VALVE ACTUATORSDOE-HDBK-1018/2-93ValvesElectricMotorActuatorsElectric motors permit manual, semi-automatic, and automatic operation of the valve. Motorsare used mostly for open-close functions, although they are adaptable to positioning the valveto any point opening as illustrated in Figure 33. The motor is usually a, reversible, high speedtype connected through a gear train to reduce the motor speed and thereby increase the torqueat the stem. Direction of motor rotation determines direction of disk motion. The electricalactuation can be semi-automatic, as when the motor is started by a control system. Ahandwheel, which can be engaged to the gear train, provides for manual operating of the valve.Limit switches are normally provided to stop the motor automatically at full open and full closedvalve positions. Limit switches are operated either physically by position of the valve ortorsionally by torque of the motor.Figure 33 Electric Motor ActuatorME-04Rev. 0Page 46
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