Komatsu PC600LC-7 Manual page 132

STRUCTURE, FUNCTION AND MAINTENANCE STANDARD
BRAKE VALVE
Operation of brake valve
• The brake valve consists of a check valve, coun-
terbalance valve, and safety valve in a circuit as
shown in the diagram on the right.
• The function and operation of each component is
as given below.
1. Counterbalance valve, check valve
Function
• When traveling downhill, the weight of the ma-
chine makes it try to travel faster than the speed
of the motor.
As a result, if the machine travels with the engine
at low speed, the motor will rotate without load
and the machine will run away, which is extreme-
ly dangerous.
To prevent this, these valves act to make the ma-
chine travel according to the engine speed
(pump discharge amount).
Operation when pressurized oil is supplied
• When the travel lever is operated, the pressu-
rized oil from the control valve is supplied to port
PA. It pushes open check valve (13A) and flows
from motor inlet port MA to motor outlet port MB.
However, the motor outlet port is closed by check
valve (13B) and spool (14), so the pressure at
the supply side rises.
• The pressurized oil at the supply side flows from
orifice E1 in spool (14) and orifice E2 in the pis-
ton to chamber S1. When the pressure in cham-
ber S1 goes above the spool switching pressure,
spool (14) is pushed to the right.
As a result, port MB and port PB are connected,
the outlet port side of the motor is opened, and
the motor starts to rotate.
10-100
TRAVEL MOTOR
PC600, 600LC-7