Low flow can cause overheating, hydraulic instabilities (suction and discharge recirculation) and mechanical unreliability in centrifugal pumps. To prevent such problems, options include both continuous and automatic (active) low-flow protection systems.

A continuous system is frequently chosen because of its simplicity. It uses a restriction orifice in a return line. This orifice is typically sized in one of two ways. The more conservative approach selects an orifice for the full minimum flow required. The less conservative one sizes the restriction orifice for a rate that, when added to the minimum expected process flow, gives the minimum flow the pump requires.

Because it operates at all times and the pump needs to have a higher capacity than the process alone requires, a continuous system may impose substantial pump and energy costs. Moreover, it

2012-07-17

Back