Siemens LMV51.140C1 - Page 202

TechnicalInstructions  LMVSeries
DocumentNo.LV5‐1000
Section6 Page30SCCInc.
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3. Ifthefixedairinletdampe rand/ orthefixedstackdamperareadjustedtoprovideadequate
differentialpressureacrosstheFGRvalveatlowfire,pressuredropsacrossthesefixeddampersat
highfirewillbehigh,re quiringalargerblower.
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Smallpressurechanges(pressureinsideaboilerroomvsthepressureinthestack)arecommon.These
aretypicallyduetodoorsbeingopenedandclosedin
theboilerroomandconvectiveeffectsinthe
stack.Dependingontheinstallation,thesechangesmightbenon‐existentortheymightbeaslargeas
2”WC.WiththearrangementshowninFigure6‐12,evensmallpressurechangescancausetheFGR
flowtobenon‐repeatable.A
fewexamplesaregivenbelow:
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Example:Atlowfire,thedifferentialpressureacrosstheFGRcontrolvalveis0.2"WC.Someexternal
changeincreasesP1by0.2”WC.Thisrepresentsaverysmallabsolutechangeinpressure,buta100%
changeinth
edifferentialpressureacrosstheFGRcontrolvalvewhichwillleadtoalargepercentage
changeinFGRflow.
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Example:Athighfire,thedifferentialpressureacrosstheFGRcon trolvalveis6.0"WC.Someexternal
influenceincreasesP1by0.2”WC.Thisrepresentsaverysmallabsolutechangeinpressureanda3.3%
changeindifferentialpressureacrosstheFGRcontrolvalve.Thiswillleadtoanegligib
lepercentage
changeinFGRflow.
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Figure6‐12:FGRBurnerwithnoVFDandanAirDamperontheBlowerOutlet
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