class 4 oral question and answers
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Home UserForums MMDOrals MMDObjective
REGISTERYOURSELFANDCOMEBACKFORMOREQUESTIONS
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Q3)IsthereanyregulationaboutaircompressorstimerequiredtofilltheAirBottles?
Ans)Twostartingcompressorsmustbefitted,ofsufficienttotalcapacitytomeettheenginerequirements.
EachcompressormustbeabletopressupAirreceiverfrom15barsto25barsin30minutes.
Twoairreceiversmusttobeprovided.
TotalairreceivercapacityistobesufficientforTwelve(12)startsofReversibleenginesandsix(6)startsfornonreversibleengines.
Q4)TYPESOFEVAPORATORSINREFRIGERATIONSYSTEM?
ANS)Inthelargerefrigerationandairconditioningplantstheevaporatorisusedforchillingthewater.Insuchcasesshellandtubetypeofheatexchangersareusedastheevaporators.Insuchplantstheevaporatorsorthechillersareclassifiedas:
1) Dryexpansiontypeofevaporators
2) Floodedtypeoftheevaporators
Incaseofthedryexpansiontypeofchillersorevaporatorstheexpansionvalvecontrolstheflowoftherefrigeranttotheevaporators.Theexpansionvalveallowstheflowoftherefrigerantdependingontherefrigerationload.Incaseoftheshellandtubetypeofevaporatorstherefrigerantflowsalongthetubeside,whilethesubstancetobechilled(usuallywater
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www.class4exam.comorbrine)flowslongtheshellside.Incaseofthefloodedtheevaporatorisfilledwiththerefrigerantandconstantleveloftherefrigerantismaintainedinsideit.Intheseevaporatorsorthechillerstherefrigerantisalongshellsidewhilethesubstancetobechilledorfreezerflowsalongthetubesideoftheheatexchanger.
Thoughthisclassificationisalsoapplicabletothedomesticrefrigeratorsandtheairconditioners,theevaporatorsusedinthesesystemsareclassifiedbasedontheirconstruction.Theevaporatorsareclassifiedbasedontheconstructionas:
1) Baretubeevaporators
2) Platesurfaceevaporators
3) Finnedevaporators
Thebaretubeevaporatorsarethesimplecoppercoilevaporatorsoverwhichthesubstancetobecooledflows.
Theplatesurfaceevaporatorsarecommonlyusedinthehouseholdrefrigerators.Theseevaporatorsarealsointheformofcoil,whichisattachedtotheplate.
Thefinnedevaporatorsarealsomadeofcoppercoilwithfinsontheexternalsurfaceaswellontheinternalsurface.
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www.class4exam.comFIN
Q5)WHATISERMATOJOINT?
ANS)Itisakindofcouplingtoabsorbvibration,fittedonpipeslikescavengedrainpipe,intankssteamheatingcoils.
Q6)EXPLAINPROPELLERSHAFTWITHDIAGRAM?
ANS)Thepropellershaftisboltedtothemainengineflywheel,passingthroughthethrustblockthenalongtheshafttunnel.Hereitissupportedbytheshaftbearingsbeforepassingthroughthesterntubetodrivetheship'spropeller.
Theshaftismanufacturedfromforgedsteel,completewithcouplingflanges.Itismachinedleavingalargerdiameteratthelocationoftheshaftbearings;thissectionhastohaveafinefinishtorunwithinthewhitemetalbearing.
www.class4exam.comTheshaftcouplingflangefacesareaccuratelymachinedandtheboltholesreamedtoaccept fittedbolts.Theyareboltedtogetherusinghightensionbolting,whichistightenedusinghydraulictensioninggear.
Thesupportingbearingsarecastintwohalvesandareusuallywhitemetallined.Thesehaveoilscrollscutintothemtodistributethesplashlubrication.Nowadaysballbearingshaftsupportsarebeingused,buttheyhavebeenreportedasbeingquitenoisywithatendencytorunhot.
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Atypicalpropshaftwhitemetalbearingwithsplashlubricationisshownhere.
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www.class4exam.comQ7)EXPLAINRUDDERCARRIERBEARINGWITHDIAGRAM?
ANS)Theruddercarrierbearingtakestheweightoftherudderonagreaselubricatedthrustface.Therudderstockislocatedbythejournal,alsogreaselubricated.Supportforthebearingisprovidedbyadoublersplateandsteelchock.Wedgetypesidechocks,weldedtothedeckstiffening,locatethebaseofthecarrierbearing.Thecarrierisofmeehanitewithagunmetalthrustringandbush.Carrierbearingcomponentsaresplitasnecessaryforremovalorreplacement.Screwdownlubricatorsisfitted,andthegreaseusedforlubricationisofawaterresistanttype(calciumsoapbasedwithgraphite).
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www.class4exam.comWeardown
Asmallallowanceismadeforweardown,whichmustbeperiodicallychecked.Thismaybemeasuredeitherbetweenpadsweldedontopoftherudderandontotherudderhorn,orbetweenthetopoftherudderstockandafixedmarkontheinnerstructureofthesteeringgearflat.Thelattergenerallyinvolvestheuseofa'Trammelgauge'whichtakestheformofa'L'shapedrodadetofitthenewconditionofthegear.Asweardownoccursitcaneasilybecheckedwiththisgauge.
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Therudderispreventedfromjumpingbyrudderstopsweldedontothesternframe.
Ruddermovementstops
Rudderstopsarearrangedasfollows;
Anglefrom Positionofstop Notecentreline
35 Ontelemotor Normallimitsystem
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37 Onsteeringgear Preventsrudderstrikingexternalstops
39 External,on Emergencystoptoprotectsternframe propeller
Theselimitsrefertoruddersoftraditionaldesignandaregovernedbyboththephysicallayoutoftherudderandactuatorbutalsoduetothestallanglesoftherudder.i.e.theangleatwhichlift(turningmoment)isreducedorlostwithincreasingangleofattack.TherearedesignsofruddersuchasBeckerflapwhichhaveincreasedstallanglesupto45
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Reasonsforcriticalcontouringofthrustface;
I.Forlubrication
ii. Conicalinordertopreventsideslipandcentralizerudder
iii. Projectedareagivesgreaterbearingareaallowingsmallerdiameterbearing
www.class4exam.comQ8)WHATARESTABILIZERS?WHATISITSPURPOSE?ONWHICHSHIPSTHEYAREREQUIREDMORE?
ANS)Shipstabilizersarefinsmountedbeneaththewaterlineandemerginglaterally.Incontemporaryvessels,theymaybegyroscopicallycontrolledactivefins,whichhavethecapacitytochangetheirangleofattacktocounteractrollcausedbywindorwavesactingontheship.
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Locationanddiagramofretractablefinstabilizersonaship.
PurposeThepurposeofcruiseshipstabilizersistoreducetherockingmotionoftheship.Theyhelpashipmovemore
www.class4exam.comsmoothly,whichcutsdownthechanceofseasicknessforpassengers.Whenthereisagreatdealofmovement,itcancauseadiscrepancybetweenwhatapersonseesandwhatherinnerearsenses.Thisiswhatcausesseasickness.Thesmoothertheride,thelesschanceforthistohappen.
FunctionCruiseshipstabilizersextendoutbelowthewaterlineontheportandstarboardsidesoftheship.Theypreventitfromrollingtotheleftandrightasitmovesthroughthewater.Theyactmuch,asdoairplanewingflaps,whichcanbeadjustedtoreduceturbulence.Althoughnostabilizerscanprevent100percentofacruiseship'smovement,theycansignificantlyreduceit.Thisisespeciallydesirableinroughconditionswhenthewavesarehighorthewindisstrong.
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www.class4exam.comHowCruiseShipStabilizersWorkfinstabilizer
Q9)EXPLAINFREEBOARD?
ANS)Thedistancefromthewaterlinetotheupperdecklevel,measuredatthelowestpointofsheerwherewatercanentertheboatorship.Incommercialvessels,thelattercriteriameasuredrelativetotheShip'sloadline,regardlessofdeckarrangementsisthemandatedandregulatedmeaning.
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Inyachts,alowfreeboardisoftenfoundonracingboats,forweightreductionandthereforeincreasedspeed.Ahigherfreeboardwillgivemoreroominthecabin,butwillincreaseweightandmaycompromisespeed.Ahigherfreeboardalsohelpsweatherwavesandreducesthelikelihoodofgreenseasontheweatherdeck.Alowfreeboardboatissusceptibletoswampinginroughseas.Freightershipsandwarshipsusehighfreeboarddesignstoincreaseinternalvolume,whichalsoallowsthemtosatisfyIMOdamagestabilityregulationsduetoincreasedreservedbuoyancy.
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Graphicalrepresentationofthedimensionsusedtodescribeaship.fisthefreeboard
Q10)WHATISSHEER?
ANS)Thesheerisameasureoflongitudinalmain
www.class4exam.comdeckcurvature,innavalarchitecture.Thepracticeofbuildingsheerintoashipdatesbacktotheeraofsmallsailingships.Thesevesselswerebuiltwiththedeckscurvingupwardsatthebowandsterninordertoincreasestabilitybypreventingtheshipfrompitchingupanddown.
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Dimensionsofahull
www.class4exam.comQ11)WHATISCAMBER?
ANS)Thecamberisameasureoflateralmaindeckcurvatureinnavalarchitecture.Thepracticeofaddingcambertoaship'sdeckoriginatedintheeraofsmallsailingships.Thesevesselswerebuiltwiththedeckscurvingdownwardsatthesidesinordertoallowwaterthatwashedontothedecktospilloff.
Q12)WHATISTUMBLEHOME?ANS)Inshipdesigning,thetumblehomeisthenarrowingofaship'shullwithgreaterdistanceabovethewaterline.Expressedmoretechnically,itispresentwhenthebeamattheuppermostdeckislessthanthemaximumbeamofthevessel.Asmallamountoftumblehomeisnormalinmanydesignsinordertoallowanysmallprojectionsatdeckleveltoclearwharves(structureontheshoreofaharborwhereshipsmaydocktoloadandunloadcargoorpassengers)
Lengthoverall(LOA)istheextremelengthfromoneendtotheother.
Lengthatthewaterline(LWL)isthelengthfromtheforwardmostpointofthewaterlinemeasuredinprofiletothesternmostpointofthewaterline.
LengthBetweenPerpendiculars(LBPorLPP)isthelengthofthesummerloadwaterlinefromthesternposttothepointwhereitcrossesthestem.
Beamorbreadth(B)isthewidthofthehull.(ex:BWListhemaximumbeamatthewaterline)
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www.class4exam.comDepthormouldeddepth(D)istheverticaldistance
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www.class4exam.comQ13)EXPLAINMOULDEDBREADTH,MOULDEDDEPTH,ANDDRAUGHT?
ANS)Breadth(extreme):
Theextremebreadth,recordedinmeterstotwodecimalplaces.Thisisthemaximumbreadthtotheoutsideoftheship'sstructure.
Breadth(moulded):
Themouldedbreath,recordedinmeterstotwodecimalplaces.Thisisthegreatestbreadthatamidshipsfromheelofframetoheelofframe.Thiswillonlybedisplayedwhenbreadthextremeisnotavailable.
www.class4exam.comMouldedDepth:
Themouldeddepth,recordedinmeterstotwodecimalplaces.Thisistheverticaldistanceatamidshipsfromthetopofthekeeltothetopoftheupperdeckbeamatside.
Draught:
Thedraft(ordraught)ofaship'shullistheverticaldistancebetweenthewaterlineandthebottomofthehull(keel),with
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thethicknessofthehullincluded;inthecaseofnotbeingincludedthedraftoutlinewouldbeobtained.Draftdeterminestheminimumdepthofwaterashiporboatcansafelynavigate.ThedraftcanalsobeusedtodeterminetheweightofthecargoonboardbycalculatingthetotaldisplacementofwaterandthenusingArchimedes'principle.Atablemadebytheshipyardshowsthewaterdisplacementforeachdraft.Thedensityofthewater(saltorfresh)andthecontentoftheship'sbunkershavetobetakenintoaccount.Thecloselyrelatedterm"trim"isdefinedasthedifferencebetweentheforwardandafterdrafts.
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www.class4exam.comDraftmarksonaship'sbow
Q14)WHATISRECENTAMENDMENTTOSOLASWITHRESPECTTOMSDS,LIFEBOAT&ETA?
