Library / Engineering / KEVOS® original book

Centrifugal Pumps by the Numbers

Head, flow, power and efficiency, pump curves and operating points, NPSH and cavitation, speed control, series and parallel pumps, and selecting a pump

Select, run and fault-find centrifugal pumps with numbers: head and power, curves and operating points, NPSH and cavitation, affinity laws, throttling, series and parallel, and life-cycle cost.

10 chapters · About 100 minutes · Free to read · Intermediate engineering and maintenance

Start reading
KEVOS® LibraryENGINEERINGCentrifugalPumps by theNumbersKEVOS® ORIGINAL BOOK10 CHAPTERS

About this book

The centrifugal pump is the most common machine in industry after the electric motor that drives it. It moves water to cooling towers, washwater to header tanks, chemicals between vessels and condensate back to boilers, and in most plants it uses more electricity than anything else that is not making product. Most pumps were selected once and are rarely questioned afterwards, and many run far from where they should: throttled, oversized, cavitating, or running against closed valves.

This book works through centrifugal pumps with one running case. It sets out what a pump does to the water, how head, flow, power and efficiency relate, how to read a pump’s curves, and where a pump will run on a system. It then deals with net positive suction head and cavitation, the affinity laws and speed control, throttling, bypass and impeller trimming, pumps in series and parallel, starting and protecting pumps, and finally selecting a pump on its life-cycle cost. Each chapter calculates with the running case, includes a plausible mistake and how it was found, and ends with an exercise and its worked answer.

It is for mechanical and maintenance engineers, technicians and operators. It assumes school algebra and a calculator or spreadsheet, and the ideas of head, friction and the system curve; the Library’s Pipe Flow by the Numbers sets those out from the beginning, and Water Hammer by the Numbers deals with the surges that pump starts and trips cause.

The running case

Every chapter follows one fictional pump. This is an illustration. A food processing plant collects washwater in a concrete sump and pumps it, as TP-3 on its drawings, to a header tank on the roof, from which it feeds the plant’s wash-down hoses by gravity. The pump is an end-suction centrifugal pump on a plinth beside the sump, lifting from a water level 0.5 to 2.0 m below its centreline, through a foot valve and 6 m of suction pipe, and delivering through 120 m of steel pipe of 105.3 mm bore to a free discharge 18.0 m above its centreline. The plant needs at least 12 L/s. The water is at about 20 °C.

The plant, its pump, the pump’s curves, prices and mistakes are invented. None describes KEVOS® work, a real business or any manufacturer’s product.

How to use the book

Read Chapters 1 to 4 first: they set out the pump’s energy conversion, its power and efficiency, its curves and its operating point, which every later chapter uses. Chapters 5 to 9 each deal with one way pumps are protected, controlled or combined, and Chapter 10 brings them together in a selection and a commissioning record. Every calculation was checked by running it.

Source limits and professional responsibility

The pump curves in this book are illustrations of typical shapes, not any product’s data; real selection uses the manufacturer’s tested curves, and real performance is confirmed by test. Pumps store and release large amounts of energy, run at high speeds, and handle liquids that may be hot, pressurised or hazardous; their installation, guarding, isolation and electrical work are governed by regulation and must be done by competent people. This book teaches the hydraulics and energy of pumps. It is not a design for any installation, and qualified review governs real work.

Who this book is for

Mechanical and maintenance engineers, technicians and plant operators who select, commission, run or fault-find centrifugal pumps on water and similar liquids.

What you will learn

  • Convert between a pump's head, flow, power and efficiency, and read every curve on a pump data sheet.
  • Find where a pump will run on a system, and how that point moves with level, ageing and valves.
  • Work out the NPSH a system makes available, compare it with what the pump requires, and prevent cavitation.
  • Use the affinity laws, throttling, bypass, impeller trimming and variable speed, and know what each costs in energy.
  • Run pumps in series and parallel, protect them at start-up and low flow, and select one on its life-cycle cost.

Inside this book

Chapters

  1. 01What a centrifugal pump doesHow an impeller and volute turn shaft power into head, why head depends on tip speed and not on the liquid, TP-3 in numbers, a pump's head measured across its flanges, and a head read from one gauge.
  2. 02Head, flow, power and efficiencyHydraulic, shaft and electrical power, pump and motor efficiency, TP-3's power curve and motor, the A$ cost of each megalitre, and a business case built on hydraulic power.
  3. 03Reading pump curvesThe four curves on a data sheet, the best efficiency point and the range around it, impeller families and speeds, what a curve promises, and a spare pump on a motor of the wrong speed.
  4. 04The operating pointTP-3's lift-dominated system curve, where it meets the pump curve, how the point moves with sump level, ageing and a clogged foot valve, and a pump chosen on a curve with no lift.
  5. 05NPSH and cavitationCavitation, NPSH available and required, TP-3's 4.0 m margin and what altitude, hot water and a clogged foot valve take from it, and a pump moved up a plinth that began to cavitate.
  6. 06Affinity laws and speed controlFlow, head and power with speed, TP-3 at reduced speed, why slowing a pump on a lift system saves little and can cost more per m³, where speed control pays, and a cube-law business case.
  7. 07Throttling, bypass and impeller trimmingFour ways to hold TP-3 to 12 L/s for a treatment unit: a throttled valve, a bypass, a trimmed impeller and a slower speed, each priced in A$ a year, and an impeller trimmed by the wrong ratio.
  8. 08Pumps in series and parallelCombined curves in parallel and in series, TP-3's duty and standby pair together for 19.8 L/s, two pumps in series pushed past their range, and a worn standby pump that ran at shut-off.
  9. 09Starting, priming and protecting a pumpPriming a pump that lifts, why a pump must not run dry or at shut-off, heat and minimum flow, starting and stopping, the protections that work, and a foot valve that let the prime go.
  10. 10Selecting and commissioning a pumpA selection procedure from duty to shortlist, specific speed, TP-3's life-cycle cost in A$ with GST, commissioning checks and the pump record, and a replacement chosen on price that cost A$3,390 more.

Related Tools and Examples

References and source notes

The manuscript and worked examples are original KEVOS® writing. References inform particular concepts; their authors do not endorse this book. Web references were consulted on 27 October 2026.

  • US Department of Energy. DOE Fundamentals Handbook: Thermodynamics, Heat Transfer, and Fluid Flow, Volume 3 of 3 (DOE-HDBK-1012/3-92) (1992). Supplied source, a US government training handbook approved for public release, read as a subject map of centrifugal pumps: energy conversion, operating characteristics, cavitation and net positive suction head, the pump laws, and pumps in series and parallel. No text, figures, examples or exercises are reproduced; the running case, its curves, numbers and checks are this book's own.
  • US National Institute of Standards and Technology. Thermophysical Properties of Fluid Systems (NIST Chemistry WebBook) (2026). Source for the density, viscosity and vapour pressure of water used in the running case and the cavitation calculations.
  • US Department of Energy and the Hydraulic Institute. Improving Pumping System Performance: A Sourcebook for Industry (second edition) (2006). General reference for pumping system energy practice: matching pumps to systems, throttling and bypass losses, speed control and life-cycle thinking. No values are quoted from it.
  • L. F. Moody, Transactions of the ASME, vol. 66. Friction factors for pipe flow (1944). Source of the roughness of commercial steel pipe, 0.045 mm, used in the running case's system curve.

Continue exploring

← All Library books