Two centrifugal pumps in series add head at a common flow. The resulting system duty still needs a combined curve.
Identify the Physical Basis
For pumps arranged in series, H_total(Q) = H_1(Q) + H_2(Q). KSB’s series-operation reference explains the common-flow addition and the higher pressure exposure of the downstream pump casing and seals. The pumps share the throughflow, but the flow after installation is determined by the new combined curve and the system curve.
Work Through an Example
At a hypothetical 3 m³/h, one pump’s curve shows 12 m of head and another shows 8 m. Their combined ordinate at that same flow is 20 m. Adding values from 3 m³/h on the first curve and 5 m³/h on the second would not construct a valid series point. Likewise, adding two separate “maximum” head values does not show head at the required duty.
Use the Result in the Review
Prepare a table using several identical Q values for both pumps. Overlay the combined curve on the system curve and record the resulting point. Review downstream inlet and casing pressure as well as net head, because upstream pressure is carried forward. Keep the selected fluid density, speed and curve revision visible. Ask the supplier to review suction conditions and control sequencing for the actual arrangement.
The storage-tank page identifies a possible transfer-interface context, not an installed two-pump configuration. A useful order discussion states the required route duty and pressure envelope. This worksheet deliberately does not prescribe a start or stop sequence for an unselected system.
Does the series combination meet the connected duty and component-pressure scope?
This blank worksheet is for your own project. It contains no H M machine trial result.
| Review field | Reference or result | Responsible person |
|---|---|---|
| Common-flow head table for both pumps | To complete | To complete |
| Combined curve and system intersection | To complete | To complete |
| Downstream absolute pressure envelope | To complete | To complete |
| Supplier-reviewed arrangement and controls | To complete | To complete |
Customer Questions
Does series operation mean double the flow?
No. Add head at common flow, then find the new system intersection.
Can the two pumps have different curves?
They can, but evaluate their common-flow performance and permitted duties.
Is the downstream pump only exposed to its own added head?
Its inlet also receives upstream pressure; component ratings need review.
Related Equipment References
Review the actual offered equipment and application separately from this educational example.
Primary References
These references support the technical principles discussed in this guide. The worked examples and review questions are educational.
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