Understanding Pump Curves
The Efficiency Characteristic
The efficiency characteristic informs the user how efficiently the pump converts energy input to the pump into fluid output energy by the pump.
There are actually two efficiencies involved in the total efficiency, the driver efficiency and the pump efficiency. The efficiency for the pump only is reported as the Pump Efficiency Characteristic, and is separate from the motor efficiency.
There are two common styles for reporting the Efficiency characteristic: Line and ISO (International Standards Organization).
The ISO method is clearly superior to the Line method for must purposes because the efficiency is mapped over the entire range of possible impeller trims. The pump user obtains more information from the ISO plot than with the Line plot.
Centrifugal pumps will have one point on the pump curve where hydraulic efficiency is best, this is called the BEP (Best Efficiency Point). Typically BEP will be about 2/3 of the way out from left to right on the head flow curve. At all other flow rates above and below the BEP hydraulic efficiencies are less than ideal.
It is interesting that the pump will run smoothest at the BEP if all other factors are within requirements. This is because at BEP, the impeller is spinning in a hydraulic environment that is most closely approaching good balance than at all other flow rates.
See the last link shown below (BEP) for further information on pump efficiency.
Follow the links below to pages focusing on other types of information provided in the Pump Characteristic and more, including graphs and explanations.
