The vapour pressure of the pumped fluid greatly influences Cavitation Behaviour and thus the System NPSHavailable.
The vapour pressure is one of the important liquid properties for pump selection and depends on the fluid temperature.
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.
In a narrower sense, in contrast to blowers and compressors for gases and compressible media, pumps for incompressible media are referred to as liquid pumps. This means that the volume of the fluid remains approximately constant as the pressure increases. In practice, this also includes liquid mixtures with a low solid or gas content.
In the case of liquid transport, the pressure of the pump is required to overcome the flow resistance that arises in the pipe system, e.g. for the circulation in a heating system.
In addition, in cases of different liquid levels, overcoming the difference in height (Hgeo) is required, e.g. fluid displacement to a higher level ie. to fill and maintain a near constant level in an overhead tank.
