Brochure
5353
3.4.3 Start/stop regulation
In systems with varying pump requirements, it can be an advantage to use
a number of smaller parallel-connected pumps instead of one larger pump.
The pumps can then be started and stopped depending on the load and a
better adjustment to the requirements can be achieved.
3.4.4 Speed control
When the pump speed is regulated, the QH, power and NPSH curves are
changed. The conversion in speed is made by means of the anity equa-
tions. These are futher described in section 4.5:
(3.1)
(3.2)
(3.3)
(3.4)
(3.5)
(3.6)
(2,19)
⋅ =
n
n
QQ
A
B
AB
n
n
HH
A
B
AB
2
⋅
=
n
n
PP
A
B
AB
3
⋅ =
n
n
NPSHNPSH
A
B
AB
2
⋅
=
PPPPP
L,avg 25%50%75%100%
0.440.350.150.06 ⋅+⋅+ ⋅+ ⋅=
[ ]
−=
Ref
L,avg
P
P
EEI
(3.1)
(3.2)
(3.3)
(3.4)
(3.5)
(3.6)
(2,19)
⋅ =
n
n
QQ
A
B
AB
n
n
HH
A
B
AB
2
⋅
=
n
n
PP
A
B
AB
3
⋅ =
n
n
NPSHNPSH
A
B
AB
2
⋅
=
PPPPP
L,avg 25%50%75%100%
0.440.350.150.06 ⋅+⋅+ ⋅+ ⋅=
[ ]
−=
Ref
L,avg
P
P
EEI
(3.1)
(3.2)
(3.3)
(3.4)
(3.5)
(3.6)
(2,19)
⋅ =
n
n
QQ
A
B
AB
n
n
HH
A
B
AB
2
⋅
=
n
n
PP
A
B
AB
3
⋅ =
n
n
NPSHNPSH
A
B
AB
2
⋅
=
PPPPP
L,avg 25%50%75%100%
0.440.350.150.06 ⋅+⋅+ ⋅+ ⋅=
[ ]
−=
Ref
L,avg
P
P
EEI
(3.1)
(3.2)
(3.3)
(3.4)
(3.5)
(3.6)
(2,19)
⋅ =
n
n
QQ
A
B
AB
n
n
HH
A
B
AB
2
⋅
=
n
n
PP
A
B
AB
3
⋅ =
n
n
NPSHNPSH
A
B
AB
2
⋅
=
PPPPP
L,avg 25%50%75%100%
0.440.350.150.06 ⋅+⋅+ ⋅+ ⋅=
[ ]
−=
Ref
L,avg
P
P
EEI
Index A in the equations describes the initial values, and index B describes the
modified values.
The equations provide coherent points on an anity parabola in the QH
graph. The anity parabola is shown in figure 3.11.
Dierent regulation curves can be created based on the relation between
the pump curve and the speed. The most common regulation methods are
proportional-pressure control and constant-pressure control.
Figure 3.11: Anity parabola in the QH graph.
H
Q
n = 100%
Coherent
points
Affinity
parabola
n = 80%
n = 50%