Fundamentals of Centrifugal Pumps

7/31/2019 Fundamentals of Centrifugal Pumps

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PRODUCT TRAINING

FUNDAMENTALS OFFUNDAMENTALS OF

CENTRIFUGAL PUMPSCENTRIFUGAL PUMPS


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Fundamentals of Centrifugal

Pumps

Fundamentals of CentrifugalFundamentals of Centrifugal

PumpsPumps

A centrifugal pump is a mechanical device thatA centrifugal pump is a mechanical device that

converts energy to hydraulic workconverts energy to hydraulic work

Energy is supplied by a driver such as an electricEnergy is supplied by a driver such as an electric

motor, turbine, or enginemotor, turbine, or engine Hydraulic work is the movement of a liquid massHydraulic work is the movement of a liquid mass

through a distancethrough a distance

This presentation is limited to centrifugal pumpThis presentation is limited to centrifugal pumptypes onlytypes only

SundyneSundyne pumps are a special design that will not bepumps are a special design that will not be

covered in this presentationcovered in this presentation


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Pumps


PumpsPumps

Just Say NO!!!!!


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Pumps


PumpsPumpsThe work takes place at an impeller whichThe work takes place at an impeller which

accelerates the liquid by whirling it throughaccelerates the liquid by whirling it throughthe impeller thus adding centrifugal forcethe impeller thus adding centrifugal force

and hence accelerationand hence acceleration


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Pumps


PumpsPumps When an object isWhen an object is

spun around in aspun around in acircle it is acceleratedcircle it is accelerated

outward byoutward by

centrifugal forcecentrifugal force


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Pumps


PumpsPumps When liquid is spunWhen liquid is spun

around in a circle, itaround in a circle, itaccelerates outwardaccelerates outward

from the center of thefrom the center of the

circle due tocircle due to

centrifugal forcecentrifugal force


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Pumps


PumpsPumps An impeller has vanesAn impeller has vanes

which are blades thatwhich are blades thatpush the liquid throughpush the liquid through

the impeller. The centerthe impeller. The center

of the impeller where theof the impeller where theliquid enters the impellerliquid enters the impeller

is called the eyeis called the eye

Vanes

Eye


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Pumps


PumpsPumps To obtain usefulTo obtain useful

work, the impeller iswork, the impeller iscontained in a casingcontained in a casing

which directs thewhich directs the

accelerated fluidaccelerated fluid

along a desired pathalong a desired path

Discharge


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Pumps


PumpsPumps

Pump Impeller and Shaft


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Pumps


PumpsPumps

Pump Impeller and Shaft

with Pressure Casing


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Pumps


PumpsPumps

Pump Impeller

and Shaft with

Pressure Casing

and Cover


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Pumps


PumpsPumps

Process

Fluid

Adjustment

Packing

Stuffingbox

Cover


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Pumps-Impellers


PumpsPumps--ImpellersImpellers Impeller DesignImpeller Design

The impeller is the most important part of theThe impeller is the most important part of thepump since it is where the work is takingpump since it is where the work is taking

place. Furthermore, the impeller plays anplace. Furthermore, the impeller plays animportant role in the design of other pumpimportant role in the design of other pump

components. It has a direct effect on the sealcomponents. It has a direct effect on the seal

cavity pressure for examplecavity pressure for example


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Pumps-Impellers


PumpsPumps--ImpellersImpellers

Many different types ofMany different types ofimpeller styles are used.impeller styles are used.

Most, but not all, have vanesMost, but not all, have vanes

that curve away from thethat curve away from theflow path so that the liquidflow path so that the liquid

is in contact with theis in contact with the

impeller longer. These areimpeller longer. These arereferred to asreferred to as reversereverse

curvecurvevane impellersvane impellers

Vanes

Eye


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Pumps-Impellers


PumpsPumps--ImpellersImpellers Impeller vanes may beImpeller vanes may be

enclosed byenclosed byshroudsshrouds..In general impellers withIn general impellers with

shrouds are slightly lessshrouds are slightly less

efficient due to the dragefficient due to the dragof the liquid on theof the liquid on the

shroudshroud


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Pumps-Impellers


PumpsPumps--ImpellersImpellers Some impeller designsSome impeller designs

may also have a shroudmay also have a shroudonly on one side of theonly on one side of the

impeller. They are alsoimpeller. They are also

said to be partiallysaid to be partiallyshrouded or semishrouded or semi--openopen

or semior semi--closedclosed


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Pumps-Impellers


PumpsPumps--ImpellersImpellers Shrouds are generally used on larger impellers toShrouds are generally used on larger impellers to

help support the vanes and maintain thehelp support the vanes and maintain theimpeller shape under extreme pressure andimpeller shape under extreme pressure and

temperature conditions. They also have thetemperature conditions. They also have the

disadvantage of limiting the particle size that candisadvantage of limiting the particle size that can

pass through the impellerpass through the impeller


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Pumps-Impellers


PumpsPumps--ImpellersImpellers There are two different impellerThere are two different impeller

types used in the process industry.types used in the process industry.They differ by the type of flowThey differ by the type of flow

through the impeller. The mostthrough the impeller. The most

common type is acommon type is a radial flowradial flowimpeller where the liquid makes aimpeller where the liquid makes a

9090oo turn as it passes through theturn as it passes through the

impellerimpeller


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Pumps-Impellers



In a turbine type impeller, the liquidIn a turbine type impeller, the liquid

also makes a turn as it passes throughalso makes a turn as it passes through

the pump, but less than 90the pump, but less than 90oo. These are. These are

most often found inmost often found in diffuserdiffuser typetype

pumps which relates to the casingpumps which relates to the casingdesign and will be discussed later.design and will be discussed later.

