Pumps operating in series versus pumps operating in parallel In water-supply and irrigation engineering, how do multiple pumps behave when connected in different configurations? Choose the correct comparison between pumps connected in series and pumps connected in parallel.
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APumps operating in series boost the discharge, whereas pumps operating in parallel boost the head.
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BPumps operating in parallel boost the discharge, whereas pumps operating in series boost the head.
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CIn both cases there would be a boost in discharge only.
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DIn both cases there would be a boost in head only.
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ENeither head nor discharge changes; only efficiency improves.
Answer
Correct Answer: Pumps operating in parallel boost the discharge, whereas pumps operating in series boost the head.
Explanation
Introduction:Pump networks are frequently arranged to meet varying field demands for head (energy per unit weight) and discharge (flow rate). Understanding how series and parallel configurations change the overall head–discharge performance is a foundational concept in fluid mechanics and water resources engineering.
Given Data / Assumptions:
- Pumps are identical or similar centrifugal pumps working near their rated region.
- Steady incompressible flow of water; minor losses in manifolds are modest.
- System curve (head loss versus discharge) is well behaved and increasing with discharge.
Concept / Approach:
In series, the same discharge passes through each pump, and heads add; in parallel, the same head is produced by each branch, and discharges add. The combined head–discharge curve of a multi-pump arrangement is constructed by adding ordinates (head) at the same flow for series, or abscissae (flow) at the same head for parallel, then intersecting with the system curve to find the operating point.
Step-by-Step Solution:
1) Series: Q is common; total head H_total = H1 + H2 (+ …).2) Parallel: H is common; total discharge Q_total = Q1 + Q2 (+ …).3) Compare effects: series → higher head to overcome larger static lift or long pipelines; parallel → greater discharge to meet higher demand at moderate head.4) Select the option that states “parallel increases discharge, series increases head”.Verification / Alternative check:
Plot a single-pump H–Q curve. For series, vertically add heads at identical Q; for parallel, horizontally add Q at identical H. The intersections with the system curve confirm the expected behavior.
Why Other Options Are Wrong:
Options C and D ignore the clear distinction between series and parallel operations. Option A inverts the correct roles. Option E is incorrect because head/discharge do change; efficiency may improve or decline depending on matching.
Common Pitfalls:
Forgetting that real pumps must also satisfy NPSH and cavitation limits; ignoring check valves in parallel headers; assuming identical pumps without considering slight curve mismatches.
Final Answer:
Pumps operating in parallel boost the discharge, whereas pumps operating in series boost the head.