marine pump

8/11/2019 Marine Pump

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MARINE PUMP


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Learning Objective:Learning Objective: Know the basic designKnow the basic designfeatures and functions of various marinefeatures and functions of various marineauxiliary machineryauxiliary machinery

Machinery: PumpsMachinery: Pumps

Specific Objectives:Specific Objectives:

Recognize the various names and locations ofauxiliary machinery found on board

Describe the basic operation of the machinery Identify the main parts of the machinery S etch and label the main parts


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Learning Objective:Learning Objective: Describe the marine pump,Describe the marine pump, types, esign !eatures an "perati"n "n b"ar #types, esign !eatures an "perati"n "n b"ar #

$peci!ic Learning Objectives:$peci!ic Learning Objectives: $tate the esign !eatures "! centri!uga% an p"sitive isp%acement pumps#$tate the esign !eatures "! centri!uga% an p"sitive isp%acement pumps# $tate the uses "! vari"us pumps "nb"ar #$tate the uses "! vari"us pumps "nb"ar # E&p%ain the pump types an princip%es "! "perati"n "! marine pump#E&p%ain the pump types an princip%es "! "perati"n "! marine pump# $tate an e&p%ain the "perati"n "! each c"mp"nents "! types "! pumps$tate an e&p%ain the "perati"n "! each c"mp"nents "! types "! pumps

Describe pump !itting %i'e g%an sea%s, re%ie! va%veDescribe pump !itting %i'e g%an sea%s, re%ie! va%ve $tate the re(uirement "! re%ie! va%ves that may be !itte "n$tate the re(uirement "! re%ie! va%ves that may be !itte "nmarine pumpsmarine pumps


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Functions of a Pump

To transport a fluid through a pipeRaise the liquid from one level to another

To give fluid a high velocityTo move the fluid against resistanceTo force a fluid through a hydraulic system

for workTo move it against resistance


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)%assi!icati"n

P"sitive Disp%acement pumps

Dynamic pressure pumps*r"t"r+ ynamic pumps "r n"n+p"sitive isp%acement pumps


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!his is one in "hich a definite volume ofli#uid is delivered for each cycle of pumpoperation$ regardless of the resistanceoffered%

!hese include reciprocating $ gear $ scre" $etc%$

!hey do not re#uire a priming device$

In fact they may used as priming devices%

P"sitive Disp%acement pumps


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In general, they would be used for smallto medium discharge rate,They can pump fluids of a wide range of

viscosityan develop high!pressure differentials, if

required"

If the outlet is completely closed, eitherthe unit driving the pump will be stalled orpump or pipe itself will break or burst, thussafety or relief valve are fitted on it"


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This is one in which the volume of the liquiddelivered for each cycle is dependent upon theresistance offered to the flow

This pump produces a force on the liquid that isconstant for each particular speed of the pump"Resistance in the discharge line produces aforce in opposite direction" #hen these forces

are equal, this liquid is in a state of equilibriumand does not flow"

N"n+P"sitive Disp%acement pumps


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$ormally, centrifugal pumps are under thisclassification and they may require primingdevice depending upon supply head%enerally, used for medium to high!pressure discharge rates, and usually areconfined to low viscosity fluids andgenerate only low to moderate pressuredifferentials"


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T'P() of P*+P

entrifugal

)crew%ear

Reciprocating

&ialetc


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)entri!uga% pump


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)crew


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-ear pump


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Recipr"cating pump


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A&ia%


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P*+P) -$ .- R/

)entri!uga%$cre.-ear Recipr"cating

A&ia%(tc",


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entrifugal pump


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entrifugal pump


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.asic components

The housing for containing the water"The impeller attached to a rotating shaft that movesthe water"The coupling that transmits the rotating action of amotor 0or other prime movers1 to the pump shaft"The seal between the housing and the rotating shaft"The bearings for ensuring that the shaft turnssmoothly"

The inlet and the outlet ports for channeling the waterflow through the pump"


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omponent division

A centrifugal pump has twomain components:

A rotating component comprised of an impeller and a shaft

A stationary component

comprised of a casing, casing cover, and bearings.