Since the liquid makes less of a turn, aSince the liquid makes less of a turn, a

turbine style impeller may be slightlyturbine style impeller may be slightlymore efficient than a similarmore efficient than a similar radialradial

flowflow impellerimpeller


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Pumps-Impellers


PumpsPumps--ImpellersImpellersThe impeller has a direct relationship toThe impeller has a direct relationship to

pump performance. The design of thepump performance. The design of theimpeller is the single most important factorimpeller is the single most important factor

in determining the flow rate and liquidin determining the flow rate and liquidpressure that a pump can generatepressure that a pump can generate


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Pumps-Impellers


PumpsPumps--ImpellersImpellersThe Master Pumps & Power catalog is anThe Master Pumps & Power catalog is an

excellent reference resource for mostexcellent reference resource for mostpump application problems. It should be apump application problems. It should be a

part of every engineers library. It is free topart of every engineers library. It is free toall of our customersall of our customers


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Pumps-Impellers


PumpsPumps--ImpellersImpellers Flow through an impeller is determinedFlow through an impeller is determined

primarily by three factorsprimarily by three factorsVane widthVane width

Number of vanesNumber of vanes Impeller speedImpeller speed


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Pumps-Impellers


PumpsPumps--ImpellersImpellers A wide vane impellerA wide vane impeller

will move more liquidwill move more liquidper unit time than aper unit time than a

narrow vane impeller.narrow vane impeller.

The flow is directlyThe flow is directly

proportional to theproportional to the

vane widthvane width


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Pumps-Impellers


PumpsPumps--ImpellersImpellers Flow (Q) through anFlow (Q) through an

impeller is alsoimpeller is alsodirectly related to thedirectly related to the

impeller speed. Theimpeller speed. The

more times anmore times an

impeller rotates perimpeller rotates per

unit time the moreunit time the morefluid is will movefluid is will move


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Pumps-Impellers


PumpsPumps--ImpellersImpellers Finally the flowFinally the flow

through a pump isthrough a pump issomewhat related tosomewhat related to

the number of vanesthe number of vanes

although it is notalthough it is not

directly proportional.directly proportional.

More vanes will moveMore vanes will movemore fluidmore fluid

F d l f C if l


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Pumps-Impellers


PumpsPumps--ImpellersImpellers An impeller createsAn impeller creates

headhead bybyaccelerating the fluidaccelerating the fluid

to a given velocity.to a given velocity.

As it spins, the fluid isAs it spins, the fluid is

accelerated outwardaccelerated outward

by centrifugal forceby centrifugal force

F d l f C if lF d l f C if l


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Pumps-Impellers


PumpsPumps--ImpellersImpellers The fluid exits theThe fluid exits the

impeller at a givenimpeller at a givenvelocity. Therefore itvelocity. Therefore it

will rise to a given heightwill rise to a given height

in a column based on thein a column based on theexit speed regardless ofexit speed regardless of

the weight of the fluidthe weight of the fluid

F d l f C if lF d l f C if lF d l f C if l


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Pumps-Impellers



Therefore a centrifugal pump is said to be aTherefore a centrifugal pump is said to be a

constant headconstant head device. At a given speed it willdevice. At a given speed it will

accelerate a liquid to a given velocity regardlessaccelerate a liquid to a given velocity regardless

of the weight of the liquid.of the weight of the liquid. A heavier liquid would require moreA heavier liquid would require more

horsepower and the discharge pressure wouldhorsepower and the discharge pressure wouldbe higher, but it would rise in a column nobe higher, but it would rise in a column no

higher than a light liquidhigher than a light liquid

F d l f C if lF d l f C if lF d l f C if l


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Pumps-Impellers


PumpsPumps--ImpellersImpellers This phenomenon is based on simple laws ofThis phenomenon is based on simple laws of

physicsphysics (V(V22 = 2 AS) where V is the velocity, A is the= 2 AS) where V is the velocity, A is the

acceleration of gravity, and S is the heightacceleration of gravity, and S is the height

Note that this formula makes noNote that this formula makes no

consideration of weightconsideration of weight

F d l f C if lF d l f C if lF d t l f C t if l


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Pumps-Impellers


PumpsPumps--ImpellersImpellers If fluids are pushed up aIf fluids are pushed up a

column to the samecolumn to the sameheight, the pressure atheight, the pressure at

the bottom of thethe bottom of the

column would becolumn would bedifferent for fluids ofdifferent for fluids of

different weight.different weight.

