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PUMPSPUMPS

PumpsPumps

DefinitionDefinition

A pump is a device that expends energy toA pump is a device that expends energy to

raise, transport fluids or compress gasraise, transport fluids or compress gas

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When a pump is to be selected for a specificWhen a pump is to be selected for a specific

job, following factors have to be taken intojob, following factors have to be taken intoaccountaccount

Suction conditionSuction condition

Stipulated discharge pressureStipulated discharge pressure

Required capacityRequired capacity

Required range of capacityRequired range of capacity

Required pump characteristicsRequired pump characteristics

Properties of the liquid being pumpedProperties of the liquid being pumped Required dimensionsRequired dimensions

Installation requirementsInstallation requirements

PumpsPumps

Pumps can be classified in a great numberPumps can be classified in a great numberof waysof ways f.if.i.;.;

Type of pumpType of pump: Volumetric displacement,: Volumetric displacement,addition of kinetic energy.addition of kinetic energy.

PropulsionPropulsion: Hydraulic, steam or electrical.: Hydraulic, steam or electrical.

Application on boardApplication on board: Discharging cargo,: Discharging cargo,stripping of tanks, injection of chemicals,stripping of tanks, injection of chemicals,emptying barrels or drums, mopping etc.emptying barrels or drums, mopping etc.

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Classification of pumpsClassification of pumps

Two main classes can be distinguishedTwo main classes can be distinguished

Positive displacement pumps (volumetricPositive displacement pumps (volumetricpumps)pumps)

Kinetic pumpsKinetic pumps

Cargo pumps: pump typesCargo pumps: pump types

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Positive displacement pumpsPositive displacement pumps

A positive displacement pump lifts a givenvolume of liquid for each cycle of operation

Two main classes can be distinguished Reciprocating

Piston, plunger and diaphragm

Rotary Gear (tandwielpomp), lobe (lob pomp?), screw (schroef

pomp), vane (schoepen pomp) and cam pumps (nokkenpomp?)

Positive displacement pumps move relatively lowvolumes of liquid at high pressure

PumpsPumps

The earliest pumps were devices for raisingThe earliest pumps were devices for raisingwater, such as the Roman and Persianwater, such as the Roman and Persian

waterwheels and the more sophisticatedwaterwheels and the more sophisticatedArchimedes screwArchimedes screw

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Screw of ArchimedesScrew of Archimedes

WaterwheelWaterwheel

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Reciprocating PumpReciprocating Pump A suction pump works by the atmosphericA suction pump works by the atmospheric

pressure when the piston is raised a partialpressure when the piston is raised a partial

vacuum is created. Atmospheric pressurevacuum is created. Atmospheric pressure

outside forces the water into the cylinder.outside forces the water into the cylinder.

When the piston is lowered again the fluidWhen the piston is lowered again the fluid

is permitted to escape by an outlet valveis permitted to escape by an outlet valve

Atmospheric pressure alone can force waterAtmospheric pressure alone can force waterto a maximum height of 10 meterto a maximum height of 10 meter

(theoretical)(theoretical)

Atmospheric pressure = 10 mAtmospheric pressure = 10 m

water columnwater column

P =gh = 1t/m3x9.81m/s2x10.4m

= 102.024t/ms2

= 102024kg/ms2

= 102024Pa of 1020.24hPa

= Atmospheric pressure

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Suction pumpSuction pump


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Bilges pump of a lifeboatBilges pump of a lifeboat

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Single acting piston pumpsSingle acting piston pumps Outletvalve

Suctionvalve

Single acting means that the piston or plunger is creating suction &

afterwards pressure. Only one side of the piston is used.

Simplex pumpSimplex pump

The simplex, orThe simplex, or singlesingle--cylinder double actingcylinder double acting (to(tocompensate variations in pumping rate) pump wascompensate variations in pumping rate) pump was

invented by Henry R. Worthington in 1840invented by Henry R. Worthington in 1840(Worthington is still a very famous stripping(Worthington is still a very famous stripping

pump)pump)

A simplex pump is a reciprocating pump. ThisA simplex pump is a reciprocating pump. Thispump has a SINGLE cylinder which forces liquidpump has a SINGLE cylinder which forces liquidout through the top outlet on both the in and outout through the top outlet on both the in and outstrokestroke

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Simplex pumpSimplex pump

Double acting means that the piston or plunger is creating

suction at one side of the piston and pressure on the other side,

at the same time

Simplex =1

piston

double acting

Duplex pumpDuplex pump(only 1 piston is visible on the picture)(only 1 piston is visible on the picture)

Duplex =2

pistons double

acting

Liquid sideSteam side

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SimplexSimplexdouble acting pumpdouble acting pump

Duplex pumpsDuplex pumps

Are very common onAre very common onboard and mostly usedboard and mostly used

as stripping pump.as stripping pump. VERY reliable.VERY reliable.

Driven by steam,Driven by steam,hydraulic pressure,hydraulic pressure,

compressed air or acompressed air or aseparate motor.separate motor.

