Class 4 Oral Question and Answers

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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



www.class4exam.comorbrine)flowslongtheshellside.Incaseofthefloodedtheevaporatorisfilledwiththerefrigerantandconstantleveloftherefrigerantismaintainedinsideit.Intheseevaporatorsorthechillerstherefrigerantisalongshellsidewhilethesubstancetobechilledorfreezerflowsalongthetubesideoftheheatexchanger.

Thoughthisclassificationisalsoapplicabletothedomesticrefrigeratorsandtheairconditioners,theevaporatorsusedinthesesystemsareclassifiedbasedontheirconstruction.Theevaporatorsareclassifiedbasedontheconstructionas:

1) Baretubeevaporators

2) Platesurfaceevaporators

3) Finnedevaporators

Thebaretubeevaporatorsarethesimplecoppercoilevaporatorsoverwhichthesubstancetobecooledflows.

Theplatesurfaceevaporatorsarecommonlyusedinthehouseholdrefrigerators.Theseevaporatorsarealsointheformofcoil,whichisattachedtotheplate.

Thefinnedevaporatorsarealsomadeofcoppercoilwithfinsontheexternalsurfaceaswellontheinternalsurface.



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.



Atypicalpropshaftwhitemetalbearingwithsplashlubricationisshownhere.

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www.class4exam.comQ7)EXPLAINRUDDERCARRIERBEARINGWITHDIAGRAM?

ANS)Theruddercarrierbearingtakestheweightoftherudderonagreaselubricatedthrustface.Therudderstockislocatedbythejournal,alsogreaselubricated.Supportforthebearingisprovidedbyadoublersplateandsteelchock.Wedgetypesidechocks,weldedtothedeckstiffening,locatethebaseofthecarrierbearing.Thecarrierisofmeehanitewithagunmetalthrustringandbush.Carrierbearingcomponentsaresplitasnecessaryforremovalorreplacement.Screwdownlubricatorsisfitted,andthegreaseusedforlubricationisofawaterresistanttype(calciumsoapbasedwithgraphite).



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

o

o



37 Onsteeringgear Preventsrudderstrikingexternalstops

39 External,on Emergencystoptoprotectsternframe propeller

Theselimitsrefertoruddersoftraditionaldesignandaregovernedbyboththephysicallayoutoftherudderandactuatorbutalsoduetothestallanglesoftherudder.i.e.theangleatwhichlift(turningmoment)isreducedorlostwithincreasingangleofattack.TherearedesignsofruddersuchasBeckerflapwhichhaveincreasedstallanglesupto45

o

o

o

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Reasonsforcriticalcontouringofthrustface;

I.Forlubrication

ii. Conicalinordertopreventsideslipandcentralizerudder

iii. Projectedareagivesgreaterbearingareaallowingsmallerdiameterbearing

www.class4exam.comQ8)WHATARESTABILIZERS?WHATISITSPURPOSE?ONWHICHSHIPSTHEYAREREQUIREDMORE?

ANS)Shipstabilizersarefinsmountedbeneaththewaterlineandemerginglaterally.Incontemporaryvessels,theymaybegyroscopicallycontrolledactivefins,whichhavethecapacitytochangetheirangleofattacktocounteractrollcausedbywindorwavesactingontheship.



Locationanddiagramofretractablefinstabilizersonaship.

PurposeThepurposeofcruiseshipstabilizersistoreducetherockingmotionoftheship.Theyhelpashipmovemore

www.class4exam.comsmoothly,whichcutsdownthechanceofseasicknessforpassengers.Whenthereisagreatdealofmovement,itcancauseadiscrepancybetweenwhatapersonseesandwhatherinnerearsenses.Thisiswhatcausesseasickness.Thesmoothertheride,thelesschanceforthistohappen.

