Brochure

5151
3.3 Pumps operated in series
Centrifugal pumps are rarely connected in serial, but a multi-stage pump
can be considered as a serial connection of single-stage pumps. However,
single stages in multistage pumps can not be uncoupled.
If one of the pumps in a serial connection is not operating, it causes a consider-
able resistance to the system. To avoid this, a bypass with a non-return valve
could be build-in, see figure 3.6. The head at a given flow for a serial-connected
pump is found by adding the single heads vertically, as shown in figure 3.6.
3.4 Regulation of pumps
It is not always possible to find a pump that matches the requested perform-
ance exactly. A number of methods makes it possible to regulate the pump
performance and thereby achieve the requested performance. The most
common methods are:
1. Throttle regulation, also known as expansion regulation
2. Bypass regulation through a bypass valve
3. Start/stop regulation
4. Regulation of speed
There are also a number of other regulation methods e.g. control of pre-
swirl rotation, adjustment of blades, trimming the impeller and cavitation
control which are not introduced further in this book.
Figure 3.6: Pumps connected in series.
Q
max
Q
operation,a
= Q
operation,b
H
max,a
H
operation, a
H
Q
H
operation, b
Q
operation
, a
= Q
operation
, b
H
operation
,a
H
operation
,b
H
max,total
H
operation,tot
= H
operation,a
+H
operation,b