4.1.1 Centrifugal pump liquid temperature under the conveying temperature is not greater than 650mm2 / S, or pump efficiency decreased significantly. (When the viscosity is more than 650mm2 / S, centrifugal pump performance decline greatly, generally do not choose centrifugal pump, but because of the centrifugal pump infusion without pulsation, no safety valve and flow adjustment is simple, so we often see in the chemical production of centrifugal Pumps are used to deliver liquids with viscosities up to 1000 mm2 / s). The flow is relatively large, while the head is relatively low teaching liquid dissolved or entrained less than 5% (volume) of liquid containing solid particles, should choose a special centrifugal pump (such as mud pump) requires large flow changes, small head changes should Selection of flat flow - Centrifugal lift head curve, requiring small changes in flow, head changes, should choose the steep drop of flow - Centrifugal pump head curve. 4.1.2 Positive displacement pump Fluid viscosity greater than 650mm2 / S, smaller flow and relatively high lift, should choose reciprocating pump. Liquid dissolved or entrained gas allows slightly more than 5% (volume) of liquid Need accurate measurement, the choice of plunger metering pump, liquid strict leak-free, optional diaphragm metering pump Lubrication of poor performance should not be used gear Pump and three screw pump, optional reciprocating pump. Small flow, the temperature is low, the pressure requirements of stability, should use a rotor pump or twin screw pump. 4.2 According to the device required flow and lift, according to the classification of the pump and the scope of the initial determination of the pump selection, due to the simple structure of the centrifugal pump, infusion without pulsation, flow adjustment is simple, so in addition to centrifugal pump is difficult to do the occasion, as far as possible selection Centrifugal pump. After the selection of the pump is confirmed, it is possible to select the pump series and materials according to the process plant parameters and the medium characteristics. Then according to the pump factory to provide samples and technical information to determine the specific pump model (specifications). 4.3 for special media pump delivery gas-containing liquid, the pump flow, lift, the efficiency has declined. The greater the gas content, the more rapid decline in efficiency. With the gas content increases, the pump appears additional noise, vibration, severe corrosion or increase when there is no flow, broken axis phenomenon. In order to ensure the reliable operation of the pump, measures can be taken to reduce the gas content in the liquid: Type Applicable viscosity range mm2 / s Vane pump Centrifugal pump <150 Vortex pump <37.5 Positive displacement pump <850 Counter pump <800 Rotary piston pump 200 ~ 10000 Single screw pump 10 ~ 560000 Double screw pump 0.6 ~ 100,000 Three screw pump 21 ~ 600