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In single stage pumps a single impeller rotates in a casing ofspiral or volute form and

in multistage pumps two or more impellers are fitted on thesame shaft, producing twice or triple 0stages1 the head orpressure without having to increase the pump speed"


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Fluid enters the impeller a&iallythrough the eye then centrifugal

action or force continues radiallyand discharges around the entirecircumference"The fluid in passing through theimpeller receives energy from thevanes giving an increase ofpressure an ve%"city# The kinetic 0velocity1 energy of thedischarging fluid is partly convertedto pressure energy by suitabledesign of impeller vanes andcasing"


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Impellers of pumps are classified based on the number ofpoints that the liquid can enter the impeller and also on theamount of webbing between the impeller blades!2Impellers can be either single ! suction or double!suction"

single!suction impeller allows liquid to enter the center ofthe blades from only one direction" double!suctionimpeller allows liquid to enter the center of the impellerblades from both sides simultaneously giving twice thedischarge at a given head""

IMPELLER


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Impellers designs can be-pen,)emi!open,(nclosed"

The open impeller consists only of blades attached toa hub"

The semi!open impeller is constructed with a circularplate 0the web1 attached to one side of the blades"

The enclosed impeller has circular plates attached toboth sides of the blades are also referred to as shrouded

impellers"


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Opendesig n

!he vanes are attached to the hub% !here is no shroud to support thevanes% !hese are good designs for pumping stringy materials such aspaper stoc % Pump efficiency is maintained by setting a close clearance bet"een theimpeller vanes and the volute or bac plate% Since there is no shroud to strengthen the vanes$ their use is oftenlimited to small inexpensive pumps

Semi-

opendesign

!he vanes are attached to the hub "ith a shroud on one side of theimpeller% !he pump efficiency is maintained by setting a close clearancebet"een the vanes and the volute or bac &plate%

Some of these semi&open impellers have pump out vanes on the bac ofthe shroud that reduce the pressure on the bac of the shroud andprevent foreign matter from lodging in bac of the impeller$ interfering"ith its operation%

Closeddesign

In this design the vanes are attached to the hub "ith a shroud on eitherside of the impeller% !hese designs maintain pump efficiency by the useof close clearance "ear rings% 'losed impellers are sensitive to clogging "ith solids so their use islimited to the pumping of reasonably clear li#uids%

(il refineries use closed impellers because of the problem of maintaininga close tolerance bet"een a semi&open impeller and the pump volute%)xplosive products "ould ignite if the impeller came into contact "ith thevolute$ but in the closed impeller version soft "ear rings "ould ma e the

contact%


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The impeller sometimes contains balancing holes that

connect the space around the hub to the suction side of theimpeller"

The balancing holes have a total cross!sectional area

that is considerably greater than the cross!sectional area ofthe annular space between the wearing ring and the hub"

The result is suction pressure on both sides of the impeller

hub, which maintains a hydraulic balance of a&ial thrust"


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)entri!uga% Pump)%assi!icati"n

/y !%".


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The manner in which fluid flows through the

pump is determined by the design of the pump

casing and the impeller"

The three types of flow through a centrifugal pump

are

! Radial flow,! &ial flow,! +i&ed flow"


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Ra ia% 0%". Pumps

In a radial flow pump, the liquid enters atthe center of the impeller and is directedout along the impeller blades in a directionat right angles to the pump shaft"

The impeller of a typical radial flow pumpand the flow through a radial flow pumpare shown in ne&t slide


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A&ia% 0%". Pumps

In an a&ial flow pump, the impeller pushes theliquid in a direction parallel to the pump shaft"

&ial flow pumps are sometimes called propellerpumps because they operate essentially thesame as the propeller of a boat"

The impeller of a typical a&ial flow pump and theflow through a radial flow pump are shown inFigure


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Mi&e 0%". Pumps

+i&ed flow pumps use characteristics of radial flow anda&ial flow pumps"

s liquid flows through the impeller of a mi&ed flowpump, the impeller blades push the liquid out away fromthe pump shaft and to the pump suction at an anglegreater than 34 o"

The impeller of a typical mi&ed flow pump and the flowthrough a mi&ed flow pump are

shown in Figure


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Mu%ti+stage)entri!uga% Pump


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pump stage is defined as that portion of a

centrifugal pump consisting of one impeller and itsassociated components"

+ost centrifugal pumps are single!stage pumps,containing only one impeller"

pump containing seven impellers within a singlecasing would be referred to as a seven!stage pump orgenerally considered as a multi!stage pump"


