Komatsu PC500LC-10R, Shop Manual, Page: 357 / 758

During downhill travel
1.
If the machine is going out of control on a downhill, the
motor runs idle and the pressure on the motor inlet side
decreases.
2.
The pressure in chamber (S1) decreases through orifices
(E1) and (E2).
3.
When the pressure in chamber (S1) decreases lower than
the spool selector pressure, the spool (14) is pushed back
to the left by the reaction force of spring (15), and the port
(MB) on the outlet side is throttled.
4.
The pressure on the motor outlet side increases and rotat-
ing resistance is generated in the motor, thus the machine
is prevented from going out of control.
5.
The spool (14) moves to a position where the force caused
by the machine weight and the hydraulic force on the mo-
tor inlet side are balanced with the pressure of motor outlet
port (MB).
6.
The motor outlet circuit is throttled and the machine travels
at speed corresponding to the pump discharged volume.
SAFETY VALVE OF TRAVEL MOTOR
SPECIFICATIONS OF SAFETY VALVE OF TRAVEL MOTOR
High pressure set pressure (when starting travel): 40.2 MPa {410 kg/cm
2
}
Low pressure set pressure (when stopping travel): 27.5 MPa {280 kg/cm
2
}
FUNCTION OF SAFETY VALVE OF TRAVEL MOTOR
3: Safety valve
When the machine stops travel (or travels downhill), the outlet
and inlet circuits of the motor are closed. Since the motor is
turned by inertial force, the pressure on the motor outlet side
increases abnormally, and the motor or piping may be dam-
aged. The safety valve releases this abnormal pressure into
the motor inlet side to protect the devices from damage.
AEP20519
10 STRUCTURE AND FUNCTION COMPONENT PARTS OF TRAVEL SYSTEM
PC500LC-10R 10-263