Electric control valve flow how to choose

The flow characteristics of the electric control valve directly affect the quality and stability of the control system, so the correct choice.

Electric control valve flow characteristics of the sub-flow characteristics and characteristics of the work flow characteristics. The flow characteristics provided by the general manufacturer are ideal flow characteristics, while the actual application needs is the work flow characteristics. Due to the pressure drop ratio S is less than 1, the working flow characteristics convex. Therefore, the choice of regulating valve flow characteristics, should first consider the choice of working flow characteristics. Then, according to the actual application to select the ideal flow characteristics. The ideal flow characteristics commonly used in production are linear, equal percentage, and quick open characteristics. The quick-opening characteristic is mainly used for the two-position control and the program control. Therefore, the selection of the flow characteristics of the regulating valve generally refers to how to select the ideal flow characteristics of linearity and equal percentage.

In actual use, the control valve is always installed in the process piping system, the control valve before and after the pressure drop is with the pipeline system resistance changes. Therefore, the choice of flow characteristics of the control valve, not only based on process characteristics, but also should be combined with the piping system to consider.

(1) According to the process characteristics, select the valve flow characteristics. Conventional controller control law is linear, the controller parameters tuning hope to adapt to a certain range of work, do not need to be adjusted often. This requires that the generalized object is linear, that is, the properties of the generalized object remain basically unchanged in the event of a load, a change in pres- sure pressure, or a change in setpoint. Therefore, from the point of view of automatic control system, the principle of selecting the working characteristic of the control valve is to make the generalized object have the linear characteristic, that is to say, in the generalized object, except for the characteristics of the rest of the regulating valve (transmitter characteristics, process characteristics) Is linear, you should use the linear flow characteristics of the control valve (that is, Kv is a constant); if the transmitter characteristics of linearity, and process characteristics of the amplification factor watts decreases with the manipulated variable increases, the control valve should be used Equal percentage flow characteristics. In short, when the generalized object (except the regulating valve) has non-linearity, the control valve should be able to overcome the non-linearity and make the generalized object approach the linearity.

(2) According to the piping conditions, the ideal flow characteristics are deduced from the required working flow characteristics. Regulating valve in the production site is always connected with the pipeline and other equipment used together, so there is necessarily the piping resistance, so that the flow characteristics of the control valve and the ideal flow characteristics of a certain difference. Therefore, the choice of control valve characteristics, but also should be combined with the system's piping to consider. According to the situation of process piping to determine the pressure drop than the S value, you can choose from the characteristics of the work flow to determine the ideal flow characteristics.