A Self-Learning Manual - Institution of Engineers Mauritius

A Self-Learning Manual
Mastering Different Fields of Civil Engineering Works (VC-Q&A Method) Vincent T. H. CHU
Losses due to adverse pressure gradient occur in pumps as the pressure
of flow increases from the inlet to the outlet of pumps and the flow travels
from a region of low pressure to high pressure. As such, it causes the
formation of shear layers and flow separation. Flow oscillation may also
occur which accounts for the noise and vibration of pumps. The effect of
adverse pressure gradient is more significant in low flow condition.
For shock losses, they are induced when the inflow into pumps is not radial
and contains swirl. In an ideal situation, the flow within the pump should be
parallel to the impellers such that the flow angle is very close to the
impeller angle. The deviation of the above situation from design causes
energy losses and vibration.
Fig. A diagram showing point of best efficiency≠operating point
7. What is the minimum volume of sump volume for pumps?
Maximum pumping rate =
Volume of sump = V
Inflow Rate =
Qi
Cycle Time Tc
= t + t
t
1
V
=
Q − Q
p
V
t 2
=
Qi
i
1
2
Q p
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