A centrifugal pump's efficiency is typically decreased under which condition?

The efficiency of a centrifugal pump is commonly reduced when operating at high head conditions. At higher heads, the pump may experience several adverse effects, including increased turbulence and reduced volumetric flow rates. When pumps are designed, they have an optimal operating range where they perform efficiently, and operating outside of this range, especially at higher heads, can lead to an increase in hydraulic losses. Consequently, as the pump works harder to overcome the elevation difference, it can suffer from a drop in efficiency due to the imbalance between the energy supplied by the pump and the useful work it actually performs in moving the fluid.

While operating at low head can also influence pump performance, it is not as significant in terms of efficiency reduction as high head operations. Priming is a necessary condition to ensure proper functioning of the pump and would generally not adversely affect efficiency as long as the pump is primed correctly. When pumping sludge, the viscosity and density of the fluid might affect performance, but it doesn’t inherently lead to a decrease in efficiency in the same way that high head conditions do. Thus, high head scenarios are more directly associated with a notable decrease in centrifugal pump efficiency.