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Horizontal duplex pumpsHorizontal duplex pumps


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Steam side & Liquid sideSteam side & Liquid side

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Vertical duplex pumpsVertical duplex pumps

Vertical duplex pumpsVertical duplex pumps

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TITI--tankerstankers

stripping pumpstripping pump

TITI--tankerstankers

stripping pumpstripping pump

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Liquid SideLiquid Side

Steam SideSteam Side

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ExpansionExpansion

tanktank

Diaphragm pumpsDiaphragm pumps

Very similar to a piston pump, piston hasVery similar to a piston pump, piston hasbeen replaced by a pulsating flexiblebeen replaced by a pulsating flexible

diaphragmdiaphragm Used on board to pump smaller quantitiesUsed on board to pump smaller quantities

Pulsating outputPulsating output

Can run dry for a certain periodCan run dry for a certain period

Sensible to compatibility problems withSensible to compatibility problems withcorrosive chemicals (compatibility problemcorrosive chemicals (compatibility problemmaterial diaphragm)material diaphragm)

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Sandpiper (blue)

Wilden (orange) Atlas Copco (Yellow)

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Gear pumpsGear pumps

Internal gear pumpExternal gear pump

In

Out

External gear pump

Internal gear pump design for automotive oil pumps

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1. Liquid enters the suction port between the rotor(large exterior gear) and idler (small interior gear)teeth. The arrows indicate the direction of thepump and liquid.

2. Liquid travels through the pump between theteeth of the "gear-within-a-gear" principle. Thecrescent shape divides the liquid and acts as a sealbetween the suction and discharge ports.

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3. The pump head is now nearly flooded, just prior3. The pump head is now nearly flooded, just priorto forcing the liquid out of the dischargeto forcing the liquid out of the dischargeport.port. Intermeshing gears of the idler and rotorIntermeshing gears of the idler and rotorform locked pockets for the liquid which assuresform locked pockets for the liquid which assuresvolume control.volume control.

4. Rotor and idler teeth mesh completely to form a4. Rotor and idler teeth mesh completely to form aseal equidistant from the discharge and suctionseal equidistant from the discharge and suctionports. This seal forces the liquid out of theports. This seal forces the liquid out of thedischarge port.discharge port.

Internal gear pump design for high

viscosity liquids

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Lobe PumpsLobe Pumps

Lobe PumpsLobe Pumps

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Lobe pumpLobe pump

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Screw pumpsScrew pumps

ScrewScrew

PumpsPumps

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Sliding vane pumpsSliding vane pumps

SlidingSliding vanevane pumppump

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SlidingSliding vanevane pumppump

Kinetic pumpsKinetic pumps

Kinetic pumps can be divided into twoKinetic pumps can be divided into twoclasses, centrifugal and regenerativeclasses, centrifugal and regenerative

(turbines).(turbines).

The first centrifugal pump was introducedThe first centrifugal pump was introduced1680, kinetic pumps were little used until1680, kinetic pumps were little used until

the 20th centurythe 20th century

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Centrifugal pumpsCentrifugal pumpscreation ofcreation of

suctionsuction The liquid enters the suction

nozzle and then into the center

of a revolving device known as

an impeller.

When the impeller rotates, it

spins the liquid sitting in the

cavities between the vanes

outward and provides

centrifugal acceleration. As liquid leaves the eye of the

impeller a low-pressure area is

created causing more liquid to

flow toward the inlet.

Centrifugal pumps creation ofCentrifugal pumps creation of

discharge pressuredischarge pressure Because the impeller

blades are curved, the

fluid is pushed in a

tangential and radialdirection by the

centrifugal force.

This force acting inside

the pump is the same one

that keeps water inside a

bucket that is rotating at

the end of a string.

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Centrifugal pumps creation ofCentrifugal pumps creation ofdischarge pressuredischarge pressure

VVii = Absolute velocity of the liquid leaving the blade= Absolute velocity of the liquid leaving the bladeVVrr = Velocity of liquid leaving blade relative to blade= Velocity of liquid leaving blade relative to blade

VVpp = Velocity of blade tip= Velocity of blade tip

The energy created by theThe energy created by the

centrifugal force iscentrifugal force is kinetic energy.kinetic energy.

The amount of energy given to theThe amount of energy given to the

liquid is proportional to theliquid is proportional to the velocityvelocity

at the edge or vane tip of theat the edge or vane tip of the

impeller (impeller (VVpp)). The faster the. The faster the

impeller revolves or the bigger theimpeller revolves or the bigger the

impeller is, then the higher will beimpeller is, then the higher will be

the velocity of the liquid at the vanethe velocity of the liquid at the vane

tip and the greater the energytip and the greater the energyimparted to the liquid.imparted to the liquid.

EEkk==22rr

Centrifugal pumps creation ofCentrifugal pumps creation of

discharge pressuredischarge pressure

ThisThis kinetic energykinetic energy of a liquid coming out of an impeller is harnessedof a liquid coming out of an impeller is harnessed

by creating a resistance to the flow. The firstby creating a resistance to the flow. The first resistance is created byresistance is created by

the pump volute (casing) that catches the liquid and slows it downthe pump volute (casing) that catches the liquid and slows it down. In. Inthe discharge nozzle, the liquid further decelerates and itsthe discharge nozzle, the liquid further decelerates and its velocity isvelocity is

converted to pressure according to Bernoullis principle.converted to pressure according to Bernoullis principle.

