Electric Motor Actuators:

Electric motors allow manual, semi-automatic or automatic operation of the valve. Electric Motors are used widely for open-close functions, while they are adaptable to positioning the valve to any point opening as described in Figure. The motor is commonly a, reversible, high speed type linked by a gear train to decrease the motor speed and by increase the torque at the stem. Way of motor rotation determines direction of disk motion. An electrical actuation could be semi-automatic, as while the motor is begins through a control system. A handwheel that could be engaged to the gear train gives for manual operating of the valve. Limit switches are generally given to stop the motor automatically at full open and full closed valve positions. The Limit switches are operated either physically through position of the valve or torsionally through torque of the motor.

Figure: Electric Motor Actuator