Electric Actuator, ElectricActuatorAlso known as electric valve actuators, the terminology varies across different industries. In the industrial pipeline valve industry, it is called a valve electric actuator; in the instrumentation industry, it is called an electric actuator. However, there is no clear distinction in the industry now. In this article, the term 'electric actuator' will be used uniformly.

Valves are frequently used important equipment in industrial pipeline control. Electric valves (electric actuators), with the development of industrial automation, are more commonly used than pneumatic and hydraulic equipment due to their readily available power source and generally maintenance-free nature. In industrial settings, electric valves must possess higher reliability and safety. When the valve performance and lifespan are guaranteed, the safety and reliability of the electric valve depend on the electric actuator; therefore, the performance and control level of the electric actuator are a comprehensive representation of the overall technical level of the electric valve. Therefore, when selecting an electric actuator, in addition to some essential factors that must be considered, reasonable technical requirements should be put forward to maximize the value of the electric valve.

　　There are many types of electric actuators. Different types and functions of electric actuators can be called electric valves when matched with valves, but often in the design and selection process, only the parameters of the valve are emphasized, and the requirements of the electric actuator are ignored or not clearly defined. This not only prevents the electric valve from performing at its best but also brings unnecessary trouble during installation, commissioning, and use, and may even cause serious consequences for production.

　　This article will explain in detail the five key points to consider when selecting an electric actuator. It is provided for your reference.

I. Selecting an Electric Actuator Based on Valve Type

　　There are many types of valves, and their working principles are also different. Generally, they use methods such as rotating the valve disc angle or lifting the valve disc to achieve opening and closing control. When matched with an electric actuator, the electric actuator should first be selected according to the type of valve.

1. Rotary Actuator (Rotation <360 degrees)

　　The rotation of the output shaft of the electric actuator is less than one revolution, i.e., less than 360 degrees, usually 90 degrees to achieve the valve opening and closing process control. This type of electric actuator is further divided into two types: direct-connected type and base crank type, according to the different installation interface methods.

a) Direct-connected type: This refers to the form in which the output shaft of the electric actuator is directly connected to the valve stem.

b) Base crank type: This refers to the form in which the output shaft is connected to the valve stem via a crank.

　　This type of electric actuator is suitable for butterfly valves, ball valves, plug valves, etc.

2. Multi-turn Electric Actuator (Rotation >360 degrees)

　　The rotation of the output shaft of the electric actuator is greater than one revolution, i.e., greater than 360 degrees, and usually requires multiple turns to achieve the valve opening and closing process control.

　　This type of electric actuator is suitable for gate valves, globe valves, etc.

3. Linear Stroke (Linear Motion)

　　The movement of the output shaft of the electric actuator is linear, not rotary.

　　This type of electric actuator is suitable for single-seated control valves, double-seated control valves, etc.

II. Determining the Control Mode of the Electric Actuator Based on Production Process Control Requirements

　　The control modes of electric actuators are generally divided into two categories: on-off type (open-loop control) and regulating type (closed-loop control).

1. On-off Type (Open-loop Control)

　　On-off type electric actuators generally implement opening or closing control of the valve. The valve is either fully open or fully closed. This type of valve does not require precise control of the medium flow rate.

　　It is especially worth mentioning that, due to the different structural forms, on-off type electric actuators can also be divided into split structures and integrated structures. When selecting, this must be specified; otherwise, mismatches such as conflicts with the control system will often occur during on-site installation.

a) Split structure (usually called ordinary type): The control unit and the electric actuator are separated. The electric actuator cannot independently control the valve and must be equipped with an external control unit to achieve control. Generally, an external controller orcontrol cabinetis used for matching.

　　The disadvantages of this structure are that it is inconvenient for overall system installation, increases wiring and installation costs, and is prone to failures. When failures occur, it is inconvenient for diagnosis and maintenance, and the cost-effectiveness is not ideal.

b) Integrated structure (usually called integrated type): The control unit and the electric actuator are packaged into one unit. No external control unit is needed to achieve local operation. Remotely, only the relevant control information needs to be output to operate it.

　　The advantages of this structure are that it is convenient for overall system installation, reduces wiring and installation costs, and is easy to diagnose and troubleshoot faults. However, many traditional integrated structure products are also imperfect, so intelligent electric actuators have emerged. Intelligent electric actuators will be further discussed later.

2. Regulating Type (Closed-loop Control)

　　The regulating type electric actuator not only has the functions of the on-off integrated structure, but it can also precisely control the valve and thereby precisely regulate the medium flow rate. Due to space limitations, its working principle will not be explained in detail here. The parameters that need to be noted when selecting a regulating type electric actuator are briefly explained below.

a) Control Signal Type (Current, Voltage)

　　The control signals of regulating type electric actuators generally include current signals (4~20mA, 0~10mA) or voltage signals (0~5V, 1~5V). When selecting, the type and parameters of the control signal must be specified.

b) Working Mode (Normally Open, Normally Closed)

　　The working mode of a regulating type electric actuator is generally normally open (taking 4~20mA control as an example, normally open means that the 4mA signal corresponds to the valve closed, and 20mA corresponds to the valve open), and the other is normally closed (taking 4-20mA control as an example, normally open means that the 4mA signal corresponds to the valve open, and 20mA corresponds to the valve closed). Generally, the working mode needs to be specified when selecting. Many products cannot be modified after leaving the factory. The intelligent electric actuators produced by our company can be modified at any time through on-site settings.

c) Signal Loss Protection

　　Signal loss protection refers to the situation where, if the control signal is lost due to line faults or other failures, the electric actuator will open or close the control valve to a preset protection value. Common protection values include fully open, fully closed, and maintaining the original position, and are difficult to modify after leaving the factory. Intelligent electric actuators can be flexibly modified through on-site settings, and any position (0~100%) can be set as protection.

III. Determine the output torque of the electric actuator based on the required torque of the valve

     The torque required for valve opening and closing determines the output torque of the electric actuator to be selected. This is usually proposed by the user or self-matched by the valve manufacturer. As an actuator manufacturer, we are only responsible for the output torque of the actuator. The torque required for normal valve opening and closing is determined by factors such as the valve diameter and working pressure. However, due to differences in processing precision and assembly technology among valve manufacturers, the torque required for valves of the same Specification from different manufacturers also varies. Even valves of the same Specification from the same manufacturer may have different torques. If the selected torque of the actuator is too small, it will cause the valve to fail to open and close normally. Therefore, the electric actuator must select a reasonable torque range. 

IV. Determine the electrical parameters based on the selected electric actuator

     Since the electrical parameters vary among different actuator manufacturers, it is generally necessary to determine their electrical parameters during design and selection. The main parameters include:Motorpower, rated current, secondary control loop voltage, etc. Often, negligence in this aspect results in mismatches between the control system and the electric actuator parameters, leading to faults such as air circuit breaker tripping, fuse blowing, and thermal overload relay protection tripping during operation.

V. Select the enclosure protection level and explosion-proof level according to the application scenario

5.1. Enclosure protection level

   The enclosure protection level refers to the level of protection of the electric actuator's housing against foreign objects and water, represented by the letters IP followed by two digits. The first digit (1～6) represents the level of protection against foreign objects, and the second digit (1～8) represents the level of waterproofness.

5.2. Explosion-proof level

   In locations where explosive gases, vapors, liquids, or combustible dust may cause fire or explosion hazards, explosion-proof requirements must be met for the electric actuator, and the explosion-proof type and category must be selected according to the different application areas. The explosion-proof level can be indicated by the explosion-proof mark EX and the explosion-proof content (refer to GB3836-2000, "Explosion-proof electrical equipment for explosive atmospheres"). The explosion-proof mark content includes: explosion-proof type + equipment category + (gas group) + temperature group.