Class IIIPreferencial Test.docx

Class IIIPreferencial Test.docx

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ClassIIIPreferencialTest

ClassIIIMarineEngineerExamination

Boiler

Q.1Whatwillyoudoifnowatershowninthewatergauges?

Checkthewatergauges;ifitblowssteam,thisisaverydangerousemergency.

First,thefireshouldbeimmediatelyextinguishedandtheboilershouldbeisolatedfromthesteamsupplysystem.

Switchoffthefeedpumps.Turnoffthefeedwatervalveandfuelsupplyvalve.Waitfortheslowcooldown.

Checktoseeifthereisanydamagetofurnace,internalstructureandotherpartsoftheboiler.

Checkthetrippingoffuelsupplyvalveasitshouldcutthesupplyoffueloilwhenwaterlevelreacheslowlowlevel

Aftertheproblemisfixed,boilercouldbeputbacktoservice.

Q.2Whatareboilertrips&alarms?

Boilertripsareactionsthatwilloccurunderundesiredsituationofboiler.Boileralarmsareaudibleandvisualsignalaboutaproblemoracondition.

Forexample,whentheboilerisinthelowwaterlevelcondition,alarmwilloccur.Whentheboilerisinthelowlowwaterlevelcondition,tripandalarmwilloccurtogether

Q.3Howtostartuptheboiler?

Firstcheckthesafetyvalves,airvent,manholecover,steamvalve,feedwaterpump,thermometerpressuregaugeandwaterlevelgaugeareingoodcondition.

Ifallareok,opentheairvent.Thencheckthefueloilsystemandcirculatethefueloilwithheatertowarmittotherequiredtemperatureandviscosity.

Thenruntheforcedraftblowertopurgethecombustionareaofanyexplosivegasaccumulation.

Puttheflamespillinlowpositionandopenthefuelvalvetofuelspraynozzle.Thenpresstheignitionswitches.

Ifthefuelfailstoignite,closethefuelvalveandrepeattheprocedure.

Topreventthermalstress,thetemperatureshouldberaisedslowly.Also,inordertolettheairtoreleasefromthesystem,theairventshouldbekeptopened.

Whenthepressurebuildsup,oneshouldclosetheairventandturntheflamespilltohighposition.

Oncetheservicepressureisreached,thesteamvalveshouldbeopenedslowly.Ifnecessary,openthesteamvalvetooiltankcarefullyinordertopreventwaterhammering.

Q.4Howtotriptheboiler?

Lowlowwaterlevel,highsteampressureandflamefailurewillalsotripouttheburner.

Q.5Whatisboilerblowdown&whyisitneeded?

Blowdownoftheboilerisdonetoremovescumandbottomdeposits.Thismeansthatblowdownisdoneeitherforscumorforbottomblowdown.

Thereasonsforboilerblowdownare:

1.Toremovetheprecipitatesformedasaresultofchemicaladditiontotheboilerwater.

2.Incaseofpollutionfromseawater,regularblowdownisnecessarytolowthechloridelevel.

3.Toremovesolidparticles,dirt,foamoroilmoleculesfromtheboilerwater.Thisismainlydonebyscumvalveandtheprocedureisknownas“scumming.”

4.Toremoveexcesswaterincaseofemergency.

chroide

Q.6Whatisboilerwatertreatment&whyisitneeded?

OnpacificJava,thechemicalsMULTI-PLUSandOXYTREATarenewlyemployed.MULTI-PLUSisforaddingphosphateandalkalinitytominimizescale-formation,corrosionandsludgeaccumulation,whileOXYTREATisforaddingtannintoremoveoxygeninthesystem.Byblowingdowntheboiler,theprecipitatescanberemoved.

Liquidtreate:

precipitates,alkanity

Condensate:

Ph

Treatmentisneededbecauseformingofscaleandcorrosionwouldreduceefficiencyanddamagetheboiler.

Scalewouldthermallyinsulatetheheatingsurface,sorisethemetaltemperatureandtheexitgastemperature.

Corrosionwouldthinnerthemetal,orevenmadeholesontubesorsurfaces,soastoendangertheboilerstructure.

Q.7Howtoblowboilerwatergaugeglass?

Checkfortheleakofthecocks.Firstcloseteamandwatercocks,openthedrain,nothingshouldblowoutifsteamandwatercocksarenotleaking.

Inordertocheckthewatercockconnectiontotheboilerisclear,openandclosethewatercocktoseeifwaterblowout.

Inordertocheckthesteamcockconnectiontotheboilerisclear,openandclosethesteamcocktoseeifsteamblowout.

Closethedrain.

Openthewatercock.Watershouldthengraduallyriseuptothetopofthegaugeglass.Thenopenthesteamcockandthewaterintheglassshouldfalltothelevelofthewaterintheboiler.

Q.8Describehowtomanualignitetheboiler?

Firstchecktheboilerpressureandtemperatureareinnormalconditionunderheatingfromtheeconomizer.

Circulatetheboilerfuelthroughtheheatertoensuresuitabletemperatureandviscosityisreached.Checkforthepressureofthecirculatedfuel.

Thenswitchthecontroloftheboilerintomanual.Thenstarttheforceddraughtfanandpasstheairthroughthefurnaceforseveral5-15minutestopurgeitofanyexhaustgasoroilvapors.