The formulae for thisThe formulae for this

relationship are as followsrelationship are as follows

hdhd. ft. =. ft. =

((psipsi X 2.31) / sp. gr.X 2.31) / sp. gr. psipsi ==

((hdhd ft. / 2.31) x sp. gr.ft. / 2.31) x sp. gr.

F d l f C if lF d l f C if lF d t l f C t if l


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Pumps-Impellers


PumpsPumps--ImpellersImpellers To illustrate, a pressure gaugeTo illustrate, a pressure gauge

at the bottom of a 231 ft. highat the bottom of a 231 ft. highcolumn filled with watercolumn filled with water

would read 100would read 100 psipsi. If the. If the

column was filled with butanecolumn was filled with butanehaving a specific gravity ofhaving a specific gravity of

only .5, the gauge would readonly .5, the gauge would read

5050 psipsi

231 ft

F d t l f C t if lF d t l f C t if lF nd m nt l f C ntrif l


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Pumps-NPSH


PumpsPumps--NPSHNPSH

In order for the pump to move fluid, the systemIn order for the pump to move fluid, the system

must be able to push fluid into the pump as fastmust be able to push fluid into the pump as fast

as the pump can push it out.as the pump can push it out.

Therefore there must be a certain minimumTherefore there must be a certain minimumrequired suction pressure for each pump based onrequired suction pressure for each pump based on

the pump flowthe pump flow

This pressure is expressed in head feet and isThis pressure is expressed in head feet and is

referred to as NPSHreferred to as NPSH --net positive suction headnet positive suction head

F d t l f C t if lF nd nt l f C ntrif lFundamentals of Centrifugal


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Pumps-NPSH


PumpsPumps--NPSHNPSH NPSH is expressed in two waysNPSH is expressed in two ways

NPSHA is the net positive suction head availableNPSHA is the net positive suction head availablefrom the systemfrom the system

NPSHR is the net positive suction head required byNPSHR is the net positive suction head required by

the pump at a particular flowthe pump at a particular flow

NPSHA must always be greater than NPSHR orNPSHA must always be greater than NPSHR or

damage to the pump will occur due todamage to the pump will occur due to

cavitationcavitation

F nd m nt l f C ntrif lF ndamentals of Centrif galFundamentals of Centrifugal


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Pumps-NPSH



CavitationCavitation is the flashing of the liquid at theis the flashing of the liquid at the

pump impeller eye caused by the pumppump impeller eye caused by the pumplowering the pressure in the eye area as itlowering the pressure in the eye area as it

accelerates fluid across the impelleraccelerates fluid across the impeller The damage occurs when the flashed gas isThe damage occurs when the flashed gas is

compressed back to a liquid as it gainscompressed back to a liquid as it gains

pressure while traveling through the impellerpressure while traveling through the impeller

Fundamentals of CentrifugalFundamentals of CentrifugalFundamentals of Centrifugal


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Pumps-NPSH



CavitationCavitation causes pump problems in two areascauses pump problems in two areas

SevereSevere cavitationcavitation can erode the pumpcan erode the pump

impeller resulting in decrease performanceimpeller resulting in decrease performance

and vibration due to imbalanceand vibration due to imbalance CavitationCavitation normally results in substantiallynormally results in substantially

higher vibration in the entire pumphigher vibration in the entire pump



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NPSH is the total suction head in feetNPSH is the total suction head in feet

of liquid (absolute at the pumpof liquid (absolute at the pumpcenterline or impeller eye) less thecenterline or impeller eye) less the

absolute vapor pressure (in feet ) ofabsolute vapor pressure (in feet ) ofthe liquid being pumpedthe liquid being pumped


Pumps-NPSH





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NPSHA is the NPSH available at the pump suction nozzle andNPSHA is the NPSH available at the pump suction nozzle and

depends on the suction system design. It must always be equaldepends on the suction system design. It must always be equal

to or greater than the NPSHRto or greater than the NPSHR

NPSHR is the NPSH required by the pump for stable operation.NPSHR is the NPSH required by the pump for stable operation.

It is determined by the pump manufacturer and is dependent onIt is determined by the pump manufacturer and is dependent on

many factors including the type of impeller inlet, impeller desimany factors including the type of impeller inlet, impeller design,gn,pump flow, rotational speed, nature of the liquid, etc. It ispump flow, rotational speed, nature of the liquid, etc. It is

usually plotted on the characteristic pump performance curvedusually plotted on the characteristic pump performance curved

supplied by the pump manufacturersupplied by the pump manufacturer


Pumps-NPSH





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Pumps-NPSH


PumpsPumps--NPSHNPSH NPSHA is a difficult calculation. It will requireNPSHA is a difficult calculation. It will require

the help of a process engineer from the plantthe help of a process engineer from the plant

NPSHA can be determined by direct fieldNPSHA can be determined by direct field

measurement if the vapor pressure is known. Ameasurement if the vapor pressure is known. Amethod for this calculation is presented latermethod for this calculation is presented later



