The flow characteristics of a diaphragm pump refers to the relationship between the relative flow of the medium flowing through the valve and the displacement (relative opening of the valve). The ideal flow characteristics mainly include straight line, equal percentage (logarithm), parabola and quick opening. The curve and spool shape are shown in Figure 1 and Figure 2. The commonly used ideal flow characteristics are only straight line, equal percentage (logarithmic), and quick opening. The parabolic flow characteristic is between straight line and equal percentage. Generally, equal percentage characteristic can be used instead. Quick opening characteristic is mainly used in two-position adjustment and program control. Therefore, the choice of diaphragm pump characteristic is actually linear and equal percentage flow characteristic s Choice.
The selection of the flow characteristics of the air diaphragm pump can be calculated theoretically, but the methods and equations used are very complicated. At present, empirical guidelines are mostly used, specifically considering the following aspects: ①Analyze and select from the adjustment quality of the regulation system; ②Consider from the process piping situation; ③Analyze from the load change situation.
By choosing the flow characteristics of the diaphragm pump, the shape and structure of the valve core can be determined according to its flow characteristics. However, due to their structural characteristics, such as diaphragm valves and butterfly valves, it is impossible to change the curved surface shape of the valve core to achieve the desired result. The required flow characteristics can be achieved by changing the shape of the feedback cam of the valve positioner.