ANS)MSDS:MATERIALSAFETYDATASHEET:DATEOFENTRYINFORCE:01JULY2009
AMENDMENTOFOCTOBER2007TOSOLAS:
www.class4exam.comAmendmenttoSOLASchapter6,toaddnewregulation51onmaterialsafetydatasheet(MSDS)torequireshipscarryingMARPOLAnnex1cargo(oil)&alsomarinefueloilstobeprovidedwithmaterialsafetydatasheetpriortoloadingsuchcargoes.TheregulationreferstotheRecommendationsformaterialsafetydatasheet(MSDS)forMARPOLAnnex1cargoes&marinefueloils,adoptedbytheorganizationthroughresolutionMSC150(77)
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Preventionofaccidentsinvolvinglifeboats:
AnamendmenttoSOLASregulationIIIconcernsprovisionsforthelaunchoffreefalllifeboatsduringabandonshipdrills.Theamendmentwillallow,duringtheabandonshipdrill,forthelifeboattoeitherbefreefalllaunchedwithonlytherequiredoperatingcrewonboard,orloweredintothewaterbymeansofthesecondarymeansoflaunchingwithouttheoperatingcrewonboard,andthenmaneuveredinthewaterbytheoperatingcrew.Theaimistopreventaccidentswithlifeboatsoccurringduringabandonshipdrills.Theamendmentisexpectedtoenterintoforceon1July2008.
Q15)WHATARETHESAFETYFEATURESINAIRCOMPRESSORS?
ANS)EveryAircompressoronashipisfittedwithseveralsafetyfeaturestoavoidabnormalanddangerousoperationalerrorsoftheequipment.Ifsafety,alarmsandtripsarenotpresentontheaircompressor,abnormaloperationmayleadtobreakdownofthecompressorandmayalsoinjureapersonworkingonoraroundit.
www.class4exam.com1.Reliefvalve:Fittedaftereverystagetoreleaseexcesspressuredevelopedinsideit.Thesettingoftheliftingpressureincreasesaftereveryascendingstage.
2.copperBurstingdisc:Aburstingdiscisacopperdiscprovidedattheairsideofthecompressor.Itisasafetydisc,whichburstswhenthepressureexceedsoverthepredeterminedvalue.
3.Fusibleplug:Generallylocatedonthedischargesideofthecompressor,itfusesiftheairtemperatureishigherthantheoperationaltemperature.Thefusibleplugismadeupofmaterial,whichmeltsathightemperature.
4.LubeOillowpressurealarmandtrip:Ifthelubeoilpressuregoeslowerthanthenormal,thealarmissoundedfollowedbyacutouttripsignaltoavoiddamagetobearingsandcrankshaft.
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5.Waterhightemperaturetrip:Iftheintercoolersarechokedortheflowofwaterisless,thentheaircompressorwillgetoverheated.Toavoidthissituationhighwatertemperaturetripisactivatedwhichcutoffsthecompressor.
6.Waternoflowtrip:Iftheattachedpumpisnotworkingortheflowofwaterinsidetheintercoolerisnotenoughtocoolthecompressorthenmovingpartinsidethecompressorwillgetseizedduetooverheating.Anoflowtripisprovidedwhichcontinuouslymonitortheflowofwaterandtripsthecompressorwhenthereisnone.
7.MotorOverloadtrip:Ifthecurrenttakenbymotorduring
www.class4exam.comrunningorstartingisveryhighthenthereisapossibilityofdamagetothemotor.Anoverloadtripisthusfittedtoavoidsuchsituation.
8.HighAirTemperatureTrip
Q16)PROCEDUREFOROVERHAULOFA/E?
ANS)D'carbofauxiliaryengine isnothingbutthecarryingoutofcertainroutinesatintervalsprescribedbythemanufacturerorexperience.Normallythefollowingshouldbedoneduringamarinedecarbtofreetheenginefromanomalies
Every3000hrs
1.takeoutcylinderhead,takethewornoutmountingsand/oroverhaulthemountings
2.Allunitscylinderhead,piston,connectingrod,and3.turbochargertobeoverhauled
4.Cleansumptankandfillwithfreshlubeoil
5.Takecrankshaftdeflectionbeforeandafterremovalofbearings
6.Whateveractionstakenshouldberecordedinthemaintenancerecordbook
D'carbpreparation:
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1.Makesuretheallstandbyauxiliaryenginesareready2.Keepallthespecialtoolsandothertoolsready
3.Gothroughthepreviousrecords/manualforclearance
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4.Putthedisplaycard"MENATWORK","DON'TSTART"
5.Closeairbottlevalvetoauxiliaryengineandenginestartandstopvalve
6.Seethattheturningbarisnotintheflywheelandshouldbeinplace
7.Opentheindicatorcocks
8.Ifthemainbearingistoberemoved,checkcrankshaftdeflections
9.Closelubeoil,fueloil,freshwaterinlet/outletvalve,drainthecoolingwaterlineandremoveconnections
A)Removalofcylinderhead:
Scavenge manifold, exhaust manifold , rocker arm, lube oildrain connection from rocker arm, rocker arm tank andcoverconnectiontoberemoved
Fueloilhighpressureconnectionfromfuelpumptotheinjector,fuelvalvecoolingconnectionsinandout(eitherdieselorwater)toberemoved
Removetherockerarmassemblyandthepushrod.Removeallthemountingssuchasstartingvalve,indicatorcock,reliefvalveandexhaustvalveassembly
Removetherockercoverandcheckanymarkingoncylinderheadnutsandstuds.Ifnotorquespannerisavailable,notedownthemarkings.
Openthecylinderheadnutwithboxspannerandextensionrod.Neverusethetorquespanner.Withboxspanneravailablenotedownthemarking.
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www.class4exam.comPutthecylinderheadliftingtoolandbeforeliftingmake
surealltheconnectionsareremoved.Alsoensurethatthelinerisnotremovedalongwiththecylinderhead
Takeoutthecopperjointbetweentheheadandtheliner
CYLINDERHEADBEFORECLEANING
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EXHAUSTV/VBEFORECLEANING
Removalofpistonandconnectingrod:
Afterliftingthehead,checkthelinersurfaceforscoremarks,blowpastetc.Crackremovetheridgesordepositsifanyonthetopsurfacetoavoidtheliftingof
www.class4exam.comlineralongwiththepistonandbreakageofpistonringswhileliftingpiston
Openthecrankcasedoorandremovethebottomendbearingboltsafterremovingthelockarrangementandtheremovethebolts
Removethebottomhalfofthebottomendbearing
BringthepistontoTDC.Makesuretheboltholesonthe
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pistontop;liftingtoolholesmustbeclearedfromcarbondeposits.Threadsshouldalsobecheckedandcleared
Putthepistonliftingtoolsandtightenthebolts
Liftthepistonandremovetopshellofbottomendbearing
Placethepistononthepistonstandandcoverthecrankcasepintoavoidtheforeignmaterialdamagingthecrankpin.
PISTONWITHRINGSB4CLEANINGPISTONWITHOUTRINGB4CLEANING
www.class4exam.comPISTONAFTERCLEANING CONNECTINGRODREMOVAL
Cleaningthecarboncontentonallthepartsofengine:
Cleanthepistonrings,measuredimensionsandkeeptheminorder
Cleanthepistonringgroovesthoroughlyandmeasurethe
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groovethicknessat3differentpoints
Checkforthedepositsonpistoncrown(Sulphur,carbonorthickvanadiumdeposits)andmeasurethedimensions
Removethegudgeonpinandcleanthegudgeonlubeoilholesaswellasthebushorsmallendbearing
Checktheboltsofconnectingrodforanycracks
Every20,000hrsengineconnectingrodboltmustbereplaced
Ifnewpistonringsaregoingtobereplaced,thenthereisnoneedformeasurement
Calibratethelinerthicknessbyusingtemplate
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www.class4exam.comLINERB4CLEANINGCOOLINGWATERSIDEOFLINER(EXTERNALVIEW)
COOLINGWATERSPACEINSIDEENGINELINERAFTERHONINGPROCESSPISTONPINREMOVALCONNECTINGRODCLEANING
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www.class4exam.comBOTTOMENDBEARINGBEFORECLEANINGBOTTOMENDBEARINGAFTERCLEANING
Assemblyoftheengineparts:
Firstputthepistonringsonebyoneandmeasurethebuttclearanceforalltherings
Thenmeasuretheaxialclearancebetweenpistonrings&grooves
PlacethepistonguideontopofthelinerandbringtheparticularcrankshafttoTDC.Applysufficientlubeoilandstartloweringthepiston.Makesurethatbuttgapshouldnotbeinlineitmaycauseblowpast
Beforeengagingcheckthecrankpinforanycracksorscratch
Checkthebottomendbearingclearanceandifneededmeasurethemainbearingclearanceaswell
Taperclearanceischecked
Checkforanycracksinthewaterjacketandinthecylinderhead
www.class4exam.comReplaceallrubberjointsandcoppergaskettobeputonthe
cylindercover
Putthecylinderheadgasketinthetopofthecylinder
Antiseizurecoatingorpowderlikemolycote,copperslipshouldbeused.Itisappliedtoavoidanyseizuremainlyonthethreadsorjointsanditwillbeeasierwhileremoval
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Tightenthecylindermountingaccordingtotorquespecifiedasinmanualandmakeallconnectionlikelubeoil,fuel,jacketcoolingwaterconnectionsetc
Fittherockerarmback
DECARBISDONETOINCREASETHEEFFICIENCYOFENGINE.
Q17)HOWWILLYOUDECIDETOCHANGETHEPISTONRING?
ANS)
1. BYCHECKINGTHEBUTTCLEARANCE.IFITSVALUEHASBEENINCREASEDTHANTHENORMALRANGE.
2. IFITSAXIALCLEARANCEHASBEENINCREASEDTHANTHENORMALRANGE.
3. BYCHECKINGTHEVISUALCONDITIONOFPISTONRING.
www.class4exam.comQ18)WHATALLCHECKSTOBEDONEINLIFTINGGEAR?(E/RLIFTINGCRANE)
ANS)
1. CHECKTHECONDITIONOFWIREROPE&GREASEIT.2. CHECKTHEVISUALCONDITIONOFCHAIN.3. CHECKTHELIMITSWITCHESINFORWARD,AFT,PORT&
STBDDIRECTIONAREWORKING.4. CHECKTHEPROPERWORKINGOFEMERGENCY
BUTTON.5. CHECKTHEVISUALCONDITIONOFINSULATEDCOVER.6. CHECKOVERLOADTRIPWORKINGSATISFACTORY.7. CHECKVISUALCONDITIONOFCHAINBLOCK,NO
CRACKSSHOULDBETHERE.8. CHECKTHATSAFETYLATCHISTHEREONCHAIN
BLOCK.
Wirerope,limitswitches,chain,chainblock,overloadtrip,emergencybutton,safetylatch
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Q19)WHATALLCHECKSTOBEDONEONPISTON?
ANS)Pistoninspectiononshipsispartoftheengineplannedmaintenanceschedule(PMS)carriedouttoensurethecomponentsiswithintheallowedtolerances.Therearetwomethodsofinspection:whenthepistonhasbeenremovedfromthelinerorinspectionthroughthelinerscavengesports.
a)PistonRemovedforInspection:
Thisexaminationwillbeundertakeninamodularformat,
www.class4exam.comsincethepistoncanbedividedintovariouscomponents.
PistonCrown
Checkforanyburningattoppartofthepiston.
Checkanywearatthesidewallsofthecrownandonringgrooves.
Checkforanycracksattopduetothethermalandmechanicalstress,checkalsoforhightemperaturecorrosion.
Checkanysignsofhotcorrosionatthetopsurfaceandacidiccorrosionatthelowerpart.
PistonRingsandGrooves
Checkforthefreemovementofthepistonrings.
Checktheringclearance/grooveclearance.
Inspectforanywear,steppingandforscuffing.
PistonSkirtandSidewall
Checkforanyrubbingmarks.
Inspectforanyweardownofwearrings.
CoolingWaterPassage
Checkforanyscaleduetopoorwatertreatment.Chokingduetohightemperature.
Finallyinspectthelockingbolts;wires,studsandOringcondition
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www.class4exam.comb)MaintenanceSchedule:
Periodicinspectionhastobedonewhentheengineisnotrunning.Itcanbecarriedoutasaboveorbyenteringthescavengespaceandinspectingthepistonandpistonringsthroughthescavengeports,withthepistonbroughtinlinebyrotatingtheengineviaaturninggear.
