Manual for the Design of Pipe Systems and Pumps - GEA ...

6.3 Modification
6.3.1 Throttling
6.3.2 Changing
the speed
In the previous example the pump design took place in four steps.
In practice, however, pumps are used at different operating points. These may be pumping
of viscous media, temperature changes or systems with integratation of pressurised
tanks.
Changes in the flow head of a system H A (throttling) are realised in practice by increasing or
reducing the resistance on the delivery side of the pump, e.g. by installing a throttling valve.
In this case the operating point is always located on the intersection of the plant characterstic
curve with the pump characteristic curve.
H
Drosselung Throttling
Fig. 23 - Throttling
B 1
gedrosseltes Throttled valve Ventil
B 2
Changing the speed (n) causes a change of the operating point and thus of the flow rate (Q)
and the flow head (H). For this purpose a frequency converter or a pole changing motor is
needed. In spite of the high purchase costs for a frequency converter, its use is in view of the
operating costs the clearly more favourable alternative to the throttling process with a throttling
valve. Speed control is used, if different operating points shall be achieved, e.g. for product
and cleaning liquid.
H
H1
H 2
Drehzahländerung
Changing the speed
Fig. 24 - Changing the speed
B 2
28
GEA Tuchenhagen
B 1
D 2
Pump characteristic
geöffnetes Opened valve
Ventil
B 3
Plant characteristic
D 1
Q 2 Q 1 Q
Q
n2 Q2 = x Q1 n1 n2 n1 2
H 2 = x H 1
n2 n1 3
P 2 = x P 1