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Atmospheric

Pressure = ha

Height = hst15 feet

NPSHA Example for Suction Lift

*Assume vapor pressureof water @ 80 F = .5psia

or 1.2 feet = hvpa*Assume atmospheric

pressure @ sea level

or 34.0 feet = ha*Assume pipe losses =

3.5 feet = hfs*NPSHA = ha - hvpa - hst - hfs*NPSHA = 34 - 1.2 - 15 - 3.5 =

14.3 feet


Pumps-NPSH





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Atmospheric Pressure = ha

Height = hst15 feet

*Assume vapor pressure

of water @ 80 F = .5psia

or 1.2 feet = hvpa*Assume atmospheric

pressure @ sea level

or 34.0 feet = ha*Assume pipe losses =

3.5 feet = hfs*NPSHA = h

a

- hvpa

+ hst

- hfs*NPSHA = 34 - 1.2 + 15 - 3.5 =

44.3 feet

NPSHA Example

for Flooded Suction


Pumps-NPSH





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Simple Method to Determine NPSHASimple Method to Determine NPSHA NPSHA is the total suction head in feet of liquid (absolute atNPSHA is the total suction head in feet of liquid (absolute at

the pump centerline or impeller eye) less the absolute vaporthe pump centerline or impeller eye) less the absolute vapor

pressure (in feet) of the liquid being pumpedpressure (in feet) of the liquid being pumped

Measure the suction pressure and convert to feet of headMeasure the suction pressure and convert to feet of head

(must be absolute not atmospheric)(must be absolute not atmospheric)

Determine the vapor pressure of the liquid and convert toDetermine the vapor pressure of the liquid and convert tofeet of headfeet of head

Subtract the vapor pressure from the suction pressureSubtract the vapor pressure from the suction pressure


Pumps-NPSH





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Pumps-Performance Curves


PumpsPumps--Performance CurvesPerformance Curves A pump manufacturer will supply a curve forA pump manufacturer will supply a curve for

every pump purchased which graphicallyevery pump purchased which graphicallyrepresents the expected pump performancerepresents the expected pump performance

For most applications, a copy of the pump curveFor most applications, a copy of the pump curve

is required information for properly selecting ais required information for properly selecting a

sealing system and flush plansealing system and flush plan



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PumpsPumps--Performance CurvesPerformance Curves

NPSHR

Head

BHP

Flow, GPM

Efficiency



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PumpsPumps--Performance CurvesPerformance CurvesContentsContents

What pump curves representWhat pump curves represent

How to read pump curvesHow to read pump curves



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Efficiency

NPSHR

Head

BHP

Flow, GPM

A Pump Curve



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Fundamentals of Centrifugalg


Summary of Pump Curve InfoSummary of Pump Curve Info

Graphical representation of performanceGraphical representation of performance

HeadHead

BHPBHP

EfficiencyEfficiency

NPSHRNPSHR



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Fundamentals of Centrifugalu d e s o Ce ug

PumpsPumps--Performance CurvesPerformance Curves Summary of Pump Curve InfoSummary of Pump Curve Info

Graphical representation of performanceGraphical representation of performance Contains more than performance dataContains more than performance data

speedspeed

stagesstages

may have info about liquidmay have info about liquid

impeller, case patternsimpeller, case patterns

wear ring clearanceswear ring clearances



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g


gg


Actual Sample CurvePricebook Curve



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Funda entals o Cent ugal


gg


Actual Sample Curve -Job Curve


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Pumps-Performance CurvesPumpsPumps--Performance CurvesPerformance CurvesTest DataTest Data

FlowFlow P2P2 -- P1 BHPP1 BHP 00 311311 2020

400400 291291 117117

800800 234234 156156

960960 195195 163163

Pressure in PSIG



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g


gg

PumpsPumps--Performance CurvesPerformance Curves Convert Pressure to Feet of HeadConvert Pressure to Feet of Head

Head = 2.31 (PHead = 2.31 (P22--PP11) / S.G.) / S.G.Head is in Feet!Head is in Feet!



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g


gg

PumpsPumps--Performance CurvesPerformance Curves Compute EfficiencyCompute Efficiency

Efficiency = Theoretical HorsepowerEfficiency = Theoretical Horsepowerdivided by Actual Horsepowerdivided by Actual Horsepower

Convert to PercentConvert to Percent



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g


g


Test DataTest Data

FlowFlow Head BHPHead BHP EfficiencyEfficiency

00 718718 2020 ******

400400 672672 117117 58%58%

800800 540540 156156 70%70%

960960 450450 163163 67%67%

Now in feet



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g

Pumps-Performance CurvesPumpsPumps--Performance CurvesPerformance Curves

0

100200

300

400

500600

700

800

0 200 400 600 800 1000 1200

Flow, GPM

TDH

Head Portion of Pump Curve



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0

2040

60

80

100

120

140

160

180

0 200 400 600 800 1000 1200

Flow, GPM

BHP

BHP Portion of Pump Curve



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010

20

30

40

50

60

7080

0 200 400 600 800 1000 1200

Flow, GPM

Eff

Efficiency Portion of Pump Curve



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NPSHNPSHNet Positive Suction HeadNet Positive Suction Head

NPSHR:NPSHR: RequiredRequiredNPSHA:NPSHA: AvailableAvailable



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NPSHNPSHNet Positive Suction HeadNet Positive Suction Head

