Pump Efficiency for Single Stage Centrifugal Pumps

Purpose of the Guide

This guide is for anyone wishing to

buy or select pumps and save

money. The aim is to help you choose a

pump of good efficiency. This will

reduce your energy costs. In some cases

the saving from just one additional

point of efficiency can pay for your

pump. We hope this Guide will also

reduce the energy used across the EU,

benefiting everyone through a better

environment.

Pump types and duties

This Guide should only be used for single stagecentrifugal pumps handling clean water at upto 95°C. Pump types covered are:

❚ End suction pumps having their ownbearings.

❚ End suction close coupled pumps, with theimpeller on the motor shaft.

❚ Double entry pumps having an axially splitcasing.

The applicable ranges of flow and head areshown on Figs 1 and 2 for pumps running atnominally 2900 and 1450 rpm.

2

❚ EUROPEAN GUIDE TO PUMP EFFICIENCY FOR SINGLE STAGE CENTRIFUGAL PUMPS

1000

100

1010 100 1000

Flow (m3/h)

Hea

d (

m)

10000

ESOB

DESC

ESCCESCCESCC

200 kW96 kW

23 kW

2.5 kW1.4 kW

ESCC End Suction Close Coupled

ESOB End Suction Own Bearings

DESC Double Entry Split Casing

1000

100

1010 100 1000

Flow (m3/h)

Hea

d (

m)

10000

ESOBESOBESOB

DESC

ESCC

680 kW

67 kW20 kW

7.4 kW

1.2 kW

ESCC End Suction Close Coupled

ESOB End Suction Own Bearings

DESC Double Entry Split Casing

Figure 1:Range coverage at best-efficiencyduties at 2900 rpm.

Figure 2:Range coverage at best-efficiencyduties at 1450 rpm.

EUROPEAN GUIDE TO PUMP EFFICIENCY FOR SINGLE STAGE CENTRIFUGAL PUMPS ❚

3

Method used forproducing the efficiency plots

Performance curves published inmanufacturers’ catalogues have been used toproduce six plots (Figs 3 to 8). The upperpump efficiency line on each plot shows the‘Catalogue mean of best-efficiency points’ atmaximum impeller diameter, after correctingfor pump head.

The lower line is an average of efficiencies forpumps typically selected for flows across therange, which are not always operating at bestefficiency point or maximum impeller diameter(Ref 1).

The two lines divide the plot into three areas:

❚ Optimum efficiency selections: highefficiency pumps operating at or close tothe best efficiency point

❚ Efficient selections: pumps whichprobably have a reasonable best efficiencybut, because of standard pump ranges,may have been quoted away from BEP(Best Efficiency Point)

❚ Lower efficiency selections: selection inthis area should only be accepted if otherparameters override (such as very lowNPSH, pump operating with short runtimes, spares inventory minimisation)

85

80

35

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30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 190 200Pump flow (m3/h)

Pum

p e

ffic

ien

cy +

C (

%)

0

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30

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45

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Effi

cien

cy c

orr

ecti

on

= C

Optimum efficiency selections

Lower efficiency selections

Efficient selections

130mHead

110m

90m

70m

50m40m

30m20m

20m

90

85

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Pump flow (m3/h)

Pum

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C (

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Effi

cien

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Head50m

40m

30m

20m15m

10m

15m 10m

Figure 3:Efficiencies of endsuction pumps withtheir own bearingsat 2900 rpm.

Figure 4:Efficiencies of endsuction pumps withtheir own bearingsat 1450 rpm.

How to use the efficiency plots:

1. Decide which type of pump you want.

2. Choose the flow and head at which youwould like maximum efficiency.

3. Get efficiency quotes from manufacturers(or use published information).

4. Check that the chosen flow and head arewithin the ranges of Figs 1 or 2.

5. Enter your chosen flow and head on theplot that suits the quotes (Figs 3 to 8).

6. Read correction factor ‘C’ on the right-handaxis.

7. Add ‘C’ to the efficiency that has been quoted.

8. Plot (quoted pump efficiency + correction‘C’) at your chosen flow.

If the point lies in the ‘Lower efficiencyselections’ area, seek higher efficiency quotes.

If the point lies in the ‘Efficient selections’area, you have a pump which may well have areasonable best efficiency but, because ofstandard pump ranges, has been quoted awayfrom BEP. You should therefore seek higherefficiency quotes, to see if you can get a pumpwith the BEP closer to your operating point.

