine con-
trol loss according to the moving distance of the
control valve spool.
1) When control valve is at neutral
Operation
• When the control valve is at neutral, jet sensor
differential pressure (PT – PD) becomes the
maximum, and the force of jet sensor output
pressure PT pushing piston (10) becomes larger
than the total of the force of spring (12) and the
force of jet sensor output pressure PD pushing
the bottom of spool (11).
PC600, 600LC-7
HYDRAULIC PUMP (PISTON PUMP)
• The main pump discharge amount is controlled
by balance of the sum of jet sensor upstream
pressure PT and NC valve output pressure
PECN and the sum of the force of NC valve
spring (12) and jet sensor downstream pressure
PD.
• The jet sensor senses the flow of the oil returning
through the control valve to the tank and use it as
PT and PD of the NC valve.
• As a result, spool (11) is pushed down, so the
flow from port c to port b is throttled, and the area
of the opening of port b and port a (drain port) be-
comes larger. In this way, NC valve output pres-
sure PECN becomes the minimum, and the main
pump discharge amount also becomes the mini-
mum.
10-55