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When designing equipment, the design institute must determine the purpose and performance of the pump and select the collapse type. This choice must first start with selecting the type and form of the pump. So what principles should be used to select a pump? What is the basis? 1. Understand the principles of pump selection 1. Make the type and performance of the selected pump meet the requirements of process parameters such as device flow, head, pressure, temperature, cavitation flow, suction lift, etc. 2. Must meet the requirements of media characteristics. For pumps transporting flammable, explosive, toxic or precious media, reliable shaft seals or non-leakage pumps are required, such as magnetic drive pumps, diaphragm pumps, and canned pumps. For pumps transporting corrosive media, the convection parts are required to use corrosion-resistant materials, such as fluorine plastic corrosion-resistant pumps and CQF engineering plastic magnetic drive pumps. For pumps transporting media containing solid particles, the convection parts are required to be made of wear-resistant materials, and the shaft seal is flushed with clean liquid when necessary. 3. Mechanically, it has high reliability, low noise and small vibration. 4. Economically, the total cost of equipment, operation, maintenance and management fees should be taken into consideration to minimize the total cost. 5. The centrifugal pump has the characteristics of high speed, small size, light weight, high efficiency, large flow rate, simple structure, pulsation-free infusion, stable performance, easy operation and convenient maintenance. Therefore, except for the following situations, centrifugal pumps should be used as much as possible: a. When there are metering requirements, a metering pump is selected. b. When the head requirement is very high, the flow rate is very small, and there is no suitable small-flow high-lift centrifugal pump to choose from, a reciprocating pump can be used. If cavitation requirements are not high, a vortex pump can also be used. c. When the head is very low and the flow rate is large, axial flow pumps and mixed flow pumps can be used. d. When the viscosity of the medium is relatively large (greater than 650~1000mm2/s), you can consider using a rotor pump or a reciprocating pump (gear pump, screw pump). e. When the medium has a gas content of 75%, the flow is small, and the viscosity is less than 37.4mm2/s, a vortex pump can be used. f. For occasions where startup is frequent or pump filling is inconvenient, pumps with self-priming performance should be selected, such as self-priming centrifugal pumps, self-priming vortex pumps, and pneumatic (electric) diaphragm pumps. 2. Know the basic basis for pump selection. The basis for pump selection should be based on the process flow, water supply and drainage requirements, and should be considered from five aspects, including liquid delivery volume, device lift, liquid properties, pipeline layout, and operating conditions. 1. Flow is one of the important performance data for pump selection, which is directly related to the production capacity and delivery capacity of the entire device. For example, in the process design of the design institute, the normal, minimum and maximum flow rates of the pump can be calculated. When selecting a pump, take the maximum flow rate as the basis and take into account the normal flow rate. When there is no maximum flow rate, 1.1 times the normal flow rate can usually be taken as the maximum flow rate. 2. The head required by the installation system is another important performance data for pump selection. Generally, the head should be enlarged by 5% to 10% to select the type. 3. Liquid properties, including the name of the liquid medium, physical properties, chemical properties and other properties. Physical properties include temperature c, density d, viscosity u, diameter of solid particles in the medium and gas content, etc. This involves the head of the system, calculation of effective cavitation margin and the type of suitable pump.: Chemical properties, mainly referring to the chemical corrosiveness and toxicity of liquid media, are an important basis for selecting pump materials and which type of shaft seal to use. 4. The pipeline layout conditions of the device system refer to the liquid delivery height, liquid delivery distance, liquid delivery direction, the lowest liquid level on the suction side, the highest liquid level on the discharge side, and other data, as well as pipeline specifications and their length, materials, pipe fitting specifications, quantity, etc., in order to calculate the system lift and check the cavitation margin. 5. There are many operating conditions, such as liquid operation T, saturated steam force P, suction side pressure PS (absolute), discharge side container pressure PZ, altitude, ambient temperature, whether the operation is intermittent or continuous, and whether the position of the pump is fixed or movable. 3. The specific operations of pump selection are based on the pump selection principles and basic conditions. The specific operations are as follows:: 1. According to the layout of the device, terrain conditions, water level conditions, and operating conditions, determine the selection of horizontal, vertical, and other types of pumps (pipeline, submersible, submersible, non-clogging, self-priming, gear, etc.) pumps. 