Discharge Recirculation (Off-Design Operation)

An undesirable flow condition that occurs at the discharge of a centrifugal pump impeller due to off-design operation. Discharge recirculation occurs when high-pressure flow streams re-enter the impeller on the low-pressure side of the impeller vane. Caused by the pump operating back on its curve, or with an inlet restriction. The reverse flow within the impeller passage shears across the outgoing flow, sets up vortexes along the pressure wall of the impeller, and causes cavitation along the pressure wall and shrouds adjacent to the impeller outlet.