I have a question about pumps in series and parallel for a professional exam
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It’s a question from the first day; I forgot whether it was in the morning or afternoon. The question provides the characteristic curves of the pump and those of the piping system, and it asks whether to calculate the shaft power for a series or parallel configuration I only know that when connected in series, the flow rate remains unchanged while the head is less than twice the original value; when connected in parallel, the head stays the same but the flow rate is half of the original value. I’m not sure exactly by how much it’s reduced. How should one calculate the head or flow rate after connecting components in series or parallel? I would appreciate some advice on how to solve this
In series, the flow rate of a single pump is the same as that of the pipeline, while the head doubles; thereafter, it is solved by combining this with the pipeline equation. In parallel operation, the flow rate of each individual pump is half of the total flow rate in the pipeline, while the head remains unchanged; thereafter, the equations related to the pipeline are used to find a solution. Tianjin University textbook P117
The flow rate when pumps are operated in parallel is greater than the flow rate of a single pump, but less than the sum of the flow rates when the two pumps operate separately. Moreover, the steeper the pipeline resistance characteristic curve, the less the increase in flow rate when operating in parallel. When there is a large variation in flow rate requirements, or when the flow rate produced by a single pump is not sufficient, it is possible to use two centrifugal pumps in parallel. When pumps are connected in series, if the starting point of the resistance characteristic curve of the delivery system is below the shut-off head of a single pump, series operation not only increases the head but also raises the flow rate; however, the resulting head is less than the sum of the heads of the two pumps. If the two pumps connected in series have different specifications, the total flow rate will be limited by the flow rate of the smallest pump among them. It depends on the pump’s performance curve.