System curve
The energy imparted to liquid by pump to achieve required flow rate is system head. There are
two components of system head that is maintained by pump:
1. Static head: Difference in elevation and pressure (independent of flow rate),
2. Dynamic head: Friction loss in the pipes, pressure drop through equipment, and miscellaneous
losses (roughly proportional with flow rate).
The system curve, or operating line, is a plot of the total pressure head versus the liquid flow rate.
When selecting a centrifugal pump for a given duty, it is important to match the pump
characteristic with system curve. The operating point should be as close as is practical to the point
of maximum pump efficiency, allowing for the range of flow-rate over which the pump may be
required to operate.
Figure 7.8 represents system head and differential head versus capacity. The intersection point of
two head curves is flow rate which will be delivered by the pump at a particular speed.
| 