One fact that must always beOne fact that must always be

remembered: A centrifugal pump doesremembered: A centrifugal pump does

not create pressure, it only provides flow.not create pressure, it only provides flow.

Pressure is a just an indication of thePressure is a just an indication of the

amount of resistance to flow.amount of resistance to flow.

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Centrifugal pumpsCentrifugal pumps


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Composing parts of a centrifugalComposing parts of a centrifugalpumppump

Composing parts of a centrifugalComposing parts of a centrifugal

pumppump

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Composing parts of a centrifugal pumpComposing parts of a centrifugal pump

Composing parts of a centrifugal pumpComposing parts of a centrifugal pump

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Composing parts of a centrifugalComposing parts of a centrifugalpumppump

ImpellersImpellers

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Dredging pumpDredging pump

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Volute Casing Dredging PumpVolute Casing Dredging Pump

Impeller Dredging PumpImpeller Dredging Pump

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Dredging PumpsDredging Pumps

Impellers cargo pumps TIImpellers cargo pumps TI--tankerstankers

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Open Cargo PumpOpen Cargo Pump

Making the volute casing tightMaking the volute casing tight

Rotating ax has to be sealedRotating ax has to be sealed

There are always 2 seals (upper & lower)There are always 2 seals (upper & lower)

Stuffing box & packing glandStuffing box & packing gland

Mechanical sealMechanical seal

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Stuffing boxStuffing box

Lantern ring =greasing

system

Stuffing boxStuffing box

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Mechanical SealMechanical Seal

Mechanical SealMechanical Seal1: Setting screw

2: O-ring

3:Tension pin

4:Carbon ring

(friction ring)

5:Ceramic ring(counter ring)

6:O-ring

7:Gland

8:Anti-rotator pin

9:Axis

10:Spring

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Mechanical sealMechanical seal

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Steam drivenSteam driven

HydraulicHydraulic

ElectricalElectrical

SteamSteam

Turbines are situatedTurbines are situatedin the engine room.in the engine room.

PumproomPumproom is situatedis situatedin the cofferdam.in the cofferdam.

Engine room isEngine room isadjacent.adjacent.

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Cargo pump + steam turbineCargo pump + steam turbine

Cargo pump + steam turbineCargo pump + steam turbine

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HydraulicHydraulic

1. Low pressure part (cargo heating)

2. High pressure: 2 electrical power packs & 1 diesel drivenpower pack (3 pumps)

Cargo pumps, emergency cargo pump, ballast pumps,foam pump, tankcleaning pump

1

2

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Submerged versus deep well pumpsSubmerged versus deep well pumps

Submerged pump: Pump body + motor areSubmerged pump: Pump body + motor aresubmerged in the liquidsubmerged in the liquid

Deep well pump: Pump body is submergedDeep well pump: Pump body is submergedin the liquid while the motor is on deckin the liquid while the motor is on deck

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Submerged Ballast pumpsSubmerged Ballast pumps

Cargo Heating and CoolingCargo Heating and Cooling

Freon H2O + Glycol

Sea Water

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ElectricalElectrical

Easy to install and tomaintain

Cheap installation

Requires a powerfullelectric supplyauxilaries

Intrinsic safe ? Less flexible inoperation

Centrifugal pump + electromotorCentrifugal pump + electromotor

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Submerged pumpsSubmerged pumps


1 tank1 tank -- 1 pump1 pump

Installed in a Installed in a wellwell

Tanks are easy toTanks are easy todraindrain

Combined with a deckCombined with a deckheaterheater

SubmergedSubmerged

pumpspumps

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SubmergedSubmergedPumpsPumps

Submerged Pumps on board of aSubmerged Pumps on board of a

chemical tankerchemical tanker

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DeepwellDeepwell

pumpspumps

Deepwell pumpDeepwell pump

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Special pumpsSpecial pumps

AirliftAirlift

EjectorEjector

Air liftAir lift

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EductorEductor

EductorEductor

Based on a tube ofBased on a tube ofVenturiVenturi

Driving liquid isDriving liquid ispushed trough apushed trough adiaphragm ordiaphragm or VenturiVenturinozzlenozzle

Pressure drops asPressure drops asspeed increasesspeed increases

Suction is createdSuction is created

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EductorEductor

EductorEductor

VERY easy to operateVERY easy to operate

No mechanicalNo mechanical

elements involvedelements involved Not influenced byNot influenced by

impuritiesimpurities

Able to pump bothAble to pump bothvapour and liquidvapour and liquid

Requires minimumRequires minimummonitoringmonitoring

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DisadvantageDisadvantage

The eductor main drawback is that theThe eductor main drawback is that thepropellant is mixd with the pumped liquidpropellant is mixd with the pumped liquid

The propellant has to be compatible withThe propellant has to be compatible withthe cargothe cargo

For liquefied gases the propellant can onlyFor liquefied gases the propellant can only

be the cargo, inert gas or nitrogenbe the cargo, inert gas or nitrogen

EductorsEductors

Since gases are transported at their boilingSince gases are transported at their boilingtemp and the atm. pressure in the tank =temp and the atm. pressure in the tank =

vapour pressure of the liquid anvapour pressure of the liquid an eductoreductorcannot suck (reduction in pressure) up cargocannot suck (reduction in pressure) up cargo

(cargo will start to boil)(cargo will start to boil)

The presence of frictional losses makes itThe presence of frictional losses makes itnecessary that there is a minimum level ofnecessary that there is a minimum level of

liquid above the centre line.liquid above the centre line.

