How vertical multistage pump types work

Centrifugal pump dictionary

Pumps are referred to as multi-stage when several impellers are arranged one behind the other and the flow rate flows through them in series.

The delivery head of a single-stage centrifugal pump is essentially determined by the design of the impeller and the circumferential speed. If the speed cannot be increased further due to other boundary conditions and if the increase in the impeller diameter leads to very low specific speeds and thus to uneconomical degrees of efficiency, the delivery head can be increased economically by connecting several stages in series (see also series operation). By changing the number of stages with otherwise constant dimensions and speeds, the flow rate of such a multi-stage pump does not change, while the power requirement and the delivery head are proportional to the number of stages.

An example of a pump with several similar stepped housings connected in tandem in a tandem arrangement is the articulated pump. This design is often used in power plant technology, e.g. as a boiler feed pump and in industrial applications where high pressures are required.

The individual stages of a multistage pump do not have to be in tandem, but can also be arranged in pairs or in groups to better compensate for the axial thrust (see counter-rotating pump). A typical example of this is the pipeline pump. Multi-stage pumps open up the higher pressure ranges of the grids of series with economic means. Further advantages of the multi-stage design are the simple tapping after a stage or the provision of empty stages for later pressure increases.

A disadvantage is the increasing sensitivity of the pump rotor to external or self-exciting vibrations with a very large number of stages.

Each stage has an impeller, a stator and (usually combined with this) a return blade (see return blade), all of which can be accommodated together in a stage housing. Regardless of the number of stages, an inlet housing with radial or axial inlet connection and the last stage in the pressure housing, which contains the relief device and a shaft seal, are arranged before the first stage. Only the common pump shaft, connecting screws and base plate have to be adapted to the respective number of stages. see Fig. 1 Multi-stage pump

Fig. 1 Multi-stage pump: with axial inlet connection