PUMP ARRANGEMENTS
Pumps are often arranged to supplement each other when one pump may not be able to meet system requirements.
Multiple pumps may also be required in places where backup or reserve supply is essential such as hospitals, clinics, residential buildings etc.
In such cases, pumps may be organized in various configurations.
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Let us take a detailed look at some of them.....
SERIES PUMPING:
This is a type of pumping in which 2 pumps are arranged in series one before the other. Applying the continuity equation, we know that the flow through each pump will be the same, but the pressure through each varies.
The pressure at each point due to each pump essentially gets added in the system. Thus for identical pumps, pressure at each point gets doubled at the same flow rate.
In the given figures, the pumps each operate at the same flow, but they raise the pressure head of the water by different levels. These are required when water is needed at a higher-pressure level.
The above graph indicates the variation of the pump curve for single pump operation and series pump operation. The pumps are hence able to raise the pressure of the same quantity of water by a greater amount in case of series arrangement.
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NOTE:
We observe here that the pump curve for a single pump also intersects the system curve at a point. Thus if one of the pumps is down for maintenance, the other one can take over and provide part flow. Thus it is necessary to choose such an appropriate pump, so that single-pump operation can meet around 80% of the design flow.
PARALLEL PUMPING:
In this case, the pumps are installed in parallel. Each pump provides its share of the flow, but the pressure across each of the pumps remains the same. This is the ideal configuration in a situation when single pump of large capacity is not available and hence two parallel pumps provide the required flow rates.
Thus, the flows of the pumps get added at each pressure level and result in a new pump curve. This arrangement is called parallel pumping. This is used when high flow rates are required at lower pressures. The pump curve changes are given in the figure below.
The given figure indicates how the pump curve changes with addition of a pump in parallel.
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Note:
Just like in series pump operation, the single pump can provide approximately 80% of the pump flow during its operation.