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Pump capacity of an eductor inPump capacity of an eductor infunction of the suction headfunction of the suction head

Use of eductorsUse of eductors

EductorsEductors are NOT used as cargo pumpsare NOT used as cargo pumpsbecause of a very low efficiencybecause of a very low efficiency

Efficiency of the pump delivering theEfficiency of the pump delivering thepropellant (driving liquid) is approx. 70%propellant (driving liquid) is approx. 70%

Efficiency of theEfficiency of the eductoreductor itself is only 30 itself is only 30 40%40%

EductorsEductors are only used as emergencyare only used as emergencysystems or as a pump in hold spaces.systems or as a pump in hold spaces.

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EductorsEductors Mostly used as an emergency system or forMostly used as an emergency system or for

holdhold--space bilge systemspace bilge system

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Pumping capacity of an eductorPumping capacity of an eductor

Frictional force between propellant andFrictional force between propellant andpumped liquidpumped liquid

SuctionSuction

HeadHead

Discharge headDischarge head

Velocity of the propellantVelocity of the propellant

Frictional lossesFrictional losses

QQ--H diagramH diagram

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Pumping HeadsPumping Heads Pump head refers to thePump head refers to the amount of energyamount of energy generallygenerally

expressed in terms of feet or metersexpressed in terms of feet or meters that a pump isthat a pump is

capable of providing to pump a given fluid.capable of providing to pump a given fluid.

Total pump head is a combination ofTotal pump head is a combination ofstatic headstatic head andandfrictional headfrictional head

Static head refers to the elevation difference between theStatic head refers to the elevation difference between theinitial body of fluid to be pumped and the exit point orinitial body of fluid to be pumped and the exit point or

fluid level at the exit pont if the exit pipe is submerged orfluid level at the exit pont if the exit pipe is submerged or

below the top of the liquid reservoir.below the top of the liquid reservoir.

Total Head=Total Static Head + Fictional HeadTotal Head=Total Static Head + Fictional Head

TotalTotal HeadHead ==

DischargeDischarge HeadHead

SuctionSuction HeadHead

DischargeDischarge HeadHead ==Discharge StaticDischarge Static HeadHead ++

FrictionFriction HeadHead ((DynamicDynamic

HeadHead))

Total head = (Static Head +Total head = (Static Head +

Dynamic Head)Dynamic Head)SuctionSuction

HeadHead

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Energy Furnished by the pumpEnergy Furnished by the pump

ReferenceReference

Since there can be aSince there can be a

difference in heightdifference in height

between the suction andbetween the suction anddischarge flanges ordischarge flanges or

connections of a pumpconnections of a pump

by convention it wasby convention it was

agreed that the staticagreed that the static

heads would beheads would be

measured with respect tomeasured with respect to

the suction flangethe suction flange

elevationelevation.

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PumpcapacityPumpcapacity/head/head Q = capacity, expressed inQ = capacity, expressed in

mm33/hour/hour

H = head expressed in mH = head expressed in mliquid column (liquid column (mLCmLC orormWgmWg if dedicated toif dedicated towater)water)

By expressing the head inBy expressing the head inmeter liquid column themeter liquid column thegraph becomesgraph becomes

independent of the densityindependent of the densityof the liquidof the liquid

mWgmWg = meter water gauge= meter water gauge

1 bar = +/1 bar = +/-- 1010 mWgmWg

When we change

density of the propelled

liquid will the height of

the column at the

discharge side change ?

NO !!!!

It is all about energy (kinetic

energy = potential energy)

2R = gH

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If RPM and dimensions of theIf RPM and dimensions of the

pump are identical the dischargepump are identical the dischargehead in meter is also constanthead in meter is also constant

Total Head andTotal Head and

Flow RateFlow Rate

Static head diminishes with the height

=> flow increases but the friction head is

function of the square of the flow.

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Pump curve/total pressure headPump curve/total pressure headExpresses the flow in function of the headExpresses the flow in function of the head

Graph representing the

Pump discharge

Total pressure head

Pressure HeadPressure Head

TheThe total pressuretotal pressure head is composed out of 2 partshead is composed out of 2 parts Static pressure HeadStatic pressure Head

Energy necessary to overcome the difference in potentialEnergy necessary to overcome the difference in potentialenergyenergy

Dynamic pressure HeadDynamic pressure Head Energy to overcome resistance of the pipes, to give a certainEnergy to overcome resistance of the pipes, to give a certain

speed at the liquid (kinetic energy), internal friction of thespeed at the liquid (kinetic energy), internal friction of thepump etc.pump etc.

