Komatsu BR380JG-1E0, Shop Manual, Page: 148 / 841

10 Structure, function and maintenance standard SEN01353-00
BR380JG-1E0
5
Relief valve portion
Outline
q
The relief valve portion consists of check
valves (2) and (3), shuttle valves (4) and (5),
and relief valve (1).
Function
q
When the crusher is stopped, the outlet port
circuit of the motor from the control valve is
closed, but the motor continues to rotate under
inertia, so the pressure at the output side of the
motor becomes abnormally high, and this may
damage the motor.
To prevent this, the abnormally high pressure
oil is relieved to port (S) from the outlet port of
the motor (high-pressure side) to prevent any
damage.
Operation
1.
When starting crusher
q
When the crusher ON switch is pressed, the
pressure oil from the pump passes through the
control valve and is supplied to port (MA). As a
result, the pressure at port (MA) rises, the
starting torque is generated in the motor, and
the motor starts to rotate. The oil from the out-
let port of the motor passes from port (MB)
thought the control valve and returns to the
tank.
2. When stopping crusher
q
When the crusher OFF switch is pressed, the
supply of pressure oil from the pump to port
(MA) is stopped. With the oil from the outlet
port of the motor, the return circuit to the tank is
closed by the control valve, so the pressure at
port (MB) rises. As a result, rotation resistance
is generated in the motor, so the braking effect
starts.
q
If the pressure at port (MB) becomes higher
than the pressure at port (MA), it pushes shut-
tle valve (A) (4) and chamber (C) becomes the
same pressure as port (MB). The oil pressure
rises further until it reaches the set pressure of
relief valve (1). As a result, a high braking
torque acts on the motor and stops the motor.
q
When relief valve (1) is being actuated, the
relief oil and the oil from port (S) passes
through check valve (B) (3) and is supplied to
port (MA). This prevents cavitation at port
(MA).