Understanding Pump Curves
Stable Curve Geometries
The curves below are for real pumps commonly sold on the pump market. They were selected to illustrate each type of pump curve. Study them to make sure you agree with the description below each curve.
Graph #1 - Stable Curve Pump
Head continuously decreases as flow increases.
And
The rate of decrease is relatively smooth, steady, and always increasing.
Graph #2 - Stable Flat Curve Pump
Head continuously decreases as flow increases, but the RATE of head drop is slow at low to mid-range flows then the rate increases at higher flows. On this pump graph the rate of head drop is slow for the first 50% of flow from shut-off to about 90 gpm, then the rate of head drop increases at higher flows beyond 90 gpm. On the flat portion of the curve, pressure change is undetectable with increasing flow rate, but this pump is still considered a stable curve pump.
Graph #3 - Stable Steep Curve Pump
Head continuously decreases as flow increases, the rate of drop is fast and steady from shut-off to maximum flow.
Summary
All 3 curves on this page represent real pumps with two common factors, they all have a smooth steady curve line, and they all exhibit a relatively continuous reduction in head as flow increases.
Some flat curve pumps exhibit little or no detectable head change as flow increases from shut-off. But as long as head does not rise with increased flow, and as long as the curve line is smooth, then that flat curve pump would be considered a steady curve pump.
Also, for a steady curve pump, the RATE of head drop may be steady for a certain flow range, but then the rate may increase as the flow rate increases near to the BEP point.
Follow the links below to pages focusing on other types of information provided in the Pump Characteristic and more, including graphs and explanations.
