Brochure

Figure 5.1: Reduction of theoretical Euler
head due to losses.
Q
H
P
Q
Recirculation losses
Leakage
Euler head
Flow friction
Incidence
Pump curve
Q
H
P
Q
Figure 5.2: Increase in power consumption
due to losses.
Mechanical losses
Disk friction
Shaft power P
2
Hydraulic power P
hyd
Hydraulic losses
Loss
Smaller
flow (Q)
Lower head (H)
Higher power
consumption (P
2
)
Mechanical
losses
Bearing
Shaft seal
X
X
X
X
X
X
X
X
Flow friction Hydraulic
losses
Mixing
Recirculation
Incidence
Disk friction
Leakage
7878
5. Pump losses
As described in chapter 4, Euler’s pump equation provides a simple, loss-
free description of the impeller performance. In reality, because of a number
of mechanical and hydraulic losses in impeller and pump casing, the pump
performance is lower than predicted by the Euler pump equation. The losses
cause smaller head than the theoretical and higher power consumption, see
figures 5.1 and 5.2. The result is a reduction in eciency. In this chapter we
describe the dierent types of losses and introduce some simple models for
calculating the magnitude of the losses. The models can also be used for
analysis of the test results, see appendix B.
5.1 Loss types
Distinction is made between two primary types of losses: mechanical losses
and hydraulic losses which can be divided into a number of subgroups. Table
5.1 shows how the dierent types of loss aect flow (Q), head (H) and power
consumption (P
2
).
Pump performance curves can be predicted by means of theoretical or em-
pirical calculation models for each single type of loss. Accordance with the
actual performance curves depends on the models’ degree of detail and to
what extent they describe the actual pump type.
5. Pump losses
Chart 5. 1: Losses in pumps and their influence on the pump curves.