FunctionCruiseshipstabilizersextendoutbelowthewaterlineontheportandstarboardsidesoftheship.Theypreventitfromrollingtotheleftandrightasitmovesthroughthewater.Theyactmuch,asdoairplanewingflaps,whichcanbeadjustedtoreduceturbulence.Althoughnostabilizerscanprevent100percentofacruiseship'smovement,theycansignificantlyreduceit.Thisisespeciallydesirableinroughconditionswhenthewavesarehighorthewindisstrong.



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.



Graphicalrepresentationofthedimensionsusedtodescribeaship.fisthefreeboard

Q10)WHATISSHEER?

ANS)Thesheerisameasureoflongitudinalmain

www.class4exam.comdeckcurvature,innavalarchitecture.Thepracticeofbuildingsheerintoashipdatesbacktotheeraofsmallsailingships.Thesevesselswerebuiltwiththedeckscurvingupwardsatthebowandsterninordertoincreasestabilitybypreventingtheshipfrompitchingupanddown.



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)



www.class4exam.comDepthormouldeddepth(D)istheverticaldistance



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



thethicknessofthehullincluded;inthecaseofnotbeingincludedthedraftoutlinewouldbeobtained.Draftdeterminestheminimumdepthofwaterashiporboatcansafelynavigate.ThedraftcanalsobeusedtodeterminetheweightofthecargoonboardbycalculatingthetotaldisplacementofwaterandthenusingArchimedes'principle.Atablemadebytheshipyardshowsthewaterdisplacementforeachdraft.Thedensityofthewater(saltorfresh)andthecontentoftheship'sbunkershavetobetakenintoaccount.Thecloselyrelatedterm"trim"isdefinedasthedifferencebetweentheforwardandafterdrafts.



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)



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.



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:



1.Makesuretheallstandbyauxiliaryenginesareready2.Keepallthespecialtoolsandothertoolsready

3.Gothroughthepreviousrecords/manualforclearance

www.class4exam.comandadjustments

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.



www.class4exam.comPutthecylinderheadliftingtoolandbeforeliftingmake

surealltheconnectionsareremoved.Alsoensurethatthelinerisnotremovedalongwiththecylinderhead

Takeoutthecopperjointbetweentheheadandtheliner

CYLINDERHEADBEFORECLEANING



EXHAUSTV/VBEFORECLEANING

Removalofpistonandconnectingrod:

Afterliftingthehead,checkthelinersurfaceforscoremarks,blowpastetc.Crackremovetheridgesordepositsifanyonthetopsurfacetoavoidtheliftingof

www.class4exam.comlineralongwiththepistonandbreakageofpistonringswhileliftingpiston

Openthecrankcasedoorandremovethebottomendbearingboltsafterremovingthelockarrangementandtheremovethebolts

Removethebottomhalfofthebottomendbearing

BringthepistontoTDC.Makesuretheboltholesonthe



pistontop;liftingtoolholesmustbeclearedfromcarbondeposits.Threadsshouldalsobecheckedandcleared

Putthepistonliftingtoolsandtightenthebolts

Liftthepistonandremovetopshellofbottomendbearing

Placethepistononthepistonstandandcoverthecrankcasepintoavoidtheforeignmaterialdamagingthecrankpin.

PISTONWITHRINGSB4CLEANINGPISTONWITHOUTRINGB4CLEANING

www.class4exam.comPISTONAFTERCLEANING CONNECTINGRODREMOVAL

Cleaningthecarboncontentonallthepartsofengine:

Cleanthepistonrings,measuredimensionsandkeeptheminorder

Cleanthepistonringgroovesthoroughlyandmeasurethe



groovethicknessat3differentpoints

Checkforthedepositsonpistoncrown(Sulphur,carbonorthickvanadiumdeposits)andmeasurethedimensions

Removethegudgeonpinandcleanthegudgeonlubeoilholesaswellasthebushorsmallendbearing

Checktheboltsofconnectingrodforanycracks

Every20,000hrsengineconnectingrodboltmustbereplaced

Ifnewpistonringsaregoingtobereplaced,thenthereisnoneedformeasurement

Calibratethelinerthicknessbyusingtemplate



www.class4exam.comLINERB4CLEANINGCOOLINGWATERSIDEOFLINER(EXTERNALVIEW)

