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Selection of Pump Type, Series, and Model I. Selection Criteria 1. Physicochemical properties of the fluid to be transported: The physicochemical properties of the fluid directly affect the performance, materials, and structure of the pump. The physicochemical properties of a medium include: name, characteristics (corrosivity, abrasiveness, toxicity, etc.), particle size and content, density, viscosity, vapor pressure, etc. If necessary, the gas content in the medium should also be listed to indicate whether the medium is prone to crystallization or not. 2. Process parameters: Process parameters are an important basis for pump selection, and should be carefully considered in light of the process flow and the range of operational variations. Flow rate Q: The volume of fluid that the pump is required to transport in the process unit; the normal, maximum, and minimum flow rates should be specified. When selecting a pump, its rated flow rate should be no less than the maximum flow rate of the system, or it should be 1.1 to 1.15 times the normal flow rate. Head H: The head value required by the process unit, also known as the calculated head. It is generally required that the rated head of the pump be 1.05 to 1.1 times the head required by the installation. Inlet pressure Ps and outlet pressure Pd: refer to the pressures at the flanges of the pump’s inlet and outlet connections. The levels of these pressures affect the pressure resistance required of the pump casing as well as the requirements for shaft sealing. Temperature: Pump inlet temperature, usually indicating normal, maximum, and minimum temperatures. Device NPSHa: also known as effective NPSHa. Operation status: Continuous or intermittent operation. II. Selection of pump type: The choice of pump type should be made based on factors such as the process parameters of the installation, the physical and chemical properties of the medium to be transported, the operating cycle, and the structural characteristics of the pump. Centrifugal pumps have advantages such as a simple structure, pulse-free liquid delivery, and easy flow regulation; therefore, they should be used whenever possible, except in the following situations. Use a metering pump when metering is required ； The head is very high while the flow rate is low; since there are no suitable centrifugal pumps with a low flow rate but high head, reciprocating pumps can be used as an alternative ； If the requirements for cavitation are not high, a vortex pump can also be used ； When the head is very low and the flow rate is high, axial-flow pumps or mixed-flow pumps should be selected ； When the viscosity is high (650–1000 mm2/s), rotary pumps or reciprocating pumps can be considered; for extremely high viscosities, specially designed high-viscosity rotary pumps and high-viscosity reciprocating pumps can be used ； When the gas content in the medium is >5%, the flow rate is low, and the viscosity is less than 37.4 mm2/s, a vortex pump can be used. If pulsation in the flow rate is allowed, a reciprocating pump can be selected. In situations where starting is frequent or pumping is inconvenient, pumps with self-priming capabilities should be used, such as self-priming centrifugal pumps, self-priming vortex pumps, and positive displacement pumps. III. Selection of Pump Series and Materials The pump series refers to pumps of the same structure and purpose produced by a pump manufacturer, such as the IH, CZ, IJ, ZA types of chemical process pumps, the AY type of oil pumps, and the ZE type of petrochemical process pumps. Once the type of pump is determined, the series and material of the pump can be selected based on the process parameters and the properties of the medium. Once it is decided to use a centrifugal pump, the following factors can be further considered: determine which type of pump is appropriate based on the properties of the medium, such as clean water pumps, corrosion-resistant pumps, chemical process pumps, and pumps designed for handling impurities. When the medium is highly toxic, valuable, radioactive, or any other substance for which leakage is not permitted, it is advisable to consider using leak-proof pumps (such as shielded pumps or magnetic drive pumps) or double-end mechanical seals equipped with systems for collecting leaked fluid and detecting leaks. For media such as liquefied hydrocarbons and other highly volatile liquids, pumps with a low net positive suction head should be selected, such as can-type pumps. Choose between horizontal pumps and vertical pumps (including submersible pumps and pipeline pumps) based on the on-site installation conditions. Choose a single-suction pump, a double-suction pump, or a low-flow centrifugal pump depending on the flow rate. Single-stage pumps, multi-stage pumps, high-speed centrifugal pumps, etc., are selected based on the required head. Once the above items are determined, it is possible to select the appropriate pump series and manufacturer based on the characteristics of different series of pumps within each category, as well as the capabilities of the manufacturers. Finally, based on the characteristics of the device and the process parameters of the pump, it is determined which category of manufacturing and inspection standards to use. When higher requirements apply, the API610 standard can be used; for moderate requirements, the GB5656 (ISO5199) standard can be chosen. IV. Determination of pump model: Once the type, series, and material of the pump have been selected, the pump’s model (i.e., specifications) can be determined based