Komatsu PC130-8, Shop Manual

Page: 154 / 1043

SEN03774-01 10 Structure, function and maintenance standard
26
PC130-8
Introduction of LS pressure
1. Work equipment valve
Function
q
The LS pressure is the actuator load pressure
at the outlet port end of the control valve.
q
Actually, pump discharge pressure (PP) is
reduced by reducing valve (3) of the pressure
compensation valve to the same pressure as
actuator circuit pressure (A) and sent to LS cir-
cuit (PLS).
q
In the travel valve, actuator circuit pressure (A)
is directly introduced to LS circuit (PLS).
Operation
q
When spool (1) is operated, pump discharge
pressure (PP) flows from flow control valve (2)
through notch (a) in the spool and bridge pas-
sage (b) to actuator circuit (A).
q
At the same time, reducing valve (3) also
moves to the right, so pump discharge pres-
sure (PP) is reduced by the pressure loss at
notch (c). It goes to LS circuit (PLS), and then
goes to spring chamber (PLSS).
q
When this happens, LS circuit (PLS) is con-
nected to tank circuit (T) from LS bypass valve
(4) (See the section on the LS bypass valve).
q
The areas at both ends of reducing valve (3)
are the same [(SA) = (SLS)], and actuator cir-
cuit pressure (PA) acts on the (SA) end. The
reduced pump discharge pressure (PP) acts
on (SLS) at the other end.
q
As a result, reducing valve (3) is balanced at a
position where actuator circuit pressure (PA)
and the pressure of spring chamber (PLSS)
are the same. Pump discharge pressure (PP)
reduced at notch (c) becomes actuator pres-
sure (A) and is introduced into LS circuit (PLS).