COOLINGWATERSPACEINSIDEENGINELINERAFTERHONINGPROCESSPISTONPINREMOVALCONNECTINGRODCLEANING



www.class4exam.comBOTTOMENDBEARINGBEFORECLEANINGBOTTOMENDBEARINGAFTERCLEANING

Assemblyoftheengineparts:

Firstputthepistonringsonebyoneandmeasurethebuttclearanceforalltherings

Thenmeasuretheaxialclearancebetweenpistonrings&grooves

PlacethepistonguideontopofthelinerandbringtheparticularcrankshafttoTDC.Applysufficientlubeoilandstartloweringthepiston.Makesurethatbuttgapshouldnotbeinlineitmaycauseblowpast

Beforeengagingcheckthecrankpinforanycracksorscratch

Checkthebottomendbearingclearanceandifneededmeasurethemainbearingclearanceaswell

Taperclearanceischecked

Checkforanycracksinthewaterjacketandinthecylinderhead

www.class4exam.comReplaceallrubberjointsandcoppergaskettobeputonthe

cylindercover

Putthecylinderheadgasketinthetopofthecylinder

Antiseizurecoatingorpowderlikemolycote,copperslipshouldbeused.Itisappliedtoavoidanyseizuremainlyonthethreadsorjointsanditwillbeeasierwhileremoval



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



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



www.class4exam.comb)MaintenanceSchedule:

Periodicinspectionhastobedonewhentheengineisnotrunning.Itcanbecarriedoutasaboveorbyenteringthescavengespaceandinspectingthepistonandpistonringsthroughthescavengeports,withthepistonbroughtinlinebyrotatingtheengineviaaturninggear.

OverhaulingthepistonasperPlannedMaintenanceSchedule(PMS).

Monitoringoftheconditionofthepistonandthepistonringsbythecompressioncurveoftheindicatordiagramthroughprocessanalysis.

Theimagesshownbelowshowexamplesoftwomeansofinspection.Inspectionofpistonandringsthroughthescavengeport



www.class4exam.comPistonremovedforcloserinspection

EmergencyRepairofPistonCrown:

Oncetheabovecheckshavebeencarriedout,whatactionscanbetakenifsomevaluesorobservationsareoutwiththespecifications?Givenbelowisalistofcommonfaultsthatmightbefoundduringinspectionandmeanstomaketemporaryemergencyrepairs.

Gaugepistoncrownandascertainshapeandweardown.If

www.class4exam.comitisbeyondrecommendedlimits,replacethepistonifthereisaspareavailable.Ifnot,rebuildtheengineandproceedtothenearestportatreducedrevolutionsandarrangereplacement.Thecrownheadshouldnotbeweldedexceptinadireemergencyandeventhenonlybyanexperiencedwelder.Rememberthatmoderndieselenginepistonshaveaspecialliningofhightemperaturealloyonthetopofthecrown.Thismeasureimprovesresistancetocorrosionaswellastohighcombustiontemperaturesthatthepistontopisexposedto

Examinethecrownforfracturesorcracks,andiffoundthepistonshould



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



ascertainthatthepistonisatTDC.Thoughmarkingsareprovidedontheflywheel,themarineengineermustknowtheothermethodsforthislikeinspectionofthecamshaftandthefuelpumpwindow.

Duringthemaintenanceofafourstrokemarinedieselengine

www.class4exam.comtherearetimeswhenwemustknowwhethertheparticularunitspistonisatthetopdeadcenterornot.ForexamplewhencheckingthetappetclearancesoftheengineitisimportanttoknowwhichunitisatTDC.

Referringtotheflywheelwouldindicatetwounits,butonlyonecanbeatinjectionTDC.Sowhichoneisit?

