Electric valve electric device selection
Column:Technical article Time:2017-12-06
Electric valves are widely used in municipal and industrial and mining enterprises of the drainage system. Electric valve by the electric device, the valve body, connecting accessories and control box and ...

I. Introduction

Electric valves are widely used in municipal and industrial and mining enterprises of the drainage system. Electric valve by the electric device, the valve body, connecting accessories and control box and other components. Electric valve electric device is to achieve the valve program, automatic control and remote control indispensable drive equipment.

Electric valve is generally selected by the professional water supply and drainage, water supply and drainage of professional and technical personnel in the design of the valve must be made of electric devices specific functional requirements, and by the professional manufacturer of electric device selection. 
However, in practical projects, it often happens that on-site installation, the valve electric drive and control system conflict and other mismatch phenomenon. This is usually due to an unreasonable or imperfect determination of the functional requirements of the electric device.

Second, the composition of the valve electric device

Electric device generally consists of the following parts: Dedicated motor reducer, to reduce the motor output speed; stroke control mechanism to regulate and accurately control the valve opening and closing position; torque limit mechanism, used to adjust the torque (or thrust ) And so that it does not exceed the predetermined value; manual, electric switching mechanism, manual or electric operation of the interlock mechanism; opening indicator to show the valve in the opening and closing process in which position. 
Among them, stroke control agencies, torque limit agencies, manual, electric switching mechanism and the opening indicator collectively referred to as the electric actuator.

Third, the electric device selection, determine the functional requirements of the points to be noticed

In the electric device selection, determine the functional requirements, the points to note include determining the IP rating of the electric device, electric device power supply voltage, electric device 90 ° operating time and the form of electric actuators.

1. Determine the IP rating of the motorized unit

In the selection of electric device, first of all, according to the working environment and the use of electrical equipment to determine the IP rating. 
General to the drainage system electric valve drive device in accordance with the different working environment can be divided into outdoor, indoor type. Outdoor electric valve drive commonly used IP protection level is IP54 or IP55, indoor electric valve drive commonly used IP protection level is IP43 or IP44. Normally, the valve electric drive to the drainage system is not submerged. The IP protection grade of the electric device shall be proposed and determined by the water supply and drainage professional and technical personnel.

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 conditions provided by the outside world.

3. Determine the 90 ° operating time of the electric unit

The so-called 90 ° operating time of the electric device, which is the time it takes for the electric valve to open and close, is determined by the manufacturer of the valve and electric device. 
Conventional 90 ° operating time 7.5 ~ 30s range, but should be consistent with the requirements of water system technology. The shorter the 90 ° operating time, the greater the electric motor power and the higher the current.

High-power pumps are usually closed-valve light-load start to reduce the pump starting current. 
In the pump outlet pipe equipped with check valves, electric valves and so on. Generally closed valve start time is 10 ~ 30s, therefore, the pump electric outlet valve electric device 90 ° operating time should be given to the drainage process to determine the valve closing time consistent. If the valve opening and closing speed too fast, easy to produce water hammer phenomenon.

In industrial and mining enterprises, water is usually provided by a safety tank or water supply accident emergency water supply system. 
Accident emergency water supply pipe is also often equipped with electric valve, in order to ensure the safety of production, electric valve accidental water supply pipe open timely, responsive, therefore, the valve electric device 90 ° running time should also be as short as possible.

4. Determine the form of electric actuator

(1) Common forms of electric actuators

1) switch type (open-loop control). 
Switch-type electric actuator to achieve the general on-off control of the valve, the valve is either in the fully open position, or in the fully-closed position, such valves do not need precise control of the media flow. Switch-type electric actuator due to the different forms of structure can be divided into split structure and integrated structure. Selection must be made on this description, or often occur at the scene of the installation and control system conflicts and other mismatch phenomenon.

2) Adjustable (closed-loop control). 
Regulating electric actuator not only has the function of integrated switch structure, but also on the valve for precise control, regulating the flow of media. The control signals include current, voltage and regulated electric actuator control signals generally have current signal (4 ~ 20mA, 0 ~ 10mA) or voltage signal (0 ~ 5V, 1 ~ 5V) parameter.

