Suction recirculation can undermine operation of a centrifugal pump at low flows. The pump’s suction specific speed and suction energy can provide insights about potential difficulties. Variable frequency drives (VFDs) frequently can provide a solution.
Fixing suction recirculation problems often costs money. Typically, getting the funding requires convincing the holder of the purse strings of what’s the real cause of a problem.
Many people have trouble grasping the idea that flow can go backward within a centrifugal pump. Over the years, I’ve often struggled to find a fundamentally correct but simple explanation.