PUMPING SYSTEMS
Keep talking, it pays dividends
PeterMaslin, KSB’s general
manager - sales & contracts, gives
a pump manufacturer’s view of
how a pumping system can be
improved by good communication
A
re we as pump manufacturers
oversensitive and paranoid or is there a
real issue that needs to be addressed?
We start to worry when a pumping system fails
to operate as the designer envisaged. More often
than not the first call is to the pump This appears to be an attractive station, but note that discharge pipes pass through the walkway
manufacturer informing him that his product is
not performing correctly and would he please are made aware of the design concepts at every discharge pipe runs. Is there the possibility of
come and sort it out. stage in a separate exchange of information with surge? Is there any likelihood of air pockets
There are many reasons why a system is the client, consultant and plant constructor they forming? What criteria were applied to size pipe
unable to perform as expected and whilst the may only be provided with the very minimum of supports and will this necessitate a vibration
pump is an obvious suspect, in practice, many of data. The result is that the pump is selected analysis? When pumping sewage, what
the problems encountered reflect some element against some base data, for example liquid, flow, minimum flow velocity has been used to
or more likely a combination of factors in the suction and discharge head. Worse still the client prevent the settling out of solids? Whilst 0.8m/s
whole system that was not considered fully may then select the successful supplier on the may be acceptable in horizontal pipes a figure of
during the design phase. basis of capital cost or even lowest whole life 1.5m/s should be used for vertical pipes. What
It would be presumptuous to infer that had all cost without considering whether the pump is screening if any will be installed and what will be
aspects been considered and details passed to truly suited to the application. the outcome should these fail?
the pump manufacturer all would have been The station layout will also have a bearing on
well, but pump manufacturers do endeavour to What can the pump manufacturer how easy the equipment will be to access for
design and market products that will operate contribute to the design? service and maintenance. Is there sufficient
without problem and be as efficient as possible A full description of the medium to be pumped space around the pumps? Is it possible to isolate
for the given application. They also have a wealth and whether there is any tolerance on the the pump? Have adequate lifting facilities been
of knowledge that they are happy to readily pumping rate will help the manufacturer to provided? Is the inlet sump accessible?
share that could save designers of pumping select a pump with the best hydraulic, operating It is important to consider how the system will
systems a lot of time, grief and money. as near to optimum efficiency as possible. When operate and be controlled. What is the control
Clients wishing to build and operate a pumping sewage it is always a good idea to philosophy and is this compatible with the
pumping station will present their ideas and select a pump with the duty point as close as hydraulic operating conditions? Pumps operating
requirements with all technical and fiscal possible to optimum efficiency as this should in parallel or series or with variable speed drives
boundary conditions to the designers. Too often greatly reduce the chance of blockages. place additional demands on control functions.
cost and time pressure can result in many The station layout and positioning of the Are there sufficient sensors within the system to
aspects of the project not being fully considered pump(s) in the station can help or hinder provide the necessary signals for control?
at the planning stage and any oversights carried performance. The position of the inflow to the Where a variable speed drives (VSD) is to be
through to construction and later commissioning station, the basic sump shape, floor slope and utilised care is necessary especially in wastewater
and operation leading to operational problems. corner fillets can all impact on performance. systems where the inappropriate use of VSD may
The remedies for all parties may be limited after Minimum and maximum suction levels may lead to blocked pumps, pipes and valves. An
the station has bee completed and will almost dictate whether a horizontal or vertical pump is issue of particular importance is the starting and
certainly be expensive. the best choice although available space may be stopping of centrifugal pumps. A long run up
There follows some examples of the design the first consideration here. Can standard proven time together with a long pipeline and high static
elements that should receive consideration when solutions be applied to predict station head may mean the pump is unable to
embarking on any system design or upgrade and performance or would it be better to perform discharge liquid in to the pipe at reasonable
where appropriate how we as a leading pump CFD calculations or even a model test? velocity. The result is that solids and abrasives
manufacturer can offer guidance. For this to Have the pipes and valves been sized to become trapped in the pump causing excessive
happen it must be recognised that it is important provide optimised flow loss? The pumps are wear and tear to components such as wear rings.
that we create an environment of open often selected on efficiency but how often do The bearings can also be subjected to additional
communication between the various parties we consider flow losses in the pipes and hence load when the pump operates at low flows and
involved in the design and construction of their contribution to an energy efficient system? if cavitation is present the mechanical seal as
pumping stations. Unless pump manufacturers Other questions that we need to ask about the well as the bearings can be damaged. ■■■
4 Consultant & Contractor File February2010