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How to choose the type of centrifugal pump China's production of many pump companies, pump types are also very numerous, the relevant state departments have collected a variety of pump samples and product specifications for the design and use of units. However, how to choose a suitable pump according to the production conditions is not an easy task and needs to consider the influence of various factors. 1. Selection basis Various types of pumps have a certain scope and conditions of use. First of all, the type of the pump should be determined according to the nature of the liquid being conveyed and the requirements of the production conditions, and then the specific type of the pump should be further determined. For example, liquid viscosity is not large, the flow rate is larger, the lift is not high, should use reciprocating pump; liquid viscosity larger, smaller flow, lift is not high or contain bubbles, the choice of vortex pump; liquid viscosity, flow rate Small, high lift, the rotor pump should be used. Centrifugal pump the most widely used, therefore, the most chemical production applications. 2. Centrifugal pump selection methods and steps Centrifugal pump selection in the following order. (1) Determine the physical and chemical properties of the liquid being transported. The physical and chemical properties of the liquid include temperature, viscosity, density, saturated vapor pressure, corrosiveness and toxicity, and the like, whether it contains solid particles or bubbles. From this it is possible to determine the type and type of pump, the material of the pump part, the type of seal, the measures to prevent pump corrosion and cavitation. (2) Determine the pump flow According to the requirements of production conditions, calculate the amount of liquid per unit time to be transported, increase a certain margin (usually 5% -10%), as the centrifugal pump flow. (3) Calculate the lift of the pump Calculate the liquid resistance loss of the pipeline according to the flow of the pump, the condition of the pipeline and the installation, find the required lift of the pump, and add a certain margin (5% -10%) as Pump selection basis. (4) Correction of viscous liquid If the kinematic viscosity of the liquid to be transported is less than 20cSt (1cSt = 1mm² / s), it is not necessary to correct the change in the flow and lift of the pump. Depending on the flow and lift of the pump and the physicochemical properties of the liquid, one type of centrifugal pump is primaries on the series of plots (spectra) of a certain type of pump. If the liquid kinematic viscosity is greater than 20cSt, then correction. The specific method is: With the required flow, head and liquid viscosity according to Figure 3-12 obtained head correction factor KH, flow correction factor KQ, respectively, divided by the required head and flow, which was corrected after the head and flow. Based on the data selected as the pump to ensure the delivery of viscous liquid requirements. (5) seeking the working point of the pump Centrifugal pump in the series of primaries choose a model of the centrifugal pump characteristic curve drawn on the pump connection pipe characteristic curve to find the working point. See if the pump is operating at a higher efficiency. If the selected centrifugal pump slightly higher flow and lift, pump margin can be used to regulate the opening of the outlet valve to adjust the flow and lift. If the choice of pump flow and lift is too large, cutting law can be used to reduce the pump flow and head. If the selected pump operating point is not within the allowable range of efficiency, then choose another type of centrifugal pump. (6) Determining the installation height of the pump Depending on the local atmospheric pressure or the liquid surface pressure of the liquid being transported, the temperature of the liquid and the saturated vapor pressure of the liquid at this temperature, the centrifugal pump model is allowed after the type of centrifugal pump is determined Suction on the vacuum level or allow NPSH to determine the installation height of the pump. (7) to determine the pump standby rate With a pump to meet the production requirements should try to use a pump operation. The use of two or more pumps in parallel operation is generally less efficient and uneconomical from an "energy saving" point of view. But when the flow rate is larger, a pump can not meet the production needs or require a spare pump, you can use two or more pumps in parallel. Large-scale pump because the starting current is too large, the impact on the power system, they often also use two smaller pumps in parallel, one by one start. Standby rate is the number of standby pump and the ratio of the number of operating pumps. For example, if two pumps are operated in parallel and the other is standby, the backup rate is 100%. If the three pumps in parallel, two operating a backup, the backup rate of 50%. The pump back-up rate should take into account the impact of various factors, including the nature of the liquid, process requirements, reliability of the pump itself, ease of maintenance, pump prices and more. For example, a centrifugal pump in a kerosene furnace or a boiler plus a pump in a thermal power plant may require one pump to operate a pump at a standstill if the pump is not allowed to operate at any time during operation. For liquids containing solid particles, pump maintenance is often stopped because of parts that are easily damaged, so a 100% backup rate must also be used. For intermittent operation of the equipment or ready to stop the pump case, you can not spare pump, to reduce investment.