Multistage Centrifugal Pumps are pumps that have several impellers and diffuser assemblie, positioned in a vertical or horizontal stack. It is possible to stack as many impellers as required however, there are limitations often determined by the horsepower of the motor.
Each impeller passes the water to they eye of the next impeller through a diffuser. The diffuser is shaped to slow down the flow of the water and convert velocity to pressure. Each impeller and matching diffuser is called a stage. As many stages are used as necessary to push the water out of the well at the required system pressure and capacity. Each time water is pumped from one impeller to the next, it’s pressure is increased.
To get more flow, the exit width of the impeller is increased and there will then be less pressure (or head) that the pump will develop because there will be less impellers on a given HP size pump. The pump will always trade-off one for the other depending on the demand of the system. If the system demands more than a particular pump can produce, it will be necessary to increase the horsepower.
Virtually all submersible are “multi-stage” pumps. All of the impellers of the multi-stage submersible pump are mounted on a single shaft, and all rotate at the same speed.