How to Select Electric Actuator for Control Valves? | THINKTANK

Selection Methods and Skills of Electric Actuators

As the most important control element in the industrial process-control valves, it is driving commonly used in electric and pneumatic types. The electric control valve simply says just a control valve body assembly with an electric actuator. There are many types and functions of electric actuators. In the process of design and selection, usually, only valve parameters are emphasized, but the relevant requirements of electric actuators are ignored or not clear. So if not pay attention to actuator requirements, debugging, use processes will also bring unnecessary trouble.

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I. Briefly introduce several electric actuators that can be matched with the control valve.

1. Rotary type electric actuator (rotation angle <360 degrees);

The rotation of the output shaft of the electric actuator is less than one circle, that is, less than 360 degrees, usually 90 degrees to achieve the valve opening and closing process control.

electric butterfly control valves electric butterfly valves electric u type butterfly valves electric ball valves threaded electric ball valves electric actuated ball valves flanged ens 1

This type of electric actuator is divided into two types: direct connection type and base crank type according to the different installation methods.

a) Direct connection type: 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 a crank. This type of electric actuator is suitable for butterfly valves, ball valves, plug valves, etc.

2. Multi-turn electric actuators (angle of rotation>360 degrees);

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

electric actuated knife gate valves electric high pressure gate valve

3. Linear type electric actuator (linear motion);

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

eletric control valves for power plant electric globe type control valve

II. Select electric actuators according to the production process control requirements of valve electric actuators

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

On/off type (open loop control)

On/off type electric actuators generally realize the full opening or closing control of the valve. The valve is in the fully open or fully closed position. This type of valve does not require precise control of the medium flow rate. For on/off type electric actuators can be divided into split structure and integrated structure due to different structural. This must be explained when selecting the model, otherwise mismatches such as conflicts with the control system during on-site installation will often occur.

a) Split structure (usually called ordinary type):

The control unit is separated from the electric actuator. The electric actuator cannot control the valve alone. It must be controlled by an external control unit. The disadvantage of this structure is that it is inconvenient for the overall installation of the system, increases the cost of the level transmitter, wiring, and installation, and is prone to failure. When a failure occurs, it is not easy to diagnose and repair, and the cost performance is not ideal.

b) Integrated structure (usually called integral type):

The control unit and the electric actuator are packaged as one, and can be operated on the spot without external control unit, and can be operated remotely 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.

Regulating type (closed loop control)

Regulating electric actuators not only have a switch-type integrated structure but also precisely adjust the medium flow, it can also accurately control the valve. The following is a brief description of the parameters that need to be noted when selecting the adjustable electric actuator.

a) Control signal type (current, voltage)

The control signal of the regulating electric actuator generally includes current signal (4&#;20mA, 0&#;10mA) or voltage signal (0&#;5V, 1&#;5V), which should be clarified when selecting the signal type and parameters.

b) Working type(opening type, closing type)

The working mode of the regulating electric actuator is generally opening type (taking 4-20mA control signal as an example, opening type means that 4mA signal corresponds to valve closing, 20mA Corresponds to valve opening), and the other is closing type (means that 4mA signal corresponds to valve opening, and 20mA corresponds to valve closing).

c) Loss of signal protection

Loss of signal protection means that when the control signal is lost due to cable faults, the electric actuator will open and close the control valve to the set protection value. The common protection values have three situations, fully open, fully closed, or keep the last position. The intelligent electric actuator can be flexibly modified through on-site settings, and any position (0~100%) can be set as the protection value.

III. Choose the electric valve actuator according to the valve operating torque

The torque required for the normal opening and closing of the valve is determined by factors such as valve diameter, working pressure, etc. However, the processing accuracy and assembly process of different valve manufacturers are different, so the torque required for the same specification valve is also different. When selecting the type of actuator, if the torque of the actuator is too small, the valve cannot be opened and closed normally. Therefore, the electric actuator must select a reasonable torque range. The output torque of the electric actuator should be 1.2 to 1.5 times the maximum torque of the valve operation.

IV. Electrical parameters of electric actuators

Due to the differences in electrical parameters of different actuator manufacturers, it is generally necessary to determine their electrical parameters during design and selection, mainly including motor power, rated current, and secondary control loop voltage.

The most important parameter of electric actuators is the output force.

For linear electric actuators, the unit is N or Kg, 10N = 1Kg, which is called thrust. For rotary type electric actuators, The unit is Nm or Kg.m, 10Nm=1Kgm.

