What is a Multistage Pump? A multistage pump is a siphon wherein the liquid courses through at least two impellers fitted in series. As a result, a pump of this kind will have several stages or liquid chambers connected in series. An impeller, a diffuser, and return guide vanes are all contained within the same stage casing for each stage. These impellers are connected in series and rotate on a single shaft that is powered by a motor or other power source. The fluid can only move linearly through the chambers of multistage pumps because of their design.