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When designing the equipment, the purpose and performance of the pump should be determined and selected. This selection must first start with the type and form of the pump. So what are the principles for selecting a pump? What is the basis?
First, understand the pump selection principles
1. Make the type and performance of the selected pump meet the requirements of the process parameters such as device flow, head, pressure, temperature, cavitation flow, and suction stroke. 2. Must meet the requirements of media characteristics. For pumps that transport flammable, explosive, toxic or valuable media, shaft seals are required to be reliable or non-leak pumps are used, such as magnetically driven pumps, diaphragm pumps, canned pumps. For pumps that transport corrosive media, corrosive-resistant materials are required for convection parts , Such as stainless steel corrosion-resistant pumps, engineering plastic magnetic drive pumps, etc. For pumps containing solid particles, the convection parts should be made of abrasion-resistant materials. If necessary, the shaft seal should be rinsed with clean liquid. 3. High mechanical reliability, low noise and small vibration. 4. Economically, the total cost of equipment cost, operation cost, maintenance cost and management cost must be taken into consideration. 5. The centrifugal pump has the characteristics of high speed, small size, light weight, high efficiency, large flow rate, simple structure, no infusion pulse, stable performance, easy operation and convenient maintenance.
a、有计量要求时，选用计量泵 b、扬程要求很高，流量很小且无合适小流量高扬程离心泵可选用时，可选用往复泵，如汽蚀要求不高时也可选用旋涡泵. c、扬程很低,流量很大时,可选用轴流泵和混流泵。 Therefore, except for the following situations, centrifugal pumps should be used as much as possible: a. When there are metering requirements, choose metering pumps. B. High head requirements, small flow and no suitable small flow. High-lift centrifugal pumps are optional. Reciprocating pumps are optional. Vortex pumps can also be used if cavitation requirements are not high. C. When the head is very low and the flow is very large, axial flow pumps and mixed flow pumps can be selected. d. When the viscosity of the medium is larger (greater than 650 ~ 1000mm2 / s), a rotor pump or a reciprocating pump (gear pump, screw pump) can be considered. e. The air content of the medium is 75%, the flow rate is small and the viscosity is less than 37.4mm2 / s. In this case, a vortex pump is available. f. For occasions with frequent starting or inconvenient filling pumps, self-priming pumps should be selected, such as self-priming centrifugal pumps, self-priming vortex pumps, and pneumatic (electric) diaphragm pumps.
Second, know the basic basis of pump selection 是选泵的重要性能数据之一，它直接关系到整个装置的的生产能力和输送能力。 The basis for pump selection should be considered from five aspects according to the process flow and water supply and drainage requirements, namely the liquid delivery volume, device head, liquid properties, pipeline layout, and operating conditions, etc. 1. Flow is an important performance data for pump selection One is that it is directly related to the production capacity and conveying 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 as the basis and take into account the normal flow. When there is no maximum flow, usually 1.1 times the normal flow can be taken as the maximum flow. 是选泵的又一重要性能数据，一般要用放大5%—10%余量后扬程来选型( 点击查看水泵扬程计算方法 ) 2. The head required by the device system is another important performance data for pump selection. Generally, the head is selected by enlarging the 5% -10% margin ( click to view the pump head calculation method ) . ，包括液体介质名称，物理性质，化学性质和其它性质，物理性质有温度c密度d，粘度u，介质中固体颗粒直径和气体的含量等，这涉及到系统的扬程，有效气蚀余量计算和合适泵的类型：化学性质，主要指液体介质的化学腐蚀性和毒性，是选用泵材料和选用那一种轴封型式的重要依据( 点击查看粘度对离心泵性能曲线的影响 )。 3. Liquid properties , including the name of the liquid medium, physical properties, chemical properties, and other properties. The physical properties include temperature c density d, viscosity u, solid particle diameter and gas content in the medium, etc. This involves the system's lift and effective gas. Erosion calculation and suitable pump type: Chemical properties, mainly refers to the chemical corrosivity and toxicity of liquid medium, is an important basis for the selection of pump materials and the type of shaft seal ( click to see the effect of viscosity on the performance curve of centrifugal pumps) ). 指的是送液高度送液距离送液走向，吸如侧最低液面，排出侧最高液面等一些数据和管道规格及其长度、材料、管件规格、数量等，以便进行系梳扬程计算和汽蚀余量的校核。 4. The pipeline layout conditions of the device system refer to some data such as the minimum liquid level and the maximum liquid level on the suction side and the maximum liquid level on the discharge side, as well as the pipe specifications and their lengths, materials, pipe specifications, and quantities. And so on, in order to perform head calculation and check of cavitation allowance. 的内容很多，如液体的操作T饱和蒸汽力P、吸入侧压力PS（绝对）、排出侧容器压力PZ、海拔高度、环境温度操作是间隙的还是连续的、泵的位置是固定的还是可移的。 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 operation is gap or continuous, and the position of the pump is fixed. Is still removable.
