Komatsu Galeo PC800-8 Shop Manual page 188

SEN00384-02
Relief valve portion
1. Outline
The relief portion consists of check valves (2)
and (3), shuttle valves (4) and (5), and relief
valve (1).
2. Function
When the swing 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 dam-
age 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 dam-
age.
3. Operation
1) When starting swing
• When the swing control lever is operated to
swing right, the pressure oil from the pump
passes through the control valve and is sup-
plied to port MA. As a result, the pressure at
port MA rises, the starting torque is generat-
ed in the motor, and the motor starts to ro-
tate. The oil from the outlet port of the motor
passes from port MB thought the control
valve and returns to the tank. (Fig. 1)
2) When stopping swing
• When the swing control lever is returned to
neutral, the supply of pressure oil from the
pump to port MA is stopped. When the return
circuit to the tank is closed by the control
valve, the pressure at port MB rises with the
oil from the outlet port of the motor. As a re-
sult, rotation resistance is generated in the
motor, so the braking effect starts.
• If the pressure at port MB becomes higher
than the pressure port MA, it pushes shuttle
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 mo-
tor. (Fig. 2)
• 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.
26
10 Structure, function and maintenance standard
PC800, 850-8