NPSHR:NPSHR: RequiredRequiredNPSHA:NPSHA: AvailableAvailable

NPSH = Actual PressureNPSH = Actual Pressure --VaporVaporPressure, then convert to feet of headPressure, then convert to feet of head



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NPSH RequiredNPSH Required

Determined during pump testDetermined during pump test

Throttling suction to pumpThrottling suction to pump

Hot waterHot water

Based on 3% head lossBased on 3% head loss--reduce NPSHAreduce NPSHA

until 3% loss in produced head is observeduntil 3% loss in produced head is observed Based on waterBased on water



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Test DataTest Data

FlowFlow Full Head 3% LossFull Head 3% Loss

00 718718 -- 22 = 69622 = 696

400400 672672 -- 20 = 65220 = 652

800800 540540 -- 16 = 52416 = 524

960960 450450 -- 14 = 43614 = 436


Pumps Performance Curves


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Pumps-Performance CurvesPumpsPumps

--Performance CurvesPerformance Curves

0

5

10

15

20

25

30

35

0 200 400 600 800 1000 1200

Flow, GPM

NPSHR

NPSHR Portion of Pump Curve


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NPSHR

Efficiency

Head

BHP

Flow, GPM

A Pump Curve

Operating Point

BEP



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The pump manufacturer will normally show theThe pump manufacturer will normally show the

point on the curve where the pump is expectedpoint on the curve where the pump is expectedto operateto operate

BEP is the best efficiency point taken at theBEP is the best efficiency point taken at the

highest point of the efficiency curvehighest point of the efficiency curve

At BEP the pump normally operates the most stablyAt BEP the pump normally operates the most stably

Operation below BEP can result in mechanical andOperation below BEP can result in mechanical andhydraulic problemshydraulic problems




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Summary of Pump Curve InformationSummary of Pump Curve InformationGraphical representation ofGraphical representation of

performanceperformanceContains more than performance dataContains more than performance data



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Pumps-Impeller EffectPumpsPumps--Impeller EffectImpeller Effect

Balance Holes



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Effect of back wear ringsEffect of back wear rings

and balance holesand balance holes Pressure at O.D. ofPressure at O.D. of

impeller breaks downimpeller breaks down

across back wear ringacross back wear ring

Balance holes bleedBalance holes bleed

pressure back to suctionpressure back to suction

Seal chamber at sameSeal chamber at samepressure as balance holespressure as balance holes



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Impeller with PumpoutVanes



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Effect of pump outEffect of pump out

vanesvanes Vane O.D. is the same asVane O.D. is the same as

the impeller O.D. and isthe impeller O.D. and is

turning at the same speedturning at the same speed Therefore vane puts upTherefore vane puts up

same head as impellersame head as impeller

Therefore back ofTherefore back ofimpeller at shaft is at sameimpeller at shaft is at same

pressure as frontpressure as front



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Impeller with no back wearrings or pumpout vanes



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Pumps-Impeller EffectPumpsPumps--Impeller EffectImpeller Effect Effect of no back wearEffect of no back wear

rings or pump out vanesrings or pump out vanes

Pressure at impellerPressure at impeller

O.D. is presentO.D. is present

behind entire impellerbehind entire impeller Seal chamber atSeal chamber at

discharge pressuredischarge pressure



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Pumps-Pump Case DesignPumpsPumps--Pump Case DesignPump Case Design If a higher pressureIf a higher pressure

differential is requireddifferential is requiredacross the pump theacross the pump the

designer has severaldesigner has several

options. Two wouldoptions. Two wouldbe to:be to:

Increase the pumpIncrease the pump

speedspeed--the flow wouldthe flow wouldalso increasealso increase

Increase the impellerIncrease the impeller

O.D.O.D.



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Pumps-Pump Case DesignPumpsPumps--Pump Case DesignPump Case Design In most cases neither is practicalIn most cases neither is practical

There is a practical limit to the impeller diameter.There is a practical limit to the impeller diameter.Beyond that limit it would be difficult to controlBeyond that limit it would be difficult to control

the tolerances to ensure proper fit and balance.the tolerances to ensure proper fit and balance.

The hardware would be prohibitively expensiveThe hardware would be prohibitively expensive

There is also a practical limit to the shaft speed.There is also a practical limit to the shaft speed.

Not only would balance be critical, but theNot only would balance be critical, but thebearing and lubrication system would be complexbearing and lubrication system would be complex

and expensiveand expensive



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Pumps-Pump Case DesignPumpsPumps--Pump Case DesignPump Case Design The third option is simpler. To achieve highThe third option is simpler. To achieve high

differential head without the expense more than onedifferential head without the expense more than onestage or impeller are used. Multistage pumps comestage or impeller are used. Multistage pumps come

in many varietiesin many varieties

Multistage voluteMultistage volute Split caseSplit case

Double caseDouble case

Multistage diffuserMultistage diffuserVerticalVertical

HorizontalHorizontal


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Pumps-Pump Case DesignPumpsPumps--Pump Case DesignPump Case Design Volute PumpVolute Pump

