How to choose the flow rate of electric regulating valve
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Release Time：2019-09-02
The flow characteristics of the electric control valve are divided into ideal flow characteristics and working flow characteristics. In general, the flow characteristics we provide are ideal flow characteristics, while practical applications require working flow characteristics. Therefore, in the choice of control valve flow characteristics, should first consider the choice of working flow characteristics. Then, the ideal flow characteristics are selected according to the practical 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 choice of regulating valve flow characteristics usually refers to how to reasonably choose the linear and equal percentage ideal flow characteristics. In actual use, the total
The flow characteristics of the electric control valve are divided into ideal flow characteristics and working flow characteristics. In general, the flow characteristics we provide are ideal flow characteristics, while practical applications require working flow characteristics. Therefore, in the choice of control valve flow characteristics, should first consider the choice of working flow characteristics. Then, the ideal flow characteristics are selected according to the practical 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 choice of regulating valve flow characteristics usually refers to how to reasonably choose the linear and equal percentage ideal flow characteristics.
In actual use, the regulating 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, it should not only be based on the process characteristics, but also consider the piping situation of the system.
(1)According to the process characteristics, the operating flow characteristics of the valve are selected. The control law of the regular controller is linear, and the parameters of the controller are expected to adapt to a certain working range without frequent adjustment. This requires the generalized object is linear, that is, in the face of load, valve pressure changes or set value changes, the characteristics of the generalized object remains basically unchanged. Therefore, from the perspective of the automatic control system, the selection principle of the working characteristics of the regulating valve is to make the whole generalized object have linear characteristics, that is, when the characteristics of the rest of the generalized object except the regulating valve are linear, the regulating valve with linear working flow characteristics should be selected; If the transmitter characteristic is linear, and the amplification coefficient of the process characteristic decreases with the increase of the manipulated variable, the control valve should be selected with equal percentage working flow characteristics. In short, when the generalized object (except the control valve) has nonlinear characteristics, the control valve should be able to overcome its nonlinear effects and make the generalized object close to linear characteristics.
(2)From the piping situation, the ideal flow rate characteristic is inferred from the required operating flow rate characteristic. At the production site, the regulating valve is always used together with the pipeline and other equipment, so there must be piping resistance, so that there is a certain difference between the working flow characteristics of the regulating valve and the ideal flow characteristics. Therefore, when selecting the characteristics of the regulating valve, the process piping of the system should also be considered.
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