OverhaulingthepistonasperPlannedMaintenanceSchedule(PMS).
Monitoringoftheconditionofthepistonandthepistonringsbythecompressioncurveoftheindicatordiagramthroughprocessanalysis.
Theimagesshownbelowshowexamplesoftwomeansofinspection.Inspectionofpistonandringsthroughthescavengeport
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www.class4exam.comPistonremovedforcloserinspection
EmergencyRepairofPistonCrown:
Oncetheabovecheckshavebeencarriedout,whatactionscanbetakenifsomevaluesorobservationsareoutwiththespecifications?Givenbelowisalistofcommonfaultsthatmightbefoundduringinspectionandmeanstomaketemporaryemergencyrepairs.
Gaugepistoncrownandascertainshapeandweardown.If
www.class4exam.comitisbeyondrecommendedlimits,replacethepistonifthereisaspareavailable.Ifnot,rebuildtheengineandproceedtothenearestportatreducedrevolutionsandarrangereplacement.Thecrownheadshouldnotbeweldedexceptinadireemergencyandeventhenonlybyanexperiencedwelder.Rememberthatmoderndieselenginepistonshaveaspecialliningofhightemperaturealloyonthetopofthecrown.Thismeasureimprovesresistancetocorrosionaswellastohighcombustiontemperaturesthatthepistontopisexposedto
Examinethecrownforfracturesorcracks,andiffoundthepistonshould
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bechanged.Ifnospareisavailablethesecanbeweldedtomanufacturersspecifications;usingthecorrectalloyweldingrods,againasameanstoproceedtothenearestportatreducedrevolutionsforareplacement.
Dismantledpistonringsshouldbekept insequentialordersoasnot tointerchangetheringswhenrefittingtothepiston.
Oncerepairsarecomplete,replacethepistonringsandcheckfornormalbuttclearance.
Ifthebuttclearanceismoreorlessthanthenormalrange,thenreplacethepistonringswithnewsetofpistonrings.
Note:ItwouldbeanextraordinarypredicamenttobeinwhereasaChiefEngineeryousailedwithoutmainenginepistonspares.However,strangethingshappenatsea,maybethespareshavebeenalreadyused,andyou'reawaitingdeliveryofreplacements.
www.class4exam.comIfanyoftheaboverepairsarecarriedout,itisimperativethataclosewatchiscarriedoutontheappropriatecylinderwiththeexhausttemperaturescloselymonitoredaswellasthepistoncoolingmediumtemperatures.
Q23)WHATISPURPOSEOFTAPPETCLEARANCE&HOWITISDONE?
ANS)Tappetclearanceisaspacebetweenthetopofthevalvestemandtherockerarm.Itspurposeistoallowforsomemechanicalexpansionandlengtheningofthevalvestemandpushrodsastheenginewarmsup.Thisclearanceisalsocalledvalvelash.
Ifinsufficient(lowerclearance)valvelashissetwhentheengineiscoldthevalveswillnotproperlyclosewhentheenginewarmsuporearlyopeningofthevalve..Iftoomuchlashisprovided(additionalclearance)thenevenaftertheenginewarmsuptherewillbesomeclearance,whichwillresultinlostmotion.Lostmotionmeanthatasthecamtriestoopenthevalvethepushrodandrockerarmmovestofirsttakeuptheclearancebeforetouchingthevalvetoopenthevalve.Theresultislateopeningofthevalve.
Whencheckingtappetclearanceonmarineengines,wehaveto
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ascertainthatthepistonisatTDC.Thoughmarkingsareprovidedontheflywheel,themarineengineermustknowtheothermethodsforthislikeinspectionofthecamshaftandthefuelpumpwindow.
Duringthemaintenanceofafourstrokemarinedieselengine
www.class4exam.comtherearetimeswhenwemustknowwhethertheparticularunitspistonisatthetopdeadcenterornot.ForexamplewhencheckingthetappetclearancesoftheengineitisimportanttoknowwhichunitisatTDC.
Referringtotheflywheelwouldindicatetwounits,butonlyonecanbeatinjectionTDC.Sowhichoneisit?
FlywheelMethod:
TheflywheelisthesimplestmethodtoknowwhichunitisatTDC.Iftheflywheelshowstwounits,simplyopenthebonnetcoversandchecksvisually.TheunitatTDCwillhaveboththeinletandtheexhaustvalveclosedandhencerelaxedsprings;theotherunitwouldhaveboththearmsoftherockerarmatdifferentlevels.InadditionthepushrodsoftheunitatTDCwouldbelooseandcanbeturnedbyhandbecauseofthereleaseoftheclearances.Thereisawordofcautionhowever:thismethodisonlyusefulinaworkinggenerator,whichyouhavejuststoppedtocheckthetappetclearances.Incaseyouhaveremovedtherockerarmsforanyreasonthespringheightandthepushrodfreenesscheckwouldleadyounowhereandmisguideyou.
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www.class4exam.comDialGaugeMethod:
Inthismethodthefuelinjectoristakenoutandfromtheopeningadialgaugeisputinside.Thentheturninggearisengagedandtheengineturnedover.Thepointerofthedialgaugewillmoveinonedirectionandthenstopandstartinoppositedirection.ThemomentthepointerofthedialgaugestopsandchangesitsdirectionofmovementistheTDCoftheunit.Thismethodisnotnormallyusedindaytodaypractice,butmaybeusedinthecalibrationoftheflywheelifitisnotcalibrated,oraftersomerepairs
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www.class4exam.comCamshaftMethod:
Thecamshaftwindowoftheenginecanbeopenedupandthecamshaftinspected.Thecamoftheenginehasabasecircle,andaccelerationanddwellperiods.Iftherollerofthefollowerisatthebasecircle,thentheparticularvalveisclosedbyspringaction.Whenboththeexhaustvalveandtheinletvalvefollowerareonthebasecircle,thentheunitisalsoatTDC.ItmustberememberedthatasafourstrokeenginehastworotationsofthecrankshaftthereisoneinjectionTDCwheretheinjectionandthecombustiontakeplace.ThesecondtimethepistonisatTDCiswhentheexhaustingofthefluegasestakesplace.ItisveryimportanttoidentifythecombustionTDC,astappetshavetobeadjustedatthatpoint.
www.class4exam.comCamProfile
CrankcaseMethod:
Inthismethodthecrankcasedoorsareopenedupandthepistonisvisuallycheckedwhetherisgoingupordown.Thisisthesurestmethod,butabitcumbersome.Itshouldbeusedwhenyouhaveastrongdoubtabouttheothermethods.
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ValveSpringMethod:
Thisisnotanindependentmethodbutisusedinconjunctionwiththeflywheelmethod.Inthismethodiftheflywheelisindicatingtwounits,youcancheckthespringsofboththeunits.TheunitinwhichthespringsarelooseistheoneatTDC.Thecautionisthatthismethodisusefulforanengineinuse.Ifyouhaveremovedtherockerarmsduringtheoverhaulandthereafteryouwanttousethismethodthenitcancause
www.class4exam.comerrors.
PushRodMethod:
Thismethodislikethespringmethodandyoucheckthatthepushrodsarefreetoturn.TheunitatTDCwillhaveloosesprings.Thecarethatmustbetakenisthatitshouldbeusedalongwiththeflywheelmethodandshouldbeusedinaworkingengine.Byaworkingengine,Imeantheenginethatwasrunningandhasbeenstoppedfortappetsadjustment.
Loosenthelocknutoftherockerarm.
TAPPETADJUSTMENT:Nowadjustthetappetclearancebetweentherockerarm&valvestembytighteningorloosingthenutbelowthelocknut.
Iftappetclearanceisless:I.Valvewillopenearly&closelateii. Airinducedthroughinletvalvemayleakout.Solessairforcombustion.iii. Powerwillbereduced.iv. Fuelconsumptionwillincrease,enginemaybecomeunbalanced,exhausttemp.willbeveryhigh.v. Inworstcondition,valvemayremainopen,resulting in lossofcompressionpressure,burningofexhaustvalve,T/Cfoulingwillincrease.Iftappetclearanceismore:
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www.class4exam.comI.Valvewillopenlate&closeearly.ii. LesserheatenergytoT/C,soreductioninscavengeair&hencepower.iii. Noproperremovalofgases.iv. Hammeringofvalvestemmaycausedamagetovalvestem.
Q24)whattocheckifEngineisnotstartingonairandfuel?
ANS)EnginenotstartingonAir:* Lowairbottlepressureorairlinevalvemaybeshut.* Airbottleisolatingvalveorautomaticvalveordistributornotfunctioning.* Controlairvalvesfaultyorlesscontrolairpressure.* Startairautomaticvalvejammed.* Turninggearengaged.* Reversinghasnottakenplacecompletely.* Controlvalveforfuelorstartisnotinitsendposition.* Burstingdiaphragmonstartairlinedamaged.* Fuelleveronmaneuveringstandnotonremotemode.* Auxiliaryblowernotrunningornotonautomode.* Emergencystophasactivated.* Interlockisoperated.*Cylinderairstartvalvedefectiveorsticky.*Pistonnotinfiringmode.
Enginenotstartingonfuel:*Lessfuelinservicetank.* Fuelfilterischocked.* Fuelsupplypumpsnotdeliveringrequiredpressure.Orfuelpumptripped.
www.class4exam.com* Fuellevelonlocalmaneuveringstand,isnotonremotestand.* Fuelrackstuck.* Fuelpumpmalfunctioning,jammedplunger.* Injectornozzleneedlestickingorholesblocked.* Compressionpressureistoolowduetobrokenpistonringorexhaustvalvenotclosingproperly.* Fuelpumpreliefvalveleaking.* Startairpressureinsufficienttoturntheenginefastenough.
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Q25)WHATTOCHECKIFENGINEISNOTCOMINGONLOAD?
ANS)*CHECKVOLTAGEOFBUSBAR&INCOMINGGENERATOR,BOTHSHOULDBESAME.
* CHECKFREQUENCYOFBUSBAR&INCOMINGGENERATOR,BOTHSHOULDBESAME.
* POWERFACTORISOK.
* SYNCHRONISINGPROCEDURESHOULDBECORRECT.
* ALWAYSBEFOREPARALLELINGINCOMINGGENERATORSPARAMETERSHOULDBEINOPERATIONALRANGE.
Q26)WHYINUMSCLASSSHIPSTHEGENERATORENGINEISSTARTEDAUTOMATICALLYWITHOUTOPENINGINDICATORCOCKGIVINGATRIALSTART?
ANS)INENGINEROOMS,WHICHHAVEWATERMISTFIREFIGHTINGSYSTEMINSTALLED,THISPROCEDURE ISNOTFOLLOWEDBECAUSEWHENTHEENGINEISGIVENA
www.class4exam.comMANUALKICKWITHOPENINDICATORCOCKS,SMALLAMOUNTOFSMOKECOMESOUTOFTHEHEADSWHICHCANLEADTOFALSEFIREALARM,RESULTINGINRELEASEOFWATERMISTINTHESPECIFIEDAREA.
Q27)WHATALLTRIPS&ALARMSAREPRESENTINAUXILIARYENGINES?
ANS)Thevarioustripsandalarmsarementionedasfollows
Alternatorbearinglowoillevelalarm&trip
Alternatorbearinghightemperaturelubeoilalarm&tripLowsumpoillevelalarmandtrip
LubelowoilpressurealarmandtripReversecurrenttrip
OverspeedtripOverloadtrip
Highandlowfrequencytrip
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Jacketcoolingwaterlowpressurealarm
Q28)WHATALLPRECAUTIONSSHOULDBETAKENTOSTARTAUXILIARYENGINEAFTEROVERHAUL?
ANS)
* Turnenginethroughflywheelforcheckinganyrestrictions.*Watertightnesstobechecked.* Airtoberemovedfromjacketwateroutletline.* Priminglubeoilpumptorunbeforestartingtheengine.* Checkthelubeoillevel.
www.class4exam.com* Checktheflowoflubeoil.* Blowthroughtheenginebeforestarting.
Q29)HOWTOCHANGEPURIFIERINTOCLARIFIER?ANS)MainDifferences:
Themaindifferencebetweenaclarifierandapurifieristhepresenceofadamringinthelatter.Inapurifier,theinterfaceorthelineofseparationbetweentheoilandwateriscreatedusingadamring.Thepositionofthedamringplaysanimportantroleinthegenerationofinterfaceandthusintheclarifyingprocess.Forexample,ifthediameterofdamringislarge,theinterfacemovesouttowardstheperipheryandasaresultsomeoilisdischargedwithwaterfromthewateroutlet.Also,ifthediameterissmall,theinterfaceformedwillbemoreinwardsandwaterwillbedischargedwiththeoilfromtheoiloutlet.
