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1. Overview

    Valve electric actuator is used to drive the valve to open and close a special transmission actuator, by the special motor, worm gear, travel and torque detection mechanism and control part of the composition. The actuator has a large starting torque, accurate valve stroke control, widely used in petroleum, chemical, hydropower, metallurgy, shipbuilding, light industry and food and other industries on the valve. Different industries and different working conditions have different requirements for valve electric actuators.

2. Classification    

    Valve actuator is generally classified according to the type of structure, mode of operation, slewing mode and working environment.

2.1、structure type

    The structure type of actuator can be divided into one-piece type and split type. Integral actuator is all the control actuators to control the operation of the actuator are installed inside the actuator, and the actuator as a whole. Integral electric actuator is divided into ordinary type and intelligent type. Split-type electric actuator is all control actuators to control the operation of the electric actuator are installed in another electric control cabinet.

2.2. Mode of work

    The operating mode of the actuator is divided into switching type and regulating type. Switching type mainly refers to the motor start-up times of the electric actuator is generally <600 times/min. switching type electric actuator is only suitable for one-time opening or closing of the valve. Regulating type mainly refers to the more frequent change of direction of the actuator, the motor start-up times are generally up to 1200 times/min.

2.3. Rotary mode

    Actuator rotations are categorised as multi-turn and partial-turn. Multi-return type mainly refers to the electric actuator to rotate more than one turn, in order to open or close the valve. This type of electric actuator and the valve to have a secondary drive mechanism. Partial rotation mainly refers to the electric actuator rotated 90 ° can open or close the valve. This type of electric actuator is directly connected to the valve.

2.4. Working environment

    The working environment of the electrical equipment is divided into explosion-proof type and ordinary type. Flame-proof type refers to the flammable and explosive environment, and requires the electrical equipment to have an explosion-proof function. Ordinary type refers to any environment other than flammable and explosive environment.

3、Selection

    The selection of the valve electrical equipment must meet the working conditions, valve switching torque, time (speed) and control requirements.

3.1, Ambient temperature

    The motor of the actuator is sealed inside the actuator, and its heat dissipation performance is poor, if the actuator is used beyond the adapted ambient temperature range, it will directly affect the insulating property, output torque and service life of the actuator. Therefore, in the high temperature environment must pay attention to the applicable temperature range of the electric actuator.

3.2 Protection level  

    The protection level of the electrical equipment is a measure of its degree of protection against dust and water, expressed in IP + two digits (Table 2), the first digit characterises the level of dust protection, the second digit characteris the level of water resistance. Indoor general environment chooses IP54 or IP55, outdoor general environment choose IP55 or IP65, if the working conditions of dust and dust particles smaller, may be from all directions on the electrical equipment has the possibility of water, should choose a higher level of protection of IP65 or IP67, if the electrical equipment may be submerged in water, should choose a higher level of protection, such as IP67 or IP68. ip68 protection The IP68 protection level means that the actuator can be submerged for 72h without water ingress at 3m underwater.

3.3. Forms of control

    The form of control mainly refers to whether the actuator is one-piece or split type. According to the use of some projects in recent years on the use of electrical installations, the general use of intelligent one-piece type. Intelligent actuator has LCD panel display and setting function, electronic position sensor and torque sensor, valve position feedback, automatic programme correction, instantaneous reversal protection, data logging, automatic diagnosis and support for fieldbus communication and other functions. Different working conditions require different forms of control for the electric actuator.  Different working conditions on the form of control of the electrical equipment requirements are not the same. From the price considerations, in regular working conditions or on occasions where the requirements of the electronic actuator is not high, generally do not choose the intelligent one-piece electric actuator. In high temperature or high cold conditions, because the performance of the control circuit board inside the one-piece electric actuator is greatly affected by the temperature, generally do not choose the intelligent one-piece type.

3.4. Torque

    Actuator torque is one of the important parameters, the maximum torque required in the valve switching process must be calculated before selection, and then calculate the output torque of the required actuator. The torque selection of the valve electric actuator should be based on the rated output torque provided by the electric actuator manufacturer. When calculating and reviewing the torque of the valve, the margin of torque should not be too large. Since the electric actuator has a torque protection function, if the margin of the switching torque of the valve is too large, the output torque of the selected electric actuator will be selected to be larger, and when the valve encounters jamming during the switching process, the weak part of the valve may be damaged before the torque protection switch of the electric actuator is actuated.

3.5, Rotation speed 

    The output rotational speed of the motor affects the valve switching time. Some conditions stipulate the valve switching time, the output speed of the electric actuator must be selected in accordance with the requirements. Some working conditions do not require the valve switching time, but the motor of the electric actuator is short-time working system, its continuous operation time does not exceed 10min, some do not exceed 15min. Therefore, even if the working conditions do not require time, the valve switching time must not exceed the maximum time required for continuous operation of the electrical equipment.  actuator's output speed and output torque have a relationship, the same motor power, its output speed, the faster the output torque will be smaller. Therefore, in the selection of electrical equipment, torque and speed must be matched.

3.6 Control requirements

    Control requirements is the user monitoring system on the requirements of the valve electric actuator, such as electric actuator is a regulating type or switching type. General regulating type electric motor can be started frequently, up to 1200 times / h, can accept and feedback 4 ~ 20mA analogue signal, closed-loop control, automatic adjustment of the valve opening to adapt to the requirements of the working conditions. Switching type electric actuator only control valve open or close, the motor cannot be started frequently, the motor continuous working time is generally 10min, some 15min. in addition, there are other requirements, such as the need to feedback to the central control room of the valve status and electric actuator control methods.

    Valve electric actuator compared with other important equipment in the pipeline system, although the value and technical content is low, but the product has its own particularity, the selection of reasonable or not will directly affect the normal operation of the pipeline system and reliable. Therefore, electric valve users should have a deep understanding of the basic parameters of the electric actuator, selection procedures and the use of the requirements to ensure the safety of the pipeline system to help.

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