on the samples and relevant information provided by the pump manufacturer. Determination of the centrifugal pump model: Determination of rated flow rate and head: The rated flow rate is generally taken as the maximum flow rate; if this value is not available, 1.1 to 1.15 times the normal flow rate is often used. The rated head is generally taken as 1.05 to 1.1 times the head of the device. For media with a viscosity greater than 20 mm2/s or those containing solid particles, it is necessary to convert them to the rated flow rate and head when transporting clean water before proceeding with the subsequent steps. Check the series performance charts: Identify the initially selected pump model based on the rated flow rate and head; there may be one model, or there may be two or more. Verification: Check whether the rated operating point of the pump falls within its high-efficiency operating range, based on the performance curve ； Check whether the net positive suction head available (NPSHr) of the pump meets the requirements. When there are two or more specifications meeting the above conditions, the pump model with the highest comprehensive score shall be selected as the final choice. Specifically, the following parameters can be compared: efficiency (higher pump efficiency is preferred), weight (lighter weight is preferred), and price (lower price is preferred). V. Determination of the prime mover power: The shaft power Pa of a centrifugal pump is given by Pa=QH/(3.6×10²×η), where Q is in m³/h, H is in meters, and η is less than 1. (If η=80%, use 0.8 in the calculation) Pa: kW. The rated power of the prime mover, P: P=KPa/ηt, where ηt is the transmission efficiency and K is the power margin coefficient of the prime mover. After determining the exact value of the rated power of the prime mover, the actual power range of that prime mover must be taken into consideration when selecting it. Select the appropriate prime mover based on the explosion area, explosion protection rating, power supply, and gas supply conditions. VI. Determination of the shaft seal type The shaft seal is a sealing device installed in the pump to prevent leakage at the junction between the pump shaft and the casing. Common types of shaft seals include packing seals, mechanical seals, and dynamic seals. Packing seal: Simple structure, low cost, easy to maintain, but high leakage rate and high power consumption. Therefore, packing seals are used for transporting ordinary media such as water ； It is generally not used for petroleum and chemical media, especially not for valuable, explosive, or toxic media. Mechanical seals: Also known as face seals, they offer excellent sealing performance, minimal leakage, and a long service life. However, they are expensive, and their processing, installation, maintenance, and repair require higher standards compared to ordinary seals. Mechanical seals are suitable for pumping petroleum and chemical media; they can be used with media of various viscosities, highly corrosive substances, and those containing particles. Dynamic sealing: It can be divided into back-vane sealing and secondary impeller sealing. When the pump is in operation, the centrifugal force exerted by the back blades or auxiliary impeller reduces the pressure of the medium at the shaft seal to atmospheric pressure or negative pressure, thereby preventing leakage during use. When the pump is stopped, the centrifugal force disappears, and at this point it is the pump shutdown sealing device that provides sealing. Packing seals are commonly used in the pump-shutting sealing devices that come with back vanes or auxiliary impellers. Filler seals come in two types: the standard type and the mechanically adjustable type. A standard packing seal is similar to ordinary packing-sealed pumps, requiring a slight positive pressure at the shaft seal to prevent dry friction of the packing. The mechanically adjustable packing pump seal uses a weight to keep the packing loose while the pump is running, and to compress the packing when the pump stops. To ensure the lifespan of the pump shutdown sealing device and reduce pump leakage, pumps equipped with dynamic seals require a limit on the pressure at the pump inlet, namely: Ps＜0.1Pd, where Ps represents the pressure at the pump inlet, in MPa ； Pd——import pressure, MPa. It features reliable dynamic sealing performance, low cost, and easy maintenance, making it suitable for transporting media containing a high amount of solid particles, such as alkali pumps in the caustic soda industry, slurry pumps in the phosphate industry, and desulfurization pumps in power plants. The disadvantage is that it consumes more power compared to mechanical seals, and the lifespan of the seal device when the pump is stopped is shorter. VI. Couplings and Their Applications Couplings are used to transmit power, compensate for any misalignment between the pump shaft and the prime mover shaft, dampen shocks, alter the natural vibration frequency of the shaft system, and prevent harmful vibrations from occurring. Common types of couplings include claw-type elastic couplings, elastic pin couplings, and diaphragm couplings. Claw-type elastic coupling: also known as elastic block coupling, it is characterized by its small size, light weight, simple structure, easy installation, and low cost; it is commonly used in applications with low power requirements or in less critical situations. Elastic pin couplings: They feature a simple structure, easy installation, simplicity in replacement, small size, light weight, and high power transmission capacity; they are widely used in various rotary pumps. Extended elastic pin couplings can also be used in chemical process pumps. Diaphragm coupling: It has a simple structure, requires no lubrication or maintenance, is resistant to high temperatures and misalignment, and can transmit large amounts of power; however, it is expensive. 