Komatsu PC88MR-10 Shop Manual page 191

Relief valve
(PC220-J6B1-041-K-00-A)
The relief valve portion consists of check valves (2) and (3), shuttle valves (4) and (5), and relief valve (1).
Function
(PC220-J6B1-044-K-00-A)
When the swing is stopped, control valve (6) blocks the motor outlet circuit, but the motor rotation is
continued by inertial force.
If the pressure of motor outlet circuit becomes abnormally high, it may cause damage to the motor.
In order to prevent the motor damage, the relief valve relieves the abnormally high pressure to port (S)
from the motor outlet (high-pressure side).
Operation
(PC138-J6B1-044-K-00-A)
When starting swing
When the control lever is operated to "Swing RIGHT", the pressurized oil from the pump is supplied
through control valve (6) to port (MA).
The pressure in port (MA) increases and generates starting torque in the motor, and the motor starts to
rotate.
The pressurized oil from the motor output returns from port (MB) through control valve (6) to the tank.
PC88MR-10
10 Structure and function
Swing motor
10-113