FlywheelMethod:

TheflywheelisthesimplestmethodtoknowwhichunitisatTDC.Iftheflywheelshowstwounits,simplyopenthebonnetcoversandchecksvisually.TheunitatTDCwillhaveboththeinletandtheexhaustvalveclosedandhencerelaxedsprings;theotherunitwouldhaveboththearmsoftherockerarmatdifferentlevels.InadditionthepushrodsoftheunitatTDCwouldbelooseandcanbeturnedbyhandbecauseofthereleaseoftheclearances.Thereisawordofcautionhowever:thismethodisonlyusefulinaworkinggenerator,whichyouhavejuststoppedtocheckthetappetclearances.Incaseyouhaveremovedtherockerarmsforanyreasonthespringheightandthepushrodfreenesscheckwouldleadyounowhereandmisguideyou.



www.class4exam.comDialGaugeMethod:

Inthismethodthefuelinjectoristakenoutandfromtheopeningadialgaugeisputinside.Thentheturninggearisengagedandtheengineturnedover.Thepointerofthedialgaugewillmoveinonedirectionandthenstopandstartinoppositedirection.ThemomentthepointerofthedialgaugestopsandchangesitsdirectionofmovementistheTDCoftheunit.Thismethodisnotnormallyusedindaytodaypractice,butmaybeusedinthecalibrationoftheflywheelifitisnotcalibrated,oraftersomerepairs



www.class4exam.comCamshaftMethod:

Thecamshaftwindowoftheenginecanbeopenedupandthecamshaftinspected.Thecamoftheenginehasabasecircle,andaccelerationanddwellperiods.Iftherollerofthefollowerisatthebasecircle,thentheparticularvalveisclosedbyspringaction.Whenboththeexhaustvalveandtheinletvalvefollowerareonthebasecircle,thentheunitisalsoatTDC.ItmustberememberedthatasafourstrokeenginehastworotationsofthecrankshaftthereisoneinjectionTDCwheretheinjectionandthecombustiontakeplace.ThesecondtimethepistonisatTDCiswhentheexhaustingofthefluegasestakesplace.ItisveryimportanttoidentifythecombustionTDC,astappetshavetobeadjustedatthatpoint.

www.class4exam.comCamProfile

CrankcaseMethod:

Inthismethodthecrankcasedoorsareopenedupandthepistonisvisuallycheckedwhetherisgoingupordown.Thisisthesurestmethod,butabitcumbersome.Itshouldbeusedwhenyouhaveastrongdoubtabouttheothermethods.



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:



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.



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



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



holesinthembutiftheydo,thenadiscwithoutanyholesis

www.class4exam.comfittedatthebottomofthestack.



www.class4exam.comPurifiersandClarifiersdifferonlyinthatclarifiersarenotsetuptoremovewater.Theirdesignaresimilartothepointthatmostpurifiersfoundonboardcanbeconvertedtouseasaclarifierwithsimplealterationofthegravitydisc



Q30)HOWTOSELECTDAMNRINGFORPURIFIER?

ANS)Fromthemonogramprovidedwithmanual,whichisdrawnwithrespecttoviscosityofoil&whichsizedamnringtobeused.

Ifmonogramnotthere,then

www.class4exam.coma. ChiefEngineersexperiencewillcomeintouse.



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



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.



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



(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



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.



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?



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.



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.



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.



Soasyoumusthavenoticed,therearetwovalvesincloseproximitynamelymaininjectionvalveandbilgeinjectionvalve.Bothofthemhavetheirownindependentcontrols.Thediameterofthebilgeinjectionvalveiskeptnearly66%ofthemainvalvediameter,whichdrawswaterdirectlyfromtheseathroughthegrid.Thisisalegalrequirementthatthediameterofthisinjectionvalveisatleast2/3timesthemainsuction,thoughitcanbemorealso.

Hencetheinjectionvalveisanarrangementwherethemainseachestcanbebypassedincaseofemergencysothatinsteadofthesea,watergetsdrawnfromwithintheshipitself.

