Rotodynamic pumps - Similarity and design of centrifugal pumps

The design of centrifugal and helical centrifugal pumps is still highly empirical, based as it is on a large number of rules of experimental and statistical origin. This state of affairs is quite logical, since in addition to the main geometric dimensions, a very large number of second-order parameters (around twenty) have to be set to define the complete geometry of the impeller and its immediate environment. These multiple, often arbitrary, choices may be guided by a variety of considerations, such as: flow regularity, reduced overall dimensions, performance optimization (efficiency, NPSH, noise and vibration), stability of characteristics, etc.

We'll look at how similarity coefficients can be used to make the first major choices regarding the free parameters involved in the design of a centrifugal pump impeller. In particular, we'll show how to determine the rotational speed that will lead to suitable efficiency levels, the smallest possible dimensions and a required NPSH compatible with the load available at the pump inlet.

An example of a centrifugal pump will then be used to define the geometric dimensions from which the hydraulic shapes of the impeller and stator components (diffuser and/or volute) are derived. This example will provide an opportunity to put into practice the rules of calculation and drawing that have already been explained.

Mechanical calculations are not covered in this example. They are not specific to pumps, and belong to the general field of pressure vessels, shaft design, sealing systems, lubrication, etc. You can refer to the ordinary rules of the field in question, such as those for foundries, which apply perfectly to pump components: impellers, volute casings, bearing housings and the various mechanical parts that make up a centrifugal pump.

Rotodynamic pumps" is the subject of several articles:

• [BM 4 300] Presentation. Description ;

• [BM 4 302] How it works ;