If the point lies in the ‘Optimum efficiencyselections’ area, you have been quoted apump with high best efficiency and you areoperating close to BEP and you are unlikely toimprove on this selection.

85

75

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65

70

80

10 30 50 70 90 110 130 150 170 190 20020 40 60 80 100 120 140 160 180

Pump flow (m3/h)

Pum

p e

ffic

ien

cy +

C (

%)

0

5

10

15

20

25

30

35

40

45

50

55

60

Effi

cien

cy c

orr

ecti

on

= C




Head130m

110m90m

70m

30m40m

50m

20m

20m

85

90

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55

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30 35 40 45 50 55 60 65 70 75 80 85 90 95 100

Pump flow (m3/h)

Pum

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C (

%)

0

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Effi

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ecti

on

= C




Head50m

40m

30m

15m

20m

25m

10m

4


Figure 5: Efficiencies of endsuction closecoupled pumps at2900 rpm.

Figure 6:Efficiencies of endsuction closecoupled pumps at1450 rpm.


5

Important note: Although a quoted low efficiencymay be due to poor pump quality, it is more likelyto be due to your chosen duty not coinciding withthat pump’s best-efficiency point. Your flow may bebelow or above the optimum for that pump. Your

head will probably require a reduced diameterimpeller. A survey has suggested that you areunlikely to receive more than one quote in five inthe ‘Optimum efficiency selections’ area.

80

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55

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130 150 170 190 210 230 250 270 290 310 330 350 370 390

Pump flow (m3/h)

Pum

p e

ffic

ien

cy +

C (

%)

0

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Effi

cien

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ecti

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= C




Head

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110m130m

150m

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Pump flow (m3/h)

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C (

%)

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Effi

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Head

20m

30m

40m

50m

60m

80m

140m120m

100m

15m 20m

40m 30m

Figure 7: Efficiencies ofdouble entry axiallysplit casing pumpsat 2900 rpm.

Figure 8:Efficiencies ofdouble entry axiallysplit casing pumpsat 1450 rpm.

Worked example:

Chosen pump type: End suction with own bearings.Chosen duty for maximum efficiency: 80 m3/h at 110 m.Quoted pump performance: 60% efficiency at 2900 rpm.

(Check materials, suction performance, etc, are satisfactory)

Is chosen duty within ranges covered: From Fig 1, yes.From Fig 3: ‘C’ = 14.Plot on Fig 3: ‘Pump Efficiency + C’ = 60 + 14 = 74%.Fig 3 suggests that an additional 3 points of efficiency or more is possible.

Action: Seek further quotes.

Correction of efficiencyfor pump head

Correction ‘C’, as shown on Figs 3 to 8, isbased on pump flow, head and speed. It isactually a correction for pump Specific Speed.Pumps of relatively low head and high flow(high Specific Speed) or high head and lowflow (low Specific Speed) lose efficiency due tounavoidable secondary hydraulic losses. WithinRef 2 there is a curve to allow efficiencycorrection for Specific Speed. This is actuallythe correction proposed by Anderson (Ref 3).Alternative curves to correct for Specific Speedcan be derived from Ref 4 and Ref 5.

None of these curves appear to provide an‘optimum’ correction for the publishedmanufacturers’ data analysed for this Guide.We have therefore chosen to use anintermediate Specific Speed correction curve,which produces the minimum scatter of thepoints plotted. There is no strict theoreticaljustification for this approach but we believethat it serves well for the purpose for whichthis Guide is intended. (Further informationcan be found in Ref 6.)

Loss of pump efficiencywith time

A pump of high efficiency is of little value if theefficiency falls rapidly with time. You canminimise this risk. Choose materials carefully,particularly for wear rings. Avoid high and lowflow operation in relation to your chosen duty.Ask for cast iron casings to be protectivelycoated if the water is known to cause seriousroughening due to corrosion.

Life Cycle Cost (LCC)

It is likely that the design of the pumpingsystem and the way the pump is operated willhave a greater impact on the energyconsumption than the pump efficiency alone.You should carry out an LCC analysis tocompare different technical alternatives ofdesigning, operating and maintaining apumping system. The LCC represents the totalexpenses to purchase, install, operate, maintainand repair a pumping system during itsprojected life. Down time and environmentalcosts are also considered.