Thereisastrainerattachedtothebilgeinjectionvalveandthepumpusedforthisvalveisnormallythelargestseawaterpump(orpumps)availableintheengineroom.Hencethis

www.class4exam.comvalveisusedtosuckseawaterfromoneofthelowestpointsintheengineroom,whichyoucanalsoseefromthesketch.Thisbasicallymeansthatwhenyouneedtoremovealotofwaterfromtheship,yousimplyneedtoopenthisvalveandrunthebigpump/s.



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.



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.



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,



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



thestartingandstoppingoperations.Thistypeofwearwouldalsobeaccompaniedbyaslowdecreaseinoilpressureoveraperiodoftime.

Openingupofcylinderheads.Incertaintypesofreciprocatingcompressorsthecylinderheadhavetoberemovedforthechangingofthefirststagesuctionanddischargevalves.Whenthecylinderheadisputbackthecorrectthicknessofthecylinderheadgasketsshouldbeusedotherwiseitwouldchangethebumpingclearance.

Wearonthemainbearings.Overallwearonthemainbearingswouldlowerthecrankshaftandwouldthuslowerthepistonandincreasethebumpingclearances.

www.class4exam.comSignificanceofBumpingClearance:

Thebumpingclearancemustbeadjustedproperlyotherwisethereisriskofdamageandlossofefficiency.Ifthebumpingclearancewerelessthevolumetricefficiencywouldincreasebutthereisriskofthepistonhittingthecylinderhead,especiallywhenthecompressorisunloadedduringstartandstopping.

Ontheotherhandtoplaysafe,theengineergivesfewmillimetersofextraclearance,thevolumetricefficiencyofthecompressorwoulddecrease,thefreeairdeliverywillfallandtherewillbeafallinpressure.Theextraclearancewouldresultinasmallvolumeofairbeingreexpandedeverytimecausingincreaseinairtemperature,fallinefficiencyandoverheatingofthecompressors.Thiswouldendangertheshipduringmaneuveringbysuddenlossofpropulsion.

HowtoCheckBumpingClearance:

Thebumpingclearancecanbecheckedbythefollowingmethods:

Incaseasuitableopeningisavailablethepistoncanbebarredtothetopdeadcentreandthenfeelergaugescanbeputinsideandtheclearancescheckedattwothree



points.

Themoreconvenientmethodistotakeleadwirefromtheenginestoreandmakeasmallballbasedontheexpectedclearanceandputitbetweenthepistonandtheheadfromthevalveopening.Thenthepistonis

www.class4exam.comslowlyturnedtothetopdeadcentrewiththehelpofaTommybar.Afterthatthepistonisagainturneddownandtheleadwireballisextractedandthethicknessmeasuredwiththehelpofamicrometer.Thismeasurementwouldgivethebumpingclearance.

Thecaution,whichmustbeobservedinthesemethodsisthat,theclearancesofthemainandthecrankpinbearinghavenotbeentakenintoaccount.Thecorrectmethodisthusthatafterturningthepistontotopdeadcentrethepistonconnectingrodmustbejackedupwiththehelpofacrowbar.Itisonlyafterthishiddenclearancehasbeenaccountedfor,willthecorrectbumpingclearancebefound.

HowtoAdjusttheBumpingClearance:

Thebumpingclearanceoncefoundtobeincorrectwouldhavetobeadjusted.Themethodsofadjustingthebumpingclearancesareasfollows:

Thecylinderheadgasketscanbechangedtoadifferentthicknessthusalteringthebumpingclearance.

Theshimsbetweenthefootoftheconnectingrodandthebottomendbearingcanbechangedthuschangingthebumpingclearance.

Howeverafteradjustingthebumpingclearancetheclearanceshouldbecheckedonceagaintomakesurethatthereisnoerrorandtheclearanceiswithintherangeasspecifiedbythemanufacturers.Itmustbestressedthatcompressorsareunforgivingandincorrectlymaintainedcompressorshaveclaimedmanyalives



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



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.



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.



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



depositsinside.

Cleaningthesteamsideofgaugeglass:

CloseboththecocksSandW.NowopenthecockSandopenthedrainvalveDandseethe

steamiscomingout.Thedrainisopenedonlyfor12secondsonlyassteammaydamagethesealingandservicelifedecreases.