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centrifugal pump with a single impeller thatcan develop a differential pressure of more than564 psid in the suction and the discharge isdifficult and costly to design and construct"

more economical approach to developing highpressures with a single centrifugal pump is toinclude multiple stage impellers on a commonshaft within the same pump casing at moderate

speed" Internal channels in the pump casing route thedischarge of one impeller to the suction of

another impeller


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The water enters the pump from the topleft and passes through each of the fourimpellers in series, going from left to right"

The water goes from the volute

surrounding the discharge of one impellerto the suction of the ne&t impeller"


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/iffuser


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/iffusers consist of a floating ring of stationary guidevanes surrounding the impeller" It is used in some pump"

The purpose of the diffuser is to increase theefficiency of the centrifugal pump by allowing a moregradual e&pansion and less turbulent area for the liquidto reduce in velocity"

The diffuser vanes are designed in a manner that theliquid e&iting the impeller will encounter an ever!increasing flow area as it passes through the diffuser"

This increase in flow area causes a reduction in flowvelocity, converting kinetic energy into flow pressure"


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7olute casing


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The casing usually has the suction and discharge branchesarranged at the back so impeller and spindle can beremoved from the front without breaking pipe 8oints"

The discharge branch is usually on the pump centre line

The number of impeller vanes is not fi&ed but usually there

are si& to ten"

The volute casing is like a divergent no99le which iswrapped around the impeller and serves two main functions

051 It enables velocity energy to be converted into pressure energy ,

the degree of conversion is governed mainly by the degree ofdivergence0:1 It accommodates the gradual increase in quantity of fluid thatbuilds at discharge from the circumference of the impeller"


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)entri!uga% Pump)"mp"nents


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entrifugal pumps vary in design and

construction from simple pumps with relativelyfew parts to e&tremely complicated pumps withhundreds of individual parts")ome of the most common components foundin centrifugal pumps are

#earing rings,)tuffing bo&es,

Packing;antern rings"


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1earing Rings

entrifugal pumps contain rotating impellers withinstationary pump casings" To allow the impeller torotate freely within the pump casing , a smallclearance is designed to be maintained between the

impeller and the pump casing"

To ma&imi9e the efficiency of a centrifugal pump, itis necessary to minimi9e the amount of liquid

leaking through this clearance from the highpressure or discharge side of the pump back to thelow pressure or suction side


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)ome wear or erosion will occur at the pointwhere the impeller and the pump casing nearly

come into contact"

This wear is due to the erosion caused by liquidleaking through this tight clearance and othercauses"

s wear occurs, the clearances become largerand the rate of leakage increases" (ventually,the leakage could become unacceptably largeand maintenance would be required on thepump


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To minimi9e the cost of pump maintenance, manycentrifugal pumps are designed with wearing ringswhich are replaceable rings that attached to theimpeller and


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$tu!!ing /"&

In almost all centrifugal pumps, the rotating shaftthat drives the impeller penetrates the pressureboundary of the pump casing" It is important thatthe pump is designed properly to control theamount of liquid that leaks along the shaft at thepoint that the shaft penetrates the pump casing"

Factors considered when choosing a methodinclude the pressure and temperature of the fluidbeing pumped, the si9e of the pump, and thechemical and physical characteristics of the fluidbeing pumped"


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-ne of the simplest types of shaft seal is the stuffing bo&which is cylindrical space in the pump casing surrounding

the shaft"

Rings of packing material are placed in this space to forma seal to control the rate of leakage along the shaft"

The packing rings are held in place by a gland which is inturn, held in place by studs with ad8usting nuts"

s the ad8usting nuts are tightened, they move the glandin and compress the packing" This a&ial compression causes the packing to e&pand radially, forming a tightseal between the rotating shaft and the inside wall of thestuffing bo&"


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The high speed rotation of the shaft generates asignificant amount of heat as it rubs against the

packing rings"If no lubrication and cooling are provided to thepacking, the temperature of the packing increasesto the point where damage occurs to the packing,the pump shaft, and possibly nearby pumpbearings")tuffing bo&es are normally designed to allow asmall amount of controlled leakage along the shaftto provide lubrication and cooling to the packing"

The leakage rate can be ad8usted by tightening andloosening the packing gland"


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Lantern Ring

It is not always possible to use a standard stuffingbo& to seal the shaft of a centrifugal pump" Thepump suction may be under a vacuum so thatoutward leakage is impossible or the fluid may betoo hot to provide adequate cooling of the packing"These conditions require a modification to the

standard stuffing bo&"

-ne method of adequately cooling the packingunder these conditions is to include a lantern ring


