Suction Recirculation (Off-Design Operation)

An undesirable flow condition that occurs at the inlet of a centrifugal pump impeller due to off-design operation. Suction recirculation is a condition where, at some reduced flow rate, the impeller eye becomes too large for the net through flow, and the inlet tip speed becomes high enough to cause the flow in the inlet portion of an impeller to separate from the vanes at the periphery and be ejected upstream, opposite to the direction of net flow entering the impeller, often well into the suction pipe. This forms eddies and vortexes within the impeller inlet and prerotation of the liquid entering the pump. Suction recirculation also causes the formation of very intense vortexes between the impeller vanes, which have high velocities at their core, and this consequently lowers the static pressure at that location. This can lead to intense cavitation accompanied by severe pressure pulsations and noise that can be damaging to the operation of the pump, and to the integrity of the impeller material.