One or two passages inOne or two passages in

the pump case guide thethe pump case guide thefluid from the impeller tofluid from the impeller to

the pump discharge or thethe pump discharge or the

next stagenext stage Single volute pumps canSingle volute pumps can

result in excessiveresult in excessive

hydraulic load on thehydraulic load on theimpeller and shaftimpeller and shaft



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Pumps-Pump Case DesignPumpsPumps--Pump Case DesignPump Case Design

Single Volute Double Suction Pump



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Pumps-Pump Case DesignPumpsPumps--Pump Case DesignPump Case Design Diffuser PumpDiffuser Pump

AA multipassagemultipassage diffuserdiffuser

oror bowl assemblybowl assembly

surrounds the entiresurrounds the entire

impeller O.D. and guidesimpeller O.D. and guides

the fluid to the dischargethe fluid to the discharge

nozzle or next stagenozzle or next stage

through multiple pathsthrough multiple paths



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Pumps-Pump Case DesignPumpsPumps--Pump Case DesignPump Case Design Diffuser PumpsDiffuser Pumps

Note that the Byron Jackson design incorporates aNote that the Byron Jackson design incorporates amixed flowmixed flow impellerimpeller

The fluid does not make a full 90The fluid does not make a full 90oo turn in the impeller.turn in the impeller.

Since it is not a radial flow impeller, it is termed a mixedSince it is not a radial flow impeller, it is termed a mixedflow impellerflow impeller

Not all turbine pumps are mixed flow. Some areNot all turbine pumps are mixed flow. Some are

furnished with radial flow impellers such as thefurnished with radial flow impellers such as thehorizontal diffuser pump shown previouslyhorizontal diffuser pump shown previously



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Multistage Volute Split Case



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Pumps-Seal Cavity PressurePumpsPumps--Seal Cavity PressureSeal Cavity Pressure Most multistage volute type pumps have front and backMost multistage volute type pumps have front and back

wear rings.wear rings.Therefore the seal cavity pressures would be asTherefore the seal cavity pressures would be as

follows:follows:

One endOne end--suctionsuction

The other endThe other end--discharge pressure of one of the stages unlessdischarge pressure of one of the stages unless

some measures are taken to reduce the pressuresome measures are taken to reduce the pressure

Most multistage volute pumps will have several tapsMost multistage volute pumps will have several taps

on the pump case where various pressures are availableon the pump case where various pressures are available

for the flush sourcefor the flush source



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Multistage Volute Double Case



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Pumps-Seal Cavity PressurePumpsPumps--Seal Cavity PressureSeal Cavity Pressure Most multistage double case volute type pumps haveMost multistage double case volute type pumps have

front and back wear rings.front and back wear rings.

Therefore the seal cavity pressures would be asTherefore the seal cavity pressures would be as

follows:follows:

One endOne end

--suctionsuction

The other endThe other end--discharge pressure of one of the stagesdischarge pressure of one of the stages

unless some measures are taken to reduce the pressureunless some measures are taken to reduce the pressure

Only pump discharge pressure is available for a flushOnly pump discharge pressure is available for a flushsourcesource



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Pumps-Seal Cavity PressurePumpsPumps--Seal Cavity PressureSeal Cavity Pressure Many of these pumps as well as other multistageMany of these pumps as well as other multistage

designs will have some provision for reducing thedesigns will have some provision for reducing the

pressure in the seal chamber at the high pressure endpressure in the seal chamber at the high pressure end

Balance lineBalance line

Close clearance bushingClose clearance bushing


P S l C i P


PP S l C i PS l C i P


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Pumps-Seal Cavity PressurePumpsPumps--Seal Cavity PressureSeal Cavity Pressure A balance line will typically bleed the high pressure sealA balance line will typically bleed the high pressure seal

chamber to about suction plus 70% of one stagechamber to about suction plus 70% of one stage

differentialdifferential

Depends on the bushing wearDepends on the bushing wear

Also depends on the allowable flow in theAlso depends on the allowable flow in thebalance line which represents pumpbalance line which represents pump

inefficiencyinefficiency


P S l C i P




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Pumps-Seal Cavity PressurePumpsPumps--Seal Cavity PressureSeal Cavity Pressure DonDont assumet assume

Check to see if theCheck to see if thebalance line existsbalance line exists

Measure the sealMeasure the seal

cavity pressurecavity pressure

The following slideThe following slide

illustrates a balanceillustrates a balancelineline--they are notthey are not

always so visiblealways so visibleConfucius say - When you

assume you make a donkey

out of u and me


P P C D i


PP P C D iP C D i


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Multistage Volute

with Balance Line


P P C D i


PP P C D iP C D i


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90


Multistage Diffuser Horizontal


P S l C i P




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Pumps-Seal Cavity PressurePumpsPumps--Seal Cavity PressureSeal Cavity Pressure Multistage Diffuser HorizontalMultistage Diffuser Horizontal

Since all the impellers face and pump the sameSince all the impellers face and pump the same

direction the seal cavity pressures are as followsdirection the seal cavity pressures are as follows

One endOne end--suctionsuction

The other endThe other end--full discharge unless some measurefull discharge unless some measureis takenis taken


P S l C i P




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Measure taken to reduce seal cavity pressure on highMeasure taken to reduce seal cavity pressure on high

pressure endpressure end

Balance drum (piston)Balance drum (piston)

