Chapter 5-Centrifugal Pumps01

8/19/2019 Chapter 5-Centrifugal Pumps01

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Chapter 5:Hydraulic Turbo Machinery

Centrifugal Pump

Dr. SALAD!" A"#AS D$A%Departamento de &ngenier'a Mec(nica

)ni*er+idad Libre

Seme+tre ,-/0&&


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There are many pump cla++i1cation+. !ne cla++i1cation i+according to the method energy i+ imparted to the li2uid: 3ineticenergy4 or po+iti*e di+placement.

A centrifugal pump i+ of 3inetic energy type 0 it impart+ energy toa li2uid by mean+ of centrifugal force produced by a rotatingimpeller.

A po+iti*e di+placement pump impart+ energy by mechanicaldi+placement. Pi+ton4 diaphragm4 plunger4 +cre64 *ane4 and gearpump+ are +ome e7ample+.

Centrifugal pump+ are 6idely0u+ed becau+e of it+ de+ign+implicity4 high e8ciency4 6ide range of capacity and head4+mooth 9o6 rate4 and ea+e of operation and maintenance.Di+placement pump+ are of lo6er 9o6 range and ha*e pul+ating

9o6 rate;.

Type+ of Pump+


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De+cription of CentrifugalPump

!ne of the mo+t common radial 9o6 turbo machine i+ centrifugal

pump. Thi+ type of pump ha+ t6o main component+. An impellerattached to the rotating +haft4 and a +tationery ca+ing4 hou+ing4or *olute enclo+ing the impeller. The impeller con+i+t+ of anumber of blade+ u+ually cur*ed; al+o +ometime+ called *ane+4arranged in a regular pattern around the +hall.


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&mpeller+ are of three type+ 0 open impeller4 +emi0open andenclo+ed or +hrouded impeller. An open impeller i+ +ho6n in


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Centrifugal pump+ can be grouped into +e*eral type+ u+ingdi=erent criteria +uch a+ it+ de+ign4 con+truction4 application4+er*ice4 etc. Thu+ one +peci1c pump can belong to di=erentgroup+ and oftentime+ thi+ become+ de+cripti*e of the pumpit+elf.

Some of the+e group+ are:

1. Based on number of impeller/s in the pump2. Based on impeller suction3. Based on shaft orientation

Type+ of Centrifugal Pump+


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1. Based on number of impeller/s in the pump:

a) Single +tage 0 pump ha+ one impeller only> for lo6 head+er*ice.

b) T6o0+tage 0 pump ha+ t6o impeller+ in +erie+> formedium head +er*ice.

c) Multi0+tage 0 pump ha+ three or more impeller+ in

+erie+> for high head +er*ice. The number of impeller+4not the number of *olute+4 determine+ thenumber of +tage+. Thu+ a pump 6ith / *olute+ but only ?impeller+ i+ normally referred to a+ a /0+tage pumpde+taged to ?0+tage4 or /@?0+tage.



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Type+ of Centrifugal Pump+2. Based on impeller suction:

a) Single +uction 0 pump 6ith +ingle +uction impellerimpeller ha+ +uction ca*ity on one +ide only;> +imple de+ignbut impeller i+ +ubected to higher a7ial thru+t imbalance dueto 9o6 coming in on one +ide of impeller only.

b) Double +uction 0 pump 6ith double +uction impeller

impeller ha+ +uction ca*itie+ on both +ide+;> ha+ lo6erBPSH" than +ingle +uction impeller. Pump i+ con+ideredhydraulically balanced but i+ +u+ceptible to une*en 9o6 onboth +ide+ of impeller if +uction piping i+ not done properly.


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Based on shaft orientation:Horiontal 0 pump 6ith +haft in horiontal plane> popular due to ea+e of+er*icingand maintenance.

ertical 0 pump 6ith +haft in *ertical plane> ideal 6hen +pace i+

limited or of apremium4 or 6hen pumping from a pit or underground barrel to increa+ethea*ailable BPSH.


