Self-priming centrifugal pumps rely on impeller rotation of the centrifugal force generated by the fluid pressure, conveying fluid. In the selection of self-priming centrifugal pump, to determine the purpose and performance of the pump and select the pump. First of all, this choice from the choice of pump type and form of the beginning, then what principle to choose the pump? What is the basis? First, the principle of pump selection 1, the type and performance of the selected pump in line with the device flow, head, pressure, temperature, cavitation flow, suction stroke and other process parameters. 2, mechanical reliability, low noise, vibration 3, the economic should take into account the equipment costs, operating costs, maintenance costs and management costs of the lowest total cost. 4, self-priming centrifugal pump with high speed, small size, light weight, high efficiency, large flow, simple structure, infusion without pulsation, stable performance, easy operation and maintenance features. Therefore, in addition to the following circumstances, should be used as far as possible self-priming centrifugal pump: a measurement requirements, the choice of metering pumps lift head is very high, the flow is small and not suitable for small flow high lift centrifugal pump self-priming can choose reciprocating pump , Such as cavitation requirements can also be used less whirlpool pump. Low head, when the flow is large, the choice of axial flow pump and mixed flow pump. Medium viscosity (greater than 650 ~ 1000mm2 / s), consider the selection of rotor pump or reciprocating pump (gear pump, screw pump) medium 75% gas content, the flow is small and the viscosity is less than 37.4mm2 / s, the optional Vortex pump. On the occasion of frequent start-up or inconvenience of irrigation, pumps with self-priming performance should be selected, such as self-priming centrifugal pumps, self-priming vortex pumps and pneumatic (electric) diaphragm pumps. Second, the pump selection based on pump selection basis, should be based on process, water supply and drainage requirements, to be considered from five aspects, both liquid delivery capacity, the device head, liquid properties, piping layout and operating conditions 1, the flow It is one of the important performance data of pump selection, it is directly related to the entire plant's production capacity and delivery capacity. Such as the design process can be calculated in the pump normal, minimum, maximum three kinds of flow. Select the pump, based on the maximum flow, taking into account the normal flow, in the absence of maximum flow, usually desirable 1.1 times the normal flow as the maximum flow. 2, the lift system required for installation of the pump is another important performance data, generally to enlarge the 5% -10% head lift to choose. 3, the liquid properties, including the name of the liquid medium, physical properties, chemical properties and other properties, the physical properties of the temperature c density d, viscosity u, medium particle diameter and gas content, etc., which involves the system lift, effective gas Erosion margin calculation and the type of suitable pump: Chemical nature, mainly refers to the liquid medium chemical corrosion and toxicity, is the selection of pump materials and choose an important basis for the type of shaft seal. 4, the installation of piping system conditions refers to the liquid from the height of the liquid into the liquid distance to the suction side such as the lowest level, the highest level of the discharge side of some data and pipe specifications and length, material, pipe specifications, the number , Etc., in order to carry out the Department of combing head calculation and NPSH check. 5, the operating conditions are many, such as the operation of the liquid T saturated steam P, suction side pressure PS (absolute), the discharge side of the tank pressure PZ, altitude, ambient temperature operation is gap or continuous, the pump position is fixed Or removable.