Abstract: A valve operator for steam turbine inlet control valves, each of the control valves being set by a corresponding valve cam. The operator comprises pilot operated hydraulic means for positioning the valve cams in a normal or power mode of operation, mechanical means for positioning the valve cams in a back-up or manual mode of operation and manual actuation means for actuating the hydraulic means in a normal mode of operation and, in the event of failure of the hydraulic means, for automatically actuating the mechanical means in a back-up mode of operation. The hydraulic actuator positions the valve cams through a rack and pinion assembly. Both the hydraulic means and the mechanical means are actuated from an input shaft driving a reduction gear box. The mechanical means comprises a dog connected to the output of the gear box and a pin on the cam shaft driven by the dog in the manual mode of operation.