There are mainly flow and head, in addition to shaft power, speed, and necessary NPSH. Flow refers to the amount of liquid output through the pump outlet per unit time, generally using volume flow; lift is the energy increment per unit weight of liquid transported from the pump inlet to the outlet. For positive displacement pumps, the energy increment is mainly in the increase in pressure energy. , so it is usually expressed by pressure increment instead of the head. The efficiency of the pump is not an independent performance parameter, it can be calculated from other performance parameters such as flow, head, and shaft power according to the formula. Conversely, the shaft power can also be obtained by knowing the flow rate, head, and efficiency.
There is a certain interdependence between the various performance parameters of the pump. The parameters can be measured and calculated by testing the pump and drawn into curves to represent them. These curves are called pump characteristic curves. Each pump has a specific characteristic curve, provided by the pump manufacturer. The recommended performance range is usually indicated on the characteristic curve given by the factory, which is called the working range of the pump.
The actual operating point of the pump is determined by the intersection of the pump curve and the pump device characteristic curve. When selecting and using the pump, the working point of the pump should fall within the working range to ensure economical and safe operation. In addition, when the same pump delivers liquids of different viscosities, its characteristic curve will also change. Usually, the characteristic curve is given by the pump manufacturer mostly refers to the characteristic curve when delivering clean cold water. For power pumps, as the viscosity of the liquid increases, the lift and efficiency decrease, and the shaft power increases. Therefore, in the industry, sometimes the liquid with high viscosity is heated to reduce the viscosity to improve the conveying efficiency.