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LMVSeriesTechnicalInstructions 

DocumentNo.LV5‐1000

SCCInc. Page31 Section6

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MethodshowninFigure6‐13:

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PressureP1relativetopressureP2(differentialpressureacrosstheFGRdamper)ismoreconstantwith

firingrate.DifferentialpressurewillbegeneratedacrosstheFGRdamperatlowfirebyusingthe

suctionofthebloweragainsttheairdamper.ThedifferentialpressureacrosstheFGRdampercanalso

beadjustedwiththespeedoftheVFD.Asfiringrateincreases,P2willincrease(lessvacuum)andP1

willincreaseduetoincreased

pressurebehindthestackdamper,yieldingamoreconsistentdifferential

pressure.Asaresult,theFGRdampercanbesizedmoreappropriatelyandshouldofferbettercontrol.

Otherpointstoconsider:

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1. IfusingO

trim,theeffectthatthetrimhasonFGRflowcanbeadjusted.Threepossibilities:

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a. Ifonlytheairdamperistrimmed(setto“airinfluenced”), trimmingclosedandreducingairflow

willincreasethevacuumatP2andincreaseFGRflowrelativetoairflow.

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b. IfonlytheVFDistrimmed(setto“airinfluenced”),trimmingslowerandreducingairratewill

reducetheva

cuumatP2andreducetheFGRflowrelativetotheairflow.

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c. Ifboththeairdamper andVFDaretrimmed(setto“airinfluenced”),trimmingclosedshould

keepthevacuumatP2relativelyconstantandkeeptheFGRflowconstantrelativetotheair

flow.

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2. DifferentialpressureacrosstheFGRdamperissignificantevenatlowfiredu

etothevacuum

providedbytheblower.SmallchangesinthedifferentialpressureacrosstheFGRdamperwillcause

smallchangesinFGRflow.FGRflowwillbemorerepeatableascomparedtothemethodinFigure

6‐12,

especiallyatlowtomidfire.

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3. Nofixedairdampersexistfortheblowerintake,andthefixeddamperinthestackmaybeableto

beopenedfurther,reducingtheblowerpressurerequirements.

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