Puttingthegaugeglassinnormaloperatingposition:

CloseallthevalvesS,WandthedrainvalveD.NowopenthecockWandletthewaterfillinsidethegauge

glass.NowopenthecockSandthenthelevelcanbeseenasthe

pressureequalizes.



www.class4exam.comQ53)HOWWILLYOUTESTTHECYLINDERRELIEFVALVEOFENGINE?

ANS)Thecylinderreliefvalveisdesignedtorelievepressuresinexcessof10%to20%abovenormal.Aspringholdsthevalveclosedanditsliftingpressureissetbyanappropriatethicknessofpackingpiece.Onlyasmallamountofliftispermittedandtheescapinggasesaredirectedtoasafeoutlet.Thevalveandspindleareseparatetoenablethevalveto

www.class4exam.comcorrectlyseatitselfafteropening.

Theoperationofthisdeviceindicatesafaultintheengine,whichshouldbediscoveredandcorrected.Thevalveitselfshouldthenbeexaminedattheearliestopportunity.

Pressuretestingwascarriedoutonabenchmountedtestrigconsistingofahighpressureaircompressor,airpressurecontrolvalve,andcalibratedgauges.Thereliefvalvewasboltedtothecompressoraccumulatorflangeandtheair



pressureincreaseduntilthevalvelifted.



www.class4exam.comQ54)HOWWILLYOUTIGHTGAUGEGLASSAFTEROVERHAULING?

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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



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.



www.class4exam.comQ59)EXPLAINCRANKCASEEXPLOSION?HOWITISPROTECTED?WHATISCRANKCASERELIEFDOOR?

ANS)Crankcaseexplosionsarealsotheresultofhighoperatingtemperaturesoftheengine.Themaincauseofcrankcaseexplosionsisthedevelopmentofhotspotsatvariousplacesinthecrankcase.Duetothereciprocatingmotionofthepistonthelubricatingoilinthecrankcaseissplashedintheair.Nowitisnecessarythattheflashpointofthelubricatingoilbemaintainedataround200degreeCelsius.Ifthisisnotdonethentherearehighchancesforthe

www.class4exam.comlubricatingoiltocatchfire.

Hotspotsarecreatedinthecrankcaseasaresultof:

Hightemperatureduetothereciprocatingmovementofthepiston,

Increaseinbearingtemperatures,

Sparksenteringthecrankcaseduetoleakypistonringsorpistonblowpast,

Firesintheadjacentscavengetrunks.

Now,whenthesehotspotscomeincontactwiththeoilinthecrankcase,theoilgetsvaporized.Whenthesevaporized



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.



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:



www.class4exam.comEnsureadequatecoolingoftheengine

EnsureproperpurificationandanalysisoflubeoilLubeoilfiltershouldbechangedoverandcleanedasper

scheduleEnsurepropercylinderlubricationbycheckingthecondition

ofpiston,pistonringsandlinerthroughscavengeorexhaustports

Cleanscavengespacesasperscheduleanddrainscavengespaceregularly

MaintainstuffingboxglandingoodconditionBealertandrectifyforanyabnormalnoiseincrankcase

Allsafetyalarmsandtripsfittedonenginetobetriedout



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.



www.class4exam.comAdeflectorisfittedontheoutsideoftheenginetosafeguardpersonnelfromtheoutflowinggases,andinsidetheengine,overthevalveopening,anoilwettedgauzeactsasaflametraptostopanyflamesleavingthecrankcase.Afteroperationthevalvewillcloseautomaticallyundertheactionofthespring.

TheCrankcasereliefdoorsarealsofittedtopreventanydamagetothecrankcaseandingressoffreshairinsidethecrankcase.

www.class4exam.comThecrankcasedoorsarespringloadedvalves,whichliftupincasethereisanyriseofpressureinsidethecrankcase.Oncethepressureisreleasedtheyreseattopreventanyingressoffreshair.Thishelpsespeciallyincaseofanyingressofairthatcanleadtoasecondaryexplosionfollowedbyalotofsurgeanddamagetothecrankcase.

