Komatsu Galeo PC138US-8 Shop Manual page 216

SEN02550-01
Relief valve
When starting
The pressurized oil from the control valve is
q
fed from port (A) to port (C). As port (C) is con-
nected to the motor, the pressure drives the
motor to rotate.
When the hydraulic pressure at port (C)
q
exceeds the specified value, relief valve (1a) is
pushed up and the hydraulic oil is fed to port
(D).However, relief valve (1b) is kept closed
independent from the hydraulic pressure at
port (C).
The hydraulic oil is fed from port (C) to cham-
q
ber (E) through the oil passages of relief valve
(1a) and sleeve (2a). By this pressure, piston
(3) is moved to the right.
When piston (3) reaches its stroke end posi-
q
tion, the hydraulic pressure from relief valve
(1a) to chamber (E) increases. Therefore,
ports (C) and (D) are closed by relief valve
(1a).
The hydraulic pressure at port (C) at the inlet
q
side is controlled so that the motor is smoothly
started to rotate.
34
10 Structure, function and maintenance standard
When stopping
When the hydraulic oil from the control valve is
q
stopped, ports (A) and (C) are closed. At the
same time, ports (D) and (B) are closed, but
the motor continues to rotate by the inertia.
When the hydraulic pressure at port (D)
q
exceeds the specified value, relief valve (1b) is
pushed up and the hydraulic oil is fed to port
(C).The hydraulic pressure applied to port (D)
at the outlet side is fed to port (C) at the inlet
side, and it is used to prevent the oil cavitation.
The hydraulic oil from port (D) passes through
q
the oil passages of relief valve (1b) and sleeve
(2b), and sent to chamber (F). By this pres-
sure, piston (3) is moved to the left.
When piston (3) reaches its stroke end posi-
q
tion, the hydraulic pressure from relief valve
(1b) to chamber (F) increases. Therefore, ports
(D) and (C) are closed by relief valve (1b).
The hydraulic pressure at port (D) at the outlet
q
side is controlled so that the motor is smoothly
stopped.
PC138US, USLC-8