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An electric valve, in simple terms, is one in which an electric actuator is used to control the valve, thereby enabling its opening and closing. It can be divided into two parts: the upper part is the electric actuator, and the lower part is the valve. Electric valve devices are essential equipment for achieving programmed, automatic, and remote control of valves, and their movement can be controlled by the magnitude of stroke, torque, or axial thrust. Since the operating characteristics and efficiency of electric valve systems depend on the type of valve, the operating specifications of the system, and the position of the valve within the pipeline or equipment, it is crucial to select the appropriate electric valve system in order to prevent overload conditions (where the operating torque exceeds the control torque). Generally, the criteria for correctly selecting an electric valve actuator are as follows: Operating torque – The operating torque is the main parameter for selecting an electric valve actuator; the torque output by the electric actuator should be 1.2 to 1.5 times the maximum torque required to operate the valve. There are two types of main structures for operating thrust electric valve devices: one type does not have a thrust disc and outputs torque directly ； Another approach is to use a thrust disc, with the output torque being converted into output thrust through the valve stem nut in the thrust disc. The number of rotation cycles of the output shaft in electric valve devices is determined by the valve’s nominal diameter, the pitch of the valve stem thread, and the number of threads on the stem. It should be calculated using the formula M = H/ZS, where M represents the total number of rotation cycles required by the electric device, H is the opening height of the valve, S is the pitch of the thread used for transmitting motion in the valve stem, and Z is the number of threads on the valve stem. If the opening and closing speed of the output speed control valve is too fast, water hammer can occur. Therefore, the appropriate opening and closing speed should be selected based on different operating conditions. Electric valve devices have specific requirements, namely the ability to limit torque or axial force. Typically, electric valve assemblies use couplings that limit torque. Once the specifications of the electric drive are determined, its control torque is also determined. It generally operates within a predetermined time frame, so the motor will not be overloaded. However, overload can occur under the following conditions: first, a low supply voltage results in insufficient torque, causing the motor to stop rotating ； Secondly, the torque limit mechanism is incorrectly set to a value higher than the torque at which the motor stops, resulting in continuous generation of excessive torque and causing the motor to cease rotating ； Third, intermittent use results in heat accumulation that exceeds the allowable temperature rise limit of the motor ； Fourth, for some reason, a fault occurs in the circuit of the torque limitation mechanism, resulting in excessive torque ； Fifth, the operating ambient temperature is too high, which relatively reduces the motor’s heat capacity.