Regulating electric actuator operating mode is generally open type (4 ~ 20mA control, for example, the electric open type 4mA signal corresponds to the valve is closed, 20mA corresponds to the valve open), and the other for the electric type (4 ~ 20mA control, for example, the electric open type is 4mA signal corresponds to the valve open, 20mA corresponds to the valve).

Loss of signal protection refers to the loss of control signals due to faults such as lines, the electric actuator will control the valve opening and closing to the set protection value, the common protection value is fully open, fully closed and remain in situ three cases.

Switch-type electric actuator also loss of signal protection.

(2) to determine the form of electric actuator

1) switch type and regulation of the determination. 
In the municipal and industrial and mining enterprises in the water supply system, the main function of the general electric valve is to open or close the water pipe, so the most commonly used is the switch-type electric actuator. However, in the process of industrial and mining enterprises, many intermediate piping cooling water system, the flow, pressure and other water supply accuracy is very high, the cooling water flow, pressure changes on the equipment production conditions have a significant impact, so in this Electric valves used in the case should be equipped with adjustable electric actuators.

In determining the electric actuator is used switch or regulation type, the first response to the specific working conditions of the electric valve to be in-depth understanding, and then to the professional manufacturer of reasonable functional requirements.

On the type of control-type control and work to determine the form, should be based on the specific production equipment and process conditions to determine.

2) The definition of split structure and integrated structure. 
Disadvantage of the split structure of the electric actuator is not easy to install the system as a whole, increasing wiring and installation costs, and prone to failure, when the fault is not easy to diagnose and repair, cost is not satisfactory.

The advantages of the integrated structure of the electric actuator is to facilitate the overall installation of the system to reduce wiring and installation costs, easy to diagnose and troubleshoot. 
However, the traditional integrated structural products also have many imperfections. Today, the municipal and industrial and mining enterprises, water supply and drainage systems or circulating water treatment systems and other controls are controlled by PLC and computer programs, and with CRT screen display. Water system control is usually concentrated in the water system control room or electrical room, the electrical room with a PLC cabinet and MCC cabinet. All on-site electrical equipment installed operation box on the scene, the operating box and the electrical cabinet connected to the PLC, and then send the signal to the MCC cabinet, the final control of the site equipment. Under such operating conditions, the use of split structure of the electric actuator is more reasonable. If the integrated structure of the electric actuator, its own function may not be fully matched with the overall design of the water system control, but prone to failure. In addition, the split structure of the electric actuator price than the integrated structure of the electric actuator is low.

For some simple water systems, low control requirements or only require on-site control of the operating conditions, consider the use of integrated structure of the electric actuator.

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 held in place. It should be determined according to the specific process conditions. Under normal circumstances, the valve should be kept in place.

High-power water pump electric valve on the outlet should be required to maintain the valve in place when the fault condition. 
Because the electric valve is interlocked with the pump control, pump open the valve, the pump off valve. If the valve is closed due to a fault and the pump is not shut down in time, it will cause water hammer damage to the pump equipment and to the electric valve's front piping, valves, etc.

On the industrial and mining enterprises of water production points, especially cooling water users at the electric valve, the electric valve failure, it should also be required to maintain its original state, so as to avoid sudden water damage to process equipment.

Other matters
Valve electric device operation torque, operating thrust, the number of output shaft rotation, stem diameter, output speed and motor power and other major parameters. This part of the parameters should be determined by the professional manufacturer.
Water system valve electric device working environment is usually room temperature, and general use of electric devices ambient temperature is -20 ~ 55 ℃, so do not mention the exact requirements.

Fourth, conclusion
Electric valve electric device selection is reasonable, for the realization of the function of electric valve has a decisive role. The specific selection of electric devices is, of course, carried out by a professional manufacturer, but before the selection, the professional and technical personnel of water supply and drainage should put forward reasonable functional requirements.