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

Step 3
Step 4
The NPSH/Q Diagram (Fig. 21) shows the NPSH req, that amounts to 1.9 m.
Fig. 21
The impeller diameter of 160 mm is required in order to read out the required motor power
in the Q/P Diagram (Fig. 22). Accordingly, at a flow rate of 24 m 3/h the motor power is 3.7
kW. Fluctuations in volume and pressure must be expected in the plant and consequently
fluctuations of the operating point, that causes variation of the power consumption P of the
pump. This is the reason why in principle an increased factor of 5% is fixed.
The result is that the motor size should be at least to 4 kW (the required 3.7 kW plus increased
safety). The next larger sized standard motor has 4 kW and should therefore be selected.
Fig. 22
The power consumption of a pump can also be calculated using the formula
P =
NPSH
[ft] [m]
20 6
5
15
4
10 3
2
5
1
0 0
0
P
[hp] [kW]
5,0
6,0
5,0
4,0
3,0
2,0
1,0
4,5
4,0
3,5
3,0
2,5
2,0
1,5
1,0
0 5 10 15 20 25 30 35
Q
ρ x Q x H
η x 367
NPSH req = 1.9 m
5 10 15 20 25 30 35
P = 3.7 kw
and using the diagrams, the missing parameters for the optimal pump design are
made available.
The required flow rate of 24 m 3 /h and the specified flow head of 33 m require the use of the
pump TP 2030 with an impeller diameter 160 mm and 4 kW motor capacity at
n = 2,900 rpm and 50 Hz.
The efficiency of this pump is about 57 % and the NPSH of the pump (1.9 m) does not
exceed the NPSH of the plant (9.4 m > 1.9 + 0.5 m) so that cavitation does not occur.
Accordingly, the pump is suitable for the application in question.
27
GEA Tuchenhagen
Ø110 Ø160
Ø110
Ø130
Ø120
Ø140
Q
Ø160
Ø150
40
40