Siemens LMV51.140C1 - Page 203

LMVSeriesTechnicalInstructions 
DocumentNo.LV5‐1000
SCCInc. Page31 Section6

MethodshowninFigure6‐13:

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:

1. IfusingO
2
trim,theeffectthatthetrimhasonFGRflowcanbeadjusted.Threepossibilities:

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.

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.

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.

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.

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.
















HOME