Series and parallel centrifugal pumps

In the different industrial and commercial processes we can find in the distribution networks of water, arrangements of pumps connected in series or in parallel in order to adapt to a greater range of pumping heights and flow ranges

Parallel  centrifugal pumps.

It is said that two or more pumps are placed in parallel when their flows converge in a Pipe. The resulting flow is the sum of all flows. In these arrangements there is no increase in discharge pressure.

Example of Parallel Pumps.

For a practical demonstration we will take as reference two Pumps whose characteristic curves are shown below.

To obtain the resulting equipment curve, we draw lines at constant availability (H) and cut the individual pump curves and record the flow rate. The resulting curve will be the value of H selected vs the sum of flow of each pump for the set value.

For the example we select 6 random values ​​of H identified in the graph as: 1,2,3,4,5,6 We measure the flow values ​​of each Pump for said flow and add them, the resulting one will correspond to the flow of the arrangement in parallel . In this case, we can see that for availability between 58m and 64m, pump 1 does not provide flow to the flow network. Both pumps will provide flow for availability between 48m and 58m.Below is the operating curve of both pumps working in parallel.

Series centrifugal pumps

Two or more Pumps are connected in series when the resulting flow of one is delivered to the next. This arrangement allows to obtain pumping heights greater than those that each pump would achieve individually

Examples of centrifugal pumps in series.

For the series pump arrangement, the curves of the two pumps shown above will be taken, 6 flow values ​​will be selected and lines at constant flow will be drawn intercepting the curve of each Pump, the availability values ​​are taken and added together.

The final graph will be the result of the selected flow rate vs the sum of availability at that flow rate. Below is the curve of both pumps running in series

From this curve we can see that the series arrangement handles a higher lifting height while maintaining the flow handled by each pump

Differences between series and parallel  centrifugal pumps.

After analyzing the curves and the information reported above we can mention the following differences between the two arrangements.

Regarding the flow, the arrangement in parallel each pump brings its value to the equivalent while in series the flow is common to both pumps.

The resulting elevation height of the parallel array retains the operating range of the associated pumps, while in series the lift height increases as it passes through the next pump.


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