Third, the specific operation of pump selection
According to the pump selection principles and basic selection conditions, the specific operations are as follows: 1. According to the arrangement of the device, terrain conditions, water level conditions, and operating conditions, determine the choice of horizontal, vertical and other types (pipeline, submersible, submerged Type, non-blocking type, self-priming, gear type, etc.). 2. According to the nature of the liquid medium, determine whether the water pump, hot water pump or oil pump, chemical pump or corrosion-resistant pump or impurity pump, or use non-blocking pump. Pumps installed in explosion areas should use corresponding explosion-proof motors according to the explosion area grade. 3. Determine the single-suction pump or the double-suction pump according to the flow rate; select the single-stage pump or the multi-stage pump, the high-speed pump or the low-speed pump, and the multi-stage pump with lower efficiency than the single-stage pump, such as the When multi-stage pumps can also be used, single-stage pumps are used first. 4. Determine the specific model of the pump and determine what series of pumps to use, then the maximum flow rate can be used. (When there is no maximum flow rate, 1.1 times the normal flow rate can usually be taken as the maximum flow rate), and the 5% -10% margin can be taken. The main parameters of these two performances of head are to determine the specific model on the type spectrum or series characteristic curve. 详细说明请点击查看水泵的扬程, 如何选取 )： The operation is as follows (for details, please click to view the pump head, how to select ):
Use the pump characteristic curve to find the required flow value on the abscissa and the required head value on the ordinate. From the two values, draw the vertical or horizontal line up and to the right. The intersection of the two lines just falls on the characteristic curve. This pump is the pump to choose, but this ideal situation is generally rare, and usually encounters the following two situations:
The first type: the intersection point is above the characteristic curve, which means that the flow meets the requirements, but the head is not enough. At this time, if the heads are similar, or the difference is about 5%, it is still optional. If the heads are much different, then choose a pump with a larger head. . Or try to reduce the pipeline resistance loss. The second type: the intersection point is below the characteristic curve, within the fan-shaped trapezoidal range of the pump characteristic curve, this model is initially determined, and then the impeller diameter is cut according to the head difference. If the head difference is small, it is not cut. The heads are very different. According to the required Q, H, according to its ns and cutting formula, the diameter of the impeller is cut. If the intersection point does not fall within the fan-shaped trapezoidal range, a pump with a smaller head should be selected. When selecting a pump, sometimes it is necessary to consider the production process requirements, and select different shapes of QH characteristic curves.
5. After the pump model is determined, the pumps or pumps that are similar to water in the physical and chemical medium of the transport medium need to go to the relevant product catalogs or samples and correct them according to the model performance table or performance curve to see if the normal operating point falls within the range. Pump priority work area? Whether the effective NPSH is greater than (NPSH). Can the geometry installation height be reversed with NPSH? 6. For liquid pumps with a viscosity greater than 20mm2 / s (or a density greater than 1000kg / m3), the characteristic curve of the water experimental pump must be converted into the performance curve of the viscosity (or the density), especially for the suction performance and Input power is calculated carefully or compared. 7. Determine the number and standby rate of pumps : Normally, only one pump is used, because a large pump is equivalent to two small pumps working in parallel (referring to the same head and flow), and the efficiency of the large pump is higher than that of the small pump. Pump, so from the perspective of energy saving, you can choose a large pump instead of two small pumps, but in the following circumstances, you can consider two pumps in parallel cooperation: a large flow, one pump can not reach this flow. For large pumps that require a 50% standby rate, two smaller pumps can be changed to work, two standby (a total of three). For some large pumps, a 70% flow rate pump can be used in parallel instead of a standby pump. When one pump is overhauled, the other pump is still responsible for 70% of production. For pumps that need to run continuously for 24 hours, three pumps should be backed up, one running, one backing up, and one maintenance. 8. In general, customers can submit their "basic conditions for pump selection", and our company will give them a selection or recommend a better pump product. If the design institute has determined the model of the pump when designing the equipment, configure it according to the requirements of the design institute. 9. Determine the number of pumps and standby rate: 流量很大，一台泵达不到此流量。 Normally, only one pump is used, because one large pump is equivalent to two small pumps working in parallel (referring to the same head and flow), the efficiency of the large pump is higher than the small pump, so it is better to choose one from the perspective of energy saving. Large pump instead of two small pumps, but in the following situations, you can consider two pumps in parallel cooperation: a large flow, one pump can not reach this flow. For large pumps that require a 50% standby rate, two smaller pumps can be changed to work with two spares (a total of three lifts). For some large pumps, a 70% flow requirement pump can be used in parallel instead of a standby pump. When one pump is overhauled, the other pump is still responsible for 70% of the production. For pumps that need to run continuously for 24 hours, three pumps should be backed up, one for backup and one for maintenance.
Heavy Pump Company (gh_7c1c194e6b1c)