Brochure

5.
Part I – Fundamentals
A centrifugal pump operated at constant speed delivers
any capacity from zero to maximum depending on the
head, design and suction conditions. Pump performance
is most commonly shown by means of plotted curves
which are graphical representations of a pump’s perfor
-
mance characteristics. Pump curves present the average
results obtained from testing several pumps of the same
design under standardized test conditions. For a single
family residential application, considerations other than
flow and head are of relatively little economic
or functional
importance, since the total load is small and the equip
-
ment used is relatively standardized. For many smaller
circulators, only the flow and pressure produced are
represented on the performance curve (Fig. 1-1).
For larger and more complex buildings and systems,
economic and functional considerations are more critical,
and performance curves must relate the hydraulic effi
-
ciency, the power required, the shaft speed, and the net
positive suction head required in addition to the flow
and pressure produced (Fig. 1-2).
Pump performance curves show this interrelation of pump
head, flow and efficiency for a specific impeller diameter and
casing size. Since impellers of more than one diameter can
usually be fitted in a given pump casing, pump curves show
the performance of a given pump with impellers of various
diameters. Often, a complete line of pumps of one design
is available and a plot called a composite or quick selection
curve can be used, to give a complete picture of the
available head and flow for a given pump line (Fig. 1-3).
Such charts normally give flow, head and pump size only,
and the specific performance curve must then be referred
to for impeller diameter, efficiency, and other details. For
most applications in our industry, pump curves are based
on clear water with a specific gravity of 1.0.
Part II – The System Curve
Understanding a system curve, sometimes called a
system head curve, is important because conditions in
larger, more complex piping systems vary as a result
of either controllable or uncontrollable changes. A pump
can operate at any point of rating on its performance
curve, depending on the actual total head of a particular
system. Partially closing a valve in the pump discharge
or changing the size or length of pipes are changes in
system conditions that will alter the shape of a system
curve and, in turn, affect pump flow. Each pump model
has a definite capacity curve for a given impeller diame
-
ter and speed. Developing a system curve provides the
means to determine at what point on that curve a pump
will operate when used in a particular piping system.
Fig. 1-1
10
20
10
JSA/MS 2-18-02 PC-2066 RevA ECN10627
CURVES BASED ON CLEAR WATER
WITH SPECIFIC GRAVITY OF 1.0
5.50"(140mm)
0
2HP
3HP
5HP
5
7.5HP
6.00"(152mm)
6.50"(165mm)
7.00"(178mm)
7.50"(191mm)
5 10 15
REQUIRED NPSH
2
0
8
4
6
Size 4 X 3 X 7.0
Min. Imp. Dia. 5.50"
Curve no. 2066
20
25 30 35
0
50
100
200
6
0
24
12
18
30
77%
75%
79%
77%
75%
65%
50%
55%
60%
70%
55%
50%
60%
65%
70%
(1.5KW)
(2.2KW)
(3.7KW)
(5.6KW)
75
30
45
60
0
15
HEAD IN FEET
300
FLOW IN GALLONS PER MINUTE
150750 225 450375 525 600
Model 3007 1760 RPM
L/SEC
FI & CI Series
AUGUST 27, 2001
FEET
HEAD IN KILOPASCALS
HEAD IN METERS
KPa
NPSH
Fig. 1-2
Fig. 1-3