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Static pressure headStatic pressure head

Static Pressure HeadStatic Pressure Head

gHHstat

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Dynamic pressure headDynamic pressure head

Hdyn = KQ2

Operating pointOperating point

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Flow Rate depends on frictionFlow Rate depends on friction

Characteristic of the dischargingCharacteristic of the discharging

lineline This graph is determined by;This graph is determined by;

Quantity being discharged.Quantity being discharged.

The flow can be laminar or turbulent (Reynolds).The flow can be laminar or turbulent (Reynolds). c =speed.c =speed. D = diameter of the pipe.D = diameter of the pipe.

V = dynamic viscosity.V = dynamic viscosity.

R > 2320 => flow is turbulent.R > 2320 => flow is turbulent.

R < 2320 => flow is laminar.R < 2320 => flow is laminar.

Number of curves, valves etc.Number of curves, valves etc.

Smoothness of theSmoothness of the interiourinteriour of the pipes.of the pipes.

Etc.Etc.

v

dcR

.

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Evolution of the pressure headEvolution of the pressure headwhen dischargingwhen discharging

When discharging the

level of the tank being

discharged is dropping,

while the level of the

tank in which we are

dischaging is rising =>static pressure head is

rising => Q is

decreasing

TrottlingTrottling a valve on thea valve on the

discharging sidedischarging side Total head is rising

Q = dropping

Since RPM was not

changed energy consumed

is identical

Static head does

not change

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Result of diminishing RPMResult of diminishing RPM

Q =identical to

previous slide

(trottling

discharging

valve) but energyconsumed is less

Influence of the viscosityInfluence of the viscosity

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2 pumps in parallel2 pumps in parallel

2 pumps in serie2 pumps in serie

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CavitationCavitation

When at theWhen at the entrance of the impeller (eye)entrance of the impeller (eye) thethepressure dropspressure drops below the vapour pressure of thebelow the vapour pressure of the

liquidliquid being pumped, the liquid starts boiling andbeing pumped, the liquid starts boiling and

gas bubbles are createdgas bubbles are created

In the impeller the pressure increases again andIn the impeller the pressure increases again andthe bubbles implode.the bubbles implode.

This implosion can be very powerful and seriousThis implosion can be very powerful and seriousdamage can be caused to the impellerdamage can be caused to the impeller


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NPSHNPSH Net positive suction head is the term that isNet positive suction head is the term that is

usually used to describe theusually used to describe the absolute pressure of aabsolute pressure of a

fluid at thefluid at the inlet to a pump (inlet to a pump ( eye) eye) minusminus thethe

vapor pressure of the liquidvapor pressure of the liquid. The resultant value is. The resultant value isknown as the Net Positive Suction Head availableknown as the Net Positive Suction Head availableoror NPSHNPSHAA

A similar term is used by pump manufactures toA similar term is used by pump manufactures todescribe thedescribe the energy losses that occur within theenergy losses that occur within thepump. This energy loss is described as NPSHpump. This energy loss is described as NPSHRR(Net Positive Suction Head Required).(Net Positive Suction Head Required).

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Net Positive Suction headNet Positive Suction head(NPSH)(NPSH)

NPSHNPSHAA is a function of your system and canis a function of your system and canbe calculated, whereas NPSHbe calculated, whereas NPSHRR is a functionis a function

of the pump and must be provided by theof the pump and must be provided by the

pump manufacturer. NPSHpump manufacturer. NPSHAA MUST beMUST be

greater than NPSHgreater than NPSHRR for the pump system tofor the pump system to

operate withoutoperate without cavitatingcavitating..NPSHNPSHAA > NPSH> NPSHRR

NPSHNPSHAA

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NPSHNPSHRR

NPSHNPSHRR = Nett Positive Suction Head= Nett Positive Suction Head

Loss of suction head between the entrance (placeLoss of suction head between the entrance (placeof the suction manometer) of the pump and theof the suction manometer) of the pump and theentrance of the impellerentrance of the impeller

The minimum pressure to be maintained at theThe minimum pressure to be maintained at theentrance of the impeller is the vapour pressureentrance of the impeller is the vapour pressure

The minimum suction pressure to be maintained atThe minimum suction pressure to be maintained atthe entrance of the pump is the Vapour Pressure +the entrance of the pump is the Vapour Pressure +NPSHNPSHRR

Cavitation will be avoided if:Cavitation will be avoided if:

HA +/HZHF + HVHVP > NPSHR

Suction Head

NPSHA

Pressure drop between

entrance pump and

entrance impeller

Pressure in excess of

the vapor pressure

Manometric

pressure

entrance pump

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PressurePressure

profile atprofile at

the pumpthe pump

entrance.entrance.

NPSHNPSH

The actual NPSH depends on the characteristics ofThe actual NPSH depends on the characteristics ofthe liquid, the pump speed, the capacity and thethe liquid, the pump speed, the capacity and thepump design.pump design.