Thenmanuallyadjusttheairinputintothelightingupmode,openthefuelvalve,presstheignitionbutton,thenpressthefuelinjectionbuttonandthenleavetheignitionpoweroftheboiler.

Thenadjustcontroltonormalservicesothattheairinputandotherparametercouldbeputintonormalservice.

Checktoseeiftheflameissteady.

Q.9Whatarethereasonscausedlowlowwaterlevel?

Lowlowwaterlevelmaybecausedbymanyreasons:

1.Blowdownvalveisaccidentallyopened

2.Feedwatersystem-feedtankisempty,feedpumpfailure,automationcontrolfailureorotherisolationfromthefeedsystem

3.Seriousleakageonthewatercontactingarea

Q.10Whatisboilercarryover（priming）?

Itisaharmfulconditioninwhichwateriscarriedoverfromtheboilertothesteamspace.

Causeofitmaybecontaminationofboilerwaterbyexcessofsaltsoroil.Foamingoccurbecauseofthem.Also,toohighofthewaterlevel,excessiveboilerloads,andsuddenloadchangescouldalsoleadtothisproblem.

Ifitreallyhappens,performthewatertestandchecktheresult,checktoseeanycontaminationforthewatertreatmentequipment,chemicalandtheprocedure.Checkthesteamloading,checktheoperatortoseeifhehavemadeanysuddenloadchangesbefore,etc..

Q.11Whatiscross-blow?

Crossblowisblowingthesteamthroughthesteamterminalcockandsteampipe,tothewatercock,throughtheglasscolumntothedrain,andalso,blowthewaterthroughthewaterterminalcockandwaterpipe,tothesteamcock,throughtheglasscolumntothedrain.

Opensteamterminalcock,watercockandthedrain,closeothercocks,thesteamterminalcock,steampipeandthecolumnareclear.Thenclosebackandopenwaterterminalcock,steamcockanddrain,closeothercocks,thewaterterminalcockandwaterpipeareclear.

Q.12Sketchtheboilerintersstructure&explainsthedifferencebetweenfiretubeboiler&watertubeboiler.

MainEngine

Q.13Whatarethecausesofcrankcaseexplosion,1st&2ndexplosion?

Forthefirstexplosion,usuallyahotspotcouldbepossiblycreatedinthecrankcase.Ifthehotspotcomesincontactwiththelubricatingoil,vaporizationtakesplace.Thevapourthencirculatestoacoolerplaceandcondensesintowhiteoilmist.Thewhiteoilmistwouldaccumulatetocreateahigherconcentrationofthemist,andupontheexplosivelimitisreached,thecrankcaseexplosionoccur.

Theprimary（first）explosionproducesashockwavewhichpropagatesinsidethecrankcaseandithasabreakingeffecttoreducethesizeofoildroplets,producingmorefuelforignition.Thepressureisfollowedwithalowpressureareawhichtriestosuckmoreairfromoutside.Ifthereisleakfromreliefvalve,thestuffingboxandcrankcasevent,agoodenvironmentwithmorefewandairwouldbepresent.UsuallythecrankcasedoormayberutureThehotspotthenignitetheflameandcauseaveryservedamageintheengineroom.

Q.14Whatthecausesareofscavengefire?

Thecauseofscavengefireisblow-byofcombustionproductbetweenlinerandpistonintothescavengeairspaces.Thisfoulingwillbegreaterifsootisproducedbecauseofincompletecombustionofthefuelinjected.

Therearesomecausesofblow-byofcombustionproduct,theyare

Worn,stickingorbrokenpistonrings,

Lubricatingquillsonlinerarenotworking,

Damagetotherunningsurfaceofliner,

Thesymptomsincludessurgingofturbocharger,risesofscavengeairtemperatureandexhausttemperature.

Thisproblemcouldbepreventedbycarefulmaintenance,whichincludesdrainingthescavengecock,regularinspectionsandcleaningofscavengespaces

DetailrefertoMarineEngineeringSeries–DieselEnginesA.J.Wharton

Q.15Comparesthe2-stroke&4-strokeengineadvantages&disadvantages.

Fora2-strokeengine,1strokeisforcompressionofgasandexplosion,anotherstrokeisfortheexhaustgastoleaveandthefuel-airmixturetobeinsertedintothecylinder.

Fora4-strokeengine,thereis1strokeforcompressionandthenexplode,1strokeforreturn,1strokeforpushingexhaustgastoleave,andthelast1fortheairandfueltobeinsertedintothecylinder.

Theadvantagesof2-strokeengineincludeshigherpowertoweightratioandlessmovingpartssuchasexhaustvalve,however,theremaybeproblemoffuel-airmixtureescapedwithexhaustgasasthereisrelativelyshortertimeforscavengingtotakeplace.

Theadvantageof4-strokeengineincludeslesschanceforthefuel-airmixtureescaped,butthereisaproblemoflowpowertoweightratio.

Q.16WhatisA/Escraperringfunction?

/Whythelubeoillevelsofmainenginesumptanksuddenlydropdownrapidly?

Oilscraperringisonthepistonthatscrapestheexcessoiloffthelinerwallonthedownstrokeofthepiston.Thisisdonetoremoveexcessoilfromcombustionchambertoenhanceauniformoillayerformation.

Thelubeoilleveldropmaybecauseofleakagefromsumptankorburningofthelubeoil.

Q.17Whatwi