When the turbine is started, the pressure of the fluid increases and sleeve 1 is shifted upward, compressing helical spring 2 and occupying the position shown. At this, spool 4 admits fluid under pressure through ports a and d to the servomotor of the check valve. Upon a drop in load and when roller 5 is released, spool 4 is raised to its upper extreme position by helical spring 3, cutting off the flow of fluid under pressure to the servomotor which is connected through port b to the tank.
$3664$SHP,FC$