There are two main methods of achieving an electric opening and closing of a valve, one relates to a quarter-turn valve only, the other to either a part-turn or multi-turn electric actuator.
Generally only applicable with an electric ball valve, is a uni-directional electric valve actuator.
A uni-directional electric actuator always rotates in the same direction with the motor being stopped at 90 degree intervals, typically by cams fixed to the output shaft striking electrical micro-switches which cut the power to the motor, and await an electrical command to run to the next position. This type of electrical actuator function reduces the cost of the electronic controls as the motor always rotates in the same direction.