Balance discBalance disc Both are similar to balance lines and close clearanceBoth are similar to balance lines and close clearance

bushingsbushings


P S l C it P


PP S l C it PS l C it P


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Balance drum (piston)Balance drum (piston)

Balance discBalance disc

Both have additional function in that they areBoth have additional function in that they are

part of the mechanism to reduce the load on thepart of the mechanism to reduce the load on thepump thrust bearingpump thrust bearing

Both are very complex and extremely preciseBoth are very complex and extremely precisemechanical devicesmechanical devices


P p P p C D i


P pP p P p C D iP p C D i


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Multistage Diffuser Vertical

Byron Jackson

Sumpmaster


P mp P mp C e De i n


P mpP mp P mp C e De i nP mp C e De i n


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Multistage Diffuser Vertical

Byron Jackson VLT

(Very Large Turbine)Process Pump with Case


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Pumps Seal Cavity Pressure


PumpsPumps Seal Cavity PressureSeal Cavity Pressure


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Pumps-Seal Cavity PressurePumpsPumps--Seal Cavity PressureSeal Cavity Pressure Vertical Turbine PumpsVertical Turbine Pumps

Measures taken depend on the pump seal cavityMeasures taken depend on the pump seal cavity

constructionconstruction

Internal seal headInternal seal head--the seal actually sits in the pumpthe seal actually sits in the pump

discharge flowdischarge flow--it can only be at pump discharge pressureit can only be at pump discharge pressure

External seal or packing headExternal seal or packing head--a close clearance bushinga close clearance bushing

and balance line arrangement are used to reduce theand balance line arrangement are used to reduce the

pressure to suction plus 70% of one stage. Again youpressure to suction plus 70% of one stage. Again you

must measure to be suremust measure to be sure






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Pumps-Seal Cavity PressurePumpsPumps--Seal Cavity PressureSeal Cavity Pressure Vertical Turbine PumpsVertical Turbine Pumps

Measures taken depend on the pump seal cavityMeasures taken depend on the pump seal cavity

constructionconstruction

Internal packing headInternal packing head--the seal chamber is athe seal chamber is a

separate piece but sits in the discharge flowseparate piece but sits in the discharge flow--usually some provision is made to reduce theusually some provision is made to reduce the

pressure in the packing or seal areapressure in the packing or seal area






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Pumps-Seal Cavity PressurePumpsPumps--Seal Cavity PressureSeal Cavity Pressure

Internal

Seal Head






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External

Seal Head






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InternalPacking

Head


Pumps-Pump Case Design


PumpsPumps--Pump Case DesignPump Case Design


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Pumps-Pump Case DesignPumpsPumps--Pump Case DesignPump Case Design There are three typical styles of pumpThere are three typical styles of pump

constructionconstruction Overhung: an example followsOverhung: an example follows

DoubleDouble--ended: several examples have been givenended: several examples have been given

similar to the previous slides and the slidesimilar to the previous slides and the slide

following the overhung pumpfollowing the overhung pump

Vertical: many variations existVertical: many variations existTurbine styleTurbine style--an example is the previous slidean example is the previous slide

Process with and without a bearing bracketProcess with and without a bearing bracket--examplesexamples

will followwill follow






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Typical end Suction

(Overhung) Process Pump






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Pumps-Pump Case DesignPumpsPumps--Pump Case DesignPump Case Design Many pumps use a double suction impellerMany pumps use a double suction impeller

design which is a single impeller with two inletsdesign which is a single impeller with two inlets

High flowHigh flow

Low NPSHALow NPSHA

Since a double suction impeller must be radialSince a double suction impeller must be radialflow, they are all in volute type cases almostflow, they are all in volute type cases almost

without exceptionwithout exception


Pumps-Seal Cavity Pressure


PumpsPumps--Seal Cavity PressureSeal Cavity Pressure


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Pumps Seal Cavity PressurePumpsPumps Seal Cavity PressureSeal Cavity Pressure Double Suction PumpsDouble Suction Pumps

In a single stage double suction pump the seal orIn a single stage double suction pump the seal orseals sit in the impeller eyeseals sit in the impeller eye

The only pressure they can see is suctionThe only pressure they can see is suction

There are limited choices to dealing withThere are limited choices to dealing with

inadequate vapor suppression margin for theseinadequate vapor suppression margin for these

pumpspumps

Close clearance throat bushing with plan 11 or 32Close clearance throat bushing with plan 11 or 32

flushflush

CoolingCooling






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Pumps Pump Case DesignPumpsPumps Pump Case DesignPump Case Design

Double Suction Radially Split






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Double Suction Axially Split






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Double Suction Overhung




PumpsPumps--Pump Case DesignPump Case DesignV i l P PV i l P P


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Pumps Pump Case DesignPumpsPumps Pump Case DesignPump Case Design Vertical Process PumpsVertical Process Pumps