Thediameterofholesinthedamringsalsoplaysanimportantroleinthecreationofinterfaceandpurificationprocess.Ifthediameteroftheholesismore,theinterfaceisformedtowardstheperipheryandoilglobulesarefoundwithwaterandsludge.Ifthediameterislesstheoilwaterinterfacemovesinwardsandwaterisreleasedwiththecleanoildischarged.
However,clarifiersdonothaveadamringbuthaveasealingringwhichsealsthewateroutlet.Thispreventstheimpuritiesandwatertoremaininsidethebowlunlessopeningthecleansingbowldischargesthemautomaticallyormanually.Also,theconicaldiscsinaclarifierusuallydonthavefeed
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holesinthembutiftheydo,thenadiscwithoutanyholesis
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www.class4exam.comPurifiersandClarifiersdifferonlyinthatclarifiersarenotsetuptoremovewater.Theirdesignaresimilartothepointthatmostpurifiersfoundonboardcanbeconvertedtouseasaclarifierwithsimplealterationofthegravitydisc
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Q30)HOWTOSELECTDAMNRINGFORPURIFIER?
ANS)Fromthemonogramprovidedwithmanual,whichisdrawnwithrespecttoviscosityofoil&whichsizedamnringtobeused.
Ifmonogramnotthere,then
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www.class4exam.comThegraphshownaboveisonetypicalofonefoundinapurifierinstructionbookforselectingappropriategravitydiscsize.Shownonthediagramisanexampleofanoilofsg0.93at0'C.Thesgat15'Cforusewiththisgraphisfoundbyprojectingalongahorizontallineto15'C.Thisstepwouldbeomittedifthesgat15'Cwerealreadyknown.Alineisthendrawnparalleltothepredrawnslopinglines.WherethedrawnslopinglinecutstheappropriateoilsupplytemperatureisothermalthenThisbecomestheselectionpointforthedisc.Thisisfoundsimplybyascertainingwhichsizebandthepointliesin.
Q31)WHATTOCHECKIFPURIFIERISOVERFLOWING?ANS)* Sizeofgravitydisc.* Highthroughput.* Temperatureoftheoil.* Operatingwaterlevelintank.
* Sealingwaterisnotpresentinpurifier.
* Bowlisnotclosedproperly.
* Sealringisdamaged.
* Bymistakeifbowlopeningwaterisfeeded.
* Increasingthespecificgravityoftheoilwilltendtopushtheinterfaceoutletandcauseoverflowfromtheheavyphaseoutletuntiltheequilibriumisrestored.Q32)HowtostopAuxEngineifnotstoppingbystophandle?ANS)
www.class4exam.coma. Pullthefuelracktozeroposition.b. Operateanytrip.
Q33)WHATAREALLTRIPS&ALARMSAREPRESENTINPURIFIER?
ANS)Typicalalarmsandshutdowns:
Thefollowinggivesagenerallistofalarmsonlysomeof
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whichmaybefitted.
o BackPressureshutdownthismeasuresthedischargeoilpressureandalarmsandinitiatesashutdownwhenbelowasetvalue
o Heavyphaseoverflow.Oilhasamuchhigherviscositythanwater.Theheavyphaseoutletisledtoasmallcatchmenttankcontainafloat.Theoutletfromthetankisrestrictedinsuchawaythatwaterflowsfreelybutoiltendstobackup.Thisinitiatesanalarmandshutdown
o Bowlnotopenthismaybedoneinseveralways,typicallybyaleverswitchoperatedbythedischargedsludgehittingastrikerplate.Theothermethodisbymeasuringthemotorcurrent,whenthebowlopensthebowlspeedisdraggeddownduetofrictioneffectsofthedischargingsludgeandwater.Themotorcurrentrisesuntilfullspeedisreestablished.Thisisdetectedbyacurrentsensingrelay
oWaterinoilThisfoundonmoderndesignswhichhaveadetectionprobemountedintheoildischarge
oHightemperaturealarmandshutdown
www.class4exam.como Low control/sealwater pressure.Where control
waterissuppliedviaafixedsmallheadertanksafloatswitchmaybefitted.
Q34)HOWTOCHARGETHEGASINREFRIGERATIONSYSTEM?ANS)*Closethereceiveroutletvalveandcollectthegasinthereceiver.*Onceallgasiscollectedinreceiverthenshutthecompressorsuctionvalve.
Checktheliquidlevel,ifitisbelowL/3,Chargingisreqd.Checktheweightoftherefrigerantbottle&keepitupright.Connectthecharginglinetotheconnectingpointandkeepitloose.Openthebottlevalveslightlyandpurgethelineintothecollectingcylinderandthentightentheconnection.Openthechargingvalveandfullyopenthebottlevalve.Checktheliquidlevelinthesightglassandmakesurenoairbubblepresentinthesystem.
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Closethechargingvalveandthebottlevalve.Openthereceiveroutletvalve&startthecompressor.Carryoutleakdetectiontest.Checkthesuctionpressure&dischargepressure.
Q35)WHATISPROPERTYOFIDEALREFRIGERANT?ANS)RequiredPropertiesofIdealRefrigerant:1) Therefrigerantshouldhavelowboilingpointandlowfreezingpoint.2) Itmusthavelowspecificheatandhighlatentheat.Becausehighspecificheatdecreasestherefrigeratingeffectperkgofrefrigerantandhighlatentheatatlowtemperatureincreasestherefrigeratingeffectperkgofrefrigerant.
www.class4exam.com3) Thepressuresrequiredtobemaintainedintheevaporatorandcondensershouldbelowenoughtoreducethematerialcostandmustbepositivetoavoidleakageofairintothesystem.4) Itmusthavehighcriticalpressureandtemperaturetoavoidlargepowerrequirements.5) Itshouldhavelowspecificvolumetoreducethesizeofthecompressor.6) Itmusthavehighthermalconductivitytoreducetheareaofheattransferinevaporatorandcondenser.7) Itshouldbenonflammable,nonexplosive,nontoxicandnoncorrosive.8) Itshouldnothaveanybadeffectsonthestoredmaterialorfood,whenanyleakdevelopsinthesystem.9) Itmusthavehighmiscibilitywithlubricatingoilanditshouldnothavereactingproperlywithlubricatingoilinthetemperaturerangeofthesystem.10) ItshouldgivehighCOPintheworkingtemperaturerange.Thisisnecessarytoreducetherunningcostofthesystem.11) Itmustbereadilyavailableanditmustbecheapalso.
ImportantRefrigerants:Propertiesat150C(1) Ammonia(NH3)(R717)Latentheat=1312.75kJ/KgSpecificvolume=0.509m3/kg
(2) DichloroDifluoromethane(Freon12)(R12)[CCl2F2]Latentheat=162kJ/KgSpecificvolume=0.093m3/kg
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(3) DifluoromonochloromethaneorFreon22(R22)[CHClF2]
www.class4exam.comLatentheat=131kJ/KgSpecificVolume=0.15m3/kg.
Q36)EXPLAINTHEPROPERTYOFLUBRICANTUSEDINREFRIGERATIONSYSTEM?
ANS)Forsatisfactoryperformance,allrefrigerationlubricantsmineraloilorsyntheticmustbecompatiblewiththerefrigerantinthesystemandhavethefollowingrequirements:
1. Goodmiscibilityandsolubilitytoassistingoodoilreturntothecompressor,whereitbelongs.
2. Chemicalstabilitytoresistchemicalreactionwiththerefrigerantorothermaterialspresentinthesystem.
3. Thermalstabilitytoeliminateexcessdepositsatcompressorhotspots.
4. Lowwaxcontenttopreventseparationofflocculentwaxfromtheoilmixtureatthelowtemperaturepointsinthesystem.
5. Lowpourpointtopreventseparatedlubricantfromcongealingandrestrictingflow.
6. Properviscosity,evenwhendilutedwithrefrigerant,toensurehighfilmstrengthatelevatedoperatingtemperaturesandstillprovidegoodfluidityundercoldestoperatingconditions.8.Nocontaminationtopreventscarringofbearingsurfaces,pluggingoflinesoroilportsandgeneraldeterioration.
www.class4exam.comSomemajorcompressormanufacturerspreferalkylbenzenerefrigerationoilforsomeapplicationswithHCFCrefrigerantblendssuchasR22,R123andR401A.However,alkylbenzenerefrigerationoilwiththeproperviscosity
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canbeusedwithmostCFCandHCFCrefrigerantsaswellashydrocarbonsandammoniainmostrefrigerationandairconditioningapplications.
The benefits of highquality alkyl benzene lubricants are highmiscibility,low foaming, excellent thermal stability, very low flock points and goodcompatibility:
1. Highmiscibility:Miscibilityistheabilityoftherefrigerantandlubricanttostaytogetherasonehomogeneoussolution.AlkylbenzenehasexcellentmiscibilitywithCFCandHCFCrefrigerants,resultingintheoilandrefrigerantremainingasonemixtureatawiderangeoftemperaturesandpressures.
2. Lowfoaming:Thelowfoamingqualityofalkylbenzenereducescarryoveratcompressorstartupandsubsequentoillossfromthecrankcase.
3. Excellentthermalstability:AlkylbenzenecanenhancethelifeofrefrigerationsystemsbyprovidingbetterthermalstabilityinthepresenceofCFCandHCFCrefrigerants.Itresistschangeunderhightemperatures,reducingproblemswithsludge,acidsandcopperplating.
4. Verylowflockpoints:Theflockpointisthehighesttemperatureatwhichwaxlikematerialsprecipitatefromtheoilintherefrigerationsystem.Becausealkylbenzeneisasyntheticlubricant,itcontainslittleornoparaffinorwax,whichcanpluguppartsofasystem.Thiscanbeverydesirableinlowtemperatureapplications.
www.class4exam.com5.Goodcompatibility:Alkylbenzenecanbeblendedwithmineraloilofthesameviscosity.Itwillnotaffectmotorinsulationandiscompatiblewithmostelastomersandadditivesoftenusedtoimprovelubricity.
Preventingcontaminationproblemsisextremelycriticalintherefiningandhandlingofallrefrigerationoils.Greatcaremustbeusedtoassurethatrefrigerationoilisfreeofmoistureandothercontaminants.Servicetechniciansmustensurethatoilremainscleananddry.
Q37)EXPLAINTHEPROCEDUREOFCHARGINGTHEOILINTOREFRIGERATIONPLANT?
ANS)Mostlyshipshavehandp/pprovidedwhichdevelopmorepressurethantheinsidepressure
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www.class4exam.comQ38)WHATDOWECHECKIFTEMPERATUREOFANYONEROOMISNOTCOMINGDOWN?
ANS)1.IFROOMDOORISNOTCLOSEDPROPERLY.
2. PARTICULARROOMSINSULATIONISBAD.
3. PARTICULARROOMSFANISNOTRUNNING.
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4. EVAPORATOROFTHATROOMISFROSTED.
5. EXPANSIONVALVEFORTHATROOMISBLOCKED.
6. SOLENOIDISNOTWORKINGFORTHATROOM.
Q39)WHATALLTHINGSTOBECHECKIFALLROOMSTEMPERATUREISNOTCOMINGDOWN?
ANS)1.COMPRESSORISNOTRUNNINGWELL.
2. PRESENCEOFMOISTUREINSYSTEM&DRIERISNOTWORKINGPROPERLYDUETOTHISEXPANSIONVALVEOFALLROOMSAREGETTINGBLOCKED.
3. LESSREFRIGERANTINSYSTEM.
Q40)WHATTODOIFDOMESTICREFRIGERATIONPLANTISSHORTCYCLING?
ANS)REASONS:
* L.PCutoutisdefective.* L.PCutoutsettingnotcorrect,toolowdifficultforCutIn.* Lessergasflow* Lessgasinsystem.* DrierChoked.* ExpansionvalvefilterchokedorExpansionvalve
www.class4exam.comMalfunction.* EvaporatorChoked.* Compressorvalvesleaking.
