Selection of electric devices for electric valves

Electric valves are widely used in the water supply and drainage systems of municipal and industrial and mining enterprises . The electric valve is composed of an electric device, a valve body, a connecting accessory and a control box. The electric device of the electric valve is an indispensable driving device for realizing valve program control, automatic control and remote control.
Electric valves are generally selected by the water supply and drainage professional. Water supply and drainage professional technicians must put forward specific functional requirements for the electric devices of the valves during engineering design, and the electric devices are selected by professional manufacturers. However, in actual engineering, there is often a mismatch between the valve electric drive device and the control system during field installation. This is usually due to unreasonable or imperfect conditions in determining the functional requirements of the electric device.
Second, the composition of the valve electric device
The electric device generally consists of the following parts: a dedicated motor speed reduction mechanism for reducing the output speed of the motor; a stroke control mechanism for adjusting and accurately controlling the opening and closing position of the valve; and a torque limiting mechanism for adjusting the torque (or thrust) And make it not exceed the predetermined value; manual, electric switching mechanism, interlocking mechanism for manual or electric operation; opening indicator to indicate the position of the valve during the opening and closing process. Among them, the stroke control mechanism, the torque limiting mechanism, the manual, the electric switching mechanism, and the opening degree indicator are collectively referred to as an electric actuator .
Third, the electric equipment selection, the key points to pay attention to when determining the functional requirements
When selecting the electric device and determining the functional requirements, the points to be noted include determining the IP protection level of the electric device, the power supply voltage of the electric device, the 90° running time of the electric device, and the form of the electric actuator .
1. Determine the IP protection level of the electric device
When selecting the electric device, first determine the IP protection level of the electric device according to the working environment and the use requirements . Generally, the electric valve driving device of the water supply and drainage system can be divided into outdoor type and indoor type according to different working environments. Outdoor electric valve driving device is commonly used IP protection IP54 or IP55, conventional IP protection level Indoor electric valve drive means is IP43 or IP44. Usually, the valve electric drive of the water supply and drainage system does not use a submersible type. The IP protection level of the electric device shall be proposed and determined by the water supply and drainage professional technicians.
2. Determine the power supply voltage of the electric device
At present, the power supply voltage commonly used by domestic users is 380V and 24V , which should be determined according to the power supply conditions that the outside world can provide.
3. Determine the 90° running time of the electric device
The so-called 90° operating time of the electric device is the time required for the electric valve to be in place and closed. This requirement is determined by the professional manufacturer of the valve and electric device. Conventional 90° operating time varies from 7.5 to 30 s , but should meet the requirements of the water system process. The shorter the 90° running time, the higher the electric motor power of the electric device and the higher the current.
High-power pumps are usually started with a closed valve light load to reduce the current that the pump starts. A check valve , an electric valve, etc. are installed on the water outlet pipe of the water pump . Generally, the valve closing time is 10 to 30 s . Therefore, the 90° running time of the electric device of the pump outlet electric valve should be consistent with the valve closing time determined by the water supply and drainage process. If the opening and closing speed of the valve is too fast, water hammer is likely to occur.
In the water of industrial and mining enterprises, there is usually an accident emergency water supply system that is supplied by a safe water tank or a water tower. The electric emergency valve is also often provided on the emergency water supply pipe. In order to ensure the safety of production, the electric valve of the accident water supply pipe is required to be opened in time and sensitive. Therefore, the 90° running time of the electric device of the valve should also be shortened as much as possible.
4. Determine the form of the electric actuator
( 1 ) Common forms of electric actuators
1 ) Switch type (open loop control). Switch-type electric actuators generally implement switching control 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. Switching electric actuators can be divided into separate structures and integrated structures due to different structural forms. This must be explained when selecting the type, otherwise mismatches such as conflicts with the control system during on-site installation will often occur.
2 ) Adjustable type (closed loop control). The regulated electric actuator not only has the function of a switch-type integrated structure, but also precisely controls the valve to regulate the flow of the medium. The control signal includes current and voltage. The control signal of the regulated electric actuator generally has a current signal ( 4 to 20 mA , 0 to 10 mA ) or a voltage signal ( 0 to 5 V , 1 to 5 V ). The type of control signal should be clearly defined during the selection. parameter.
