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2.2.Idealandrealcharacteristicsofapumpandamotor
29
where:
q
s-specificcapacityofthemotor,understoodastheminimumvolumeof
theworkingfluidexpressedincm3whichshouldbedeliveredtothemotorin
ordertheshafttoperformonerevolution,atthesupplypressureequalto
thedischargepressurep
s±p
I-p
o±0,
n
s-rotationalvelocityoftheshaftofthemotor.
Afterimplementingdependency(2.15)inFormula(2.14),andtakingintoaccount
thatω
s±2πn
s,andafterallthenecessarytransformations,theformulaforcalculating
torqueM
stontheshaftofthemotorisasfollows:
M
st
1
2
q
S
s
|'
p
s
(2.16)
Whenanalysingtheprocessofenergytransformationinthemotor,itisneces-
sarytoconsidertwocharacteristicquantities:
-theoreticalcapacityQ
stofthemotor(seeFormula2.15),
-theoreticaltorqueM
stontheshaftofthemotor(seeFormula2.16).
Atthesametime,itisassumedthattheshaftrevolvesattheconstantspeedn
s,
andintheworkingfluidflowingthroughthemotor,adecreaseinpressurep
s±p
I-p
o
isobserved.
Theprocessofenergytransformationshouldbeanalysedregardingtwokindsof
motors:
-anidealmotorwithouttheenergyloss,
-arealmotorwithenergyloss.
Figure2.6apresentstheenergybalancefortheidealmotor.Thefiguredepicts
streams,standingfortheoreticalcapacityQ
standtheoreticaltorqueM
st,whichflow
throughthemotorwithoutanyloss.
Fig02060Balanceofthecharacteristicquantitiesofthemotor.
a)idealmotor,b)realmotor.