Pump Performance Curves

The performance of a pump is defined in two ways. For the catalog data for a pump, the polynomial coefficients, which form the equation that defines the characteristics of the pump, are stored, whereas for an actual pump, a series of tests are taken and the results of these tests are stored only as points.

For a pump curve, everything is expressed in terms of flow (or Q as it is referred to). There are actually three curves for each pump (head, power, and efficiency), and these take the form of polynomial equations.

For example, if the equation to define the efficiency of a pump can be expressed as:

P = 3Q^3 + 2.7Q^2 + 1.91Q + 27.34, where P = Power and Q = Flowrate

There would be four records instantiated in the R_Pump_Curve_Coeffs class, and they would have the following values:

Coefficient_Type Coefficient_Index Coefficient_Value

P 1 3

P 2 2.7

P 3 1.91

P 4 27.34

From these values, the polynomial that defined the power can be reconstituted.

The equations are derived from a best-fit curve that follows the results of a series of tests where they vary the flow rate, measure the head and power, and derive the efficiency.

If you solve the equation for max value of efficiency, you get the best efficiency point (BEP). The values for the efficiency at this point as well as the values for the flowrate, head, and mechanical power at this point, are denormalized out and stored in the R_Pump_Curve_Cat class along with the Min and Max operating flow values for that pump.