When selecting the output force, it should be determined according to the maximum driving force of the control valves. Generally, the actuator is required to retain 30% of the margin to be safe. Because the calculation of the driving force of the valve is very complicated, the following gives some empirical data of common valves:

Electric Actuator Torque for Gate Valves (DN25~DN, Pressure Rating 1~320Kg/cm2, 0.1~32MPa&#;Toque Unit: Kg.m)

gate valve torque

Electric Actuator Torque for Globe Valves (DN15~DN350, Pressure Rating 6~320Kg/cm2, 0.6~32MPa, Toque Unit: Kg.m)

globe valves torque

Electric Actuator Torque for Ball Valves (DN50~DN, Pressure Rating 6~100Kg/cm2, 0.6~10MPa, Toque Unit: Kg.m)

ball valves torque

Electric Actuator Torque for Butterfly Valves (DN50~DN, Pressure Rating 2.5~25Kg/cm2, 0.25~2.5MPa, Toque Unit: Kg.m)

butterfly valves torque

Electric actuator is an indispensable part of automatic control system and a very important driving device in industrial process control system. It uses electric energy as power, accepts a certain signal and amplifies its power, and converts it into the corresponding angle or linear displacement of the output shaft to push various control mechanisms to complete the operation process. It has the characteristics of easy access to power, simple installation and debugging, etc. It can be used on many industrials such as food and beverage, water treatment, oil and gas, mining industry etc..

1.Basic introduction to electric actuators

There are many types of electric actuators, mainly in the following two classifications.

&#; According to the different movement forms of the actuator, it can be divided into 3 categories.

Serial number

Actuator type

Movement angle

Main application

1

Rotary

Corner <360 degrees

Suitable for ball valves, plug valves, butterfly valves, etc.

2

Multi-turn

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Corner>360 degrees

Suitable for gate valve, globe valve, etc.

2

Linear

Linear motion

Suitable for single- seat control valve, double-seat control valve, etc.

&#; According to the different functions of the valve, it can be divided into two categories: switch type and adjustment type. The main difference: the switch type generally realizes the open or close control of the ball valve, and does not require precise control of the medium flow. The regulating type not only has the structure of the switch type, but also can accurately adjust the flow of the medium.

2.

Electric actuator

structure and working principle

The main structure of the electric actuator is mainly composed of three parts: servo motor, mechanical deceleration and position transmitter.

&#; Reduction box includes base, gear, hand wheel, turbine worm, output shaft, coupling, etc.

&#; Motors include DC motors, single-phase motors, three-phase motors, variable frequency motors, etc.

&#; Position transmitter, mainly to receive and output position current signal.

3.Advantages and disadvantages of electric actuators

The main advantages are:

&#; Easy to use the power source

&#; High signal sensitivity and precision, and long transmission distance, easy to control

&#; Easy installation and simple wiring

&#; It also has the characteristics of strong anti-deviation ability.

The main disadvantages are:

&#; The structure is more complex, prone to failure, and the technical level of the maintenance personnel is high.

&#; Too frequent adjustment will easily cause the motor and electrical components to overheat and burn out, and will also increase the wear of the reduction gear.

&#; The operating speed of the actuator slower.

4.Electric actuator selection steps

Step 1: Type selection of electric actuator:

&#; First, select the type of electric actuator according to the type of valve required: there are many types of valves, and the working principles are different. Some realize the switch control by rotating the valve plate angle, and some realize the opening and closing switch control by lifting the valve plate. Therefore, when choosing an electric actuator, you should first look at the type of valve and which control method is needed.

&#; According to the production process requirements, determine the control mode of the electric actuator: whether to choose the on off type or the adjustment type.

Step 2:Determine the output torque of the electric actuator according to the torque required to open and close the valve:

It is necessary to first understand the maximum torque required to open and close the valve, and then select an electric actuator suitable for the output torque according to the torque. The torque for open and close the valves are determined by factors, for example the size of the valve diameter and working pressure etc.

Step 3: Determine the electrical parameters according to the selected electric actuator:

Because of the parameters of electric actuator manufactured from different company. But it is necessary to check their electrical parameters ( such as torque, motor power, rated current, voltage, etc.). The negligence in this regard results in the mismatch between the parameters of the control system and the electric actuator, resulting in faults such as tripping of the spacer, blown fuse, and thermal overload relay protection tripping during operation.

Step 4: Select the enclosure protection grade and explosion-proof grade according to the application.

Step 5: Choose a suitable gearbox or thrust conversion device.

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