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
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
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.