8 Steps to Become a Pump Selection Expert

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I. Basic Basis 1. Flow rate is one of the important performance parameters for selecting a pump. It is directly related to the production capacity and conveying capacity of the entire device. If the process design in the design institute can calculate the normal, minimum, and maximum flow rates of the pump. When selecting a pump, the maximum flow rate should be used as the basis, taking into account the normal flow rate as well. In cases where a maximum flow rate is not available, 1.1 times the normal flow rate can typically be used as the maximum flow rate. 2. The head required by the plant system is another important performance parameter for selecting a pump. Generally, the head should be selected with a 5% to 10% margin of amplification. 3. Properties of the liquid. This includes the name of the liquid medium, its physical properties, chemical properties, and other characteristics. Physical properties include temperature, density, viscosity, the diameter of solid particles in the medium, and the gas content; these factors are relevant to calculating the system’s head, the effective net positive suction head, and the appropriate type of pump. Chemical properties, mainly referring to the chemical corrosivity and toxicity of liquid media, are important criteria for selecting pump materials and the type of shaft seal to use. 4. The pipeline layout conditions of the installation system refer to the liquid delivery height, distance, and direction. Data such as the lowest liquid level on the suction side and the highest liquid level on the discharge side, along with pipeline specifications including length and material, as well as fitting specifications and quantities, are required to calculate the head loss and verify the net positive suction head. 5. There are many aspects to the operating conditions. For liquid handling, factors such as the saturated vapor pressure P of the fluid, the suction side pressure PS (absolute), the pressure in the discharge side container PZ, altitude, ambient temperature, whether the operation is intermittent or continuous, and whether the pump’s location is fixed or movable. II. The impact of corrosion Corrosion has always been one of the most troublesome hazards for chemical processing equipment; a slight carelessness can lead to equipment damage, while in more severe cases it can cause accidents or even disasters. According to relevant statistics, about 60% of damage to chemical processing equipment is caused by corrosion; therefore, when selecting chemical pumps, it is essential to pay attention to the scientific choice of materials. There is a common misconception that stainless steel is a \"universal material\" that can be used in any medium or under any environmental conditions; this is very dangerous. Below are the key points for material selection when dealing with some commonly used chemical media: 1. Sulfuric acid – As one of the highly corrosive media, sulfuric acid is an important industrial raw material with a wide range of applications. Sulfuric acid at different concentrations and temperatures causes varying degrees of corrosion to materials. For concentrated sulfuric acid with a concentration of over 80% and a temperature below 80°C, carbon steel and cast iron exhibit good corrosion resistance; however, it is not suitable for sulfuric acid that flows at high speeds, and thus cannot be used as material for pumps and valves ； Common stainless steels such as 304 (0Cr18Ni9) and 316 (0Cr18Ni12Mo2Ti) also have limited utility in sulfuric acid media. Therefore, the pump valves used for transporting sulfuric acid are typically made of high-silicon cast iron (which is difficult to cast and process) or highly alloyed stainless steel (grade 20 alloy). Fluoroplastics exhibit good resistance to sulfuric acid, making the use of fluorinated-lined pumps (F46) a more economical option. 2. Hydrochloric acid: The vast majority of metal materials are not resistant to corrosion by hydrochloric acid (including various stainless steel materials); high-molybdenum high-silicon iron can only be used in hydrochloric acid at temperatures below 50°C and with a concentration of less than 30%. Unlike metal materials, the vast majority of non-metallic materials exhibit good corrosion resistance to hydrochloric acid; therefore, rubber-lined pumps and plastic pumps (such as polypropylene, fluoroplastics, etc.) are the best choices for transporting hydrochloric acid. 3. Nitric acid: Most metals are rapidly corroded and damaged by nitric acid. Stainless steel is the most widely used material resistant to nitric acid; it exhibits good corrosion resistance against nitric acid at all concentrations at room temperature. It is worth noting that stainless steels containing molybdenum (such as 316 and 316L) do not have better corrosion resistance to nitric acid than ordinary stainless steels (such as 304 and 321), and in some cases their resistance is even lower. For high-temperature nitric