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

5.8 Q-H characteristic
diagram
Before designing a pump, it is important to ascertain the characteristic curve of the plant
that allows you to select the right pump by help of the pump characteristic curve
The operating performance of centrifugal pumps is rarely represented in the form of tables,
but mainly in the form of characteristic curves (Fig. 15). These pump characteristic curves are
measured at line machines at constant speed and show the flow rate (Q in m 3/h) and the flow
head (liquid column in m) of the pump. The flow head H of a pump is the effective mechanical
energy transferred by the pump to the pumped liquid, as a function of the weight force
of the pumped liquid (in m liquid column). It is independent of the density (r) of the pumped
liquid; that means a centrifugal pump transfers liquids regardless of the density up to the
same flow head. However, the density must be taken into account for the determination of
the power consumption P of a pump.
The actual flow head of the pump is determined by the flow rate H A of the plant, which
consists of the following components:
0
HA = Hgeo +
pa ρ
-
x
pe g
+
v 2
a - v 2
e
2g
+ Σ Hv H geo
pa - pe ρ x g
0
v a 2 - v e 2
Σ H v
2g
geodetic flow head = the difference in height to overcome between the liquid
level of the suction and the delivery side
difference of pressure heights between liquid level of the suction and
delivery side with closed tanks
speed difference (can be neglected in practice)
sum of pressure drops (pipe resistances, resistance in fittings and formed parts in
suction and delivery pipes)
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GEA Tuchenhagen