Komatsu PC200-8M0 Shop Manual page 179

402 Hydraulic system, Part 2
Functions and operation by valve
When load pressure (P2) is low
a When all control levers are in NEUTRAL posi-
tion, or when load pressure (A2) is lower than
output pressure (PR) of the self-pressure
reducing valve
q Force of spring (8) and the force exerted by the
pressure (PR) (0 MPa {0 kg/cm
engine is stopped), are applied to valve (7) in
the direction to disconnect the circuit ports (P2)
and (A2).
When the pressurized oil flows in from port
q
(P2), valve (7) balances at a position where
[Force (Area fd x Pressure P2) = Force of
spring (8) + Force (Area fd x Pressure PR)]
holds.
q The opening of valve (7) is adjusted so that
pressure (P2) remains at a constant level
higher than pressure (PR).
q When pressure (PR) rises above the set pres-
sure, poppet (11) opens.
q The pressurized oil flows from port (PR) to ori-
fice (a) in spool (14), then flows to seal drain
port (TS) from the opening of poppet (11).
q Differential pressure generated across orifice
(a) in spool (14) moves spool (14) in the direc-
tion that the spool closes the opening between
ports (P2) and (PR).
q Pressure (P2) is reduced to a constant pres-
sure (the set pressure) by the opening and
supplied for use as pressure (PR).
PC200, 200LC, 220, 220LC-8M0
When load pressure (P2) is high
As load pressure (A2) increases with the dig-
q
ging operation, etc, the pump discharge
increases accordingly.
Pressure (P2) increases, and [Force (Area fd
q
x Pressure P2] becomes larger than [Force of
spring (8) + Force (Area fd x Pressure PR)].
2
}, when As a result, valve (7) moves fully to the right.
Since the area of the opening between ports
q
(P2) and (A2) increases, the passage resis-
tance reduces, reducing the engine horse-
power loss.
q When pressure (PR) rises above the set pres-
sure, poppet (11) opens.
q The pressurized oil flows from port (PR) to ori-
fice (a) in spool (14), then flows to seal drain
port (TS) from the opening of poppet (11).
q Differential pressure generated across orifice
(a) in spool (14) moves spool (14) in the direc-
tion that the spool closes the opening between
ports (P2) and (PR).
q Pressure (P2) is reduced to a constant pres-
sure (the set pressure) by the opening and
supplied for use as pressure (PR).
SEN06120-00
37
10-402