Komatsu Galeo PC138US-8 Shop Manual page 162

SEN02549-02
Introduction of LS pressure
1. Work equipment valve
Function
The LS pressure is the actuator load pressure
q
at the outlet port end of the control valve.
Actually, pump discharge pressure (PP) is
q
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).
In the travel valve, actuator circuit pressure (A)
q
is directly introduced to LS circuit (PLS).
Operation
When spool (1) is operated, pump discharge
q
pressure (PP) flows from flow control valve (2)
through notch (a) in the spool and bridge pas-
sage (b) to actuator circuit (A).
At the same time, reducing valve (3) also
q
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).
28
10 Structure, function and maintenance standard
When this happens, LS circuit (PLS) is con-
q
nected to tank circuit (T) from LS bypass valve
(4) (See the section on the LS bypass valve).
The areas at both ends of reducing valve (3)
q
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.
As a result, reducing valve (3) is balanced at a
q
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).
PC138US, USLC-8