26

2021

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06

How to choose the electric valve correctly?

Author:


In pipeline engineering, the correct selection of electric valves is one of the guarantee conditions for meeting usage requirements. If the electric valve used is selected improperly, it will not only affect the use, but also cause adverse consequences or serious losses. So, how do we use electric valves correctly? Let Xiaobei slowly explain to you:

In pipeline engineering, the correct selection of electric valves is one of the guarantee conditions for meeting usage requirements. If the electric valve used is selected improperly, it will not only affect the use, but also cause adverse consequences or serious losses. So, how do we use electric valves correctly? Let Xiaobei slowly explain to you:

 

What is an electric valve?

 

Simply put, an electric valve uses an electric actuator to control the valve to open and close the valve. It can be divided into upper and lower parts, the upper part is the electric actuator, and the lower part is the valve. It can also be called air conditioning valve.

 

The electric valve is a high-end product among automatic control valves. It can not only realize the switching function, but the regulating electric valve can also realize the valve position adjustment function. The stroke of the electric actuator can be divided into two types: 90° angular stroke and straight stroke. Special requirements can also meet the full stroke of 180°, 270° and 360°. A angular-stroke electric actuator is used with a angular-stroke valve to realize internal rotation of the valve within 90° to control the fluid on and off of the pipeline; a straight-stroke electric actuator is used with a straight-stroke valve to realize the up and down movement of the valve plate to control the fluid on and off of the pipeline.

 

Technical principles

 

Electric valves are usually connected by an electric actuator and a valve, and become an electric valve after installation and debugging. The electric valve uses electric energy as power to connect the electric actuator to drive the valve to realize the switching and regulating actions of the valve. In order to achieve the purpose of switching or adjusting the pipeline medium.

 

Electric valves are generally driven by motors. It takes a certain amount of time to complete the opening or closing action, which can be adjusted. Relatively resistant to voltage shock. Solenoid valves are quick to open and close, and are generally used in places with small flow rates and small pressures that require high switching frequency; the opposite is true for electric valves. The opening of the electric valve can be controlled, and the states are open, closed, half-open and half-closed. It can control the flow of the medium in the pipeline but the solenoid valve cannot meet this requirement. 

 

The three-wire electric valve has three lines: F/R/N. F represents the forward action (or open action) control line, R represents the reverse action (or close action) control line, and N represents the ground wire. The solenoid valve is a type of electric valve; it uses the magnetic field generated by the solenoid coil to pull the valve core, thereby changing the on-off state of the valve body. When the coil is powered off, the valve core relies on the pressure of the spring to return.

 

What types of electric valves are there?

 

1. Electric valves can be divided into switch-type electric valves and regulating-type electric valves according to valve position functions;

 

2. According to the valve position form, it can be divided into: electric ball valve and electric butterfly valve;

 

3. According to the shape of the valve body, it can also be divided into: ordinary electric valves and micro electric valves;

 

4. Electric valves are generally of switch type and regulating type;

 

5. According to the wiring, it can be divided into three-wire and two-wire systems. Large-caliber ones are mostly three-wire systems, while small-caliber ones can be divided into two-wire and three-wire systems.

 

Working environment of electric valve

 

In addition to paying attention to the pipeline parameters of electric valves, special attention should be paid to the environmental conditions in which they work, because the electric device in the electric valve is an electromechanical device, and its working conditions are greatly affected by its working environment.  Normally, the working environment of electric valves is as follows:

 

1. Indoor installation or outdoor use with protective measures;

 

2. Installed outdoors and exposed to wind, sand, rain, dew, sunlight, etc.;

 

3. In an environment with flammable or explosive gas or dust;

 

4. Environment in humid tropics and dry tropics;

 

5. The pipeline medium temperature is as high as 480℃ or above;

 

6. The ambient temperature is below -20℃;

 

7. Easily flooded or immersed in water;

 

8. Environment with radioactive materials (nuclear power plants and radioactive material testing facilities);

 

9. Environment on ships or docks (with salt spray, mold, moisture);

 

10. In situations with severe vibration;

 

11. Situations prone to fire; 

 

For electric valves in the above environment, their electric device structures, materials and protective measures are different. Therefore, the corresponding valve electric device should be selected according to the above working environment.

 

 

Electric valve functional requirements

 

According to engineering control requirements, for electric valves, the control function is completed by electric devices. The purpose of using electric valves is to achieve non-artificial electrical control or computer control of the valve's opening, closing and adjustment linkage. The current use of electric devices is no longer just for saving manpower. Since the functions and quality of products from different manufacturers vary greatly, the selection of electric devices and the selection of matching valves are equally important to the project.

 

The valve electric device is an indispensable device for realizing valve program control, automatic control and remote control. Its movement process can be controlled by the stroke, torque or axial thrust. Since the working characteristics and utilization rate of the valve electric device depend on the type of valve, the working specifications of the device and the position of the valve on the pipeline or equipment, the correct selection of the valve electric device is crucial to preventing overload (the operating torque is higher than the control torque) is crucial.

 

 

When choosing electric valves, you should pay attention to the following points:

 

1. Operating torque Operating torque is the most important parameter for selecting the valve electric device. The output torque of the electric device should be 1.2 to 1.5 times the maximum operating torque of the valve.

 

2. There are two host structures for operating thrust valve electric devices: one is not equipped with a thrust plate and directly outputs torque; the other is equipped with a thrust plate and the output torque is converted into output thrust through the valve stem nut in the thrust plate.

 

3. The number of rotations of the output shaft of the valve electric device. The number of rotations of the output shaft of the valve electric device is related to the nominal diameter of the valve, the valve stem pitch, and the number of thread heads. It should be calculated according to M=H/ZS (M is the total requirement that the electric device should meet. The number of turns, H is the valve opening height, S is the valve stem transmission thread pitch, Z is the number of valve stem thread heads).

 

4. Valve stem diameter For multi-turn rising stem valves, if the larger stem diameter allowed by the electric device cannot pass through the valve stem of the matched valve, it cannot be assembled into an electric valve. Therefore, the inner diameter of the hollow output shaft of the electric device must be larger than the outer diameter of the valve stem of the rising stem valve. For partial-turn valves and concealed-stem valves in multi-turn valves, although there is no need to consider the passage of the valve stem diameter, the valve stem diameter and keyway size should also be fully considered when selecting and matching, so that they can work normally after assembly.

 

5. If the opening and closing speed of the output speed valve is too fast, water hammer may easily occur. Therefore, the appropriate opening and closing speed should be selected according to different usage conditions.

 

6. The valve electric device has its own special requirements, that is, it must be able to limit the torque or axial force. Usually valve electric devices use couplings that limit torque. When the specifications of the electric device are determined, its control torque is also determined.