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Electric valves are widely used in the water supply and drainage systems of municipal and industrial enterprises. An electric valve consists of an electric actuator, the valve body, connecting accessories, and a control box. The electric actuator of an electric valve is an essential driving device for achieving programmed, automatic, and remote control of the valve. Electric valves are generally selected by the water supply and drainage specialists. During the engineering design phase, these specialists must specify the required functions for the valve’s electric drive, after which specialized manufacturers select the appropriate electric drive units. However, in actual engineering projects, mismatches such as conflicts between the valve electric actuator and the control system often occur during on-site installation. This is usually due to unreasonable or incomplete aspects in determining the functional requirements of the electric device. Composition of valve actuator devices An actuator device generally consists of the following components: a dedicated electric motor and a reduction mechanism, which are used to reduce the output speed of the electric motor ； Travel control mechanism, used to adjust and precisely control the opening and closing position of the valve ； Torque limiting mechanism, used to regulate torque (or thrust) and prevent it from exceeding a predetermined value ； Manual and electric switching mechanism, an interlock mechanism for manual or electric operation ； An opening indicator, used to show the position of the valve during its opening and closing process. Among them, the travel control mechanism, torque limitation mechanism, manual/electric switching mechanism, and opening indicator are collectively referred to as electric actuators. Key points to consider when selecting electric devices and defining functional requirements When selecting electric devices and determining their functional requirements, it is important to take into account factors such as the IP protection rating of the device, its supply voltage, its operating time at 90°, and the type of actuator used. 1. Determine the IP protection rating of the electric device When selecting an electric device, it is necessary first to determine its IP protection rating based on the working environment and usage requirements. Electric valve actuators for general water supply and drainage systems can be divided into outdoor types and indoor types depending on the working environment. The commonly used IP protection rating for outdoor electric valve actuators is IP54 or IP55, while the commonly used IP protection rating for indoor electric valve actuators is IP43 or IP44. Generally, electric actuators for valves in water supply and drainage systems do not use submersible types. The IP protection rating of electrical devices should be proposed and determined by plumbing and water supply professionals. 2. Determine the power supply voltage for the electric device. The commonly used power supply voltages among domestic users are 380V and 24V; the specific voltage should be determined based on the power supply conditions available externally. 3. Determine the 90° operation time of the electric actuator. The 90° operation time of an electric actuator refers to the time required for the electric valve to reach its fully open or fully closed position; this requirement is determined by the specialized manufacturers of valves and electric actuators. The normal 90° operation time ranges from 7.5 to 30 seconds, but it must meet the requirements of the water system process. The shorter the 90° operating time, the greater the motor power of the electric device and the higher the current. High-power water pumps usually use closed-valve light-load starting to reduce the starting current of the pump. Check valves, electric valves, etc. are installed on the water pump outlet pipe. The typical time required to close the valve at start-up is 10–30 seconds; therefore, the 90° operation time of the electric actuator for the electric valve on the water pump’s outlet pipe should be consistent with the valve-closing start-up time specified in the water supply and drainage process. If the opening and closing speed of the valve is too fast, water hammer can occur. In the water used by industrial and mining enterprises, an emergency water supply system supplied by a safety water tank or water tower is usually installed. Electric valves are also commonly installed on the emergency water supply pipes for accidents. To ensure production safety, it is necessary that these electric valves open promptly and respond quickly; therefore, the 90° rotation time of the valve’s electric actuator should also be minimized as much as possible. 4. Determine the type of electric actuator (1) Common types of electric actuators 1) On-off type (open-loop control). Switch-type electric actuators are generally used to control the opening and closing of valves, which are either in a fully open position or a fully closed position; such valves do not require precise control over the flow rate of the medium. Depending on their structural design, switch-type electric actuators can also be divided into split-type and integrated types. This must be specified during the selection process; otherwise, mismatches such as conflicts with the control system often occur during on-site installation. 