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 ar  double-suction volute 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

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

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

• Propeller pump with blade pitch adjustment
  See Fig. 4 Characteristic curves selection chart
• Mixed flow pump with pre-swirl control equipment
  See Fig. 5 Characteristic curves selection chart

The individual characteristic curves selection charts of several pump sizes or type series are shown in one comprehensive selection chart in an H/Q diagram. See Fig. 6 Characteristic curves selection chart

By trimming the impeller, the characteristic curve of every pump size can be adapted within its selection chart range to match the required operating point.