Five points of knowledge of valve electric actuator
There are quite a variety of valves, and the working principle is not the same. Generally, the opening and closing control is realized by rotating the valve plate angle and lifting valve plate. When it is matched with the electric actuator, the electric actuator should be selected according to the type of the valve.
1.1. Angle-stroke electric actuator (angle <360 degrees)
The rotation of the output shaft of the electric actuator is less than one week, that is, less than 360 degrees, usually 90 degrees, to achieve the opening and closing process control of the valve. Such electric actuators are divided into direct connection type and base crank type according to different installation interface modes.
a) Direct connection: refers to the form in which the output shaft of the electric actuator is directly connected to the valve stem.
b) Base crank type: refers to the form in which the output shaft is connected to the valve stem through the crank. These electric actuators are suitable for butterfly valves, ball valves, plug valves and the like.
1.2. Multi-turn electric actuator (angle > 360 degrees)
The rotation of the output shaft of the electric actuator is greater than one week, that is, greater than 360 degrees. Generally, multiple turns are required to control the opening and closing process of the valve. Such electric actuators are suitable for gate valves, globe valves, and the like.
1.3. Straight stroke (linear motion)
The movement of the output shaft of the electric actuator is linear, not in the form of rotation. These electric actuators are suitable for single-seat control valves, two-seat control valves and more.
2. Determine the control mode of the electric actuator according to the production process control requirements
The control mode of the electric actuator is generally divided into two types: switch type (open loop control) and adjustment type (closed loop control).
2.1. Switch type (open loop control)
Switching electric actuators generally control the opening or closing of the valve. The valve is either in the fully open position or in the fully closed position. Such valves do not require precise control of the medium flow. It is particularly worth mentioning that switch-type electric actuators can be divided into split structures and integrated structures due to different structural forms. This must be explained during the selection, otherwise it will often occur in the field installation and conflict with the control system and other mismatches.
a) Separate structure (commonly referred to as common type): The control unit is separated from the electric actuator. The electric actuator cannot realize the control of the valve separately. It is necessary to add the control unit to realize the control. Generally, the external controller or control cabinet is used. Matching. The disadvantage of this structure is that it is not convenient for the whole system to be installed, the wiring and installation cost are increased, and the fault is easy to occur. When the fault occurs, it is not convenient for diagnosis and maintenance, and the cost performance is not satisfactory.
b) Integrated structure (commonly referred to as integral type): The control unit is integrated with the electric actuator, which can be operated locally without external control unit. The remote control can be operated only by outputting relevant control information. The advantage of this structure is that it facilitates the overall installation of the system, reduces wiring and installation costs, and is easy to diagnose and troubleshoot. However, the traditional integrated structure products also have many imperfections, so the intelligent electric actuators are produced. The intelligent electric actuators will be described later.
2.2. Adjustable type (closed loop control)
The regulated electric actuator not only has the function of a switch-type integrated structure, but also allows precise control of the valve to precisely regulate the flow of the medium.
a) Control signal type (current, voltage)
The control type electric actuator control signal generally has a current signal (4~20mA, 0~10mA) or a voltage signal (0~5V, 1~5V). The type and parameter of the control signal should be specified when selecting the type.
b) working form (electric open type, electric off type)
The working mode of the regulating electric actuator is generally electric opening type (taking 4~20mA control as an example, the electric opening type means that the 4mA signal corresponds to the valve closing, the 20mA corresponds to the valve opening), and the other is the electric switching type. (Taking 4-20 mA control as an example, the electric opening type means that the 4 mA signal corresponds to the valve opening, and the 20 mA signal corresponds to the valve closing).
c) loss of signal protection
Loss of signal protection means that the electric actuator will control the valve to open and close to the set protection value when the control signal is lost due to faults such as the line. The common protection values are full open, full off, and in-situ. Not easy to modify afterwards.
3. Determine the output torque of the electric actuator according to the torque required by the valve
The torque required for the valve to open and close determines the output torque of the electric actuator. It is usually recommended by the user or the valve manufacturer can choose it. As the actuator manufacturer, it is only responsible for the output torque of the actuator. The torque is determined by factors such as valve size and working pressure. However, due to the difference in machining accuracy and assembly process of valve manufacturers, the torque required for different specifications of valves produced by different manufacturers is also different, even if it is produced by the same valve manufacturer. The torque of the specification valve is also different. When the torque selection of the actuator is too small, the valve cannot be normally opened and closed. Therefore, the electric actuator must choose a reasonable torque range.
4. Determine electrical parameters based on selected electric actuators
Because the electrical parameters of different actuator manufacturers are different, it is generally necessary to determine the electrical parameters during design selection, mainly motor power, rated current, secondary control loop voltage, etc. Often in this aspect of negligence, the result of the control system and electric actuator parameters do not match the work time to open trip, fuse blow, thermal overload relay protection take-off and other faults.
5. Select the enclosure protection grade and explosion-proof grade according to the use occasion.
5.1. Enclosure rating
The protection level of the outer casing refers to the external object and waterproof level of the electric actuator. It is represented by the letter IP followed by two digits. The first position is 1 to 6 for the foreign object level, and the second is 1 to 8 for the waterproof. grade.
5.2. Explosion-proof grade
In places where explosive gas, steam, liquids, flammable dust, etc. may cause fire or explosion hazard, it is necessary to provide explosion-proof requirements for electric actuators, and select explosion-proof forms and categories according to different application areas. The explosion-proof grade can be expressed by the explosion-proof mark EX and the explosion-proof content (refer to Explosion-proof electrical equipment for explosive environment GB3836-2000). The contents of the explosion-proof mark include: explosion-proof type + equipment category + (gas group) + temperature group.
If you still want to know more, please contact us.