Correct selection of 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 the electric regulating valve are divided into ideal flow characteristics and working flow characteristics. The flow characteristic provided by a general manufacturer is an ideal flow characteristic, while the actual application requires the characteristic of the flow of flow. As the pressure drop is less than 1 S, the flow characteristics are convex. Therefore, when selecting the flow characteristics of the regulating valve, the selection of the flow characteristics should be considered first. Then, the ideal flow characteristics are selected according to the actual application. The ideal flow characteristics commonly used in production are linear, equal percentage and fast opening characteristics. The fast opening characteristic is mainly used for two position control and program control. Therefore, the choice of flow characteristics of regulating valve usually refers to how to reasonably select the ideal flow characteristics of linear and equal percentage.


In actual use, the regulating valve is always installed in the process pipeline system. The pressure difference between the front and back of the regulating valve varies with the resistance of the pipeline system. Therefore, when selecting the flow characteristics of the regulating valve, it should be considered not only according to the process characteristics but also the piping situation of the system.


(1) according to the characteristics of the process, the flow characteristics of the valve are selected. The control law of the conventional controller is linear. The parameters of the controller are adjusted to adapt to a certain range of work and do not need to be adjusted regularly. This requires that the generalized object is linear, that is, when the load, the pressure change before the valve or the change of the set value, the characteristics of the generalized object remain the same. Therefore, from the perspective of the automatic control system requirements, selection principle of the working characteristic of the regulating valve is to make the generalized object with linear characteristics, namely in the generalized object, characteristics of remainder valve outside (transmitter characteristics, process characteristics) is linear, the flow characteristics of control valve selection should line work (i.e. Kv is a constant); if the transmitter characteristics are linear, and the process characteristics of the amplification coefficient is decreased with the increase of tile manipulated variables and decreases, the control valve flow characteristics such as the percentage of work should be selected. In conclusion, when the generalized object (except the control valve) has nonlinear characteristics, the regulator should be able to overcome its nonlinear influence and make the generalized object approximate to the linear characteristic.


(2) according to the situation of piping, the ideal flow characteristics are deduced from the required flow characteristics. At the production site, the regulating valve is always connected with the pipes and other equipments, so there must be a piping resistance, which makes the flow characteristics of the regulating valve and the ideal flow characteristics different. Therefore, when selecting the characteristics of the regulating valve, it should be considered in combination with the process piping of the system. According to the pressure drop ratio S value, the ideal flow characteristics can be determined from the selected work flow characteristics.