Detailed information about the NPSH is publishedDetailed information about the NPSH is publishedby the manufacturer of the pump.by the manufacturer of the pump.

On discharging there is not very much you can doOn discharging there is not very much you can doabout static suction head and liquid vapourabout static suction head and liquid vapourpressure.pressure.

The only thing we can do is control the NPSHThe only thing we can do is control the NPSHand the dynamic suction head by reducing theand the dynamic suction head by reducing theliquid flow.liquid flow.

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Pump =stopped

Pressure recorded on the suction

manometer = hydrostatic pressure

+ pressure of the tank atmosphere

(IG)

Pump=runningPressure recorded on the suction

manometer = hydrostatic pressure

+ tank atmosphere pressure

dynamic pressure head

Pressure on the suction manometer

must be > NPSH + VP

How to avoidHow to avoid cavitationcavitation ??

RPMRPM

NPSHNPSH

Dynamic suction headDynamic suction head

TrottleTrottle delivery valvedelivery valve

Pressure at the entrance of thePressure at the entrance of thepump will risepump will rise

Q willQ will => Dynamic suction=> Dynamic suctionhead willhead will

Sound of

Cavitation

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Vacuum stripperVacuum stripper

Vacuum stripperVacuum stripper

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VacuumVacuum

system onsystem onboard of theboard of the

TITI--tankers +tankers +

vacuum pumpvacuum pump

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Cargo pumps on board of gasCargo pumps on board of gas

carrierscarriersThe unloading of liquefied gas is done by one, or aThe unloading of liquefied gas is done by one, or a

combination of the following methods:combination of the following methods:

Submerged centrifugal pumpSubmerged centrifugal pump Submerged centrifugal pump and a booster pumpSubmerged centrifugal pump and a booster pump

on deckon deck

SubmergedSubmerged eductoreductor

Pressurizing and a deck mounted cargo pumpPressurizing and a deck mounted cargo pump

pressurizingpressurizing

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Suction lift, suction head & NPSHSuction lift, suction head & NPSH

A closed vertical pipe is submergedA closed vertical pipe is submergedintointo cold watercold water..

Air is sucked out & a 100% vacuumAir is sucked out & a 100% vacuumis createdis created

Level rises as a consequence of theLevel rises as a consequence of thepressure difference (max. 10m)pressure difference (max. 10m)

When the atm. pressure in the pipe =When the atm. pressure in the pipe =vapour pressure of water the watervapour pressure of water the waterstarts to boil & it is impossible tostarts to boil & it is impossible to

raise the water any further.raise the water any further. This level is called maximumThis level is called maximum

theoretical suction lift (function oftheoretical suction lift (function ofatm. Pressure, vapour pressure andatm. Pressure, vapour pressure andtemp. of the water)temp. of the water)

Patm

Abs. Vac.

Suction lift, suction head & NPSHSuction lift, suction head & NPSH A pump is started at the water level andA pump is started at the water level and

then gradually liftedthen gradually lifted

At a certain moment the flow stops.At a certain moment the flow stops.

This happens before the theoreticalThis happens before the theoreticalsuction lift (suction lift (f.if.i. water & normal atm.. water & normal atm.pres. suction lift is max 10 meters) haspres. suction lift is max 10 meters) hasbeen reached (loss of energy within thebeen reached (loss of energy within thepump & suction pipe)pump & suction pipe)

Water starts to boil at the entrance of theWater starts to boil at the entrance of theimpellerimpeller

This height is called the permissibleThis height is called the permissiblesuction lift.suction lift.

The difference between the theoretical &The difference between the theoretical &the permissible suction lift is called thethe permissible suction lift is called theNPSHNPSH

Max. theoretical suctionMax. theoretical suction

lift = NPSH +lift = NPSH +

Permissible suction liftPermissible suction lift

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Water is replaced byWater is replaced by fully refrigeratedfully refrigeratedpropane (propane (--4444C at atm. pres.)C at atm. pres.)..

When a vacuum is created the liquidWhen a vacuum is created the liquidwill not rise, the liquid just starts towill not rise, the liquid just starts to

boil.boil.

Liquid propane is at his boiling pointLiquid propane is at his boiling point((equilibrumequilibrum), any reduction in pressure), any reduction in pressure

will trigger the boiling of the liquidwill trigger the boiling of the liquid

Suction lift, suction head & NPSHSuction lift, suction head & NPSH

In a cargo tank the pressureIn a cargo tank the pressureover the liquid = vapourover the liquid = vapourpressurepressure

If the pump is started at theIf the pump is started at the

level of the liquid the pump willlevel of the liquid the pump willdo nothing. The liquid will startdo nothing. The liquid will startto boilto boil immidiatellyimmidiatelly..

We gradually immerge theWe gradually immerge thepump in the liquid.pump in the liquid.

At a certain level below theAt a certain level below theliquid the pump starts to work.liquid the pump starts to work.

This level is called the NPSH.This level is called the NPSH.

HydrosaticHydrosatic pressure = internalpressure = internalfriction losses.friction losses.

