Characteristic Curve Best Efficiency Point/Zone

What is Best Efficiency Point/Zone.

It is always advisable to operate pump at BEP (Best Efficiency Point). But most of the time it may not be possible. Hence as a thumb rule, -10% to +10% of BEP (B) is known as BEZ (Best Efficiency Zone) (zone between A-C) .

It is not only economical to run the pump at BEZ(Best Efficiency Zone) (A-C), but it is also called as sweet point of the pump. That means, pump operates smoothly at this zone.

What if pump does not operate at this zone? Well there are many things that take place if pump is not working at this zone. The most important is Vibration. Why? There are many explanations which I will not discuss in depth in this version. Just to satisfy curiosity, cavitation is one of the factor. Design factor is another, where the pump is designed to operate at BEZ(Best Efficiency Zone) where hydraulic radial forces are taken care of. In case pump is operation to right or left of BEZ(Best Efficiency Zone), the hydraulic radial load is not balanced and it is passed to the shaft.

It is advisable to select a pump with duty point on the +10% side (C) i.e. right side of BEP(Best Efficiency Point) in new installation. We can always throttle the pump and bring the SH curve to intersect QH curve at BEP(Best Efficiency Point) (B). This is done in case in future, more demand of flow is required, pump will be still operate within BEZ(Best Efficiency Zone).