There are mainly flow and lift, in addition to shaft power, speed and required NPSH. The flow rate refers to the amount of liquid output through the pump outlet per unit time. Generally, the volume flow rate is used; the head is the energy increment of the liquid per unit weight from the pump inlet to the outlet. For the volumetric pump, the energy increase is mainly reflected in the increase of pressure energy. , so it is usually expressed in terms of pressure increment instead of head. Pump efficiency is not an independent performance parameter, it can be calculated from other performance parameters such as flow, head and shaft power. Conversely, the shaft power can also be obtained by knowing the flow rate, head and efficiency.
There is a certain interdependence relationship between the various performance parameters of the pump. The pump can be tested and the parameter values are measured and calculated separately and plotted as curves. These curves are called pump characteristic curves. Each pump has a specific characteristic curve that is supplied by the pump manufacturer. The recommended performance section is usually indicated on the characteristic curve given by the factory and is called the working range of the pump.
The actual operating point of the pump is determined by the intersection of the curve of the pump and the characteristic curve of the pump. The selection and use of the pump should keep the working point of the pump within the working range to ensure economical and safe operation. In addition, when the same pump delivers liquids with different viscosities, its characteristic curve also changes. Usually, the characteristic curve given by the pump manufacturer mostly refers to the characteristic curve when conveying clean cold water. With the power pump, as the viscosity of the liquid increases, the head and the efficiency decrease, and the shaft power increases. Therefore, in the industry, the liquid having a large viscosity is sometimes heated to make the viscosity small to improve the conveying efficiency.