The Selection Of The Valve Air Opening/gas Shutoff And The Determination Of The Positive And Negative Action Of The Regulator,

The selection of the valve air opening/gas shutoff and the determination of the positive and negative action of the regulator, the selection of the valve air opening/gas shutoff must be determined in terms of process production requirements and safety requirements. The principle is that when the signal pressure is interrupted, the safety of the process equipment and production should be ensured, that is, the valve automatically enters a safe state when the regulating valve loses the signal pressure source. After selecting the valve opening or closing mode, the positive and negative effects of the regulator must be determined according to the form of the valve, so that the regulating valve and the regulator constitute a negative feedback control system. That is, for the gas-opening valve, if the controlled parameter is larger than the given parameter, the valve is required to be closed, then the regulator selects the reaction; for the gas-closing valve, if the controlled parameter is greater than the given parameter, the valve is required to be closed, then the regulator Just use positive action. By adjusting the flow rate of the valve, it is not only related to the opening degree of the valve, but also related to the pressure difference between the two ends of the valve. The flow characteristic of the valve before and after the pressure difference is the ideal characteristic of the valve. The flow characteristic of the valve differential pressure changes before and after the valve is the working of the valve. characteristic. The ideal characteristics depend entirely on the shape of the spool. 

Typical four flow characteristics are: (1) Straight flow characteristics. When a spool with linear flow characteristics is used, the magnification of the regulating valve is constant. Its characteristic is that the flow rate is relatively large at a small opening degree, the regulation effect is strong, and the oscillation is easy to occur; the relative change of the flow rate at the opening degree is small, the adjustment effect is weak, and the adjustment is slow. (2) Equal percentage flow characteristics (log flow characteristics). When a spool with equal percentage flow characteristics is used, the amplification factor of the regulating valve increases as the flow rate increases, but the relative change values of the flow rates are equal. It has a small magnification at a small opening, and the adjustment effect is gentle and stable; it has a large magnification at a large opening and a sensitive adjustment effect, which is often adopted for this purpose. (3) Parabolic flow characteristics (when the valve core with parabolic flow characteristics is used, the adjustment performance is good at a small opening degree, and its characteristic curve is between the straight line and the equal percentage characteristic curve. (4) The fast opening flow characteristic is quickly opened. There is no mathematical expression for the flow characteristics. When using a spool with a fast opening flow characteristic, there is a large flow rate when the opening degree is small. As the opening degree increases, the flow rate quickly reaches a maximum value, which is suitable for rapid Open and close shut-off valve or two-position adjustment system.