How to Choose the Flow of Electric Control Valve?

Electric control valve is an important executive unit instrument in industrial automation process control. With the increasing degree of automation in the industrial field, it is being used more and more in various industrial production fields. Compared with the traditional pneumatic control valve, the electric control valve has obvious advantages: energy saving, environmental protection and quick and convenient installation. According to the power used by the actuator, the valve is divided into three types: linear characteristic, equal percentage characteristic and parabolic characteristic according to its function and characteristics.

 

Valves mainly include linear actuator valve, electric actuated globe valve, motor operated ball valve and electrically operated butterfly valve, etc.

 

Electric control valves are used in the fields of industrial automation systems such as electric power, chemical industry, metallurgy, environmental protection, water treatment, light industry, and building materials.

 

Flow Characteristics of Electric Control Valve

 

The flow characteristic of the electric control valve is the relationship between the relative flow of the medium flowing through the electric control valve and its opening under the condition that the pressure difference between the two ends of the valve remains constant. The flow characteristics of the electric linear control valve are linear, equal percentage and parabolic.

 

The flow characteristics of the electric control valve directly affect the control quality and stability of the system, so it needs to be selected correctly.

 

The flow characteristics of the electric control valve are divided into ideal flow characteristics and working flow characteristics. The flow characteristics provided by general manufacturers are ideal flow characteristics, but the actual application requires working flow characteristics. Since the pressure drop ratio S is less than 1, the operating flow characteristics are convex. Therefore, when selecting the flow characteristics of the regulating valve, the working flow characteristics should be considered first. Then, select the ideal flow characteristics according to the actual application. The ideal flow characteristics commonly used in production are linear, equal percentage and quick opening characteristics. The quick opening characteristic is mainly used for two-position control and program control, so the selection of the flow characteristics of the regulating valve usually refers to how to reasonably select the linear and equal percentage ideal flow characteristics.

 

In actual use, the motorised actuator valve is always installed in the process piping system, and the pressure difference before and after the regulating valve changes with the resistance of the piping system. Therefore, when selecting the flow characteristics of the regulating valve, not only should it be based on the process characteristics, but also the piping of the system should be considered.

 

1. According to the process characteristics, select the valve working flow characteristics. The control law of the conventional controller is linear. After the parameters of the controller are adjusted, it is hoped that it can adapt to a certain working range and does not need to be adjusted frequently. If the transmitter characteristic is linear, and the process characteristic amplification factor watt decreases with the increase of the manipulated variable, the control ball valve should use the equal percentage working flow characteristic. In short, when the generalized object (except the regulating valve) has non-linear characteristics, the regulating valve should be able to overcome its nonlinear influence and make the generalized object close to linear characteristics.

 

2. According to the piping conditions, the ideal flow characteristics are inferred from the required operating flow characteristics. In the production site, the regulating valve is always used in conjunction with pipelines and other equipment, so there must be piping resistance, which makes the working flow characteristics of the regulating valve different from the ideal flow characteristics. Therefore, when selecting the characteristics of the electric actuator control valve, the process piping of the system should also be considered.