Installation and Operation Manual
SA-07-11-87, Rev A
17
January 2019
System Head Curve
The point of intersection between the system
curve and the pump characteristic curve
determines the flow or operation for the
centrifugal pump. For steady flow to occur, the
system curve must intersect the pump
characteristic curve at a significant angle. The
following diagram gives examples of satisfactory
and unsatisfactory angles of intersection.
Figure 7. Typical Operation
Note: In Figure 7, the curve for pump A has a
significant angle of intersection with
system curves D and E. The system
curve D could represent a system with
the control valve wide open while curve
E could represent the same system but
with the throttle valve closed to reduce
flow from flow 1 to flow 2. Pump curve
B, on the other hand, will provide only
flow 2, even with the control valve wide
open (curve D). When the control valve
is partially closed to create system
curve E, the curve E and lower pump
curve B are practically parallel. The lack
of a significant angle of intersection
means that the system is unstable,
pump flow is likely to fluctuate
erratically and not respond to control
valve position.
A
B
Valve Partially Closed
Valve Wide
Open
