How to correctly select the flow rate of the electric control valve?

 

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 electric control valves 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. How to correctly select the flow rate of the electric control valve?

 

 

How to choose the working flow characteristics of electric control valve

1. According to the process characteristics, select the working flow characteristics of the electric actuated valves. 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. This requires the generalized object to be linear, that is, the characteristics of the generalized object remain basically unchanged when it encounters load, pressure changes in front of the valve or changes in the set value.

 

Therefore, from the perspective of the automatic valve control system, the principle of selecting the operating characteristics of the regulating valve is to make the entire generalized object have linear characteristics, that is, in the generalized object, the characteristics of the rest except the regulating valve (transmitter characteristics, process characteristics) When it is linear, a regulating valve with linear working flow characteristics should be selected (that is, Kv is a constant);

 

If the transmitter characteristic is linear, and the process characteristic amplification factor watt decreases with the increase of the manipulated variable, the electric 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 motor operated valve actuator should be able to overcome its non-linear 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 electric actuated gate 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 control valve, the process piping of the system should also be considered. After determining the pressure drop ratio S value according to the process piping conditions, the ideal flow characteristics can be determined from the selected working flow characteristics. In actual use, the motor actuated 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.