Abstract: A valve operator powered selectively either by an electric motor or by a manually operable handwheel, the driving connections from both the motor and the handwheel to the valve including one or more planetary gear sets each having a central pinion rotatable by the motor, a ring gear surrounding the pinion, and planet gears interposed between and meshed with the pinion and the ring gear, the planet gears being rotatable about their own axes and mounted eccentrically on a spider member rotatable about the gear axis, the spider member being operable by its rotation to transmit operating power to the valve being controlled. The ring gears of all of the gear sets are fixed in a rotatable gear case which is turned by the handwheel. A pair of non-reversing torque control devices, disposed respectively between the gear set and the motor, and between the gear set and the handwheel, prevent rotation of the motor by operation of the handwheel, and rotation of the handwheel by operation of the motor.