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2.2.Idealandrealcharacteristicsofapumpandamotor
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Theprocessofenergytransformationinthepumpisdescribedbytwocharacter-
isticquantities:
-theoreticaldeliveryQ
gtofthepump(seeFormula2.4),
-theoreticaltorqueM
gtdeliveredontothedriveshaftofthepump(seeFor-
mula2.5).Inthatcaseitisassumedthattheshaftofthepumprevolvesat
aconstantspeedn
g,andintheworkingfluiddeliveredfromtheinlettotheoutlet
ofthepump,anincreaseinthep
g±p
o-p
Iisgenerated.
Theprocessofenergytransformationshouldbeanalysedfortwokindsof
thepump:
-fortheidealpumpfeaturingnoenergyloss,
-fortherealpumpfeaturingenergyloss.
Figure2.4apresentstheenergybalancefortheidealpump.Thefigureshowsthatthe
streamsrepresentingtheoreticaldeliveryQ
gtandtheoreticaltorqueM
gtflowthrough
thepumpwithnoloss.
Fig02040Balanceofthecharacteristicquantitiesofthepump.
a)idealpump,b)realpump.
WhatstemsfromFormula(2.4)isthattheoreticaldeliveryQ
gtoftheidealpump,
assumingconstantrotationalvelocityoftheshaftn
g±const,isconstantanddoesnot
dependonloadingthepumpwithpressurep
g.Therefore,Figure2.5adepictschar-
acteristicsoftheoreticaldeliveryQ
gtoftheidealpumpdependingonitsloadp
g,
namelyQ
gt±f(p
g).Thecharacteristicsisillustratedwiththestraighthorizontalline.