acid, titanium and titanium alloy materials are commonly used. 4. Acetic acid: It is one of the most corrosive organic acids; ordinary steel suffers severe corrosion in acetic acid at all concentrations and temperatures. Stainless steel is an excellent material resistant to acetic acid, and 316 stainless steel containing molybdenum can also be used in high-temperature environments as well as with dilute acetic acid vapor. For demanding applications such as high-temperature, high-concentration acetic acid or environments containing other corrosive agents, high-alloy stainless steel or fluoroplastic pumps can be used. 5. Alkalis (sodium hydroxide): Steel is widely used in sodium hydroxide solutions at temperatures below 80°C and with concentrations up to 30%. Many factories still use ordinary steel at temperatures of 100°C and concentrations below 75%; although corrosion increases, it remains cost-effective. Ordinary stainless steel does not have a significant advantage over cast iron in terms of corrosion resistance to alkaline solutions; it is not recommended to use stainless steel unless a small amount of iron is allowed to be present in the medium. For high-temperature alkaline solutions, titanium and titanium alloys or highly alloyed stainless steels are commonly used. 6. Ammonia (ammonium hydroxide): Most metals and non-metals suffer only mild corrosion in liquid ammonia and ammonia water (ammonium hydroxide); only copper and its alloys are not suitable for use. 7. Saltwater (seawater): Ordinary steel exhibits a low rate of corrosion in sodium chloride solutions as well as in seawater and brackish water; coating protection is generally required. Various types of stainless steel also have a low rate of uniform corrosion, but local corrosion may occur due to chloride ions, so 316 stainless steel is usually the better choice. 8. Alcohols, ketones, esters, ethers: Common alcohol-based media include methanol, ethanol, ethylene glycol, propanol, etc.; ketone-based media include acetone, butanone, etc.; ester-based media include various methyl esters, ethyl esters, etc.; ether-based media include dimethyl ether, diethyl ether, butyl ether, etc. These substances generally have no corrosive properties, and most common materials can be used with them. When making a selection, it is necessary to consider the properties of the medium and relevant requirements in order to make a proper choice. It is also worth noting that alcohols, esters, and ethers are soluble in various rubbers, which helps to avoid mistakes when selecting sealing materials. III. Influence of other factors: In general industrial pumps, the leakage in the piping system can be ignored within the process flow; however, the impact of process changes on flow rate must be taken into account. If agricultural pumps are used for water conveyance through open channels, leakage and evaporation rates must also be taken into account. Pressure: suction pool pressure, discharge pool pressure, pressure difference in the piping system (head loss). Piping system data (pipe diameter, length, types and quantities of piping accessories, geometric elevations from the suction tank to the pressure tank), etc. If necessary, the device characteristic curve should also be prepared. IV. Impact of pipes When designing and arranging pipes, the following points should be taken into consideration: A. Select an appropriate pipe diameter – a larger pipe diameter results in a lower flow velocity at the same flow rate, thereby reducing resistance losses; however, it increases costs. A smaller pipe diameter leads to a sharp increase in resistance losses, which in turn requires a pump with higher head pressure, more power to operate the pump, and consequently higher costs and operating expenses. Therefore, a comprehensive consideration from both technical and economic perspectives is necessary. B. The discharge pipe and its fittings should take into account the maximum pressure they can withstand. C. The piping layout should be arranged as straight as possible; accessories within the pipes should be minimized, and the length of the pipes should also be reduced as much as feasible. When bends are necessary, the radius of curvature of those bends should be 3 to 5 times the diameter of the pipe, with the angle being as large as possible, ideally greater than 90°. D. A valve (such as a ball valve or globe valve) and a check valve must be installed on the discharge side of the pump. Valves are used to adjust the operating point of the pump, while check valves prevent the pump from rotating in reverse when fluid flows backward, thus protecting the pump from water hammer effects. (When the liquid flows back, a huge reverse pressure is generated, which can damage the pump.) V. Influence of flow rate and head: Determination of the flow rate: A. If the minimum, normal, and maximum flow rates are specified in the production process, the maximum flow rate should be taken into consideration. B. If only the normal flow rate is specified in the production process, a certain