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There are many types of electric actuators. Electric actuators and valves of different types and functions can be called electric valves. However, in the process of designing and selecting, only the parameters of the valve are neglected or the electric actuator is not clearly defined. The relevant requirements not only prevent the electric valve from exerting its best performance, but also cause unnecessary trouble during installation, commissioning and use, and even cause serious consequences for production.
This article will focus on the points of consideration for the selection of Rotork electric actuators and provide a brief introduction to the related functions of current intelligent electric actuators. It will be the mainstream product required for the development of industrial automation control today and in the future.
Electric actuator selection considerations
First, choose the electric actuator according to the valve type
There are many kinds of valves, and the working principle is not the same. Generally, the opening and closing control is realized by rotating the valve plate angle, lifting valve plate, etc. When matching with the electric actuator, the electric actuator should be selected according to the type of valve first.
1. Angle stroke electric actuator (turning 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 valve opening and closing process control. Such electric actuators are divided into two types: direct-connected and base-crank, depending on the way they are installed.
a) Direct connection: refers to the form where the output shaft of the electric actuator is directly connected with the valve stem.
b) base crank: refers to the output shaft through the crank and the valve stem connection form.
Such electric actuators are suitable for butterfly valves, ball valves, plug valves and the like.
2. Multi-turn electric actuator (turning angle >360 degrees)
The rotation of the output shaft of the electric actuator is more than one week, that is, greater than 360 degrees. Generally, it takes more than one revolution to realize the valve opening and closing process control.
Such electric actuators are suitable for gate valves, globe valves and the like.
3. Straight stroke (straight motion)
The movement of the output shaft of the electric actuator is a linear movement type, not a rotation type.
Such electric actuators are suitable for single-seat control valves, two-seat control valves, and the like.
Second, determine the control mode of the electric actuator according to the production process control requirements
Electric actuator control mode is generally divided into switch type (open-loop control) and adjustment (closed-loop control) two categories.
1. Switch Type (Open Loop Control)
Switch-type electric actuators generally control the opening or closing of valves. Valves are either in the fully open position or in the fully closed position. Such valves do not require precise control of the flow of medium.
It is particularly worth mentioning that switch-type electric actuators can be divided into separate structures and integrated structures due to different structural forms. This must be explained when selecting a model, otherwise it often happens when there is a mismatch between the installation on site and the control system.
a) Separate structure (commonly referred to as common type): The control unit is separated from the electric actuator. The electric actuator cannot independently realize the control of the valve. It is necessary to add a control unit to achieve the control. Generally, the external controller or control cabinet is used. Supporting.
The disadvantage of this structure is that it is not convenient for the overall system installation, increases the wiring and installation costs, and is prone to failure. When the fault occurs, it is inconvenient for diagnosis and maintenance, and the cost performance is not ideal.
b) Integrated structure (commonly referred to as integral type): The control unit is integrated with the electric actuator and can be operated in real-time without the need of external control unit. The remote control can output the relevant control information.
The advantage of this structure is that it facilitates the overall system installation, reduces wiring and installation costs, and is easy to diagnose and troubleshoot. However, traditional integrated structural products also have many imperfections, so intelligent electric actuators are produced. The following will be explained about smart electric actuators.
2. Adjustable (closed loop control)
Adjustable electric actuators not only have the function of a switch-type integrated structure, they can also accurately control the valve, so as to accurately adjust the media flow. Due to limited space, its working principle is not detailed here. The following is a brief description of the parameters to be specified when selecting a type of electric actuator.
a) Control signal type (current, voltage)
Adjustable electric actuator control signals generally have a current signal (4 ~ 20mA, 0 ~ 10mA) or voltage signal (0 ~ 5V, 1 ~ 5V), the type and parameters of the control signal must be clear when selecting the type.
b) Work forms (electrical open, electrical shutoff)
The operating mode of the regulating electric actuator is generally electric open type (4 to 20mA control as an example, the electric open type refers to the 4mA signal corresponds to the valve close, 20mA corresponds to the valve open), and the other is the electric cut type (For 4-20mA control, for example, the open type means that the 4mA signal corresponds to the valve open, 20mA corresponds to the valve close). Under normal circumstances, the selection must be made in a clear manner. Many products cannot be modified after leaving the factory. Ogilvy & Mather valve-controlled intelligent electric actuators can be modified at any time through on-site settings.
c) Loss of signal protection
Loss of signal protection means that when the control signal is lost due to faults such as lines, the electric actuator will open and close the control valve to the set protection value. The common protection values ​​are full open, fully closed, and hold in situ. After not easy to modify. Ogilvy & Mather valve-controlled intelligent electric actuators can be flexibly modified through on-site settings, and any position (0 to 100%) can be set as the protection value.
Third, according to the required torque of the valve to determine the output torque of the electric actuator
The torque required to open and close the valve determines how much output torque the electric actuator chooses. Generally, it is proposed by the user or the valve manufacturer chooses itself. As the actuator manufacturer, only the output torque of the actuator is responsible for the normal opening and closing of the valve. The torsional force is determined by the valve size, working pressure and other factors, but because the valve manufacturers processing accuracy, assembly process is different, so different manufacturers of the same specifications of the required torque is also different, even with the same valve manufacturers There are also differences in the torque of the specification valve. When the torque of the actuator is selected to be too small when selecting the type, the valve cannot be opened and closed normally. Therefore, the electric actuator must select a reasonable torque range.
Fourth, according to the selected electric actuator to determine the electrical parameters
Due to the differences in the electrical parameters of different actuator manufacturers, the electrical parameters usually need to be determined when designing and selecting the type. The main ones are the motor power, rated current, and secondary control loop voltage, which are often negligence in this regard. The result is a control system. Failure to match the parameters of the electric actuator results in faults such as open-circuit tripping of the work space, blown fuses, and protection against jump-off of thermal overload relays.
Fifth, according to the use of occasions to choose shell protection grade, explosion-proof grade
Rotork electric actuator operation method:
1. Manual operation: Press the manual/automatic handle so that it is in the manual position. Rotate the handwheel to engage the clutch, then release the handle, the handle will automatically spring back to the initial position, the handwheel will remain engaged until the actuator is operated electrically, the handwheel will automatically disengage, return to the motor drive state. If required, lock the clutch in any state with a padlock with a 6.5mm iron hook.
2. Electric operation: Check the power supply voltage, it should be consistent with the identifier on the actuator nameplate, then you can turn on the power. No need to check the phase. If you do not perform a preliminary inspection, do not perform electrical operations. At a minimum, use infrared setters to complete the initial setup.
Select Live/Stop/Remote Operation: The red selector can be selected for either on-site or remote operation. The stop function is still active when the selector is locked in a local or remote position. The selector can also be locked in a stopped state to prevent electric operation on site or remotely. Turn the red selector knob counterclockwise to the on-site position. The adjacent black knobs can be turned to the on and off positions respectively. Turning the red knob clockwise stops the operation. If the red selector knob is turned counterclockwise to the remote position, the remote control can only be used to turn on and off. At this time, turning the red knob clockwise can still stop the actuator.
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