Eight factors to consider when purchasing a pump

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http://p1.pstatp.com/large/pgc-image/1533023232973365de9444f I. Basic criteria 1. Flow rate is one of the important performance parameters for selecting pumps. 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 taken as the basis, with consideration also given to the normal flow rate. In the absence of a specified maximum flow rate, 1.1 times the normal flow rate can generally be used as the maximum flow rate. 2. The head required by the installation system is another important performance parameter for selecting a pump. Generally, the head should be selected with a 5% to 10% margin of increase. 3. Liquid properties. This includes the name of the liquid medium, its physical properties, chemical properties, and other characteristics. The physical properties include temperature, density, viscosity, the diameter of solid particles in the medium, and the gas content, etc. These factors are relevant to determining the system’s head pressure, calculating the effective net positive suction head, and selecting the appropriate type of pump. Chemical properties, primarily 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 required for pumping and to verify the net positive suction head. 5. There are many aspects to the operating conditions. For liquid handling, these include the saturated vapor pressure P, 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 dangerous. It is essential to choose the appropriate material based on the specific environment. I will provide more detailed information on which materials to use in different environments next time. III. 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. The impact of pipes: When designing and arranging pipes, the following points should be taken into account: A. Choose the pipe diameter appropriately. 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, greater power consumption, and higher costs as well as operating expenses. Therefore, it should be considered from both technical and economic perspectives. B. The discharge pipe and its fittings should take into account the maximum pressure they can withstand. C. The pipe 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 pipes, 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 the liquid 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: If minimum, normal, and maximum flow rates are specified in the production process, the maximum flow rate should be taken into consideration ； If only the normal flow rate is specified in the production process, a certain margin should be considered. If the basic data only provides mass flow rate, it should be converted to volume flow rate. For the ns100 pumps with high flow rates and low head, a flow rate margin of 5% is applied; for the ns50 pumps with low flow rates and high head, a flow rate margin of 10% is used. For pumps with 50 ≤ ns ≤ 100, the flow rate margin is also 5%. For pumps of poor quality or operating under harsh conditions, a flow rate margin of 10% should be adopted. 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 necessary; the medium itself is often used for lubrication and cooling purposes. 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 noting 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 coolant (a double-end face mechanical seal is necessary). When it is not allowed for 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 but also the suspension bearing chamber requires a cooling system. The pump structure is generally of a central support type, and metal diaphragm seals are the preferred choice for mechanical seals, although they are expensive (their cost is more than 10 times that of ordinary mechanical seals). VII. The 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 magnetic pump isolation sleeves and shielded pump shielding sleeves, the problem of pitting in materials, and the reliability of static seals, among others. Here is a brief introduction to some basic aspects of sealing. 1. For static sealing, the common forms of seals are gaskets and rings; among these, O-rings are the most widely used ； For dynamic seals, 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, with its pressure generally being 0.07–0.1 MPa higher than that of the medium. 2. Sealing materials: The static sealing material for chemical pumps is generally fluororubber; polytetrafluoroethylene is used 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 works best with another; 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 materials based on the characteristics of the medium being handled. VIII. Effect of viscosity: The viscosity of the medium 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 lower efficiency. The parameters for typical samples represent the performance when transporting clean water; conversions are required when transporting viscous media (the correction factors for different viscosities can be found in the relevant conversion tables). For the transfer of slurries, pastes, and viscous liquids with high viscosity, it is recommended to use screw pumps.