margin should be considered. For the ns100 pumps with high flow rates and low head, a flow margin of 5% is applied; for the ns50 pumps with low flow rates and high head, a flow margin of 10% is used. For pumps with 50 ≤ ns ≤ 100, the flow margin is also 5%. For pumps of poor quality or operating under harsh conditions, a flow margin of 10% should be adopted. C. If the basic data only provides mass flow rate, it should be converted to volume flow rate. VI. Influence of Temperature: The transportation of high-temperature media places higher demands on the pump’s structure, materials, and auxiliary systems. Below are the cooling requirements associated with different temperature levels: 1. For media with temperatures below 120°C, a dedicated cooling system is usually not required; instead, the medium itself is used for lubrication and cooling. Such as DFL(W)H chemical pumps, DFL(W)PH shielded chemical pumps (for temperatures above 90°C, the protection class of the shielded motor should be H grade) ； The standard version of DFCZ and IH chemical pumps can achieve an upper temperature limit of 140°C to 160°C thanks to their suspension structure℃ ； The maximum operating temperature for IHF fluoroplastic pumps can reach 200℃ ； Only the ordinary CQB magnetic pump is designed for use at temperatures not exceeding 100°C. It is worth mentioning that media that are prone to crystallization or contain particles should be equipped with a sealing surface flushing pipeline (interfaces are provided during design). 2. For media with temperatures above 120°C and below 300°C, a cooling chamber is generally required on the pump cover, and the sealing chamber should also be connected to a coolant (a double-end face mechanical seal is necessary). When it is not allowed for the coolant to penetrate into the medium, the medium itself should be cooled before being fed in (this can be achieved using a simple heat exchanger). 3. For high-temperature media above 300°C, not only the pump head section but also the suspension bearing chamber requires a cooling system. The pump structure is generally of a central support type, and metal bellows-type mechanical seals are preferred, although they are expensive (their cost is more than 10 times that of ordinary mechanical seals). VII. Impact of sealing performance: Leak-free operation is an eternal goal for chemical processing equipment, and it is precisely this requirement that has led to the increasing use of magnetic pumps and shielded pumps. However, there is still a long way to go before true leaklessness can be achieved, such as the lifespan issues of the isolation sleeves in magnetic pumps and shielded pumps, the pitting problem of materials, and the reliability of static seals, among others. Here is a brief introduction to some basic aspects of sealing. 1. Sealing types: For static seals, there are generally only two types: gaskets and seals, with O-rings being the most widely used type of seal ； For dynamic sealing, chemical pumps rarely use packing seals; mechanical seals are preferred instead. Mechanical seals come in single-face and double-face types, as well as balanced and unbalanced versions. Balanced mechanical seals are suitable for sealing high-pressure media (typically those with pressures greater than 1.0 MPa). Double-face mechanical seals are used mainly for media that are high-temperature, prone to crystallization, viscous, contain particles, or are toxic and volatile. An isolation fluid must be injected into the sealing chamber using double-face mechanical seals, and its pressure is usually 0.07–0.1 MPa higher than the pressure of the medium. 2. Sealing materials: Fluororubber is generally used as the static sealing material for chemical pumps, while polytetrafluoroethylene is employed only in special cases ； The material selection for the stationary and rotating rings of mechanical seals is quite important. It’s not true that one combination of cemented carbides with another is always the best; high costs are one issue, but it’s also unreasonable if there is no difference in hardness between the two materials. Therefore, it’s best to choose the appropriate materials based on the characteristics of the medium involved. (Note: API 610, 8th edition, of the American Petroleum Institute provides detailed specifications for typical configurations of mechanical seals and piping systems in Appendix D.) VIII. Effect of viscosity: The viscosity of the fluid has a significant impact on the performance of the pump. As viscosity increases, the pump’s head curve declines; both the head and flow rate at the optimal operating conditions decrease, while power increases, resulting in a reduction in efficiency. The parameters for standard samples represent the performance when transporting clean water; adjustments are necessary when transporting viscous media (the correction factors for different viscosities can be found in the relevant conversion tables). For transporting slurries, pastes, and viscous fluids with high viscosity, it is recommended to use screw pumps.