Theopeningpressureandsizesofthevalvesarespecifiedbydifferentclassificationsocieties,dependingonthevolumeofthecrankcase.Thenumberofdoorstobepresentalsodependson



theboreofthecylinder.

Q60)EXPLAINFUNCTIONOFOILMISTDETECTOR?

ANS)TheOilmistdetectortakescontinuoussamplesfromthemainenginecrankcaseandcheckwhetherthesampleconcentrationsofmistarewellbelowthelevelatwhichacrankcaseexplosioncantakeplace.Theoilmistisdrawnintotheinstrumentwiththehelpofsmallfan,whichtakessuctionfromeachcrankcasethroughsamplingtubesprovidedoneachcrankcase.

Theoilmistdetectorconsistsofasmallrotatorwithwhichittakessamplefromonecylinderatatimeandtherotatorthenturnstothenextafterapproximately4seconds.Thesamplefromtherotatorgoestothemeasuredcellandthereferencecelltakessamplefromrestofthecrankcasetoevaluatethedifferenceinoilmist.

Anoverallmistdensityofthecrankcaseisalsomeasuredbycomparingthesampleswiththefreshaironceeveryrotation

www.class4exam.com

ofthesamplingvalveisdone.Abeamoflightfromacommonlampisreflectedthroughmirrorsandoutputismeasuredfrom



aphotocell.

Undernormalconditionstheoutputfromthereferenceandmeasuredcontactissameandhencenodeflectionismeasured.However,adeflectionintheoutputgivesanalarmindicationandthevalverotatorstopsatpositiontoknowwhichchamberhashighmistconcentration.

Someenginesareevenfittedwithslowdownalarmssothatwhentheoilmistalarmsrings,theengineautomaticallyslowsdowntopreventcrankcaseexplosion.

Q61)HOWTHETESTINGOFCRANKCASERELIEFDOORISCARRIEDOUT?

www.class4exam.comANS)*THEMAINTESTINGOFCRANKCASERELIEFDOORISCARRIEDOUTATSHORE.

*BUTTHENALSOSOMEOFTHINGSTOBEINSPECTEDDURINGCRANKCASEINSPECTION:

1. Checkcrankcaseexplosionreliefdoorwiremesh(shouldbewet),springtension,andsealingringcondition.

2. Checktheproperfunctioningofspringofvalvebyinsertingstudinit.

3. Visualconditionofvalve.



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?



ANS)Agearpumpusesthemeshingofgearstopumpfluidbydisplacement.[1]Theyareoneofthemostcommontypesofpumpsforhydraulicfluidpowerapplications.Gearpumpsarealsowidelyusedinchemicalinstallationstopumpfluidwithacertainviscosity.Therearetwomainvariations;externalgearpumpswhichusetwoexternalspurgears,andinternalgearpumpswhichuseanexternalandaninternalspurgear.Gear

www.class4exam.compumpsarepositivedisplacement(orfixeddisplacement),meaningtheypumpaconstantamountoffluidforeachrevolution.Somegearpumpsaredesignedtofunctionaseitheramotororapump.Asthegearsrotatetheyseparateontheintakesideofthe



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.



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



underpressure.

Becausethegearsaresupportedonbothsides,externalgearpumpsarequietrunningandareroutinelyusedforhighpressureapplicationssuchashydraulicapplications.Withnooverhungbearingloads,therotorshaftcan'tdeflectandcauseprematurewear.

Q64)EXPLAINWORKINGOFCENTRIFUGALPUMP?ANS)Centrifugalpumpprinciplesandworkingprocedure



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Apumpisamachineusedtoraiseliquidsfromalowpointtoahighpoint.Inacentrifugalpumpliquidentersthecentreoreyeoftheimpellerandflowsradiallyoutbetweenthevanes,itsvelocitybeingincreasedbytheimpellerrotation.Adiffuserorvoluteisthenusedtoconvertmostofthekineticenergyintheliquidintopressure.

