motor size calculation
motor size calculation
(OP)
Hi,
knowing the Total head for a pump, how do you find out the coorect motor.
I detremined the power consumed by the pump but i am not too sure about the efficiencies to work it out with the efficiencies (pump and motor)
knowing the Total head for a pump, how do you find out the coorect motor.
I detremined the power consumed by the pump but i am not too sure about the efficiencies to work it out with the efficiencies (pump and motor)





RE: motor size calculation
If motor will operate continuously at full load, I believe it is common practice to select motor approx 133% larger than required. This allows some margin for errors in the calculation or unexpected factors which may increase motor load. (better to get one a little to big than a little too small and have to run it overloaded). Also this means that if calculated load is correct, motor will be operating approx 75% - which is often the most efficient point (from motor standpoint) within the motor range.
RE: motor size calculation
RE: motor size calculation
Using the Cameron Hydraulics handbook calculate the brake horsepower. I assume you know the flow in GPM so use the formula bhp=(gpm*H (ft)*sp gr)/(3960*eff) The efficiency number is the pump efficiency and can be found on the curve.
I use two checks.
(1)- I use the 90% rule which means under operating conditions the Hp should not exceed 90% of the nameplate Hp. Talk to your process people about the highest possible flow demand which could involve a larger size impeller in the future. Take this into account when choosing a motor.
(2) - Where small motors are involved I select a non overloading motor. Use the pump curve for the chosen impeller diameter and determine the Hp for the maximum possible flow. Then select the next larger size motor.
Hope this helps
RE: motor size calculation