Special lecture on moving equipment "Pumps", learn some knowledge every day (1) Pump selection "enrich yourself"”
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This post was last edited by tclz007 on 2013-12-9 18:56. I will learn some knowledge every day to enrich my series of special lectures on automatic equipment "Pumps". I will summarize the post on learning some knowledge every day and will continue to update it. http://bbs.hcbbs.com/thread-1256318-1-1.html Some people may think that it is a terrible thing to have nothing to do during the day at work, working like a handyman, not knowing what to do, not knowing what to study, day after day, year after year, unable to see your future! We must work hard from now on, even if we learn every day * A little bit of knowledge will add up to a lot, and enrich yourself. Now you have to clarify your goals. Only by enriching your brain first can you enrich others. . . . . . Just spend a few minutes a day and you will see the future! ! ! (Anyway, I have learned it. Whether you learn it or not is up to you, except for those who know how to do it, like Haichuan Dana. . . ) Without further ado, let’s start from the basics today~~! When designing equipment, the pump selection and design institute must determine the purpose and performance of the pump and select the pump 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. Pump selection principles: 1. Make the selected pump type and performance 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 be made of corrosion-resistant materials, such as AFB stainless steel 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 considered to be the lowest. 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 maintenance. Therefore, except for the following situations, centrifugal pumps should be used as much as possible: 1. When there are metering requirements, choose a metering pump. 2. When the head requirements are very high, the flow rate is very small, and there is no suitable small flow high head centrifugal pump to choose from, a reciprocating pump can be used. If the cavitation requirements are not high, a vortex pump can also be used. When the head is very low and the flow rate is large, axial flow pumps and mixed flow pumps can be used. 3. When the medium viscosity is large (greater than 650~1000mm2/s), you can consider using a rotor pump or a reciprocating pump (gear pump, screw pump). 4. 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. 5. For occasions with frequent starts or inconvenient pump filling, pumps with self-priming performance should be selected, such as self-priming centrifugal pumps, self-priming vortex pumps, and pneumatic (electric) diaphragm pumps. 2. 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. It 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. The physical properties include temperature c, density d, viscosity u, solid particle diameter and gas content in the medium, 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 head and check the cavitation margin. 5. There are many contents of 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. The above-mentioned basis should be proposed by the design institute or the user, or by technical personnel to assist the user, and the centrifugal pump data sheet or water pump ordering inquiry form should be carefully filled out. The following is the special lecture "Pump" of my special series of dynamic equipment. 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Please support, listen and discuss ； If you have any directions that need introduction, please contact me. If there are many requests, I will make a special post to explain~~! :) A series of special lectures on moving equipment "Pumps", a summary of the knowledge learned every day, and will be updated continuously. http://bbs.hcbbs.com/thread-1256318-1-1.html Welcome everyone to come and listen. I have already broadcasted. I hope that people like me who want to gain knowledge every day will listen. Let’s learn together every day. * , discuss~~! (Did you learn anything today)
Basis and method for selecting centrifugal pumps. There are many companies producing pumps in my country, and there are also many types of pumps.* * Relevant departments have compiled samples and product specifications of various pumps for design and user selection. However, it is not easy to select a suitable pump according to production conditions. Various factors need to be considered. 1. Basis for selection: Each type of pump has a certain scope of application and conditions of use. First, the type of pump should be determined based on the nature of the liquid being transported and the requirements of the production conditions, and then the specific model of the pump should be further determined. For example, when the liquid viscosity is not large, the flow rate is large, and the lift is not high, a reciprocating pump should be used. ； When the liquid has a high viscosity, a small flow rate, a low lift, or contains bubbles, a vortex pump can be used. ； When the liquid viscosity is large, the flow rate is small, and the head is high, a rotor pump should be used. Centrifugal pumps have the widest range of applications and, therefore, are most widely used in chemical production. 2． Methods and steps for selecting a centrifugal pump. The selection of a centrifugal pump is carried out 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, corrosivity and toxicity, etc., and whether it contains solid particles or bubbles. From this, we can determine the type and model of the pump, determine the materials of pump parts, the type of seals, and measures to prevent pump corrosion and cavitation, etc. (2) Determine the flow rate of the pump. According to the requirements of the production conditions, calculate the amount of liquid that needs to be transported per unit time. After adding a certain margin (generally 5%-10%), it is used as the flow rate of the centrifugal pump. (3) Calculate the lift of the pump. Based on the flow rate of the pump and the conditions of the pipeline and device, calculate the liquid resistance loss of the pipeline, find the lift required by the pump, and add a certain margin (5%-10%) as the basis for pump selection. (4) Correction of viscous liquids If the kinematic viscosity of the liquid being transported is less than 20cSt (1cSt=1mm²/s), since the flow rate and head of the pump do not change much, correction is not necessary. Based on the flow rate and head of the pump as well as the physical and chemical properties of the liquid, a type of centrifugal pump is selected based on a series of diagrams (spectrograms) of a certain type of pump. If the liquid kinematic viscosity is greater than 20cSt, correction will be made. The specific method is: After using the required flow rate, head and liquid viscosity to obtain the head correction coefficient KH and flow correction coefficient KQ according to Figure 3-12, divide them by the required head and flow rate respectively to obtain the corrected head and flow rate. The requirements for transporting viscous liquids can only be ensured based on the data used for pump selection. (5) Find the working point of the pump. Select the characteristic curve of a certain type of centrifugal pump on the centrifugal pump series diagram and draw the characteristic curve of the pump's connecting pipeline to find the