The term ‘stage’ in the context of pumps simply refers to the number of impellers within a centrifugal pump. A single-stage pump uses just one impeller, and a multi-stage pump utilises two or more impellers in hydraulic series. The number of impellers generally correlates to the maximum output pressure that a centrifugal pump can achieve, hence why multistage pumps of either the vertical or horizontal type are utilised in pressure boosting applications (where overcoming static as well as dynamic head is necessitated) whereas single stage pumps tend to be utilised in closed-loop systems such as heating and cooling applications where resistance to flow is much lower.