02 Examples of proper and improper pump selection: Selecting the most appropriate and reasonable pump is something that should be done whenever possible. However, there are still instances where pump selection proves to be highly unreasonable in industrial pumping systems. Pump selection technicians must continuously learn from such cases—especially from those that serve as negative examples. Example 1: A chemical processing plant needs to select a chemical pump capable of transporting a medium with weak alkaline properties, at a flow rate of Q=400 m3/h and a head of H=40 m; the specific gravity of this medium is approximately 1. Based on the pump parameters and the properties of the medium, the CZ and IJ pumps can be considered as initial options. The performance parameters of the CZ pump range over a wider spectrum than those of the IJ pump, giving it greater versatility; therefore, from the CZ pump series, the CZ150-400 and CZ200-400 pumps were selected. Both pumps have an efficiency of 78%, with the former operating at higher flow rates while the latter operates at lower flow rates. The CZ150-400 pump has a smaller diameter, is lighter in weight, and is less expensive. After comprehensive comparison, the CZ150-400 pump is the most suitable choice. A mechanical seal is to be used, and the material for the flow-through components is 304L. Example 2: A large oil field needs to select a crude oil transfer pump capable of handling a flow rate of Q=500,400 m3/h and a head of H=170 m. The specific gravity of the fluid is approximately 1, and the required net positive suction head for the pump is 5 meters. Based on the pump parameters and the properties of the medium, the initial choices are the KSY450-210A double-suction center-split pipeline oil transfer pump or the DG450-60x3 multi-stage centrifugal pump; both pumps have an efficiency of 78%. The NPSH value for the former is 5.1 meters, while it is 4.9 meters for the latter ； The former has a rotational speed of 2950 r/min, is of the double-suction center-open type, is compact in size, easy to maintain, and allows for an appropriate reduction in the net positive suction head at the impeller inlet ； The latter has a rotation speed of 1450 r/min; it is of multi-stage design, is larger in size, and not easy to maintain ； For comprehensive evaluation, the KSY450-210A pump is preferred. Counterexample 1: A SOW350-400 double-suction split-case pump produced by Shanghai Liancheng Pump Industry Company is in use in the plumbing department of Yibin Siliya. The original head of this pump was 75 m, with a motor power of 355 kW. It was found that the head was too high during operation; therefore, the impeller was cut to reduce the head to 42.5 m, resulting in a flow rate of 2235 m3/h. The motor remained unchanged, but the operating current was close to the rated value, causing frequent tripping. The power consumption was very high, making it inefficient for long-term use. Cause analysis: During the initial selection of the pump, the required head was set too high; as a result, the pump’s head capacity was excessive. When in use, excessive cutting was done to the diameter of the impeller, which led to a poor fit between the impeller and the pump casing, thereby resulting in very low pumping efficiency. Counterexample 2: A large power plant selected a vertical cast-welded self-priming pump for its desulfurization process, taking into account the constraints related to site installation as well as the advantage of the pump’s ability to self-priming. However, the efficiency of vertical self-priming pumps is usually below 50%, resulting in very high electricity consumption over time. Its dynamic seal is sometimes unreliable as well; the pump has many flow components (all of which come into contact with the medium), so pump manufacturers lower the standards when selecting materials. There are numerous pump accessories (all of which make it difficult to ensure proper manufacturing quality and assembly precision), the total cost of the pump is high, and maintenance is inconvenient. An alternative is to opt for a horizontal desulfurization pump. Only the pump body, pump cover, and impeller are wetted parts; the bracket is made of HT200 material. This pump is relatively inexpensive, highly efficient and energy-saving, easy to maintain. Its spare parts are readily available and highly interchangeable. It should be noted that this vertical cast-welded structure self-priming pump originally had a nice name: \"seal-less automatic control self-priming pump.\" In reality, it is the auxiliary impeller with high power consumption that provides sealing; this type of pump is still suitable for use in sewage treatment systems where operation is intermittent. Counterexample 3: A large chemical plant selected a TLB125-100-315 negative-pressure seal pump to transport corrosion-resistant chemical media. This pump was designed based on the structural features of sand pumps and slurry pumps, utilizing the hydraulic design principles of the IH125-100-315 pump. Since there is negative pressure at the shaft seal, the pump manufacturer claims it to be a leak-free pump. However, this is not the case in reality: the overhang length of the pump impeller has increased, the rotor lacks sufficient rigidity, and there have even been instances of shaft breakage.