Page 19 - Centrifugal Pumps Design and Application

4 Centrifugal Pumps: Design and Application

Figure 1-1. System head curve.

losses for various flow rates. For any desired flow rate, the head to be
generated by the pump or pumps, can be read directly (Figures 1-1 and
1-2),

NPSHA

Net positive suction head available (NPSHA) is of extreme importance
for reliable pump operation. It is the total suction head in feet of liquid
absolute, determined at the suction nozzle and referred to datum, less the
vapor pressure of the liquid in feet absolute. This subject is discussed in
detail in Chapter 9.

Shape of Head Capacity Curve

The desired shape of the head capacity (H-Q) curve is determined dur-
ing analysis of the system. Most specifications call for a continuously
rising curve (Figure 1-3) with the percentage rise from the best efficiency
point (BEP) determined by system limits and mode of operation, Unsta-