Actions:a. CheckL.P.cutoutsetting,cutoutpressureOK.b. Checkflowofgasbyseeingsightglass,whichshouldshowfullflowofrefrigerant.c. Ifnofullfloweitherlessgasordrierchocked,changethedrier.d. Checklevelinreceiver,iflow,thenchargesgas.e. Expansionvalvefilterchoked,thencleanit.f. ExpansionvalvemalfunctioningChangeit.g. EvaporatorchokedBlowthruevaporatorwithnitrogen.
Q41)HOWWILLYOUOVERHAULACENTRIFUGALPUMP?
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ANS)Centrifugalpumpshavebeenusedinindustryforahundredandfiftyyearsormore.Theyareusedtoconverttheenergyfromthepumpdrivertokineticandpotentialenergyintothefluid,viatheimpeller.Theyareusedaboardshipstocirculateseawaterandfreshwatercoolingforthemainengine.
Aship'sengineroomcontainsseveraldifferenttypesofpumpsincludingcentrifugalpumps.
RemovalofPumpforInspectionandMaintenance:
1Isolatepumpelectricalcircuitbreakeronmainswitchboardandattachawarningnotice.(DoNotOperateMenatWork).
2. Switchoffandlockpumpsupplyatitslocalsupplypanel.Attachawarningnoticetopumplocalsupplypanel.
3. Closesuctionanddischargevalves,chainandlockhandwheels.
www.class4exam.com4. Openpumpsuctionanddischargepipedrainvalvestobilgeandwhenwaterceasestoflow;crackopenthepipes/pumpflangejointscarefullytoensurethatpumphasdrainedoffandissafeforopening.
5. Fixashackletoliftingpadeyeabovepumpandhangchainblock;ensuringSWLofblock,slingsandshacklesaresatisfactory.
6. Useacenterpunchtomatch/markcouplingandcasing,thenremovethecouplingbolts.
7. Disconnect,fixi/dtagandremovemotorsupplycables;tapingoverbareendswithinsulatingtape.
8. Connectshackleandslingtomotoreyeboltandliftmotorclearofpumpusingoverheadchainblock.Laymotoronitssideoutofharmsway,protectingmachinedsurfacesonbothpumpandmotorcouplinghalvesagainstdamage.(Cardboardandmaskingtapeisquickandefficientmethod.)
9. Disconnectallexternalfittingsfrompumpcasinge.g.coolingpipe,pressuregauge,oilreservoirsandaircock.
10. Removebolting fromtopcoverandremovecover.Scrapeoffoldgasketandcheckmatingsurfaces,andrenewgasketonassembly.(Lightsmearofgreaseongasket/faces)
11. Thepumpshaftwithimpellercanbeliftedoutofcasing.
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12. Dismantletheimpeller,andremovethewearring.
13. Removetheglandpackinganddisregard;replacingitonrebuild.Remembertocutendsofpackingat45andstaggerjointswhenrepackinggland.
www.class4exam.comInspectionProcedureforPumpandMotor:
Pump:
1. Impeller,pumpshaftandinternalvolute/casingcannowbeinspectedforerosion,pittingandwear.
2. Ifrequiredrectifypittingorerosionintheimpellerandcasingwithtwopartalloyepoxyputty.(SeemyarticleintheReferencesection)
3. Checkmaindriveshaftbearingsandthrustbearingsforwearandreplaceifrequired.
4. Checkwearringclearanceusingfeelergauges;inmydayatseaitwasgeneralpracticeistoreplacewithnewringsatmajoroverhaul.
5. Checkimpeller/shaftkeyandkeywaysfordamageandunduewear,Unscrewimpellershaftsecuringnutandcheckthreadsareinsatisfactorycondition;retightentomanufacturerstorquesettings.
6. Giveallpartsagoodcleanremovinganydirt/mediumresiduebeforereassemblyusingnewpartsasrequired.
7. Enterdateofoverhaulandpartsrenewedinthepumpmaintenancerecordcard.
DriveMotor
1.Gripmotordriveshaft/couplingfirmlyandcheckforexcessaxialandlongitudinalmovement.Rotateshaftatspeedbyhand,allowingittoruntoastopwhilstlisteningforexcessnoisefrombearings.Anydoubtoneithercount,thebearingsshouldbereplaced.
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www.class4exam.com2. Meggercheckmotorwindingstoensurenodampnessispresentandwindingsareingoodcondition.Anysuspectreadingsindicateafullmotorstriptocheckconditionofrotorandstator.
3. Ifthesechecksaresatisfactory,greasebearingsasrequired.Somebearingsarenowsealedforlifeandwillnotrequiregreasing.
ProceduretoStartthePump:
1. Unlockandremovechainsfrominlet/outletvalvewheelsandopenbothvalvesfull.
2. Openaircockandexpelairfromlineandpumpwhilecheckingforanyleaks
3. Turntheshaftcouplingandensureshaftisfreetorotate.
4. Reconnectmotor.
5. Removedangernoticesfrompumppowersuppliesandreinstatebreakers.
6. Startandrecordcurrentdrawnbythemotorunderstartingandrunningconditions.Checkandrecordthedischargepressure.
Q42)WHATISPURPOSEOFBILGEINJECTIONVALVE?
ANS)wehavebeentalkingaboutvarioustypesofemergencysituationsonboardaship.Needlesstosaysomeofthemostdangeroussituationsarisenotduetogroundingorcollisionofships(thoughtheyareriskytoo)butmainlycouldbeduetothosesituation,whicheitherinvolveafireorflooding.
www.class4exam.comBoththesetypesofemergencies(fireandflooding)involvetheuse/roleofseawater.Ifthereisafire,seawateristhebiggestresourceofwateravailableinthesea.Similarlyifitinvolvesfloodingoftheengineroom,cargospacesoranyotherplaceontheshipforthatmatter;youwouldagainrequirepumpingtheseawateroutoftheship.Inboththesecasesyourequirepumps.
Wehave studieda lot about seawaterpumps,marine bilge pumps andpipingarrangementonshipsincludingvarioustypesofvalves.
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Soasyoumusthavenoticed,therearetwovalvesincloseproximitynamelymaininjectionvalveandbilgeinjectionvalve.Bothofthemhavetheirownindependentcontrols.Thediameterofthebilgeinjectionvalveiskeptnearly66%ofthemainvalvediameter,whichdrawswaterdirectlyfromtheseathroughthegrid.Thisisalegalrequirementthatthediameterofthisinjectionvalveisatleast2/3timesthemainsuction,thoughitcanbemorealso.
Hencetheinjectionvalveisanarrangementwherethemainseachestcanbebypassedincaseofemergencysothatinsteadofthesea,watergetsdrawnfromwithintheshipitself.
Thereisastrainerattachedtothebilgeinjectionvalveandthepumpusedforthisvalveisnormallythelargestseawaterpump(orpumps)availableintheengineroom.Hencethis
www.class4exam.comvalveisusedtosuckseawaterfromoneofthelowestpointsintheengineroom,whichyoucanalsoseefromthesketch.Thisbasicallymeansthatwhenyouneedtoremovealotofwaterfromtheship,yousimplyneedtoopenthisvalveandrunthebigpump/s.
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REFERENCE:
http://www.brighthub.com/engineering/marine/articles/485
81.aspx#
ChecksandPrecautions:
Emergencysituationcanariseanytime(thatswhyiscalledemergency)soitwouldnotbeagoodideatofindoutthatyourvalveisstuckduetorustornonoperation.Henceitisagoodpracticetocheckfortheoperationasamatterofroutine.
Thespaceneartheinjectionvalvesshouldbekeptclearofallobstaclessincenormallyonewouldrushtoopenthevalveinanactualemergency,andhenceshouldbeminimalobstaclesinthespacearoundthevalve.
www.class4exam.comNotonlyshouldthevalvebeeasilyapproachableand
operational,butitalsoneedstobecheckedregularlyforactualsuctionandoperation.Thiscanbedoneoccasionallybyactuallyrunningthepumpandtryingtodrawoutwaterfromthebilgespacesusesthisvalve.
Thevalvesshouldbeclearlymarkedsincemoreoftenthannot,peopledogetconfusedinemergencysituationsandyoucertainlydontwanttobeopeningsomewrongvalveatsuchacriticaltime
Q43)BRIDGEINFORMSLOTOFSMOKECOMINGFROMFUNNEL.WHATALLTHINGSWESHOULDDO?
ANS)
Reduceloadonengine.Checkpurifieroperatingalright/reducethroughputtohavebetterpurification.Drainwaterfromsettling&servicetank.Checkscavengeairtemperature&adjustifrequired.Sootblowtheeconomizer.
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Ensure,fueloilendheateroutlettemperaturepropercorrespondingtoattainviscosityatthepointofinjection.Check,ifanyparticularExhausttemperatureishigherthanothers,ifso,thenstoptheengine,Changetheinjectorwithaspareoverhauledinjector.Checkallfuelpumptimingsarecorrectornot.DismantleandcarryoutoverhaulofT/C.SendfueloilforLaboratoryanalysis.
www.class4exam.comReasons:
Impropercombustion.BurningofcarbonparticlescollectedatEGE.Overloadingofengine.Lotsofsmokeisalsoseeninscavengefire.Exhaustvalveisdefective.Fuelvalveisdefective.Purifiernotworkingefficiently.Fueloilqualityisbad.
Q44)FLOODINGINENGINEROOM,WHATWILLBEYOURACTION?
ANS)
Informbridge&Chiefengineer.Raiseengineerscall/emergencyalarm.Beforestartingbilgepumpnotedownthepositionofvessel&timeofstarting.Otherengineerswillinbetweentrytolocatetheholeorburstofpipeandrepair.Ifingressofwaterveryhigh,startanotherpump.Reducetheenginer.p.m.Changeovermainseawatersuctiontoemergencybilgesuction.Iflevelisstillcominguptrytoprotectthemotorfromshortcircuiting,Ifsituationisnotcomingincontrol,preparelifeboatforlowering.
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www.class4exam.comQ45)HOWWILLYOUTEST&OVERHAULTHEDEFECTIVEFUELINJECTOR?
ANS)SafetyPrecautions:* Checkwhetheralltoolsandsparesareavailableornot.* Ifso,thenstarttheStandbygenerator.* Checkallparametersarenormal.* Nowsharetheloadwiththehelpofsynchroscope.* Againcheckalltheparametersarewithinnormalrange.* PutfullloadontheStandbygenerator.* Stopthegeneratoronwhichworkhastobecarriedout.* PutMENATWORKtag.* Shuttheairstartingvalve,fueloilinlet&outletvalvesandisolatesthesystem.* Letlubeoilprimingpumprunforhalfhourafterthenstopit.* Removethelocknutofthehighpressurepipe.* Now,removethehighpressurepipe.* Takeoutthefuelinjectorusingittool.* Putitonthetestingkit.* Checktheliftingpressure,atomization,pressurefallingsteadily,anddrippingofoil.* Now,takeouttheinjectorfromthetestingkit,putindieseloil&cleanit.* Makesuretheworkshoptableshouldbeclean,noragsorjutetobethere.* Puttheinjectorontheviceandtightenit.* Loosenthelocknutoftheinjector.* Nowloosenthecompressionnuttoreleasethespringpressure,andthentakeoutthespring.* Openthecapnutandtakeouttheneedleandguide.* Putthepartsonthecleanedtable.* Checktheconditionofspringbydroppingonthefloorplate,itshouldjumpandalsocheckitbytighteningintheviceandthenreleasing.Thedifferenceinthelength,nocrackstobe
www.class4exam.comthere.* Checkvisuallyneedle,thereshouldntbeanyscoringmarksbecauseitismadeofNitritematerial.* Trytoinserttheneedleinsidetheguide;theneedleshouldonitsownweight.* CheckthesizeofinjectingholesbyusingGoorNogogauge.* IfgogaugeisgoingthenholesizeisOK.* Ifnogogaugegoing,thenitmeansthesizehasincreased,
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thennozzleneedstobechanged.* Nowassembletheinjectoranddotheliftingpressuresettingontestkitbyadjustingthecompressionnut.* Afterthischecktheinjectoragainforitsliftingpressure,atomization,steadyfallofpressureanddripping.
Q46)WHATISBUMPINGCLEARENCEINAIRCOMPRESSOR,HOWTOMEASUREIT&HOWTOADJUSTIT?
ANS)TheadjustmentofBumpingClearanceisaverycriticaladjustmentoftheclearancevolume.Ifmorethevolumetricefficiencyofthecompressorsuffersandiflesstheunloadedpistonmayhitthecylinderheadanddamageboth.Inthisarticlewediscusstheneedofthisclearanceanditsadjustment.
