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Choosing an electric motor power for a pump. 1
- Thread starter sav350
- Start date
Multiply
Flowrate * density * head and divide by the pump's efficiency at that flowrate. Add IMO, about 20 to 25% and you'll get close to sufficient power required. Pick a motor size from the standard sizes available.
Examine performance from start-up speed to maximum operating speed.
Determine if you need additional controls.
Lastly, find some engineer that has experience with pump applications to review your work. Internet answers or supervision don't count. This part is the most important aspect of this problem.
Flowrate * density * head and divide by the pump's efficiency at that flowrate. Add IMO, about 20 to 25% and you'll get close to sufficient power required. Pick a motor size from the standard sizes available.
Examine performance from start-up speed to maximum operating speed.
Determine if you need additional controls.
Lastly, find some engineer that has experience with pump applications to review your work. Internet answers or supervision don't count. This part is the most important aspect of this problem.
Proper units and conversion factors are crucial for power calculation.
Water HP is given by, (gpm x 8.33 x SG x head(ft)/33000)
and Water kW is given by, (head(m) x flow(ltr/min)/6000)
BHP or BKW is calculated by dividing WHP or WKW with efficiency of the pump.
IHP or IKW is calculated by dividing BHP or BKW with efficiency of pump (couplings can be treated as 100% efficient)
Then motor can be selected considering some FOS. (say, 10 to 20%)
Water HP is given by, (gpm x 8.33 x SG x head(ft)/33000)
and Water kW is given by, (head(m) x flow(ltr/min)/6000)
BHP or BKW is calculated by dividing WHP or WKW with efficiency of the pump.
IHP or IKW is calculated by dividing BHP or BKW with efficiency of pump (couplings can be treated as 100% efficient)
Then motor can be selected considering some FOS. (say, 10 to 20%)
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1
- #4
If you have selected the pump from a pump performance curve it would normally have the power curve shown as well, if not, the easy way to calculate the power at the point of consideration is,
Q*H*SG/102*E = kW
Q = (litres/sec)
H= (metres)
E= pump efficiency - as a decimal - at the point of consideration
S.G. = 1 if water
102 = constant to assemble all the other factors and conversions.
This gives you the power requirement at the "duty point", from here you need to consider a number of other factors which comes down to experience of pumping systems;
can the pump run-out further on its performance curve at any time during operation?
is the pump duty constant or variable?
is S.G. constant?
what are the start-up charactristics of the system?
is voltage to the motor constant?
factor in ambient temperature and altitude and dusty operating conditions if applicable.
What is important is to select a motor that will not be forced to operate in an overload condition at any point within its application / hydraulic range - if this is not possible other measures must be introduced to protect the motor.
In most cases, the motor size is dictated by what is available from the standard range of motors up to around 200kW over this size you can usually specify the rating that you need.
Trust this helps.
Naresuan University
Phitsanulok
Thailand
Q*H*SG/102*E = kW
Q = (litres/sec)
H= (metres)
E= pump efficiency - as a decimal - at the point of consideration
S.G. = 1 if water
102 = constant to assemble all the other factors and conversions.
This gives you the power requirement at the "duty point", from here you need to consider a number of other factors which comes down to experience of pumping systems;
can the pump run-out further on its performance curve at any time during operation?
is the pump duty constant or variable?
is S.G. constant?
what are the start-up charactristics of the system?
is voltage to the motor constant?
factor in ambient temperature and altitude and dusty operating conditions if applicable.
What is important is to select a motor that will not be forced to operate in an overload condition at any point within its application / hydraulic range - if this is not possible other measures must be introduced to protect the motor.
In most cases, the motor size is dictated by what is available from the standard range of motors up to around 200kW over this size you can usually specify the rating that you need.
Trust this helps.
Naresuan University
Phitsanulok
Thailand
Just a clarification for something that may or may not be obvious to all. There would be no point in selecting a motor power rating for a pump's maximum flow capacity, if the piping or process flow will not also reach that capacity. Superimpose the pump's curve on the system curve to find the maximum power required from the perspective of operating the system as a whole.
Going the Big Inch!
Going the Big Inch!
rotaryengineer1
Mechanical
What is the importance of minimum continuous stable/thermal flow for a centrifugal pump?
Best explanation I've seen is here,
Going the Big Inch!
Going the Big Inch!
Also try for good information on pumps.
Geoffrey D Stone FIMechE C.Eng;FIEust CP Eng
Geoffrey D Stone FIMechE C.Eng;FIEust CP Eng
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