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EquipmentandOptionalAccessories-WhatTheyDo
POPSAFETYVALVE
Youmusthavea popsafetyvalveonyourboiler.Steamexpandsasitisheated.
Ifthereisno placeforthesteamtoexpandinto,pressurewillbuildupinsidethe
boilerandsystem.Shouldthishappen,thepopsafetyvalvewillautomatically
openata pre-determinedpressure.Thiswillrelievethestrainontheboilerand
system.Runa pipefromthesafetyvalveoutlet(pipemustbesamesizeasoutlet
andtheopenendmustnotbethreaded)toan opendrain,tuborsink,or other
suitabledrainagepointnotsubjecttofreezing.Failuretodosomaycausewater
damageorinjuryshouldreliefvalverelease.Donotcapoffthedrainlinefrom
thisvalve!Eachpopsafetyvalveisprovidedwitha liftingdevicefortestingand
shouldbetestedmonthlyduringtheheatingseason.Refertosafetyvalve
manufacturer'sinstructionspackagedwithsafetyvalve.
STEAMPRESSUREGAUGE
Everysystemshouldhavea pressuregaugeinstalledintheboiler.Thisgauge
enablesyoutomonitorthepressureinthesystem.Ifthesafetydevicesfailtoshut
offyourboileratthepropersettings,notifyyourservicetechnicianimmediately
WATERLEVELGAUGE
Thewaterlevelin theboilercanbeseenthroughtheglasstubeinthewater
levelgaugeatsideofboiler.Correctcoldboilerwaterlevelisstampedonside
jacketpanel.Whenmakingsteam,thewaterlevelwilldroponetothreeinches.
Thewaterlevelshouldbecheckedregularly.
STEAMPRESSURECONTROL
Thesteampressurelimitcontrol(pressuretrol)shutsofftheoiltotheburnerifthe
steampressureintheboilerreachesthecut-offsetpoint(i.e.thesumofthecut-in
andthedifferentialsetpoints).Burnerretireswhenthesteampressuredropsto
thecut-insetpoint.Systempressurerequirementsarebasedonthesizeand
conditionofthepipes,andtheload.
Forgoodsystemoperation,thecut-insettingofthepressuretrolshouldnever
be less than twicethe systempressuredrop. In a typicalsinglefamily
residencewith a cleanonepipeheatingsystemand castiron radiation,this
meansthatthecut-inwillusuallybesetattheminimumsetting,i.e._/2psi.
Steamradiationis usuallysizedbasedon squarefeet of equivalentdirect
radiation(EDR).Thisis basedon a steampressurein theradiatorofjust less
than1 psi.Therefore,in our examplesystemfromabove,wewouldsetthe
differentialadjustmentat1psi,i.e.thesteampressurerequiredintheradiators.
Thiswillgiveusa cut-offsetpointd 1_12psi.
Theaboveisan exampleofa typicalonepipesystem.Forlargersystemsor
othertypesofsystemssuchastwo pipesystems,or systemswithconvectors
or fan coil units,the pressuretrolsettingswill needto be determinedon a
system-by-systembasis.
The cut-insetpointisdeterminedbythesystempressuredroptothefurthest
radiatoror terminalunit.Doublethesystempressuredropasa safetyfactor,
resultinginthe rulethatthecut-insettingshouldneverbe lessthantwicethe
systempressuredrop.
Thedifferentialset#ointisthesteampressurerequiredattheterminalheating
units.
Nowyourboilerwill operatein the correctpressurerange.It will maintain
enoughsteampressuretosendthesteamouttothefurthestradiator,andnot
go overtheoptimumsteampressurethatisrequiredattheradiators.
67D-t LOWWATERCUT-OFF
Thefloat-typelowwatercut-offshutsofftheburnerwhenthewaterlevelis
belowasafepoint.Theburnerwillstartwhenthewaterisrefilledtoa
minimumsafelevel.
WATERFEEDER(Optional)
Awaterfeederworkswiththelowwatercut-off(LWCO)tomaintaina
minimumsafelevelofwaterforboileroperation.It'susedtokeeptheboiler
runningbycompensatingforminorevaporativesteamleaks,andtoprevent
freeze-upsifthehomeownersareawayanda returnlineshouldspringa
leak,Theautomaticwaterfeederisa safetydevice,nota
convenienceitem.Itisnotdesignedtomaintaina "normal"waterline.The
waterfeederdoesnottaketheplaceofa responsiblepersonmonitoringand
maintainingthe"normal"waterline.Steamboilersrequirepersonal
attention.
Four electricwater feedersare offeredby McDonnell-Millerwhichare
compatiblewiththe 67D-1LWCO.The model#101Aand #WF2-U-120
waterfeedersareusedwith120voltwiringcircuits,asfoundanthissteam
boiler.The McDonnell-Millermodel#101A-24and#WF2-U-24are used
with 24 volt circuits,which may be usefulin a retrofitinstallationwhich
alreadyhasa 120voltto 24volttransformer.
TheWF2-U-120and WF2-U-24(Uni-Match)waterfeedersareequipped
witha solidstateelectroniccontrolwhichfeedswaterwhensignaledbythe
LWCO.Thewaterfeedrateisfieldadaptablefar 1,2, or 4 gpm.These
waterfeedershavean adjustableslideswitchtomatchthetimingcyclean
theLWCO.Whenusinga McDonnell-MillerLWCOtheslideswitchneeds
toselectposition#1.Thetimingcyclecreatesaninitialdwellperiodofone
minuteto allowcondensateto be returnedto the boiler.If afterthedwell
periodthewaterhasnatreachedtheminimumsafelevelandcompletedthe
LWCOcircuit,thenwaterisfedattheselectedflowratefaroneminute.The
dwellpedodistheninitiatedagainfaroneminute.Ifthewaterlevelhasstill
not reachedthe minimumsafe level,then wateris addedagain at the
selectedflowrateforoneminute.Thiscyclecontinuesuntilwaterreaches
the minimumsafe leveland the circuitis completed.DunkirkRadiator
recommendsusinga Uni-Matchwaterfeederataflawrateof1or2gpm.If
the steamboilerrequireshigherflow rateson a regularbasisa service
technicianshouldbenotified.
The1OlAwaterfeedermaybe used,howeverthewaterfeedrateistoo
high and needsto be regulatedor throttled.The IO1Awillfeedupto 6
gpm,muchgreaterthanthedesiredflowrateof1-2gpm.Also,thereisno
dwellperiodto providea marginfor condensateto returnto the boiler.
Thesetwofactorsincreasethechancesofoverfeedingwatertothesteam
boiler.Excessivewaterinthesteamboilerwillproducenoise
Consultthe water feedermanufacturer'sinstallationguidelinesfor more
detailson waterfeederselection,recommendedpipingarrangement,and
start up procedures.Dunkirk Radiator supports McDonnell-Miller's
recommendationtoarrangetheinstalledpipingsoa brokenuniontestcan
beimplemented.
DRAINVALVE
Thismanualvalveprovidesa meansofdrainingallwaterfromtheboilerand
system.Itshouldbeinstalledinthe3/a"teewherethewatersupplyline
enterstheboiler(Fig.8).Youcanalsousethisvalvetolowerthewaterlevel
ifitistoohigh.
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