WhatisBumpingClearance?
Bumpingclearanceasthenamesignifiesisaclearancegivensothatthepistonofthemarinereciprocatingcompressorwouldnotbumpintoitscylinderhead.Innewcompressorsthemanufacturersadjustthisclearanceandthemarineengineersareblissfullyunawareofitsimportance.Howevertheshipdoesnotremainnewforeverandeverymachinedemandsoverhaulingandthatiswheretheproblemsstart.Evenroutine
www.class4exam.comjobslikeliftingthecylinderheadtochangethelowpressureorfirststagevalvescanchangethebumpingclearanceifthecorrectthicknessgasketsarenotusedoriftheheadisovertightenedthussqueezingoutthegaskets.Manyengineersmissthisvitaladjustmentduringoverhaulofthecompressorsandefficiencyandfreeairdeliveryofthecompressorsuffers.
BumpingClearanceChangesoverTime
Thebumpingclearanceinanewmachineissetproperlybythemanufacturersduringconstructionbutoveraperiodoftimetheclearancechangesbecauseofthefollowingreasons:
Wearatthecrankpinbearing.Thecrankpinbearingwearsdownduetouseandthisclearancecantravelrightuptothepistonandanunloadedpistoncanhitthecylinderhead.Thistypeofwearcanberecognizedwhenthecompressormakesimpactsoundsrunningunloadedat
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thestartingandstoppingoperations.Thistypeofwearwouldalsobeaccompaniedbyaslowdecreaseinoilpressureoveraperiodoftime.
Openingupofcylinderheads.Incertaintypesofreciprocatingcompressorsthecylinderheadhavetoberemovedforthechangingofthefirststagesuctionanddischargevalves.Whenthecylinderheadisputbackthecorrectthicknessofthecylinderheadgasketsshouldbeusedotherwiseitwouldchangethebumpingclearance.
Wearonthemainbearings.Overallwearonthemainbearingswouldlowerthecrankshaftandwouldthuslowerthepistonandincreasethebumpingclearances.
www.class4exam.comSignificanceofBumpingClearance:
Thebumpingclearancemustbeadjustedproperlyotherwisethereisriskofdamageandlossofefficiency.Ifthebumpingclearancewerelessthevolumetricefficiencywouldincreasebutthereisriskofthepistonhittingthecylinderhead,especiallywhenthecompressorisunloadedduringstartandstopping.
Ontheotherhandtoplaysafe,theengineergivesfewmillimetersofextraclearance,thevolumetricefficiencyofthecompressorwoulddecrease,thefreeairdeliverywillfallandtherewillbeafallinpressure.Theextraclearancewouldresultinasmallvolumeofairbeingreexpandedeverytimecausingincreaseinairtemperature,fallinefficiencyandoverheatingofthecompressors.Thiswouldendangertheshipduringmaneuveringbysuddenlossofpropulsion.
HowtoCheckBumpingClearance:
Thebumpingclearancecanbecheckedbythefollowingmethods:
Incaseasuitableopeningisavailablethepistoncanbebarredtothetopdeadcentreandthenfeelergaugescanbeputinsideandtheclearancescheckedattwothree
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points.
Themoreconvenientmethodistotakeleadwirefromtheenginestoreandmakeasmallballbasedontheexpectedclearanceandputitbetweenthepistonandtheheadfromthevalveopening.Thenthepistonis
www.class4exam.comslowlyturnedtothetopdeadcentrewiththehelpofaTommybar.Afterthatthepistonisagainturneddownandtheleadwireballisextractedandthethicknessmeasuredwiththehelpofamicrometer.Thismeasurementwouldgivethebumpingclearance.
Thecaution,whichmustbeobservedinthesemethodsisthat,theclearancesofthemainandthecrankpinbearinghavenotbeentakenintoaccount.Thecorrectmethodisthusthatafterturningthepistontotopdeadcentrethepistonconnectingrodmustbejackedupwiththehelpofacrowbar.Itisonlyafterthishiddenclearancehasbeenaccountedfor,willthecorrectbumpingclearancebefound.
HowtoAdjusttheBumpingClearance:
Thebumpingclearanceoncefoundtobeincorrectwouldhavetobeadjusted.Themethodsofadjustingthebumpingclearancesareasfollows:
Thecylinderheadgasketscanbechangedtoadifferentthicknessthusalteringthebumpingclearance.
Theshimsbetweenthefootoftheconnectingrodandthebottomendbearingcanbechangedthuschangingthebumpingclearance.
Howeverafteradjustingthebumpingclearancetheclearanceshouldbecheckedonceagaintomakesurethatthereisnoerrorandtheclearanceiswithintherangeasspecifiedbythemanufacturers.Itmustbestressedthatcompressorsareunforgivingandincorrectlymaintainedcompressorshaveclaimedmanyalives
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www.class4exam.comQ47)DURINGMANEUVERINGBURSTINGDISCOFANAIRCOMPRESSORGETDAMAGED.WHATWILLBEYOURACTION?
ANS)
Informthebridgeabouttheproblemandgivelesserstartingairkicks.Startthestandbycompressor.Isolatethecompressorwhoseburstingdiscisdamaged.Coverthemotorofaffectedaircompressortoavoidwaterfallingonit.Changetheburstingdisc,ifavailableonboard.Ifnotavailable,thenlettheseawatergointotheEngineroombilges,otherwiseifFreshwatercooled,thenjoinaflexiblehoseandputintotheexpansiontank.
Q48)EXPLAINTHEOVERHAULINGPROCEDUREFORCYLINDERHEAD?
ANS)*ENGINESHUTDOWN.
STARTINGAIRISSHUTOFF&TURNINGGEARISENGAGED.AIRTOEXHAUSTVALVESPRINGISISOLATED.FUELOILTOPARTICULARUNITISISOLATED.COOLINGWATERTOPARTICULARUNITISISOLATED&DRAINED.
REMOVECOOLINGWATERCONNECTIONS.REMOVEFUELOILCONNECTIONS.REMOVESTARTINGAIRCONNECTION.
www.class4exam.comREMOVE THE BELLOW PIECE BETWEEN THE EXHAUSTVALVE&MANIFOLD.DISCONNECT AIR SPRING CONNECTION TO EXHAUSTVALVE.REMOVE HYDRAULIC PIPE CONNECTION & DRAIN PIPECONNECTIONFROMEXHAUSTVALVE.CLEAN THE THREADS ON CYLINDER COVER STUDS &CONTACTSURFACESFORJACKS.LOWERTHETENSIONINGJACKSONTOTHESTUDS.CONNECTHYDRAULICPUMPSNAPCONNECTORWITHJACK.INJACK,SCREWONTHELOCKINGRINGUNTILTHEPISTON
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INJACKGOESDOWN&THENSLACKBACKABOUTHALFTURNOTHERWISETHEJACKCOULDNOTBEABLETOREMOVEFROMTHENUTOFSTUD.STARTTHEHYDRAULICPUMPFORJACKS&VENTTHEAIRFROMJACKS.NOW SHUT THE VENTS & RAISE THE HYDRAULIC PUMPPRESSURETO1000BARS.DUETOTHISTHECYLINDERHEADSTUDSSTRETCH,WHICHALLOWSNUTSTOBESLACKENEDBACKBYUSINGATOMMYBAR.THEJACKSARETHENREMOVED&THECYLINDERHEADSTUDNUTSREMOVED.NOWTHECYLINDERHEADLIFTINGTOOLISATTACHED,THEHEAD&WATERGUIDERINGLIFTEDUSINGTHEENGINEROOMCRANE&LANDEDINASAFEPOSITIONONBLOCKSOFWOODENPLANKTOPROTECTTHESEATINGFACES.
Q49)EXPLAINTHEPROCEDUREOFOVERHAULINGTHEPISTONOFLARGEDIIESELENGINE.
www.class4exam.comANS)*ASABOVETHECYLINDERHEAD&WATER
GUIDINGRINGAREREMOVED.
BEFORETHEPISTONCANBELIFTED&REMOVEDFROMCYLINDERLINER,THEWEARRIDGEATTHETOPOFTHELINERMUSTBEREMOVED.IFTHISISNOTDONETHENTHEPISTONRINGSWILLJAMAGAINSTTHEWEARRIDGEASTHEPISTONISREMOVED.THISISVERYIMPORTANTTOREMOVETHEWEARRIDGEBYUSINGAPROPERGRINDINGTOOL,IFDUETOANYMISTAKETHELINERGETSDAMAGEDATWEARRIDGESPOSITIONi.e.WHENTHEPISTONISATTDCTHISPOSITIONISJUSTBELOWTHETOPRING,THEDAMAGEWILLLEADTOBLOWBY.THEPISTONROD ISNEEDTOBEDISCONNECTEDFROMTHECROSSHEAD.FORTHISPISTONISMOVEDTOBDC&TWOJACKSARESCREWEDONTOTHETHREADSOFTHESTUDSSECURINGTHEPISTONRODTOTHECROSSHEAD.THEJACKSSHOULDBEPOSITIONEDDIAGONALLY.ENSURETHATJACKSARESLACKEDBACKABOUTHALFATURN,SOTHATTHEYCANBEREMOVEDAFTERTHENUTSHAVEBEENLOOSENED.CONNECTTHESNAPCONNECTOROFHYDRAULICPUMPTOTHEJACK&ENSURETHATJACKPISTONSAREATTHEBOTTOMOFTHECYLINDERS.
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VENTTHEAIRFROMTHE JACKSUSINGTHEVENTINGSCREW&THENRAISETHEPRESSURETO1000BARORRECOMMENDEDPRESSUREBYUSINGTHEHYDRAULICPUMP&SLACKTHENUTSUSINGTOMMYBAR.AFTERRELIEVINGTHEPRESSUREONTHEJACKSTHEPROCESSISREPEATEDFORTHEOTHERTWONUTS.BOLTTWODISTANCEPIECESTOTHEPISTONRODFOOT.THESEPUSHTHESTUFFINGBOXOUTOFITS
www.class4exam.comHOUSING,WHENTHEPISTONISMOVEDATTDC.NOWUNBOLTTHESTUFFINGBOX.CLEANOUTTHETHREADEDHOLESINTHEPISTONCROWN.BOLTONTHELIFTINGTOOLTOTHEPISTON&ATTACHENGINEROOMCRANE.LIFTTHEPISTONFROMTHEENGINE&PLACEINCRADLEREADYFORCLEANING&EXAMINATION.
Q50)AUXILIARYBOILEREXTINGUISHES,WHATISYOURACTION?
ANS)Reasons:Acceptthealarm.Findoutthereasonforextinguishing:Iftoolowwaterlevelalarmcame,thencheckpumpisdevelopingcorrectpressureornot,itisworkingproperly.Iftrippedonhighpressure,letthesteampressurecomedown.Fueloillowpressurealarm,thencheckfunctioningoffuelpump,oilinservicetank.Fueloillowtemperaturealarm:thenusetheheater.Flamefailuretrip,thencleanflameeye,checkthefurnace&overhaultheburner.
Q51)WHATISDYEPENETRATIONTEST?WHYITISDONE?&HOWITISDONE?
ANS)THISISTHEMOSTCOMMONMETHODUSEDTODETECTCRACKSINCOMPONENTSONBOARDSHIP.
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www.class4exam.comPENETRANTISSAMEPENETRATINGOILUSEDTOLOOSEARUSTEDNUT&BOLTEXECPTITCONTAINSADYEWHICHWILLFINDITSWAYINTOTHESMALLESTOFCRACKS,EVENTHOSEINVISIBLETOTHENAKEDEYE.
SOMEOFTHEMAREFLUORESCENTDYE,WHICHISTHENUSEDINCONJUCTIONWITHANULTRAVIOLETLIGHT,WHICHMAKESTHECRACKSGLOWGREENWHENORDINARYLIGHTINGISREDUCED.
SOMEOFTHEMAREDEVELOPERWHICHMAKESTHEDYESTANDOUTASAREDLINE.THISTYPEUSUALLYCOMESINTHREEAEROSOLS.
FIRSTISCLEANER,WHICHISSPRAYEDONIT.THENTHECOMPONENTISALLOWEDTODRY.THENTHEPENETRATINGDYEISSPRAYEDON&AFTER5MINUTESTHEEXCESSCOATINGONSURFACEISWIPEDOFF.THEDEVELOPERISSPRAYEDONWHICHWILLHIGHLIGHTANYCRACKPRESENT.