2) Regulative type (closed-loop control). The adjustable electric actuator not only possesses the functions of a on/off integrated structure but also enables precise control of the valve to regulate the flow rate of the medium. Control signals include current and voltage. The control signals for regulated electric actuators are usually either current signals (4–20mA, 0–10mA) or voltage signals (0–5V, 1–5V); it is necessary to determine the type of control signal and its parameters when selecting such actuators. The operating mode of regulated electric actuators is generally normally open (taking 4–20mA control as an example; in this case, a 4mA signal corresponds to the valve being closed, while 20mA corresponds to the valve being open). Another mode is normally closed (again using 4–20mA control as an example; here, a 4mA signal corresponds to the valve being open, and 20mA corresponds to the valve being closed). Signal loss protection refers to the mechanism by which, in the event that a control signal is lost due to faults in the lines or similar issues, the electric actuator opens or closes the control valve to a predetermined protective position; the common protective positions are fully open, fully closed, or maintaining the current position. Switch-type electric actuators also have signal loss protection. (2) Determining the type of electric actuator 1) Selection between on-off type and control type. In the water supply systems of municipal and industrial enterprises, the main function of electric valves is to open or close water pipelines; therefore, on-off type electric actuators are the most commonly used. However, in the cooling water systems of many intermediate piping networks in the process equipment of industrial and mining enterprises, the accuracy requirements for parameters such as flow rate and pressure are very high; changes in cooling water flow rate and pressure have a significant impact on the production conditions of the equipment. Therefore, electric valves used in such situations should be equipped with adjustable electric actuators. Before deciding whether to use a on-off type or a control type electric actuator, it is first necessary to gain a thorough understanding of the specific operating conditions of the electric valve to be used, and then submit reasonable functional requirements to specialized manufacturers. The determination of the type and operation mode of the regulatory control model should be based on the specific production conditions and operating circumstances of the process equipment. 2) Determination of the split structure and integrated structure types. The disadvantage of electric actuators with a split structure is that they make it difficult to install the entire system, increase wiring and installation costs, and are prone to failures; when such failures occur, it is hard to diagnose and repair them, resulting in an unsatisfactory cost-performance ratio. The advantage of electric actuators with an integrated structure is that they facilitate the overall installation of the system, reduce wiring and installation costs, and make it easy to diagnose and troubleshoot faults. However, traditional integrated structural products also have many shortcomings. Today, the control of water supply and drainage systems, as well as closed-loop water treatment systems in municipal and industrial enterprises, is carried out using PLCs and computer programs, with CRT screen displays available. The control of water systems is typically centralized in the water system control room or electrical room, where PLC cabinets and MCC cabinets are located. For all on-site electrical equipment, only an operation panel is installed on site; this panel is connected to the PLC cabinet in the electrical room, and the signals are then sent to the MCC cabinet to ultimately control the equipment on site. Under such operating conditions, it is reasonable to use electric actuators with a split structure. If an electric actuator with an integrated structure is used, its functions may not fully match the overall design of the water system control, which can instead lead to malfunctions. Additionally, the price of electric actuators with a split structure is also lower than that of those with an integrated structure. For some applications where the water system is simple, the control requirements are low, or only on-site control is needed, electric actuators with an integrated design can be considered. 3) Determination regarding signal loss protection. When control signals are lost due to faults such as those in the wiring, it should be determined based on the specific process conditions whether the valve should be fully open, fully closed, or remain in its current position; under normal circumstances, the valve is expected to remain in its original position. The electric valve on the outlet pipe of high-power water pumps should be designed to remain in its original position in the event of a failure. Because this electric valve is interlocked with the water pump – the valve opens when the pump starts, and it closes when the pump stops. If the valve closes due to a fault and the water pump does not shut down in time, water hammer damage will be caused to the water pump equipment as well as the pipelines and valves located before the electric valve. For electric valves at various water usage points in industrial and mining enterprises, especially those used for cooling water, it is also required that they remain in their original position in the event of a failure, so as to prevent damage to process equipment due to a sudden interruption in water supply. 5. Other matters The electric actuator for valves has other key parameters such as operating torque, operating thrust, number of revolutions of the output shaft, valve stem diameter, output speed, and motor power. All of these parameters should be determined by professional manufacturers. The operating environment for the electric actuators of water system valves is usually at normal temperature, while the operating temperature range for general electric actuators is –20 to 55°C; therefore, no specific requirements need to be specified. The proper selection of the electric actuator for an electric valve plays a decisive role in enabling the valve to function properly. While the specific selection of electric devices is carried out by professional manufacturers, reasonable functional requirements should be proposed by water supply and drainage professionals prior to the selection process.