5.2 Pump Chart - Relationships

The pump dealer needs to know the "required flow" and the "total dynamic head" (total head) to consult manufacturer pump charts, in making a selection for a specific pump.

Statements about a pump's maximum head or maximum flow can be misleading, because these values come from the extreme and opposite ends of the pump chart.

Note on the example of the Pump Chart that the maximum "head" occurs at a low flow.

The maximum flow occurs at a low-pressure head. Somewhere in between at a point of maximum pump efficiency we find the pump's most efficient flow and pressure head combination. The pump chart shows the relationships of head and flow for a given pump.

Note also in the Pump Chart that the maximum efficiency (peak) shown by the efficiency-flow line is 70%. The other line shows the relationship between head and flow for the pump.

In studying the two lines, note that the pump efficiency is low for the maximum head and maximum flow situations. The pump does the most work at the point where the efficiency is highest; this point is at 140 ft of head and 225 gpm flow. However, if we allow the pump to work in a range where it is 63% efficient or better, there is a range of higher and lower head and flow values for which the pump can be used.

A dealer uses the pump chart information to select the best available pump for each head and flow combination.