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Equipment
and Optional
Accessories
-What They D o
POPSAFETYVALVE
Youmusthavea popsafetyvalveon yourboiler.Steamexpands as it is heated.
Ifthereisno placeforthe steamto expandinto,pressure willbuildup insidethe
boilerand system. S hould this happen, t he popsafetyvalvewillautomatically
openat a pre-determined p ressure. T hiswill relievethestrainon theboilerand
system. R una pipefromthesafetyvalveoutlet(pipemustbe samesizeasoutlet
andtheopenend mustnot bethreaded) t o an opendrain,tub or sink,or other
suitable drainage pointnotsubjecttofreezing.Failureto do somaycausewater
damageor injuryshouldreliefvalve release. D o notcapoff thedrainlinefrom
this valve!Eachpop safety valveis provided witha liftingdevicefortestingand
shouldbe testedmonthly duringthe heatingseason.Refer to safetyvalve
manufacturer's i nstructions p ackaged withsafetyvalve.
STEAMPRESSURE GAUGE
Everysystemshouldhavea pressure gaugeinstalled in the boiler.Thisgauge
enables youto monitor t he pressure in thesystem. I f thesafetydevices failto shut
off yourboileratthepropersettings, n otifyyourservicetechnician immediately
WATERLEVELGAUGE
Thewaterlevelin theboilercanbeseenthroughtheglasstubein thewater
levelgaugeatsideof boiler.Correct c oldboilerwaterlevelis stampedon side
jacketpanel.Whenmaking steam,thewaterlevelwilldroponeto threeinches.
Thewaterlevelshouldbe checkedregularly.
STEAMPRESSURE CONTROL
Thesteampressure limitcontrol(pressuretrol) shutsofftheoil to theburnerifthe
steampressure in theboilerreaches thecut-offsetpoint ( i.e.thesumofthecut-in
andthedifferential setpoints). Burner retires whenthe steampressure dropsto
thecut-insetpoint. S ystem pressure requirements a rebasedon thesize and
condition of thepipes,andtheload.
Forgood systemoperation, t he cut-insettingof the pressuretrol shouldnever
be less than twice the system pressuredrop. In a typical singlefamily
residence with a cleanone pipe heatingsystemand castiron radiation, t his
means thatthecut-inwillusually beset attheminimum setting, i .e._/2psi.
Steam radiationis usuallysized based on squarefeet of equivalentdirect
radiation(EDR).Thisis basedon a steampressure in the radiatorofjust less
than 1 psi. Therefore,in our example systemfrom above,we would set the
differential a djustment at 1 psi, i.e.thesteampressure required in the radiators.
This willgiveusa cut-off s etpoint d 1_ 12 psi.
The aboveis an exampleof a typicalone pipe system.Forlargersystemsor
othertypesof systems suchas two pipesystems, o r systems with convectors
or fan coil units,the pressuretrol settingswill needto be determined on a
system-by-system basis.
The cut-insetpointis determined bythe systempressure drop to the furthest
radiatoror terminalunit. Doublethe systempressuredropas a safetyfactor,
resulting in the rulethat the cut-insettingshouldneverbe lessthantwicethe
systempressure drop.
Thedifferential set#oint i s thesteampressure required at theterminal h eating
units.
Now your boiler will operatein the correctpressurerange.It will maintain
enoughsteampressure to sendthe steamoutto the furthestradiator, a nd not
go overtheoptimum steampressure that isrequired at theradiators.
67D-t LOWWATERCUT-OFF
Thefloat-type lowwatercut-offshutsoff theburnerwhenthewaterlevelis
belowa safe point.Theburnerwillstartwhenthewateris refilled to a
minimum safelevel.
WATERFEEDER(Optional)
A waterfeederworkswiththe lowwatercut-off(LWCO) t o maintain a
minimum safelevelofwaterforboileroperation. I t'susedto keepthe boiler
running by compensating f or minorevaporative steamleaks,andto prevent
freeze-ups if thehomeowners are awayanda returnline shouldspringa
leak,The automaticwaterfeederis a safetydevice,not a
convenience item. Itis notdesigned to maintain a "normal" w aterline.The
waterfeederdoesnottake theplace of a responsible personmonitoring and
maintaining the"normal" w aterline.Steamboilersrequirepersonal
attention.
Four electric water feeders are offered by McDonnell-Miller whichare
compatible with the 67D-1 LWCO.The model#101A and #WF2-U-120
waterfeedersareusedwith 120volt wiringcircuits,asfoundan this steam
boiler.The McDonnell-Miller model#101A-24and #WF2-U-24are used
with 24 volt circuits,which may be useful in a retrofitinstallation which
alreadyhasa 120voltto 24 volttransformer.
The WF2-U-120and WF2-U-24(Uni-Match) w aterfeedersare equipped
with a solidstateelectronic controlwhichfeedswaterwhensignaled bythe
LWCO.The water feed rate is field adaptablefar 1, 2, or 4 gpm. These
water feedershave an adjustable slideswitchto matchthe timingcyclean
the LWCO.Whenusinga McDonnell-Miller LWCOthe slideswitchneeds
to selectposition #1.The timingcyclecreatesan initialdwellperiodof one
minuteto allowcondensate to be returnedto the boiler.If afterthe dwell
periodthewaterhasnat reached the minimum safeleveland completed the
LWCOcircuit,thenwateris fedat theselected flowratefarone minute. T he
dwellpedodis theninitiated againfar oneminute.If thewaterlevelhasstill
not reachedthe minimumsafe level,then water is addedagain at the
selectedflow ratefor one minute.This cyclecontinuesuntilwaterreaches
the minimumsafe level and the circuitis completed.DunkirkRadiator
recommends usinga Uni-Match waterfeederata flawrateof 1 or 2 gpm.If
the steamboiler requireshigherflow rates on a regularbasis a service
technician shouldbe notified.
The 1OlA water feedermay be used,howeverthe waterfeed rate is too
high and needsto be regulatedor throttled.The IO1Awillfeed up to 6
gpm, muchgreaterthanthe desiredflow rate of 1-2 gpm.Also,thereis no
dwell periodto providea marginfor condensate to returnto the boiler.
Thesetwo factorsincrease thechancesof overfeedingwaterto the steam
boiler.Excessive waterin thesteamboilerwillproducenoise
Consultthe water feeder manufacturer's i nstallation guidelines for more
detailson waterfeederselection,recommended p ipingarrangement, and
start up procedures. Dunkirk Radiator supports McDonnell-Miller's
recommendation to arrangethe installed pipingso a brokenuniontest can
be implemented.
DRAINVALVE
Thismanual v alveprovides a meansof draining all waterfrom theboilerand
system. I t shouldbe installed in the3/a"teewherethewatersupplyline
enterstheboiler(Fig.8).You canalsousethis valveto lowerthewaterlevel
ifit istoo high.
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