In addition to those previously shown, there are aIn addition to those previously shown, there are a

class of pumps that are process pumps mounted in aclass of pumps that are process pumps mounted in a

vertical configuration. They are almost always volutevertical configuration. They are almost always volute

single stage pumps. There are two stylessingle stage pumps. There are two styles

Rigid couplingRigid coupling--no bearing bracketno bearing bracket

Flexible coupling with bearing bracketFlexible coupling with bearing bracket






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Vertical InlineProcess Pump with

Rigid coupling-

No bearing bracket






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u ps u p C se es gu psu ps u p C se es gu p C se es g

Vertical InlineProcess Pump with

flexible coupling

and bearing bracket


Pumps-Seal Cavity Pressure


PumpsPumps--Seal Cavity PressureSeal Cavity Pressure Si th p p p t l p p thSince these p mps are process style p mps the


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p ypp yy Since these pumps are process style pumps, theSince these pumps are process style pumps, the

seal cavity pressure can be at anything betweenseal cavity pressure can be at anything between

and including suction and dischargeand including suction and discharge

The normal rules apply. It is necessary to knowThe normal rules apply. It is necessary to know

the impeller and case construction to estimatethe impeller and case construction to estimatethe seal cavity pressurethe seal cavity pressure


Pumps-Problem Constructions


PumpsPumps--Problem ConstructionsProblem Constructions Some p mp designs have inherent mechanicalSome pump designs have inherent mechanical


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ppp Some pump designs have inherent mechanicalSome pump designs have inherent mechanical

problems because of their design and resultantproblems because of their design and resultant

impeller and shaft loadsimpeller and shaft loads

Vertical inline rigid coupling no bearingVertical inline rigid coupling no bearing

bracketbracket Overhung double suction or two stageOverhung double suction or two stage

Single voluteSingle volute




PumpsPumps--Problem ConstructionsProblem Constructions Some pump designs have inherent mechanicalSome pump designs have inherent mechanical


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ppp Some pump designs have inherent mechanicalSome pump designs have inherent mechanical

problems because of their design and resultantproblems because of their design and resultant

impeller and shaft loadsimpeller and shaft loads

Shaft deflection and vibration are common toShaft deflection and vibration are common to

these designsthese designs Something must be done to address theSomething must be done to address the

mechanical situationmechanical situation




PumpsPumps--Problem ConstructionsProblem Constructions


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ppp Cure or eliminate problem pumpCure or eliminate problem pump

constructionsconstructions LL33/D/D44 < or = 40< or = 40

Vertical inline with rigid couplingVertical inline with rigid couplingTwo stage or double suction overhungTwo stage or double suction overhung

Internal sealed (glandless) pump designsInternal sealed (glandless) pump designs

Something we havenSomething we havent discussedt discussed

No seal chamber orNo seal chamber or stuffingboxstuffingbox--similar to internal sealsimilar to internal seal

arrangementforarrangementforvertical turbine pumpsvertical turbine pumps




PumpsPumps--Problem ConstructionsProblem Constructions LL33/D/D44 < or = 40< or = 40


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ppp LL /D/D < or = 40< or = 40

L = distance in inches from center of radialL = distance in inches from center of radialbearing to center of impellerbearing to center of impeller

D = diameter of shaft in inches under the sealD = diameter of shaft in inches under the seal

sleevesleeve




PumpsPumps--Problem ConstructionsProblem Constructions LL33/D/D44 < or = 40 Solutions< or = 40 Solutions


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ppp LL /D/D < or = 40 Solutions< or = 40 Solutions

Replace bearing bracket andReplace bearing bracket and stuffingboxstuffingboxwithwith7th edition upgrade7th edition upgrade

Modify existing pump with heavier shaft andModify existing pump with heavier shaft and

more robust bearingsmore robust bearings

Close clearance non galling wear rings andClose clearance non galling wear rings and

throat bushingthroat bushing




PumpsPumps

--Problem ConstructionsProblem Constructions

Vertical inline with rigid couplingVertical inline with rigid coupling


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pp Vertical inline with rigid couplingVertical inline with rigid coupling

Fine for low horsepower (


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pp Vertical inline with rigid coupling (continued)Vertical inline with rigid coupling (continued)

Close clearance non galling wear rings and throatClose clearance non galling wear rings and throatbushingbushing

Add external bearing assembly on top of seal flangeAdd external bearing assembly on top of seal flange

May require more first obstructionMay require more first obstruction--add motoradd motor

spacer ring and lengthen pump shaftspacer ring and lengthen pump shaft

May be oil mist or grease lubricatedMay be oil mist or grease lubricated




PumpsPumps

--Problem ConstructionsProblem Constructions

Two stage or double suction overhung, old API pumps withTwo stage or double suction overhung, old API pumps with


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ppg g p plarge calculated shaft deflection, single volute pumpslarge calculated shaft deflection, single volute pumps

Same problem as LSame problem as L33

/D/D44

< or = 40< or = 40 Replace bearing bracket andReplace bearing bracket and stuffingboxstuffingboxwith 7thwith 7th

edition upgradeedition upgrade

Modify existing pump with heavier shaft and moreModify existing pump with heavier shaft and more

robust bearingsrobust bearings

Close clearance non galling wear rings and throatClose clearance non galling wear rings and throatbushingbushing

Fundamentals of Centrifugal Pumps

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