The mechanical power requirement of a centrifugal pump (shaft power) is directly proportional to the density of the pumped medium.
P 2 ~ ρP 2 = shaft power
ρ = density of the pumped mediumIn contrast, the throttle curve of the pump H (Q) and the efficiency η (Q) are independent of the density.These relationships are automatically taken into account by the pump selection software.
In particular, the following criteria must be taken into account:(1) General suitability of the pump type
In principle, centrifugal pumps are only suitable up to a certain viscosity, which depends on the size. A positive displacement pump should be selected for very high viscosities.(2) Pump characteristics
The pump characteristics are usually measured with water under standard conditions. If the density and viscosity are different, the characteristics must be converted accordingly. This is usually done automatically by the pump selection software if it is a Newtonian fluid.(3) Material selection
The selection of suitable materials is extremely important, especially if the pumped medium contains abrasive or aggressive components. Many manufacturers offer media resistance information for this. For such use, however, direct contact with the manufacturer is definitely recommended.(4) Seal selection
In addition to the media-material resistance, the characteristics of the pumped medium must be taken into account when selecting a suitable seal. In the case of dangerous substances (e.g. toxic or explosive media) or particularly valuable fluids, it is usually necessary to use a leak-free solution. Pumps without a shaft seal with a canned motor or magnetic coupling are ideal here.(5) Solid or gas fractions
If the pumped medium contains solid and / or gas components, special pump designs that are intended for this must be selected. For example, suitable impellers prevent the pump from blocking when there are solid or fibrous components. Gas proportions affect the suction behavior of centrifugal pumps. A higher gas content leads to an increase in the required NPSH value and thus to the earlier occurrence of cavitation.
The maximum and minimum temperatures of the pumped medium are of particular importance for the design of the pump. They are taken into account in the selection of materials and seals and, if necessary, in a media-material resistance test.The fluid properties (density, viscosity) change with the temperature. The power requirement of the pump is directly proportional to the density. Therefore, the temperature must be taken into account from the operating range with the maximum density. Furthermore, for viscous media (ν > 10 mm²/s), the shape of the pump performance curve must be converted.