A well-documented guide has been publishedby Hydraulic Institute and Europump (Ref 7).The guide explains how the operating costs ofa pumping system are influenced by systemdesign, and shows in detail how to use an LCCanalysis to estimate these costs. Using therecommendations of the guide, you shouldtake into account not only the initialinvestment cost, but also all the other costsand expenses of operating the system duringits projected life.

Basic principles ofchoosing a pump

The fundamentals of pump selection arecovered in Appendix 3 of Ref 6, together withnotes on the basics of centrifugal pumpcharacteristics, reducing impeller diameter,reducing speed, and the effect of wear.

Efficiency plots used inthis Guide compared toother sources

For practical reasons it has only been possibleto source a limited amount of data to producethe plots in this Guide. To assess howmeaningful the results are, it is useful tocompare them with other sources. The bestefficiencies (corrected to optimum SpecificSpeed) for end suction pumps having theirown bearings at 2900 rpm are plotted in Fig 9.The mean of these points is markedCatalogue ‘mean’. Additional curves (all atoptimum Specific Speed) are derived asfollows:

❚ ‘Hydraulic Institute’Fig 1A (Ref 2).

❚ ‘Anderson’Fig 7.3 (Ref 3).

❚ ‘Maximum practically attainable’(EUROPUMP) - Figs 7 to 10 (Ref 4).

❚ ‘Theoretically attainable’(EUROPUMP) - Using Figs 7 to 10 of Ref 4(Ref 5).

From Fig 9 we deduce that the Catalogue‘mean’ curve is suitable for use in this Guide.The ‘Hydraulic Institute ‘ANSI/API’’ curveis low, particularly at low flows. This isprobably mainly due to the use of relativelylarge wear ring clearances, as required forpumps in special materials or to meet theAmerican Petroleum Institute (API) Standard.

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7

References

1. ‘Evaluation of efficiency values considering theeffect of pump size modularity’, Stoffel, B.,Ludwig, G., and Meschkat, S., TechnicalUniversity of Darmstadt, 2002.

2. ‘Efficiency prediction method for centrifugalpumps’, Hydraulic Institute, 1994.

3. ‘Centrifugal pumps and allied machinery’,Anderson, H.H., Elsevier AdvancedTechnology, 1994.

4. ‘Attainable efficiencies of volute casingpumps’, Europump Guide No. 2, 1999.

5. ‘Theoretically attainable efficiency ofcentrifugal pumps’, Stoffel, B. and Lauer, J.,Summary of the final report on the researchproject for VDMA, Technical University ofDarmstadt, 1994.

6. ‘Study on improving the efficiency of pumps’,Report produced for the EuropeanCommission – SAVE, 2001. Available viahttp://energyefficiency.jrc.cec.eu.int/motorchallenge

7. ‘Pump life cycle costs: A guide to LCC analysis for pumping systems’, Europumpand Hydraulic Institute, 2000. (ISBN 1-880952-58-0)

85

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55

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Pump flow (m3/h)

Pum

p e

ffic

ien

cy a

t o

pti

mum

Sp

ecif

ic S

pee

d (

%)

Theoretically attainable

Hydraulic Institute‘Large Pumps’

Maximum practicallyattainable

Catalogue ‘mean’Anderson

Hydraulic Institute‘ANSI/API’

Figure 9:Comparison ofefficiencies of endsuction pumps fromvarious sources.

This Guide has been produced by a Project Teamcomprising:

❚ Future Energy Solutions (UK) Project Leader

❚ CETIM (France)

❚ David T Reeves (UK)

❚ NESA (Denmark)

❚ University of Darmstadt (Germany)

❚ EUROPUMP (membership)

The work was funded principally by theEuropean Commission with additionalfunding provided by the Project Team. Pumpmotor system energy efficiency continuesthrough the European Commission throughthe Motor Challenge Programme; more information can be found athttp://energyefficiency.jrc.cec.eu.int/motorchallenge/index.htm

For further information please contact:

European Commission, JRC

Dr Paolo BertoldiDG Joint Research CentreI-21020 IspraVareseItaly

Tel. +39 0332 789299Fax +39 0332 [email protected]://energyefficiency.jrc.cec.eu.int

EUROPUMP

EUROPUMP Diamant BuildingBD A. Reyers 80B-1030 Brussels

Tel. +32 2 7068230Fax +32 2 [email protected]


© European Commission. This edition printed May 2003.

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Pump Efficiency for Single Stage Centrifugal Pumps