working point. See if the pump is operating in a higher efficiency range. If the flow rate and lift of the selected centrifugal pump are slightly higher, it can be used as a margin for the pump, and the flow rate and lift can be adjusted by adjusting the opening of the outlet valve. If the flow rate and head of the selected pump are too large, the cutting law can be used to reduce the flow rate and head of the pump. If the selected pump working point is not within the allowable efficiency range, then another model of centrifugal pump will be selected. (6) Determine the installation height of the pump. After the model of the centrifugal pump is determined, the installation height of the pump is determined based on the local atmospheric pressure or the liquid surface pressure of the transported liquid, the temperature of the liquid and the saturated vapor pressure of the liquid at that temperature, and the allowable suction vacuum height or allowable cavitation margin given on the centrifugal pump sample. (7) Determine the backup rate of the pump. When one pump can meet the production requirements, you should try to operate with one pump. Using two pumps or multiple pumps operating in parallel is generally less efficient and is uneconomical from the perspective of "energy saving". However, when the flow rate is large and one pump cannot meet the production needs or a backup pump is required, two or more pumps can be connected in parallel. When a large pump has a large starting current and affects the power system, two smaller pumps are often connected in parallel and started one by one. The reserve rate refers to the ratio of the number of standby pumps to the number of operating pumps. For example, if two operating pumps are operated in parallel and one is in standby, the standby rate will be 100%. If three pumps are connected in parallel, two are operating and one is in standby, the standby rate is 50%. The standby rate of a pump should comprehensively consider the influence of various factors, including the nature of the liquid, process requirements, reliability of the operation of the pump itself, ease of maintenance, price of the pump, etc. For example, if the centrifugal oil pump of the heating furnace in the kerosene plant or the boiler water pump of the thermal power plant is not allowed to stop the pump at any time during operation, one pump must be operated and the other pump must be in standby, that is, the standby rate is 100%. For transporting liquids containing solid particles, because pump parts are easily damaged and the pump is frequently shut down for maintenance, a 100% backup rate must be adopted. For equipment that operates intermittently or when the pump can be stopped at any time, the backup pump may not be needed to reduce investment.
General procedure for pump selection 1. Based on various factors such as the layout of the device, terrain conditions, water level conditions, operating conditions, economic plan comparison, etc. 2. Consider choosing horizontal, vertical and other types (pipe type, right-angle type, variable angle type, corner type, parallel type, vertical type, vertical type, submersible type, removable type, submersible type, non-blocking type, self-priming type, gear type, oil-filled type, water-filled warm type). 3. According to the nature of the liquid medium, determine the clean water pump, hot water pump, oil pump, chemical pump, corrosion-resistant pump or impurity pump, or use a non-clogging pump. 4. Pumps installed in explosion areas should use explosion-proof motors according to the level of the explosion area. 5. Depending on the flow rate, choose a single suction pump or a double suction pump.: Depending on the lift, you should choose a single-suction pump or a multi-suction 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, a single-stage pump should be selected. 6. Determine the specific model of the pump and what series of pumps to use. After selecting the pump, you can determine the specific model on the type spectrum or series of characteristic curves based on the two main performance parameters of the maximum flow rate and the head after enlarging the margin by 5% to 10%. 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 not rare, and the following situations are usually encountered.: A. 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. B. The second kind: If the intersection point is below the characteristic curve and within the fan-shaped trapezoidal range of the pump characteristic curve, the model is initially 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. 7. 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? 8. For liquid pumps that deliver viscosity greater than 20 mm2/s, the experimental pump characteristic curve based on water must be converted into a performance curve of that viscosity. In particular, the suction performance must be carefully calculated or compared. 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.: 9.1 The flow rate is very large, and one pump cannot reach this flow rate. 9.2 For large pumps that need to have a 50% backup rate, two smaller pumps can be used, and two pumps are on standby (a total of three lifts). 9.3 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. 9.4 For pumps that need to operate continuously for 24 hours, three pumps should be kept in reserve for operation, one for backup and one for maintenance.
Basic things are often forgotten after using them. The brain should be recharged in a timely manner.
I think so too. From now on, I will learn it every day to mobilize everyone’s enthusiasm~~!
This thing is good, learn it* . . . . . .
This post was last edited by hcwang12345 on 2013-11-23 14:23. The information is very good, and the introduction to pump selection is very systematic and comprehensive. However, I feel that this design is a bit too conservative. For example, "9.4 For pumps that need to operate continuously for 24 hours, three pumps should be kept in reserve (for operation, one for backup, and one for maintenance). Nowadays, many pumps are only overhauled once a year or two years. One operation and one backup are enough! if: It is really "a pump that needs to run continuously for 24 hours should have three pumps for operation, one for backup and one for maintenance" to ensure normal operation. I think there is a problem with the selection and the quality of the pump! This is purely a personal opinion!
doubt! Take a look at the bold red 1 below. Basis for selection: Each type of pump has a certain scope of application and conditions of use. First, the type of pump should be determined based on the nature of the liquid being transported and the requirements of the production conditions, and then the specific model of the pump should be further determined. For example, when the liquid viscosity is not large, the flow rate is large, and the lift is not high, a reciprocating pump should be used. ； When the liquid has a high viscosity, a small flow rate, a low lift, or contains bubbles, a vortex pump can be used. ； When the liquid viscosity is large, the flow rate is small, and the head is high, a rotor pump should be used. Centrifugal pumps have the widest range of applications and, therefore, are most widely used in chemical production.
Thank you for sharing, it’s worth learning*
From now on, there will be one article every day, come and learn every day!