The working mode of the regulating electric actuator is generally electric opening type (take 4 to 20 mA control as an example, the electric opening type means that the 4 mA signal corresponds to the valve closing, the 20 mA corresponds to the valve opening), and the other is the electric switching type. (For example, 4 to 20 mA control, 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).
Loss of signal protection means that when the control signal is lost due to a fault such as a line, the electric actuator will control the valve to open and close to the set protection value. The common protection values ​​are full open, full off and hold in place.
Switched electric actuators also have loss of signal protection.
( 2 ) Determining the form of the electric actuator
1 ) Determination of switch type and adjustment type. In the water supply system of municipal and industrial and mining enterprises, the main function of the electric valve is to open or close the water pipe. Therefore, the switch type electric actuator is commonly used. However, in the cooling water system of many intermediate piping of industrial and mining enterprises, the accuracy of water supply requirements such as flow rate and pressure is very high. The change of cooling water flow and pressure has a great influence on the production conditions of the equipment. The electric valve used in the case shall be equipped with an adjustable electric actuator.
Before determining whether the electric actuator is switched or adjusted, firstly, it should thoroughly understand the specific working conditions of the electric valve used, and then propose reasonable functional requirements to professional manufacturers.
The determination of the type and working form of the regulated control type shall be determined according to the specific production conditions and working conditions of the process equipment.
2 ) Determination of the split structure and the form of the integrated structure. The disadvantage of the electric actuator of the split structure is that it is inconvenient to install the whole system, increase the wiring and installation cost, and is prone to failure. When the fault occurs, it is not convenient for diagnosis and maintenance, and the cost performance is not satisfactory.
The advantage of the integrated electric actuator is that it facilitates the overall installation of the system, reduces wiring and installation costs, and is easy to diagnose and troubleshoot. However, traditional integrated structural products also have many imperfections. Nowadays, the control of water supply and drainage systems or circulating water treatment systems of municipal and industrial and mining enterprises are controlled by PLC and computer programs, and have CRT screen display. The control of the water system is usually centralized in the water system control room or electrical room, and the PLC cabinet and MCC cabinet are installed in the electrical room . All on-site electrical equipment is only equipped with an operation box. The operation box is connected with the PLC cabinet in the electrical room , and then the signal is sent to the MCC cabinet. The Zui terminal controls the equipment on the site. Under such conditions, it is reasonable to use an electric actuator with a split structure. If an electric actuator with an integrated structure is used, its own function may not be completely matched with the overall design of the water system control, and it is easy to cause a malfunction. In addition, the price of the electric actuator of the split structure is also lower than that of the electric actuator of the integrated structure.
For some water systems that are simple, have low control requirements, or require only on-site control, an integrated electric actuator can be considered.
3 ) Determination of loss of signal protection. When the control signal is lost due to faults such as lines, the valve should be fully open, fully closed or kept in place. It should be determined according to the specific process conditions. Under normal circumstances, the valve should be kept in place.
The electric valve on the high-power water pump outlet pipe should be in the in-situ state when the fault is required. Because the electric valve is interlocked with the water pump, the pump opens and the pump closes. If the valve is closed due to a fault and the pump fails to shut down in time, water hammer damage will be caused to the pump equipment and the front piping and valves of the electric valve.
For the industrial water points of industrial and mining enterprises, especially the electric valves of the users of cooling water, when the electric valve is faulty, it should also be required to maintain the in-situ state, so as to avoid damage to the process equipment caused by sudden water cut.
5. Other matters
The valve electric device has other main parameters such as operating torque, operating thrust, number of output shaft rotations, stem diameter, output speed and motor power. This part of the parameters should be determined by the professional manufacturer.
The operating environment of the water system valve electric device is usually normal temperature, and the ambient temperature of the general electric device is - 20 to 55 °C , so it is not necessary to specify.
Fourth, the conclusion
Whether the selection of the electric device of the electric valve is reasonable is decisive for realizing the function of the electric valve. The specific selection of electric devices is of course carried out by professional manufacturers, but before the selection, the water supply and drainage professional technicians should provide reasonable functional requirements.