Why do pumps require minimum flow and how is it ensured?

Minimum flow prevents: overheating (energy dissipates as heat when not transferred to fluid), cavitation and recirculation at impeller eye, mechanical damage from vibration and hydraulic forces, and bearing damage. Minimum flow is typically 10-30% of BEP flow depending on pump design. Methods to ensure: continuous recirculation line with orifice (simple but wastes energy), automatic recirculation valve (opens below setpoint), minimum flow control valve, or variable speed operation that reduces speed at low flow.