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Applying FernoulliG+ e2uation bet6een point+ and ,4 6e ha*e

Since %, %; i+ often much +maller than P, P;@γ 4 it can be eliminatedand thu+ the+tatic pre++ure i+ gi*en by

"eturning to ulerG+ e2uation

Analy+i+ of Centrifugal Pump


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The be+t de+ign for a pump 6ould be one in 6hich angular

momentum entering the impeller i+ ero4 +o that ma7imumpre++ure ri+e can ta3e place4 thu+ if u6 I -> u -4 6 I - i.e. α I J-K then I f and ulerG+e2uation become+


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The la+t e2uation i+ of the form

6here a and a, are function of machine geometry.

The con+tant a I @g repre+ent+ ideal head de*eloped by thepump for ero 9o6 rate and it i+ referred to a+ +hut o= head.

The +lope of cur*e of head *er+u+ 9o6 rate depend+ on +ign and

magnitude of a,.



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1. Radial vanes: for radial *ane+ β I J-K4 and a, I -. The 6hirl

component of ab+olute *elocity ,6 at e7it i+ e2ual toperipherial *elocity u, and head i+ independent of 9o6 rate a++ho6n in


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The e=ect of blade angle β, at outlet on e7it *elocity triangle.


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!*erall e8ciency i+ de1ned a+ po6er output di*ided by po6erinput


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Specic Speed&t i+ po++ible to correlate aturbo pump of a gi*en familyto a dimen+ionle++ numberthat characteri+e+ it+ operationat ma7imum condition. Such anumber i+ termed +peci1c

+peed and i+ gi*en by

The *alue of ω i+ u+ually

ba+ed on motor re2uirementand *alue+ of O and H aretho+e at ma7imum e8ciency.

The type of pump i+ +electedba+ed on *alue of ω

p .


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Cavitation and Net ositive Suction !ead "NS!)

The ca*itation ha+ to be a*oided in the pump. To characteri+epotential for ca*itation the di=erence bet6een the total head on+uction +ide and *apour pre++ure head i+ u+ed. The di=erence i+called net po+iti*e +uction head BPSH;

Total head near the pump impeller i+

Li2uid *apour pre++ure head i+



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umps in Series

hen a high head i+ re2uired4 the re2uired total head could bedi*ided on t6o or more unit+. hen the pump+ are arranged in+erie+ the inlet of +econd pump i+ connected to the outlet of the1r+t pump +o that +ame 9o6 rate pa++e+ through each pump4 butthe head+ generated by the t6o pump+ are added together for a

gi*en 9o6 rate.

H

A

H

A

H

A

H

FH I HA QHF

Pump+ in Serie+ and Parallel


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umps in arallel

)+ually u+ed 6hen large capacitie+ are re2uired in +uch the totalcapacity could be di*ided to t6o or more identical unit+. henthe pump+ are arranged parallel each pump handle+ part of the9o6 rate becau+e the inlet+ of the pump+ a+ 6ell a+ the outlet+are coupled together. Thu+ the total 9o6 rate pa++ing through the

+y+tem i+ e2ual to the +um of the 9o6 rate+ pa++ing through theindi*idual pump+ at a gi*en head4 6hich i+ +ame for each pump.

Pump+ in Serie+ and Parallel

O

A

O

A

O

A

M t hi P t S t


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Matching Pump+ to a Sy+temDemand

The +y+tem demand cur*e i+

de1ned a+ ele*ation head plu+friction and minor lo++e+.

H I ele*ation head Q pipefriction lo++e+ Q minor lo++e+


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&n a7ial 9o6 pump4 there i+ no radial 9o6 and li2uid particle+ enter andlea*e the impeller at +ame radiu+.


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&nlet and outlet *elocity diagram+ for a7ial 9o6 pump

A7ial


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Chapter 5-Centrifugal Pumps01

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