Suction lift, suction head & NPSH

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Difference between suction headDifference between suction head& suction lift& suction lift The term The term suction liftsuction lift is used when the is used when the

supply is below the centreline of the pump.supply is below the centreline of the pump.

Suction lift is always negativeSuction lift is always negative

Pressure at the entrance of the pump < atm.Pressure at the entrance of the pump < atm.pressurepressure

The term The term suction headsuction head is used when the is used when thesupply is above the centreline of the pumpsupply is above the centreline of the pump

Suction pressure > atm. PressureSuction pressure > atm. Pressure

Suction lift Suction head

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Pumps on board of a gas carrierPumps on board of a gas carrier

On fully ref. gas tankers pressure in theOn fully ref. gas tankers pressure in thetanks is very low => pumps are installed attanks is very low => pumps are installed at

the bottom of the tankthe bottom of the tank

On fully pres. gas tankers pressure in theOn fully pres. gas tankers pressure in thetanks is high so the pumps may be mountedtanks is high so the pumps may be mounted

on deck. During discharge the pressure ison deck. During discharge the pressure ismaintained by compressors.maintained by compressors.

Pumps on board of gas carriersPumps on board of gas carriers

It is impracticable to use screwIt is impracticable to use screw-- or pistonor pistonpumps because of the complex constructionpumps because of the complex construction

of these pumps.of these pumps.

Centrifugal pumps orCentrifugal pumps or eductorseductors are usedare used

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They may operate alone or in parallelwith one another.

They may also operate in series with adeck-mounted booster pump and a cargo

heater during discharge of LPG to

pressurised storage

Some fully pressurised ships dischargecargo by pressurising tanks with vapour

and booster pumps are fitted to speed the

cargo transfer.

Centrifugal pumps are the main cargoCentrifugal pumps are the main cargo

pumps on board of gas carrierspumps on board of gas carriers

ProPro

Simple designSimple design

High capacityHigh capacity

No pulsationsNo pulsations No damage from closedNo damage from closed

discharge valvedischarge valve

ContraContra

Difficult to construct forDifficult to construct forlow capacitieslow capacities

Difficult to construct forDifficult to construct for

high differential pressurehigh differential pressureper stageper stage

Only efficient at limitedOnly efficient at limitedrange of speedsrange of speeds

Not self primingNot self priming

Can allow backflow in theCan allow backflow in theabsence of a check valveabsence of a check valve

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Pump TowerPump Tower

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PumpPumpTowerTower

Pump TowerPump Tower

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90

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Spanningen doorSpanningen door

sloshingbelastingen (links),sloshingbelastingen (links),thermische belastingen (midden),thermische belastingen (midden),

gecombineerde spanningen (rechts).gecombineerde spanningen (rechts).

Sloshing in partly filled tanksSloshing in partly filled tanks

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Sloshing in partly filled tanksSloshing in partly filled tanks

NormalNormal -- versus a reinforced pumpversus a reinforced pumptowertower

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Pumps on board of the regasificationPumps on board of the regasificationvesselsvessels

FeedFeed

pumpspumps

620m620m33/h/h

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HighPressurepump-100bar

Single &Single &

multistagemultistage

pumpspumps

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Single Stage CPSingle Stage CP

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Single StageSingle Stage

CPCP

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Multistage CPMultistage CP

PerformancePerformance

curve for acurve for a

multimulti--stagestage

deepwelldeepwell

pumppump

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The flowThe flow--head curve (Curve A)head curve (Curve A)

Curve A = pumpCurve A = pumpcapacity, given incapacity, given in

terms of flow rateterms of flow rate

(m3/hr), as a(m3/hr), as a

function of the headfunction of the head

given in metresgiven in metres

liquid column (liquid column (mlcmlc).).

The net positive suction headThe net positive suction head

curve (Curve B)curve (Curve B)

The NPSH requirementThe NPSH requirementat any flow rate is theat any flow rate is the

positive head of fluidpositive head of fluid

required at the pumprequired at the pump

suction over and abovesuction over and above

the cargos vapourthe cargos vapour

pressure to preventpressure to prevent

cavitationcavitation at theat the

impellerimpeller

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NPSH considerations are particularlyNPSH considerations are particularlysignificant when pumping liquefied gasessignificant when pumping liquefied gases

because the fluid being pumped is always atbecause the fluid being pumped is always at

its boiling point. It must be rememberedits boiling point. It must be remembered

that ifthat if cavitationcavitation is allowed to occur withinis allowed to occur within

a pump, not only will damage occur to thea pump, not only will damage occur to the

impeller but the shaft bearings themselvesimpeller but the shaft bearings themselves

will be starved of cargo. This will restrictwill be starved of cargo. This will restrict

cooling and lubrication at the bearings andcooling and lubrication at the bearings and

damage will quickly result.damage will quickly result.

The power consumption curveThe power consumption curve

(Curve C)(Curve C)

Curve C shows the powerCurve C shows the powerabsorbed as a function ofabsorbed as a function ofpump capacity. This curvepump capacity. This curveis normally given for ais normally given for a

specific liquid density andspecific liquid density andcan be converted for anycan be converted for anyliquid by multiplying by theliquid by multiplying by theratio of specific gravities.ratio of specific gravities.