Q52)HOWWILLYOUCARRYOUTTHEBLOWDOWNOFGAUGEGLASSOFBOILER?
ANS)Gaugeglassblowdownprocedure:
Gaugeglassshouldbeblownbeforelightingupofboiler,afterstoppingtheboilerandregularlyifthelevelingaugeglassissuspectedtobewrong.
Cleaningthewatersideofgaugeglass:
www.class4exam.com* ClosethevalveSandWasshowninthefigure.
NowopenthecockWandseeifthewateriscomingoutofthedrainvalveDindicatingthedrainlineisclear.
NowclosethedrainvalveDandkeepthecockWopenandseeifthewaterlevelrisesinthegaugeglass;thisindicatesthelinetogaugeglassisalsoclear.
Repeatthestepstwotothreetimestoremovenudsand
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depositsinside.
Cleaningthesteamsideofgaugeglass:
CloseboththecocksSandW.NowopenthecockSandopenthedrainvalveDandseethe
steamiscomingout.Thedrainisopenedonlyfor12secondsonlyassteammaydamagethesealingandservicelifedecreases.
Puttingthegaugeglassinnormaloperatingposition:
CloseallthevalvesS,WandthedrainvalveD.NowopenthecockWandletthewaterfillinsidethegauge
glass.NowopenthecockSandthenthelevelcanbeseenasthe
pressureequalizes.
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www.class4exam.comQ53)HOWWILLYOUTESTTHECYLINDERRELIEFVALVEOFENGINE?
ANS)Thecylinderreliefvalveisdesignedtorelievepressuresinexcessof10%to20%abovenormal.Aspringholdsthevalveclosedanditsliftingpressureissetbyanappropriatethicknessofpackingpiece.Onlyasmallamountofliftispermittedandtheescapinggasesaredirectedtoasafeoutlet.Thevalveandspindleareseparatetoenablethevalveto
www.class4exam.comcorrectlyseatitselfafteropening.
Theoperationofthisdeviceindicatesafaultintheengine,whichshouldbediscoveredandcorrected.Thevalveitselfshouldthenbeexaminedattheearliestopportunity.
Pressuretestingwascarriedoutonabenchmountedtestrigconsistingofahighpressureaircompressor,airpressurecontrolvalve,andcalibratedgauges.Thereliefvalvewasboltedtothecompressoraccumulatorflangeandtheair
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pressureincreaseduntilthevalvelifted.
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www.class4exam.comQ54)HOWWILLYOUTIGHTGAUGEGLASSAFTEROVERHAULING?
www.class4exam.com
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ANS)ITSHOULD
11 7 3 1 5 9
10 6 2 4 8 12
BETIGHTEDFROMINSIDETOOUTSIDEONCE&THENOUTSIDETOINSIDE.
THETIGHTINGSHOULDBEDONEONLYBYHANDTIGHT.
Q55)HOWWILLYOUREMOVETHEBROKENSTUD?ANS)*FIRSTDRILLTHEBROKENSTUDLITTLEBIT.
THENUSETHREADEXTRACTOROFLEFTHANDTHREADFORMAKINGTHREADINHOLE.NOWPUTTHESTUDOFSAMETHREADINITBYUSINGTWONUTS.ONCETHESTUDISINSIDETHETHREADTHENREMOVETHEBROKENSTUDBYUSINGTHESAMESTUD&TWONUTS.
Q56)WHEREISPOSITIONOFUNLOADERINA/C&REF.COMPRESSOR?
ANS)ITISLOCATEDNEARTHESUCTIONVALVEOFCOMPRESSOR.
www.class4exam.comQ57)WHATALLCLEARENCESARETAKENINCENTRIFUGALPUMPAFTEROVERHAUL?
ANS)*CLEARENCEBETWEENWEARRING&IMPELLER.
CLEARENCEBETWEENWEARRING&CASING.CLEARENCEBETWEENSHAFT&BUSH.
Q58)HOWWILLYOUCARRYOUTBLOWDOWNOFBOILER?
ANS)Boilerblowdownisdonetoremovecarbondepositsand
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otherimpuritiesfromtheboiler.Blowdownoftheboilerisdonetoremovetwotypesofimpuritiesscumandbottomdeposits.Thismeansthatblowdownisdoneeitherforscumorforbottomblowdown.Moreover,thereasonsforboilerblowdownare:
1.Toremovetheprecipitatesformedasaresultofchemicaladditiontotheboilerwater.
2.Toremovesolidparticles,dirt,foamoroilmoleculesfromtheboilerwater.Thisismainlydonebyscumvalveandtheprocedureisknownasscumming.
3.Toreducethedensityofwaterbyreducingthewaterlevel.
4.Toremoveexcesswaterincaseofemergency.ProcedureforScummingandBottomBlowDown
www.class4exam.comBelowis theprocedure forboilerblowdownusing theblowdownvalvelocatedatthebottomoftheboiler.Inordertodoscumming,insteadofbottomblowdown,thescumvalveistobeopened.
Stepsforblowdownprocedureareasfollows:
Kindlyreferthediagramtounderstandtheblowdownprocedureproperly.
1.Opentheoverboardorshipsidevalve(1)first.
2.Opentheblowdownvalve(2),thisvalveisanonreturnvalve.
3.Theblowdownvalveadjacenttotheboiler(2)shouldbeopenedfullysoastopreventcuttingofthevalveseat.
4.Therateofblowdowniscontrolledbythevalve(3).
5.Afterblowdownclosethevalveinreverseorder.
6.Ahotdrainpipeevenwhenallvalvesareclosedindicatesaleakingblowdownvalve.
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www.class4exam.comQ59)EXPLAINCRANKCASEEXPLOSION?HOWITISPROTECTED?WHATISCRANKCASERELIEFDOOR?
ANS)Crankcaseexplosionsarealsotheresultofhighoperatingtemperaturesoftheengine.Themaincauseofcrankcaseexplosionsisthedevelopmentofhotspotsatvariousplacesinthecrankcase.Duetothereciprocatingmotionofthepistonthelubricatingoilinthecrankcaseissplashedintheair.Nowitisnecessarythattheflashpointofthelubricatingoilbemaintainedataround200degreeCelsius.Ifthisisnotdonethentherearehighchancesforthe
www.class4exam.comlubricatingoiltocatchfire.
Hotspotsarecreatedinthecrankcaseasaresultof:
Hightemperatureduetothereciprocatingmovementofthepiston,
Increaseinbearingtemperatures,
Sparksenteringthecrankcaseduetoleakypistonringsorpistonblowpast,
Firesintheadjacentscavengetrunks.
Now,whenthesehotspotscomeincontactwiththeoilinthecrankcase,theoilgetsvaporized.Whenthesevaporized
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particlestraveltothecoolerpartofthecrankcasetheygetcondensedintoawhitemist,whichhasoilparticlesproperlydispensedinit.Theprocessthattakesplaceissomewhatsimilartoatomization.Thiswhitemistwhenagaintravelstothehotspotarea,caneasilycatchfire,whichmightalsoleadtoanexplosion.Thefireortheexplosioncreatesimmensepressureinsidethecrankcaseandifthispressurecrossesthepermissiblelimit,crankcaseexplosiontakesplace.Theexplosionwillrupturethecrankcasedoorsandevencauseheavydamagetotheinsideoftheengine.
Itisabitdifficulttoreadtheearlysignsofcrankcaseexplosions.Thisisbecausetheindicationsaresimilartomanyotheremergencysituations.Buttherearefewpreexplosionsignsthatcanberead.Crankcaseexplosionwilllead:
Suddenincreaseintheexhausttemperature
Suddenincreaseintheloadontheengine
www.class4exam.comIrregular running of the engine
Incongruousnoiseoftheengine
Smellofthewhitemist.
Incaseoftheseindications,enginespeedshouldbebroughtdownimmediatelyandthesupplyoffuelandairshouldbestopped.Thesystemshouldthenbeallowedtocooldownbyopeningtheindicatorcocksandturningontheinternalcoolingsystem.
Prevention:
Preventingthegenerationofhotspotscandopreventionofcrankcaseexplosion.Itcanalsobepreventedbythefollowingways:
Byprovidingproperlubricationtothereciprocatingparts,thusavoidinghightemperatures.
Avoidingoverloadingoftheengine
Usingbearingswithwhitemetalmaterial,whichpreventsriseintemperature.
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Usingoilmistdetectorinthecrankcasewithpropervisualandaudiblealarm.Oilmistdetectorsraiseanalarmiftheconcentrationofoilmistrisesabovethepermissiblelimit.
Pressurereliefvalvesshouldbefixedonthecrankcasefortheinstantreleaseofpressure.Theyshouldbeperiodicallypressuretested.
Crankcasedoorsshouldbemadeofstronganddurablematerial.Ventpipesshouldn'tbetoolargeandshould
www.class4exam.combecheckedforanychokeup
Pressurereliefvalvesshouldbeprovidedwithwiremeshtopreventthereleaseofflamesinsidetheengineroom.
Safedistanceshouldbekeptfromthecrankcaseandthereliefvalvesincasetheindicationsaresighted.
Incaseofindication,thecrankcasedoorsshouldneverbeopenedtillthetimethesystemhastotallycooleddown.Oncethesystemhascooleddown,properinspectionandmaintenanceshouldbecarriedout.
Fireextinguishingmediumshouldbekeptstandby.Inmanysystems, inertgas floodingsystem isdirectlyconnectedtothecrankcase.
OILMISTDETECTOR:Lubricatingoilissuppliedtothemainengineunderpressurefromthemainlubeoilpump.Itpassesthroughthecrankshaft,lubricatingandcoolingthemainandbottomendwhitemetalbearing,returningtothesump.Itisalsosuppliedtothecrossheadguidesandpistonrodbearing,fromwhichitcascadesdowntothemainsump.Duringthisactivityanoilmistisproduced,whichistobeexpected,howeverifthereisahotcomponenttheoilmistwillbeincreasedandvaporizewiththerealriskoffireandexplosionintheenginecrankcase.Thepurposeoftheoilmistdetectoristodetectanyincreaseinthedensityoftheoilmist,settingoffanalarmtowarnthewatchkeepingengineerofpotentialdanger.
PreventiveMeasuresofCrankcaseExplosion:
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www.class4exam.comEnsureadequatecoolingoftheengine
EnsureproperpurificationandanalysisoflubeoilLubeoilfiltershouldbechangedoverandcleanedasper
scheduleEnsurepropercylinderlubricationbycheckingthecondition
ofpiston,pistonringsandlinerthroughscavengeorexhaustports
Cleanscavengespacesasperscheduleanddrainscavengespaceregularly
MaintainstuffingboxglandingoodconditionBealertandrectifyforanyabnormalnoiseincrankcase
Allsafetyalarmsandtripsfittedonenginetobetriedout
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satisfactorilyProperwatchonallrunninggearstemperatureand
pressurestobemaintainedBlowthroughallsamplingtubesofOilMistDetector(OMD)
regularly
ZeroadjustmentandsensitivityofOMDtobecheckedregularly
Checkforanyoilleakageatcrankcasereliefdoorsandcheckfortheoperationbyhandortool
Checkflametrapforcleanliness
ProtectionagainstCrankcaseExplosion:
OilMistDetectorWarningpriortoacrankcaseexplosion
Crankcasereliefdoors
www.class4exam.comReleasespressureinsidecrankcaseduetoprimaryexplosion,preventruptureofcrankcaseandenteringfreshairintothecrankcase.
CRANKCASERELIEFDOOR:
Asapracticalsafeguardagainstexplosions,whichoccurinacrankcase,explosionreliefvalvesordoorsarefitted.Thesevalvesservetorelieveexcessivecrankcasepressuresandstopflamesbeingemittedfromthecrankcase.Theymustalsobeselfclosingtostopthereturnofatmosphericairtothecrankcase.
Variousdesignsandarrangementsofthesevalvesexistwhere,onlargeslowspeeddiesels,twodoortypevalvesmaybefittedtoeachcrankcaseor,onamediumspeeddiesel,onevalvemaybeused.OnedesignofexplosionreliefvalveisshowninFigure.Alightspringholdsthevalveclosedagainstitsseatandasealringcompletesthejoint.
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www.class4exam.comAdeflectorisfittedontheoutsideoftheenginetosafeguardpersonnelfromtheoutflowinggases,andinsidetheengine,overthevalveopening,anoilwettedgauzeactsasaflametraptostopanyflamesleavingthecrankcase.Afteroperationthevalvewillcloseautomaticallyundertheactionofthespring.