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lantern ring is a perforated hollow ringlocated near the center of the packing bo& thatreceives relatively cool, clean liquid from either

the discharge of the pump or from an e&ternalsource and distributes the liquid uniformly aroundthe shaft to provide lubrication and cooling"

The fluid entering the lantern ring can cool theshaft and packing, lubricate the packing, or sealthe 8oint between the shaft and packing against

leakage of air into the pump in the event thepump suction pressure is less than that of theatmosphere"


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Positive displacement pump


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IN2RODU)2ION

positive displacement pump is one in which a definiteconstant volume of liquid is delivered for each cycleregardless of the resistance to flow offered by the system ofpump operation"The positive displacement pump differs from centrifugal

pumps, which deliver a continuous flow for any given pumpspeed and discharge resistance"Positive displacement pumps can be grouped into threebasic categories based on their design and operation=

Reciprocating pumps, Rotary pumps, /iaphragm pumps"


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Recipr"cating pump

This principle can be most easily demonstrated byconsidering a reciprocating positive displacement pumpconsisting of>

a single reciprocating piston in a cylinder with a singlesuction port and a single discharge port"

heck valves in the suction and discharge ports allow flowin only one direction"


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/uring the suction stroke, the piston moves to the left,causing the check valve in the suction"

/uring the discharge stroke, the piston moves to theright, seating the check valve in the suction line andopening the check valve in the discharge line"

The volume of liquid moved by the pump in onecycle 0one suction stroke and one discharge stroke1 isequal to the change in the liquid volume of the

cylinder as the piston moves from its farthest leftposition to its farthest right position"


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Reciprocating Positive Displacement Pump Operation


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Reciprocating positive displacementpumps are generally categori9ed in fourways>

/irect!acting or indirect!acting)imple& or duple&)ingle!acting or double!actingPower pumps"


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Direct+Acting and In irect+cting Pumps

)ome reciprocating pumps are powered by prime movers thatalso have reciprocating motion, such as a reciprocating pump

powered by a reciprocating steam piston"

The piston rod of the steam piston may be directly connected to theliquid piston of the pump or it may be indirectly connected with a beamor linkage"

/irect!acting pumps have a plunger on the liquid 0pump1 end that isdirectly driven by the pump rod 0also the piston rod or e&tensionthereof1 and carries the piston of the power end"

Indirect!acting pumps are driven by means of a beam or linkageconnected to and actuated by the power piston rod of aseparate reciprocating engine"


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$imp%e& and Dup%e& Pumps

simple& pump , sometimes referred to as a single pump, isa pump having a single liquid 0pump1 cylinder" duple& pump is the equivalent of two simple& pumpsplaced side by side on the same foundation"

The driving of the pistons of a duple& pump is arranged insuch a manner that when one piston is on its upstrokethe other piston is on its downstroke, and vice versa"

This arrangement doubles the capacity of theduple&pump

compared to a simple& pump of comparable design"


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$ing%e Acting and D"ub%e+Acting Pumps

single!acting pump is one that takes a suction, fillingthe pump cylinder on the stroke in only one direction ,called the suction stroke, and then forces the liquid outof the cylinder on the return stroke , called the dischargestroke"

double!acting pump is one that, as it fills one end ofthe liquid cylinder, is discharging liquid from the other

end of the cylinder"-n the return stroke, the end of the cylinder 8ustemptied is filled, and the end 8ust filled is emptied"


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P".er Pumps

Power pumps convert rotary motion to lowspeed reciprocating motion by reductiongearing, a crankshaft, connecting rods andcrossheads"Plungers or pistons are driven by the crossheaddrives"

Rod and piston construction, similar to duple&double!acting steam pumps, is used by the liquidends of the low pressure, higher capacity units"


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The higher pressure units are normally single!acting plungers, and usually employ three 0triple&1

plungers" Three or more plungers substantiallyreduce flow pulsations relative to simple& andeven duple& pumps"Power pumps typically have high efficiency and

are capable of developing very high pressures" They can be driven by either electric motors orturbines" They are relatively e&pensive pumpsand can rarely be 8ustified on the basis of

efficiency over centrifugal pumps"


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)crew Pump


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%ear pump


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Reciprocating pump


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&ial Flow Pump


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)ummary

*ses of pumps pplication on board ships

Types of pumpsommonly used types on board-perational principle of the common types

of pumps

marine pump

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