Komatsu Galeo PC800-8 Shop Manual page 145

10 Structure, function and maintenance standard
Self pressure reducing valve
Function
• This valve reduces the discharge pressure of the
fan pump and supplies it as the control pressure
for the solenoid valve, EPC valve, etc.
Operation
1. When engine is stopped
• Since poppet (4) is pressed against the seat by
spring (3), the portion of the circuit from port (PR)
to port (T) is cut off.
• Since valve (6) is pressed to the left by spring (5),
the portion of the circuit from port (P3F) to port
(PR) is open.
• Since valve (1) is pressed to the left by spring (2),
the portion of the circuit from port (P3F) to port
(P3) is closed.
2. Fan pump discharge pressure (P3F)
is reduced
a When the load pressure (P3) is lower than out-
put pressure (PR) of self pressure reducing
valve
• Valve (1) receives the force of spring (2) and
pressure (PR) (which is {0 MPa {0 kg/cm
engine is stopped) in the direction to close the
circuit between ports (P3F) and (P3).
• As the pressurized oil flows in from port (P3F),
following balance is reached: [(φd area × P3F
pressure) = the force of spring (2) + (φd area ×
PR pressure)].
• Opening of valve (1) is adjusted to maintain pres-
sure (P3F) at a constant pressure above pres-
sure (PR).
• As (PR) pressure reaches a level higher than the
set pressure, poppet (4) opens.
• The pressurized oil flows from port (PR) to inter-
nal orifice (a) of spool (6) and then flows to tank
drain port (T) through the opening of poppet (4).
• The differential pressure is generated through in-
ternal orifice (a) of spool (6), actuating spool (6)
to close the opening from port (P3F) to (PR).
• Referencing the given open area, the self pres-
sure reducing valve reduces pressure (P3F) to a
specific level (set pressure) in order to supply the
difference as pressure (PR).
PC800, 850-8
2
} when
SEN00383-03
23