TheCrankcasereliefdoorsarealsofittedtopreventanydamagetothecrankcaseandingressoffreshairinsidethecrankcase.
www.class4exam.comThecrankcasedoorsarespringloadedvalves,whichliftupincasethereisanyriseofpressureinsidethecrankcase.Oncethepressureisreleasedtheyreseattopreventanyingressoffreshair.Thishelpsespeciallyincaseofanyingressofairthatcanleadtoasecondaryexplosionfollowedbyalotofsurgeanddamagetothecrankcase.
Theopeningpressureandsizesofthevalvesarespecifiedbydifferentclassificationsocieties,dependingonthevolumeofthecrankcase.Thenumberofdoorstobepresentalsodependson
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theboreofthecylinder.
Q60)EXPLAINFUNCTIONOFOILMISTDETECTOR?
ANS)TheOilmistdetectortakescontinuoussamplesfromthemainenginecrankcaseandcheckwhetherthesampleconcentrationsofmistarewellbelowthelevelatwhichacrankcaseexplosioncantakeplace.Theoilmistisdrawnintotheinstrumentwiththehelpofsmallfan,whichtakessuctionfromeachcrankcasethroughsamplingtubesprovidedoneachcrankcase.
Theoilmistdetectorconsistsofasmallrotatorwithwhichittakessamplefromonecylinderatatimeandtherotatorthenturnstothenextafterapproximately4seconds.Thesamplefromtherotatorgoestothemeasuredcellandthereferencecelltakessamplefromrestofthecrankcasetoevaluatethedifferenceinoilmist.
Anoverallmistdensityofthecrankcaseisalsomeasuredbycomparingthesampleswiththefreshaironceeveryrotation
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ofthesamplingvalveisdone.Abeamoflightfromacommonlampisreflectedthroughmirrorsandoutputismeasuredfrom
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aphotocell.
Undernormalconditionstheoutputfromthereferenceandmeasuredcontactissameandhencenodeflectionismeasured.However,adeflectionintheoutputgivesanalarmindicationandthevalverotatorstopsatpositiontoknowwhichchamberhashighmistconcentration.
Someenginesareevenfittedwithslowdownalarmssothatwhentheoilmistalarmsrings,theengineautomaticallyslowsdowntopreventcrankcaseexplosion.
Q61)HOWTHETESTINGOFCRANKCASERELIEFDOORISCARRIEDOUT?
www.class4exam.comANS)*THEMAINTESTINGOFCRANKCASERELIEFDOORISCARRIEDOUTATSHORE.
*BUTTHENALSOSOMEOFTHINGSTOBEINSPECTEDDURINGCRANKCASEINSPECTION:
1. Checkcrankcaseexplosionreliefdoorwiremesh(shouldbewet),springtension,andsealingringcondition.
2. Checktheproperfunctioningofspringofvalvebyinsertingstudinit.
3. Visualconditionofvalve.
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Q62)WHATISSPARKEROSIONCHECKINCRANKCASEINSPECTION?
ANS)SparkErosionChecks:
Sparkerosioniscausedbyvoltagedischargedbetweenthemainbearingsandtheirrespectivejournals.Thisvoltageoriginatesfromthedevelopmentofgalvanicactionbetweentheshipssteelhullandthepropellershaft,withtheseawateractingasanelectrolyte.Thisisthentransferredtothemaincrankshaftwhere,duetodissimilarmetals,erosioncanoccurbetweenthewhitemetaledmainbearinganditsjournal.Sparkerosioncanonlyoccurifthecurrentisnotgrounded.Thechecksconsistofavisualcheckforwhitemetalfragmentsaroundthemainbearingsandrespectivejournalsandcheckingforanyelectriccurrentbetweenthemainbearingwhitemetalandjournal.Thisshouldbecarriedoutusingamicroampcurrentmeterorsimilardeviceformeasuringsmallamperagesandvoltages.Thisshouldreadnomorethan50mV;
www.class4exam.comanyhigherthanthisindicatingthatshaftgroundingisnotworking.Groundingiscarriedoutbyfittingacathodicprotectionsystemtothemainpropellerdriveshaft,consistingofasetofslipringsontheshaftandcarbonpickupbrushes.Thebrushesarewiredandgroundedtoagoodearthontheshipsstructureclosebythesliprings.Bothcomponentsshouldbecheckedregularlyforwear;especiallyifacurrentispickedupbetweenmainbearingsandjournalduringcrankcaseinspection.Adrawingofonetypeofcathodicprotectionisshownbelow.Theoilfilmactsasadielectric,sothepuncturevoltageinthebearingdependsonthethicknessoftheoilfilm.Rememberthatastheoiltemperaturerises,itsviscositydecreases,andsimilarlyastheloadincreases,oilfilmthicknessdecreases.Thereforeaswellasadequategrounding,thetemperatureandpressureoftheoilmustbemaintainedtoprovidethedielectriceffect.Intheearlystagesofsparkerosion,slightlyroughenedpittedareasareacceptable.However,ifthisisallowedtocontinue,theroughnesswillescalatewiththesmallerosionspickingupthewhitemetal,hencethesilverywhiteappearancearoundthemainbearing/journal.
Q63)EXPLAINWORKINGOFGEARPUMP?
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ANS)Agearpumpusesthemeshingofgearstopumpfluidbydisplacement.[1]Theyareoneofthemostcommontypesofpumpsforhydraulicfluidpowerapplications.Gearpumpsarealsowidelyusedinchemicalinstallationstopumpfluidwithacertainviscosity.Therearetwomainvariations;externalgearpumpswhichusetwoexternalspurgears,andinternalgearpumpswhichuseanexternalandaninternalspurgear.Gear
www.class4exam.compumpsarepositivedisplacement(orfixeddisplacement),meaningtheypumpaconstantamountoffluidforeachrevolution.Somegearpumpsaredesignedtofunctionaseitheramotororapump.Asthegearsrotatetheyseparateontheintakesideofthe
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www.class4exam.compump,creatingavoidandsuction,whichisfilledbyfluid.Thefluidiscarriedbythegearstothedischargesideofthepump,wherethemeshingofthegearsdisplacesthefluid.Themechanicalclearancesaresmallintheorderof10m.Thetightclearances,alongwiththespeedofrotation,effectivelypreventthefluidfromleakingbackwards.
Therigiddesignofthegearsandhousesallowforveryhighpressuresandtheabilitytopumphighlyviscousfluids.Manyvariationsexist,including;helicalandherringbonegearsets(insteadofspurgears),lobeshapedrotorssimilartoRootsBlowers(commonlyusedassuperchargers),andmechanicaldesignsthatallowthestackingofpumps.Themostcommonvariationsareshownbelow(thedrivegearisshownblueandtheidlerisshownpurple).
Suctionandpressureportsneedtointerfacewherethegearsmesh(shownasdimgraylinesintheinternalpumpimages).Someinternalgearpumpshaveanadditional,crescentshapedseal(shownabove,right).
Generallyusedin:dieseloil,crudeoil,lubesoil&sludgeetc.
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Externalgearpumpsaresimilarinpumpingactiontointernalgearpumpsinthattwogearscomeintoandoutofmeshtoproduceflow.However,theexternalgearpumpusestwoidenticalgearsrotatingagainsteachother:amotordrivesone
www.class4exam.comgearanditinturndrivestheothergear.Ashaftsupportseachgearwithbearingsonbothsidesofthegear.
1. Asthegearscomeoutofmesh,theycreateexpandingvolumeontheinletsideofthepump.Liquidflowsintothecavityandistrappedbythegearteethastheyrotate.
2. Liquidtravelsaroundtheinteriorofthecasinginthepocketsbetweentheteethandthecasingitdoesnotpassbetweenthegears.
3. Finally, themeshing of the gears forces liquid through the outlet port
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underpressure.
Becausethegearsaresupportedonbothsides,externalgearpumpsarequietrunningandareroutinelyusedforhighpressureapplicationssuchashydraulicapplications.Withnooverhungbearingloads,therotorshaftcan'tdeflectandcauseprematurewear.
Q64)EXPLAINWORKINGOFCENTRIFUGALPUMP?ANS)Centrifugalpumpprinciplesandworkingprocedure
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Apumpisamachineusedtoraiseliquidsfromalowpointtoahighpoint.Inacentrifugalpumpliquidentersthecentreoreyeoftheimpellerandflowsradiallyoutbetweenthevanes,itsvelocitybeingincreasedbytheimpellerrotation.Adiffuserorvoluteisthenusedtoconvertmostofthekineticenergyintheliquidintopressure.
Thearrangementofacentrifugalpumpisshowndiagrammaticallyinfigurebelow
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Fig:Centrifugalpumpingoperation
Avertical,singlestage,singleentry,centrifugalpumpforgeneralmarinedutiesisshowninFigurehere.Themainframeandcasing,togetherwithamotorsupportbracket,housethepumpingelementassembly.Thepumpingelementismadeupofatopcover,apumpshaft,animpeller,abearingbushandasealingarrangementaroundtheshaft.Thesealingarrangementmaybeapackedglandoramechanicalsealand
www.class4exam.comthebearinglubricationsystemwillvaryaccordingtothetype
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www.class4exam.comAverticalmultistagesingleentrycentrifugalpumpusedfordeepwellcargopumpingisshowninFigurebelow.Thiscanbeconsideredasaseriesofcentrifugalpumpsarrangedtosupplyoneanotherinseriesandthusprogressivelyincreasethedischargepressure.Thepumpdriveislocatedoutsidethetankandcanbeelectric,hydraulicoranyappropriatemeanssuitableforthelocation.
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www.class4exam.comAdiffuserisfittedtohighpressurecentrifugalpumps.Thisisaringfixedtothecasing,aroundtheimpeller,inwhichtherearepassagesformedbyvanes.Thepassageswidenoutinthedirectionofliquidflowandacttoconvertthekineticenergyoftheliquidintopressureenergy.Hydraulicbalance
www.class4exam.comarrangementsarealsousual.Someofthehighpressuredischargeliquidisdirectedagainstadrumorpistonarrangementtobalancethedischargeliquidpressureontheimpellerandthusmaintainitinanequilibriumposition.
Centrifugalpumps,whilebeingsuitableformostgeneralmarineduties,arenotselfprimingandrequiresomemeansofremovingairfromthesuctionpipelineandfillingitwithliquid.Wheretheliquidtobepumpedisatalevelhigherthanthepump,openinganaircocknearthepumpsuctionwillenabletheairtobeforcedoutasthepipelinefillsupundertheactionofgravity.Ifthepumpisbelowseawaterlevel,andseawaterprimingispermissibleinthesystem,thenopeningaseawaterinjectionvalveandtheaircockonthepump
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willeffectpriming.
Alternativelyanairpumpingunitcanbeprovidedtoindividualpumpsorasacentralprimingsystemconnectedtoseveralpumps.Thewaterringorliquidringprimercanbearrangedasanindividualunitmountedonthepumpanddrivenbyit,orasamotordrivenunitmountedseparatelyandservingseveralpumps.Theprimerconsistsofanellipticalcasinginwhichavanedrotorrevolves.TherotormaybeseparatefromthehubandprovidetheairinletanddischargeportsasshowninFiguredown.Alternativelyanotherdesignhastherotorandhubasonepiecewithportsonthecover.Therotorvanesrevolveandforcearingofliquidtotakeuptheellipticalshapeofthecasing.Thewaterring,beingelliptical,advancesandrecedesfromthecentralhub,causingapumpingactiontooccur.Thesuctionpipingsystemisconnectedtotheairinletportsandthesuctionlineisthusprimedbytheremovalofair.Theairremovedfromthesystemisdischargedtoatmosphere.Areservoirofwaterisprovidedtoreplenishthewaterringwhennecessary.
www.class4exam.comFig:Waterringprimer
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Whenstartingacentrifugalpumpthesuctionvalveisopenedandthedischargevalveleftshut:thenthemotorisstartedandtheprimingunitwillprimethesuctionline.Oncethepumpisprimedthedeliveryvalvecanbeslowlyopenedandthe
www.class4exam.comquantityof liquidcanberegulatedbyopeningorclosingthedeliveryvalve.Whenstoppingthepumpthedeliveryvalveisclosedandthemotorstopped.
Regularmaintenanceonthemachinewillinvolveattentiontolubricationoftheshaftbearingandensuringthattheshaftsealorglandisnotleakingliquid.Unsatisfactory