# Characteristic curves selection chart

A characteristic curves selection chart is the graphic representation of several characteristic curves which shows the effect of various changing parameters on machines in one diagram. Examples of such parameters are the impeller diameter (see Impeller trimming), pre-swirl control (see Figs. 1 and 10 Cooling water pump), rotational speed (see Closed-loop control), propeller blade pitch angle (see Impeller blade pitch adjustment) and pump size. Figure 1 shows the characteristic curves selection chart of a double-suctionvolute casing pump whose head (H) and power input (P) curves are represented for several impeller diameters. The NPSH value does not usually change when the impeller is trimmed. See Fig. 1 Characteristic curves selection chart

Fig. 1 Characteristic curves selection chart: Selection chart of a double-suction volute casing pump with characteristic curves for five different impeller diameters at a rotational speed of n = 1450 rpm

In head selection charts, pump efficiencies are frequently plotted as constant efficiency curves. The head (H) selection charts of centrifugal pumps with radial and axial impellers at different rotational speeds also show the pump efficiencies as constant efficiency curves. The numerical values are frequently related to the values achieved at the best efficiency point and are therefore represented as dimensionless numbers. See Fig. 2 to 5 Characteristic curves selection chart

Fig. 2 Characteristic curves selection chart: Centrifugal pump with speed adjustment, specific speed ns=20 rpm

Fig. 3 Characteristic curves selection chart: Centrifugal pump with speed adjustment, specific speed ns=200 rpm

Fig. 4 Characteristic curves selection chart: Propeller pump with blade pitch adjustment, specific speed Fig. 5 Characteristic curves selection chart: Centrifugal pump with mixed flow impeller and pre-swirl control, specific speed

Similarly, the blade pitch angles are given as a further parameter in the head selection charts of the following pumps: