Table Of ContentCENTRIFUGAL PUMPS
and
ALLIED MACHINERY
4th Edition
HaroldAnderson
ELSEVIER
ADVANCED
TECHNOLOGY
ISBN 185617231 7
Copyright© 1994 ELSEVIERSCIENCEPUBLISHERS LTD
Allrights reserved
Thisbookissoldsubjecttotheconditionthatitshallnotbywayoftradeorotherwisebe
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conditionbeingimposedonthesubsequentpurchaser.
Otherbooksinthisseriesinclude:
HydraulicHandbook
SealsandSealingHandbook
HandbookofHose,Pipes.CouplingsandFittings
HandbookofPowerCylinders,ValvesandControls
PneumaticHandbook
PumpingManual
PumpUser's Handbook
SubmersiblePumpsandtheirApplications
CentrifugalPumps
Handbook ofValves,PipingandPipelines
HandbookofFluidFlowmetering
HandbookofNoiseandVibrationControl
HandbookofMechanicalPowerDrives
Industrial FastenersHandbook
HandbookofCosmeticScienceandTechnology
GeotextilesandGeomembranesManual
ReinforcedPlasticsHandbook
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v
Preface
HaroldAnderson'scontributiontotheworldofpumpingspannedmorethan60years and
includedmany publicationsonthetechnologyofpumpsandalliedmachinery.This book
provides updated informationtomany ofhisprevious works and concludes his life ina
manner so typical of his generous professional style; presenting his knowledge and
experiencefor the benefitofothers.
AFellowofThe InstitutionofMechanicalEngineers,aLife FellowofThe American
SocietyofMechanicalEngineersandseveral prestigiousinternationalawardsareindica
tion of the regardin which HaroldAnderson was held by hispeers.
ThroughouthiscareerasanEngineer,aPumpDesigner,anAuthorandInventor,HHA
loved to discuss engineering and to communicate his own ideas, innovations and his
solutions to technicalproblems but he was also quick toacknowledge, complimentand
supportothers on their work.
HHA'senthusiasmforengineeringwasmatchedinhisencouragementandsupportfor
allwhoworkedwithhim.Hismanypublishedarticles,papersandhisbooksnowprovide
alasting source ofhelp and inspiration to both academic and vocational workers in all
aspectsofpumping.
This last HHA book incorporates and updates alot of his earlierwork, including his
unique"AreaRatio" methodforpumphydraulicdesign and performanceestimation. It
also gives some very sound advice on pump mechanical design which is typical ofhis
innovateand practical approachtoengineering.
"Centrifugal Pumps andAlliedMachinery" is a reference book for engineers at all
levelswhoareconcernedwithpumps, theirspecification,design, behaviouroroperation.
The book is setout inaclear andconvenientstyle; nine sectionsdeal with the practices
ofpump engineering from its fundamentals, through pump and system design, pump
applications, installation and operation. Information, pump design data and sound
practicaladviceispresentedonmany pumpingandrelated topicsandmosttypes ofpump
from the very smalleststandarddesign tolarge high powermachines.
HHA died beforethis book waspublished.Asone ofmany pumpengineerswho was
fortunate enough to be schooled by HHA in the art and science ofpump design, I am
privileged tohave this opportunity tointroducehis lastpublication.
DEREKJ. BURGOYNE C.Eng., F.I.Mech.E.
PumpEngineering & Training Services
Cuckfield, West Sussex, England.
vii
Acknowledgements
The publisher would like to thank all of the companies and individuals involved in the
publicationof this book.
A special debt ofthanks is owed to Harold Anderson's family - especially his son
Christopher- and also Thompsons, Kelly &Lewis ofVictoria, Australiawho supplied
muchneededinformationafter Harold'sdeath.
HaroldhadworkedcloselywithElsevierforanumberofyearsandhissoundadviceand
expertisewill be sorely missedby all who knew him.
HaroldH.Anderson(1906-1994)
INTRODUCTION
Historical
The raising ofwater has been one ofman's earliestneeds, and indeed, the first call for
ingenuity in providing power arose from pumping duties. To this extent it may be
suggestedthat the art ofpumpingisolder than the artofpowerproduction.
Theearliestdevicesforlifting waterarestillinoperationinIndia, Egypt, etc.Atypical
exampleisthebasketorscooploweredintoariverbymeansofabalancebeamorshadouf,
orinlaterdevelopmentbyapulley,rope,andabeastofburden.Suchdeviceswouldappear
tobe asold asman himself.
A definite step forward in the mechanization of pumping was the development ofa
liftingwheel carryingontherim anumberofbuckets which dip into theriver, andraise
thewater toanirrigationchannel, thewheel beingpropelledbyprimitivegearingwhich,
in turn, isdriven byanimal orhuman power.
Alaterdevelopmentistobefoundintheself-propelledwheelswhichareacombination
ofanouterwaterwheeldrivenbytheriverflowandaninnerwheelhavingbucketswhich
liftthewaterfromtherivertoanirrigationchannel.Typicalexamplesofthesewheelsmay
beseenontheYellow RiverinChina. OtherdevelopmentsweretheArchimedeanscrew,
the hand operatedreciprocatingpump, and the chain pump.
The reciprocating steam engine was first applied to the duty of pumping water from
mines. Reciprocating pumps, and engines, were later developed in parallel to large
powers,culminatinginthe1000kWwaterworkspumpingenginesofthe 1890's,someof
which are still in use today.
Centrifugalpumps drivenbyslowspeedengineswereapplied tolowheadduties inthe
19th century. As an illustration, two experimental gunboats, the Water Witch and the
Viper, were fitted by the Admiralty in 1866 with jet propulsion. The relatively low
efficiencyofthepumps then availablerenderedthismethod ofpropulsionuneconomic,
althoughpresentdayefficiencieshavejustifiedthedevelopmentofasmalljetpropelled
boatwhichbyavoidingtheconventionalpropellers,canfloatinafewinchesofwaterand
can eliminaterisks ofpropellerinjury towater skiers.
2 CENTRIFUGALPUMPS
In 1875 Osborne Reynolds produced the first turbine pump, ie diffuser pump, with
considerably improvedefficiency.
ModernPumps
Theinventionofthesteamturbineandtheelectricmotorprovidedhighspeedpowerwhich
was ideally suited to the centrifugal pump. As a result the rapid development of the
centrifugalpumpenabledittoreplacereciprocatingpumpsonallbutthehighestpressure
small quantity mediumpressure duties, particularly when handling viscous liquids.
ApplicationofPumpingMachines
Pumpshave nowbeendevelopedforevery possibledutyoflifting orraisingpressureof
liquids; quantities, pressures, temperatures and viscosities varying within the widest
boundaries, and the powers ranging almost to the size of the largestprime movers yet
made. The duties can be sub-dividedasfollows:
(a) Transportofvaluable water etc, towhere itisrequired. This section includesthe
provision of a clean water supply to domestic and industrial consumers. The
problemofirrigationofland,thepumpingofwaterfromboreholes,themovement
ofwaterforfireextinguishingandthetransportationofoilareimportantduties in
this section.
(b) Theremoval ofobjectionablewater,etc.Thisgroupincludestheproblemsofmine
drainage,drydockdrainage, sewagepumpingandlanddrainage. Mines often sell
water towater works.
(c) The circulation andprocess group. Here weareconcernedwith processes which
demandacirculationof water toprovide or withdrawheat, tofeed steam boilers,
totransfervariousliquidsinchemicalandprocess industries,andintherefiningof
oil.This group alsoincludes thepumpingofpulp forthepaper industriesand the
scrubbingof gases, forexampleinthenitrogen fixation industry.
(d) The transmissionofpower bythepumpingofliquids. Herewehave alarge group
ofpumpsprovidinghighpressure watertooperatecranes,presses, shears,lifts,etc
indocks, steelworksandsimilar environments.Inasmallerdegree oilispumped
tooperatebrakes, servomechanisms,aeroplanecontrols, etc., where thevalue of
thehydraulictransmissionliesintheremote andsensitivecontrol obtainedandin
weight saving.
(e) Theuseofajetofwatertocut,peelordig.Thisgroupincludesthedescalingofsteel
bars,theremoval ofbarkfromtreesandthesluicing ofchinaclayandgoldoreby
waterjets.
(f) The storage of energy by pumping water to an elevated reservoir. such duties
demand very large pumps inorder tojustifythecivil engineeringcosts, but such
storageofenergyisamaterialfactorinimprovingtheoverallefficiencyandthelife
ofthermal and nuclear power stations.
(g) Thejetpropulsion ofships and space vehicles.
(h) The use of water for the purpose of transporting solids. In the food industry,
potatoes, coffee beans, sugar beat, fruit and fish; in civil engineering work,
dredgingandsandstowage; inpowerstations, thehandling ofashes,coal,etc,and
INTRODUCTION 3
Figure 1.1- Vertical borehole pumps inaSouthAmericanwaterworks
eachhandling1.4mi/s againstaheadof55m.
inamultitudeofindustriesthetransportingofthevariousslurriesisreadilyeffected
by the use of water.
U) Pumpingoffood liquids, chemicalandprocessliquids.
The Designand ManufactureofPumps- The Types ofPump
The simplesttype of pump is the reciprocatingpump, of which the villagepump is the
earliestexample.Beingadisplacementmachineitwillforceagivenquantity,correspond
ingtoitsspeedandsweptvolumeofcylinder,throughthepipingofapressuresystem.The
pressuredeveloped isdeterminedby thepressuredifferences, static lift and the friction
losses in the system. The volume pumped is determined by the speed. If, however, the
dischargevalveofareciprocatingpump isclosedwehavetheproblemoftheirresistible
force andtheimmovableobject. Iftheinertiaoftherotating partsissufficientlygreat the
pump cylinder will burst. If the cylinder has sufficient strength the reciprocating and
rotating parts will be brought to rest and the drive stalled since liquids are almost
incompressible. It is interesting to note that this feature may incertain cases be used to
develop very high pressures by taking advantage of the inertiaof rotating masses. The
reciprocatingpump isthereforeofvalue fordeveloping very high pressures and has the
advantage that an approximately constant quantity can be handled against varying
pressure.
Acentrifugalpumpimpellerthrowsthewateroutwardswithsufficientforcetogenerate
ahead, thus overcomingthe static pressureandfriction head inthe system towhich the
pump isconnected. When acentrifugalpump operates againstaclosedvalve oragainst
a system having a greater pressure than the pump can generate, no harm results, the
impellermerely churningtheliquid. (Itmaybenecessary toremovetheresultingexcess
4 CENTRIFUGALPUMPS
heat.) Therotationalspeed determinestheheadofacentrifugalpumpbutdeterminesthe
quantityofareciprocatingpump.
Rotarypumpsaretruedisplacementpumps.Theydonotrelyupontheoperatingspeeds
toproducethepressurebutobtainpumpingeffectbytheirelementspassinginturnthrough
thesame space orbysliding vanes; theyincludevanepumps, screw pumps,gearpumps,
etc.
ReciprocatingPumps
Areciprocatingpumpcomprises: piston, cylinder,inlet and outletvalues, and adriving
mechanism.Inthesimplestcasethepumphasasinglecylinder,thepistonoperatinginone
directiononly,iesingleacting.Theinletwaterisraisedbyvacuumfromthesumporwell,
atmosphericpressureservingtoforce the water throughthe suctionpipingand the inlet
valve. Whenthepistonreverses,theinlet valvecloses andtheoutletvalve isforcedopen
bythepressureimposedupon thewater bythepiston, water being deliveredthroughthe
outletpipe.
Itwillbeappreciatedthatifthespeedofareciprocatingpump isincreased,alimitwill
arisebeyondwhichatmosphericpressureisinsufficienttoforcewaterintothepumpatthe
samespeedasthepiston. Thiscauses abreak inthecontinuityofthewater inthesuction
pipe, referredtoascavitation, and gives rise to vibration, noise, and chemicalattackby
anydissolvedgases whichmaybereleasedfromthewaterowingtothehigh vacuumand
Figure 1.2- Largedoubleentry splitcasingpump
INTRODUCTION 5
the breaking ofthe water column. When the water passes into the pump and reaches a
higherpressureasaresult ofthepiston movement,thevapour recondenseswithasevere
shockandcauses animpactonthemetal walls ofthepump. The damagetothemetal is
known as cavitation pitting, and is a combination of chemical attack and mechanical
impact. It causes the metal to become spongy and, if allowed to persist, ultimately
penetrates themetal wall.
In orderto avoid this contingency the amountof suction lift and the operating speed
must be carefully chosen using the experience gained on previous machines, so as to
ensurethat theplant isoperatingwithin safety limits.
CentrifugalPumps (includingAxial Flow Pumps)
A centrifugal pump comprises an impellerrotating at a high speed within a stationary
casing. Centrifugal force isbest explainedby the following examples. If tea in acup is
stirredvigorouslyitwillriseattheendofthecuptoaslightlyhigherlevelthanatthecentre.
This is due to centrifugal force and is further explained by another example. A train
travellingathighspeed alongastraightlinewilltrytocontinuealong thatstraightlineby
virtue ofitsinertia. When acurve isapproachedthespeed must bereducedtoavoid the
risk of a train leaving the rails inits endeavourtorun along astraightline. In asimilar
mannertheteainthecup tryingtotravel inastraightlineisconstrainedbythecurvature
ofthe cup with the result that theliquid piles upattherestraining wall.
This phenomenonistakenadvantageofinacentrifugalpump wheretheliquidisspun
round atsufficientspeed toraise thelevel orpressurebyanamountrangingup to 1000
or 2000 minextremecases.
Thefunction ofthecasingis,firstlytorestrainthewaterintoanapproximatelycircular
orspiralpath,andsecondlytocollectthewaterasitisdeliveredfromtheimpeller.Asthe
waterpassesthroughthepumpitisacceleratedinatangentialdirection. Workisexpended
inraisingthespeedofthewater.Thepump headisthereforemadeupofcentrifugalhead
due torotationandimpacthead due totheincreaseofspeed asthewater passes through
theimpeller.Thecasingpicksupthewaterandconvertspartofitskineticenergyorenergy
due to velocity into energy ofpressuretimes mass.
Indesigningcentrifugalpumps itisfound that, uptoacertain point, theperformance
can be calculated by known hydraulic and mechanical laws but beyond this point
experienceofpreviousmachinesmust becalled intoaccount. Inthisrespectitisperhaps
truetosay thatpump manufactureistosome extentanartaswell asscience. Geometric
scaling from a known small machine to a new large one is a convenient method of
designingbut thephemonenaattending such changeofsizemust bethoroughly investi
gated.
HeadandQuantity
The head generated by a pump will obviously have some reference to the velocity of
rotationsincetheheadisprimarilyduetothekineticenergyimpartedtothewater.Kinetic
energy varies as the square ofthe velocity.
Asafirst approximation,therefore, itcan besaid thatthehead generatedvaries asthe
square of the peripheral velocity of the impeller. Similarly, the quantity pumped will
6 CENTRIFUGALPUMPS
depend upon the area ofthepump passages and upon thespeed offlow which inturn is
determined by the peripheral speed of the impeller.
Tests are analyzed by plotting the variation of head and quantity from the above
relationships againstasuitable variable intheproportionsof thepumpitself.
Efficiency
The efficiencyofthepump isprimarilydeterminedbythesize, speed andproportionsof
the impellerand casing. The head generatedby thepump suffers from losses due to the
frictionwithinthewallsoftheimpellerandcasing. Thisfriction isproportionatelygreater
in the case ofa smallerpump. The reason for this may be explained as follows: if we
consideraonecmsquarepassage,thecapacityofthepassageforhandlingwater is1ern";
theresistancetoflowisrepresentedbytheperimeterofthewalls,thatis4em.Ifhowever
the dimensionsofthe walls areincreasedto2em square, giving anarea of4ern",itwill
beseen that theareahasincreasedfour-fold, buttheperimeterhasonly creasedtwo-fold
to8ern.The wallfriction, therefore, whichisrepresentedbythelengthofperimeter,has
arelatively smallereffecton largerareas.
A thorough investigation of friction was made byProfessorOsborneReynolds, who
providedarelationshipbetweenthefriction lossdue totherubbingagainstthewalls and
thefriction lossduetochurningeddiesofwaterwithinthepassageitself.Therelationship
betweenthese two losses was expressedbya 'Reynolds' number.
ProfessorReynoldsinoneofhisexperimentspassedaquantityofwaterthroughaglass
tube. In the centre of the glass tube he introduced a thin thread of dye. On low water
velocitiesthedye passedthroughthepipes asastraightclean thread. When the speed of
the water wasincreased,eddies started and,asaresult, thethread wascompletelybroken
up.The pointatwhich thebreak-upoccurredisreferredtoasthecriticalvelocity.Below
thiscriticalvelocity, pipefriction wasfound tovaryasthevelocity, being almostentirely
wallfriction. Abovethecritical velocity thepipefriction variedasapowerofthevelocity
approximatelyintheneighbourhoodof 12 Theexactvalue ofthispowerdependedupon
•
the Reynolds number, largernumbers representingmainly eddy losses, giving ahigher
powertotheloss. Kinetic energy varies asvelocity square. Frictionlosses vary assome
otherpowerof velocity. Achange of velocity and size, therefore, will alter the friction
relative tothe total head and consequently alter the efficiency ofthepump.
It is, therefore, possible to use the Reynolds numberas adeterminantoffriction and
from this, itisasimplesteptouseaformofReynoldsnumbertodeterminebychangeof
relativefriction losses inthepump how efficiency will changewith size and speed.
A very simple and every-day exampleof Reynolds' experimentisseen inthe smoke
risingfrom acigarette.Thesmoke islighterthanthesurroundingairandthedifferencein
weight will give it an upward thrust. The thrust acts continuously, thus causing a
progressiveincrease inthe speed of the smoke asitrises.
The smokenearthecigarettewillhave aslow speed andthefurther the smokeisfrom
thecigarettethehigheritsspeedwillbe.Atsomepointitwillreachitscriticalspeedabove
whichflow isunsteady. In still airitisparticularly noticeable that the smokerises from
thecigaretteinastraightthreadforafootorsothenverydefinitelybreaks upineddiesand
waves.