Thearrangementofacentrifugalpumpisshowndiagrammaticallyinfigurebelow



Fig:Centrifugalpumpingoperation

Avertical,singlestage,singleentry,centrifugalpumpforgeneralmarinedutiesisshowninFigurehere.Themainframeandcasing,togetherwithamotorsupportbracket,housethepumpingelementassembly.Thepumpingelementismadeupofatopcover,apumpshaft,animpeller,abearingbushandasealingarrangementaroundtheshaft.Thesealingarrangementmaybeapackedglandoramechanicalsealand

www.class4exam.comthebearinglubricationsystemwillvaryaccordingtothetype



www.class4exam.comAverticalmultistagesingleentrycentrifugalpumpusedfordeepwellcargopumpingisshowninFigurebelow.Thiscanbeconsideredasaseriesofcentrifugalpumpsarrangedtosupplyoneanotherinseriesandthusprogressivelyincreasethedischargepressure.Thepumpdriveislocatedoutsidethetankandcanbeelectric,hydraulicoranyappropriatemeanssuitableforthelocation.



www.class4exam.comAdiffuserisfittedtohighpressurecentrifugalpumps.Thisisaringfixedtothecasing,aroundtheimpeller,inwhichtherearepassagesformedbyvanes.Thepassageswidenoutinthedirectionofliquidflowandacttoconvertthekineticenergyoftheliquidintopressureenergy.Hydraulicbalance

www.class4exam.comarrangementsarealsousual.Someofthehighpressuredischargeliquidisdirectedagainstadrumorpistonarrangementtobalancethedischargeliquidpressureontheimpellerandthusmaintainitinanequilibriumposition.

Centrifugalpumps,whilebeingsuitableformostgeneralmarineduties,arenotselfprimingandrequiresomemeansofremovingairfromthesuctionpipelineandfillingitwithliquid.Wheretheliquidtobepumpedisatalevelhigherthanthepump,openinganaircocknearthepumpsuctionwillenabletheairtobeforcedoutasthepipelinefillsupundertheactionofgravity.Ifthepumpisbelowseawaterlevel,andseawaterprimingispermissibleinthesystem,thenopeningaseawaterinjectionvalveandtheaircockonthepump



willeffectpriming.

Alternativelyanairpumpingunitcanbeprovidedtoindividualpumpsorasacentralprimingsystemconnectedtoseveralpumps.Thewaterringorliquidringprimercanbearrangedasanindividualunitmountedonthepumpanddrivenbyit,orasamotordrivenunitmountedseparatelyandservingseveralpumps.Theprimerconsistsofanellipticalcasinginwhichavanedrotorrevolves.TherotormaybeseparatefromthehubandprovidetheairinletanddischargeportsasshowninFiguredown.Alternativelyanotherdesignhastherotorandhubasonepiecewithportsonthecover.Therotorvanesrevolveandforcearingofliquidtotakeuptheellipticalshapeofthecasing.Thewaterring,beingelliptical,advancesandrecedesfromthecentralhub,causingapumpingactiontooccur.Thesuctionpipingsystemisconnectedtotheairinletportsandthesuctionlineisthusprimedbytheremovalofair.Theairremovedfromthesystemisdischargedtoatmosphere.Areservoirofwaterisprovidedtoreplenishthewaterringwhennecessary.

www.class4exam.comFig:Waterringprimer



Whenstartingacentrifugalpumpthesuctionvalveisopenedandthedischargevalveleftshut:thenthemotorisstartedandtheprimingunitwillprimethesuctionline.Oncethepumpisprimedthedeliveryvalvecanbeslowlyopenedandthe

www.class4exam.comquantityof liquidcanberegulatedbyopeningorclosingthedeliveryvalve.Whenstoppingthepumpthedeliveryvalveisclosedandthemotorstopped.

Regularmaintenanceonthemachinewillinvolveattentiontolubricationoftheshaftbearingandensuringthattheshaftsealorglandisnotleakingliquid.Unsatisfactory

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