When CP motors haveWhen CP motors havebeen sized for LPG orbeen sized for LPG orammonia and whenammonia and whendischarging VCM (s.g.discharging VCM (s.g.0.97) RPMs will have to0.97) RPMs will have toreduced to avoidreduced to avoidoverheatingoverheating

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Head = (P1P2)/SG

Cargo = ammonia SG 0.65 atambiant temperature

Head = (7 kg/cm2 x 10)/0.65 =

108mlc

Effective Head = 108mlc + 5 = 113

mlc

According the Q-H curve outputwill be 105m3/h

HP = 90x0.65 = 58.5HP

The head = energy (work) necessary toovercome the difference in potential energy

In an initial approach the dynamic part is ignored The head developed is therefore approximated to

the static pressure difference expressed as acolumn of the liquid pumped in metres of fluid.

P1& P2 in kg/cm2

h1, h2 en h3 in mLcHead = ht(h3+P2)

Head = (h1+h2+h3)(h3+P2)Head = P1 +h2P2

Head = (P1-P2) + h2Head = 108mlc + 5mLc = 113mlc

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ht

h3

h1

h2

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Deepwell PumpsDeepwell Pumps

Pump characteristics forPump characteristics fordifferent s.g. of liquiddifferent s.g. of liquid

Running Pumps in Parallel andRunning Pumps in Parallel and

SerieSerie

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Pumping PowerPumping Power

TheThe minimumminimum necessarynecessary pumpingpumping powerpowershouldshould bebe usedused inin orderorder toto reducereduce heatheat inputinput

toto thethe cargocargo andand toto limitlimit thethe riserise inin saturatedsaturated

vapourvapour pressurepressure ofof thethe delivereddelivered cargocargo..

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Deepwell PumpsDeepwell Pumps DeepwellDeepwell pumps are the most common type ofpumps are the most common type of

cargo pump for LPG carriers. The figure shows acargo pump for LPG carriers. The figure shows atypicaltypical deepwelldeepwell pump assembly. The pump ispump assembly. The pump isdriven electrically or hydraulically (through adriven electrically or hydraulically (through a

sealing arrangement) by a motor which is mountedsealing arrangement) by a motor which is mountedoutside the tank. The drive shaft is held in carbonoutside the tank. The drive shaft is held in carbonbearings inside the cargo discharge tube and thesebearings inside the cargo discharge tube and thesebearings are lubricated and cooled by the cargobearings are lubricated and cooled by the cargo

flow.flow.

DeepwellDeepwell PumpsPumps

The centrifugal impeller is mounted at theThe centrifugal impeller is mounted at thebottom of the cargo tank and frequentlybottom of the cargo tank and frequently

comprises two or three stages together withcomprises two or three stages together witha first stage inducer: this latter is used toa first stage inducer: this latter is used to

minimise the NPSH requirement of theminimise the NPSH requirement of the

pump.pump.

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Shaft SealingShaft Sealing

Shaft sealing at the cargo tank dome consists of aShaft sealing at the cargo tank dome consists of adouble mechanical seal flushed with lubricatingdouble mechanical seal flushed with lubricatingoil. This stops cargo leakages to atmosphere. Theoil. This stops cargo leakages to atmosphere. The

accurate alignment of the motor coupling, thrustaccurate alignment of the motor coupling, thrustbearing and mechanical oil seal is important.bearing and mechanical oil seal is important.

Furthermore, the length of the drive shaft can be aFurthermore, the length of the drive shaft can be a

problem and the longer it becomes the moreproblem and the longer it becomes the moresupport is needed.support is needed.

Submerged PumpsSubmerged Pumps

SubmergedSubmerged motormotor pumpspumps areare installedinstalled atat thethebottombottom ofof cargocargo tankstanks andand enableenable veryvery lowlow pumppump--

downdown levelslevels toto bebe achievedachieved.. PowerPower isis suppliedsupplied toto thethe motormotor throughthrough speciallyspecially

sheathedsheathed cablescables..

These pumps are cooled and lubricated by cargoThese pumps are cooled and lubricated by cargoflow and are, therefore, prone to damage due toflow and are, therefore, prone to damage due toloss of flow, special provisions are provided.loss of flow, special provisions are provided.

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Submerged pumps need to be

designed for the particular gradesof cargo found on the ship'sCertificate of Fitness. For examplecontrary to the hydrocarbon gases,ammonia is an electric conductor

and can also be a particularlycorrosive cargo for some materialssuch as copper wires and electrical

insulation.

Submerged Pump for LPGSubmerged Pump for LPG

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BoosterBooster

PumpsPumps

Booster Pumps Horizontal &Booster Pumps Horizontal &

VerticalVertical

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Booster pumpsBooster pumps

System characteristics of parallelSystem characteristics of parallelpumps working in series with a boosterpumps working in series with a boosterpumppump

Booster pumpsBooster pumps

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