Pump Power Requirements; Pump Performance Curves; Pump Efficiency - Honeywell AUTOMATIC CONTROL SI Edition Engineering Manual

CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS

Pump Power Requirements

The pump curve in Figure 53 is part of a family of curves for a
pump. Each curve of the family represents a different size impeller
used with the pump at a specified rpm. It relates to the power
input required just to move the water (water power) as follows:
Water power, W = flow x pressure
Where:
flow = L/s
pressure = kPa
The motor driving the pump must have a power rating in excess
of water power to take care of bearing and seal friction,
recirculation within the housing, and impeller efficiency.
NOTE: Water power increases with pressure and flow. If flow
is allowed to increase, the motor may overload.
380mm DIA
300
355mm DIA
240
330mm DIA
180
300mm DIA
280mm
DIA
250mm
120 DIA
48
NPSH
60
0
0 12.5
50%
60%
70%
75%
55
NPSH
25 37.5 50
CAPACITY (L/s)
Courtesy of Aurora Pump
Fig. 54. 1150 RPM Typical Pump Curve.

Pump Performance Curves

Commercial pumps have performance curves showing the
following data for a given pump speed:
— Total pressure in kPa versus flow in L/s
— Total pressure versus flow for various impeller diameters
— Pump efficiency at various operating points
— Net positive suction pressure. Net positive suction
pressure is the absolute pressure in kPa required at the
suction inlet to prevent cavitation due to "boiling" and
formation of bubbles in the water.
Figure 54 is a typical performance curve showing some of
the preceding data. Impeller diameters are shown on the left.

Pump Efficiency

Pump efficiency is a comparison of water power developed
in the pump and motor power applied by the motor to the shaft
and impeller.
80%
81%
69
NPSH
81%
80%
103
NPSH
138
NPSH
5.5 7.5
KW
KW
62.5 75
ENGINEERING MANUAL OF AUTOMATIC CONTROL
338
75%
70%
60%
50%
22
KW
15
18.5
11
KW
KW
KW
87.5 100 112.5
C4090