Handwheel 1 is turned manually to start the turbine. This lifts upper plate 2 of the valve. Steam, passing through the valve, forces lower plate 3 of the valve downward, turning lever 9 about fixed axis A and raising weight 4 which can be set at various places along the axis of lever 9. Servomotor 5 is provided for rapidly closing the valve in case of a drop of load to prevent reversal of the steam. During normal operation of the steam turbine, fluid is delivered to the upper end of servomotor 5. The pressure of the fluid holds piston 6 down against stop a, compressing spring 8. At this, plate 3, linked to rod 7 of the piston, is also in its lower position. Upon a drop of load, the upper end of the servomotor is connected to the drain. Spring 8 lifts piston 6 and rapidly raises lower plate 3 onto its seat, preventing steam reversal.
$3959$LHP,Va$