The main 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, the volume flow is used. Head is the increment of the energy per unit weight of the pumped liquid from the inlet to the outlet of the pump. For the positive displacement pump, the main body of energy increase is the pressure increase. , so usually expressed in increments of pressure instead of lift. 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. On the contrary, 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, which can be tested by the pump, and the parameters are measured and calculated, and plotted as curves. These curves are called pump characteristics. Each pump has a specific characteristic curve that is provided by the pump manufacturer. The recommended performance section is also usually indicated on the characteristic curve given by the plant and 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 characteristic curve. To select and use the pump, the operating point of the pump should fall within the working range to ensure economical and safe operation. In addition, when the same pump delivers liquids with different viscosities, the characteristic curve also changes. In general, the characteristic curve given by the pump manufacturer mostly refers to the characteristic curve when delivering clean cold water. For a power-driven pump, as the viscosity of the liquid increases, the head and efficiency decrease, and the shaft power increases. Therefore, in some cases, the viscous liquid is heated in the industry to reduce the viscosity to improve the transportation efficiency.