Komatsu PC88MR-10 Shop Manual page 192

10 Structure and function
Swing motor
When stopping swing
When the control lever is returned from "Swing RIGHT" to "NEUTRAL", the pressurized oil from the pump
is not supplied to port (MA).
Since the return circuit to the tank for the pressurized oil from the motor outlet is closed by control valve (6),
the pressure in port (MB) increases.
Rotation resistance is generated in the motor and the brake starts to work.
When the pressure in port (MB) exceeds that in port (MA), it pushes shuttle valve (4).
The pressure in chamber (C) becomes the same with port (MB) and increases to the set pressure of relief
valve (1).
High braking torque is applied to the motor to stop.
While relief valve (1) is in operation, the relieved pressurized oil and the pressurized oil from port (S) are
supplied to port (MA) through check valve (3).
Cavitation in port (MA) is prevented.
Swing modulating relief valve function
The swing motor relief valve has characteristics of preventing sudden increase of the relief pressure to
reduce shocks generated when the machine stops and starts swinging.
10-114
(PC88MR-J6B3-042-K-00-A)
PC88MR-10