② Operating principle Operating principle When the swing control lever (1) is set to the swing position, the pilot oil go to the swing control valve (2) and to SH of the time delay valve (3) via the shuttle valve (4), this pressure move spool (5) to the leftward against the force of the spring (8), so pilot pump charged oil (P4) goes to the chamber G. This pressure is applied to move the piston (28) to the upward against the force of the spring (30). Thus, it releases the brake force. a. 3 30 5 28 G SH 8 1 1 Swing control lever 2 Swing control valve (MCV) 3 Time delay valve 4 Shuttle valve 5 Spool 8 Spring 12 Gear pump 28 Brake piston 30 Brake spring 12 P4 2 2 4 2-19