Abstract: A motor operated valve, typically a butterfly valve driven by a synchronous electric motor (16), is provided with a torque sensing arrangement wherein an cyclic electrical signal representative of the rotational speed of the motor is produced by magnets (22) on disc driven by the motor and Hall effect switches (23,24). The frequency of this signal is compared in a circuit (43) with the frequency of current supplied to the motor to provide an indication of motor torque. Switches (46,47) define preset torque limits for the valve. If the limits are exceeded, a signal is fed to control logic (41) which operates switches (18) to control the supply current to the motor. The speed signal from the Hall effect switches is also fed to a counter (31) to develop a count representative of movement of the valve. The output of counter (31) is compared with preset valves defined by switch circuits (37,38) to define limits of travel for the valve.

Abstract: A wormwheel (1) has teeth (2) over at least a portion of its periphery. The teeth (2) are shaped such that the pitch diameter (5) is greater at one face (3) of the wormwheel than the other and does not increase along the path of the tooth from said one face (3) to the other face (4). Because of this tooth shaping the wormwheel may be cast and is thus suitable for mass production. Wormwheels of this type are particularly, but not exclusively, suitable for use in valve actuators. In order to facilitate the casting process the wormwheel is formed with only one integral bearing (10) and has an internally splined opening (8) in which can be received a bearing sleeve (18) which may also be adapted to receive the valve stem within its own axial opening (21). A variety of bearing sleeves suitable for use with different valve stems may be provided for cooperation with the same wormwheel thereby eliminating the need for special adaptors and reducing the number of parts required to construct a range of valve actuators.

Abstract: A motor operated valve, typically a butterfly valve driven by .[.a synchronous.]. .Iadd.asynchronous .Iaddend.electric motor (16), is provided with a torque sensing arrangement wherein an cyclic electrical signal representative of the rotational speed of the motor is produced by magnets (22) on disc driven by the motor and Hall effect switches (23,24). The frequency of this signal is compared in a circuit (43) with the frequency of current supplied to the motor to provide an indication of motor torque. Switches (46,47) define preset torque limits for the valve. If the limits are exceeded, a signal is fed to control logic (41) which operates switches (18) to control the supply current to the motor. The speed signal from the Hall effect switches is also fed to a counter (31) to develop a count representative of movement of the valve. The output of counter (31) is compared with preset valves defined by switch circuits (37,38) to define limits of travel for the valve.