Komatsu Galeo PC138US-8 Shop Manual page 214

SEN02550-01
Brake valve
Operation when pressure oil is supplied
When the travel lever is operated, the pressur-
q
ized oil from the control valve is fed to port (A)
and check valve (1) is opened. The oil is fur-
ther sent from port (C) to port (D) through the
motor.
At the same time, when the pressure of the
q
hydraulic oil that entered in chamber (G)
through orifice (f) exceeds spring (3) reaction
force, counterbalance valve (2) moves to the
right, opening ports (D) and (B), and the motor
becomes ready to rotate.
As ports (A) and (E) also open, parking brake
q
piston (4) is pressed down by the hydraulic
pressure. This releases the parking brake and
the motor starts to rotate.
32
10 Structure, function and maintenance standard
Operation when pressure is shut off
When the travel lever is returned to its neutral
q
position, the hydraulic oil circuit from the con-
trol valve is closed. And counterbalance valve
(2) starts to return to the left by spring (3) reac-
tion force.
The hydraulic oil in chamber (G) tends to flow
q
to port (A) through orifice (f). However, the
back pressure is generated by closing of orifice
(f), controlling the return speed of counterbal-
ance valve (2) to the right.
The motor tends to rotate by inertia even when
q
the hydraulic oil from the control valve is
stopped.During this time, the oil return circuit is
gradually closed by controlling the movement
speed of counterbalance valve (2) and by
using its cutout portion. By this, the motor is
smoothly stopped.
PC138US, USLC-8