2. According to the nature of the liquid medium, determine whether it is a clean water pump, a hot water pump, an oil pump, a chemical pump, a corrosion-resistant pump or an impurity pump, or use a non-clogging pump. Pumps installed in explosion areas should use corresponding explosion-proof motors according to the level of the explosion area. 3. Determine whether to choose a single suction pump or a double suction pump according to the flow rate. ； Depending on the lift, you should choose a single-stage pump or a multi-stage pump, a high-speed pump or a low-speed pump (air conditioning pump). The efficiency of a multi-stage pump is lower than that of a single-stage pump. If both a single-stage pump and a multi-stage pump can be used, choose a single-stage pump first. 4. Determine the specific model of the pump. After determining which series of pumps to choose, you can determine the specific model on the type spectrum or series characteristic curve according to the maximum flow rate (when there is no maximum flow rate, usually 1.1 times the normal flow rate can be taken as the maximum flow rate) and the head after enlarging the margin by 5% to 10%. The operation is as follows: Use the pump characteristic curve to find the required flow value on the abscissa and the required lift value on the ordinate. Draw a vertical or horizontal line upward and rightward from the two values respectively. If the intersection of the two lines falls exactly on the characteristic curve, then the pump is the one to be selected. However, this ideal situation is generally rare, and the following two situations usually occur.: The first type: The intersection point is above the characteristic curve, which means that the flow rate meets the requirements, but the head is not enough. At this time, if the head is about the same, or differs by about 5%, it can still be used. If the head differs a lot, choose a pump with a larger head. Or try to reduce pipeline resistance loss. The second type: If the intersection point is below the characteristic curve and within the fan-shaped trapezoidal range of the pump characteristic curve, the model is preliminarily determined, and then the impeller diameter is decided based on the difference in lift. If the lift difference is very small, it will not be cut. If the lift difference is large, cut the impeller diameter according to the required Q, H, and according to its ns and cutting formula. If the intersection point does not fall within the fan-shaped trapezoidal range, a pump with a smaller lift should be selected. When selecting a pump, it is sometimes necessary to consider the production process requirements and select different shapes of QH characteristic curves. 5. After the pump model is determined, for water pumps or pumps whose transport medium has a physical and chemical medium similar to water, it is necessary to go to the relevant product catalog or sample and make corrections based on the performance table or performance curve of the model to see if the normal operating point falls in the priority working area of the pump? Whether the effective NPSH is greater than (NPSH). Can you also use NPSH to correct the geometric installation height? 6. For liquid pumps with a viscosity greater than 20mm2/s (or a density greater than 1000kg/m3), the water experimental pump characteristic curve must be converted into a performance curve of that viscosity (or density). In particular, the suction performance and input power must be carefully calculated or compared. 7. Determine the number of pumps and backup rate: For normal operation of the pump, generally only one is used, because one large pump is equivalent to two small pumps working in parallel (meaning the lift and flow rate are the same), and the efficiency of the large pump is higher than that of the small pump. Therefore, from the perspective of energy saving, it is better to choose one large pump instead of two small pumps. However, in the following situations, two pumps can be considered to work in parallel.: The flow rate is very large, and a pump cannot achieve this flow rate. For large pumps that need to have a 50% backup rate, two smaller pumps can be used to work, and two pumps are on standby (a total of three pumps). For some large pumps, pumps with 70% flow requirements can be used in parallel operation without a backup pump. When one pump is overhauled, the other pump can still bear 70% of the production transportation. For pumps that need to operate continuously for 24 hours, three pumps should be kept in standby, one for operation, one for backup and one for maintenance. 8. Under normal circumstances, customers can submit their "basic conditions for pump selection", and our company will make selections or recommend better pump products. If the design institute has already determined the pump model when designing the equipment, configure it according to the requirements of the design institute. 9. Determine the number of pumps and backup rate: For normal operation of the pump, generally only one is used, because one large pump is equivalent to two small pumps working in parallel (meaning the lift and flow rate are the same), and the efficiency of the large pump is higher than that of the small pump. Therefore, from the perspective of energy saving, it is better to choose one large pump instead of two small pumps. However, in the following situations, two pumps can be considered to work in parallel.: The flow rate is very large, and a pump cannot achieve this flow rate. For large pumps that require a 50% backup rate, two smaller pumps can be used to work, and two backup pumps (three lifts in total). For some large pumps, pumps with 70% flow requirements can be used in parallel operation without a backup pump. When one pump is inspected, the other pump can still bear 70% of the production transportation. For pumps that need to operate continuously for 24 hours, three pumps should be kept in standby, one for operation, one for backup, and one for maintenance.