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Sealless magnetic drive pumps: Are they products that are limited in terms of lining materials, performance, and size? – It is often said that the pump industry is a “mature” industry, which usually means that no further significant advancements can be expected. In fact, the pump is one of the oldest machines in industrial history. There is still room for improvement and innovation; these efforts are primarily aimed at enhancing the reliability and service life of the machines. First, improvements were made in areas such as production, materials, the hydraulics of the bearing system and design details, as well as the guidance and sealing of rotating components. A major advancement is the introduction of sealless designs (magnetic drive and shielded pumps). The use of other or improved materials has, time and again, opened up new possibilities for applying these proven pump designs. The main driving force behind the development of sealless pump design is the requirements of nuclear power plants and increasingly stringent environmental regulations (Germany’s Clean Air Act, the U.S. Clean Air and Clean Water Acts). Today, in many applications within the chemical industry, leak-free pumps are mandatory. In this case, the operator can only choose between complex mechanical seal systems, canned pumps, and magnetically driven pumps. It is generally agreed that complex mechanical seal systems are quite difficult to operate; shielded pumps are used only in special and mandatory cases, while magnetic drive pumps meet the widest range of requirements. Pumps are one of the oldest machines in industrial history. Its development is mainly reflected in improvements and innovations in reliability and service life. For example, in aspects such as production, materials, design details of the bearing system, guidance and sealing of rotating components, etc. For many operators, from a technical standpoint as well as in terms of cost (the total cost over its lifetime), magnetic pumps are a better choice. The continuously improving safety standards, the need to reduce maintenance costs, and the high reliability of magnetic pumps make them a better choice. This is particularly applicable to magnetically driven centrifugal pumps with plastic linings. Its main application areas are the fine chemical and pharmaceutical industries, where it is used for transporting corrosive chemicals and other critical fluids. “The competition among the \"best\" materials is resolved here in a very practical way: such pumps offer a combination of the best materials – plastic as the lining material for the flow-through parts, metal as the supporting material, and ceramics as the material for the plain bearings, etc. Since such favorable combined properties of materials cannot be obtained from any single material, plastic-lined pumps are usually cheaper than \"pure\" plastic pumps or \"pure\" metal pumps, especially when those latter types need to be made from very expensive special metals; moreover, they are more reliable than \"pure\" plastic pumps. Magnetic drive centrifugal pumps with plastic lining are designed specifically for transporting highly corrosive media, and they offer practical advantages such as durability and reliability. All overcurrent components are either thick full-fluorinated perfluoroalkoxy plastic housings made of solid polytetrafluoroethylene fluoroplastic, or they are made of sintered silicon carbide. As early as 1983, the first magnetic pump with a plastic lining, the MCK series, was introduced; it was later developed for transporting highly corrosive media. Robustness, reliability, and high interchangeability among components of different sizes are some of the specific advantages of this series. All components exposed to excessive currents either have a thick full-fluorinated alkoxyl (PFA) fluoroplastic casing (pump casing, plain bearing housings, impellers, shafts, and inner magnetic cylinders), or are made of solid polytetrafluoroethylene (PTFE) fluoroplastic (inner isolation shields) or sintered silicon carbide (SSiC) (sliding bearings). Plastic-lined sealed magnetic drive pumps have secured a solid and accepted position in the pump market. They are not omnipotent; they are used to transport highly corrosive media with temperatures generally below 210°C, and they are important problem solvers. The dual isolation shield system between the inner and outer magnetic cylinders ensures leak-free operation of the medium. The inner isolation shield made of fluoroplastic has strong corrosion resistance, while the outer isolation shield fabricated from carbon fiber composite material can withstand certain pressure loads. This principle has the following main advantages: the shielding system does not absorb any additional bearing forces; it simply functions as a pressure vessel with a high degree of safety margin. The isolation cover system is not fragile and does not break easily (similar to a ceramic design). The shielding cover provides double safety, as the outer carbon fiber shielding material is also highly corrosion-resistant. Typically, eddy currents present in metal shields cause energy loss, but this will not be the case here; moreover, it also prevents heat from entering the medium. The eddy current problem is usually a key criterion in the use of plastic pumps, as the power consumption due to eddy currents can account for more than one-tenth of the power required by metal magnetic pumps. Compared to mechanically sealed pumps, it offers higher reliability, lower lifecycle costs, and reduced maintenance expenses, which is why it was quickly accepted by the market. It was initially used in the specialty chemicals sector of the chemical industry, but later also in the pharmaceutical and basic chemical industries, FDA applications, and ultra-pure media (semiconductor industry). It eventually evolved into a substitute for high-alloy metal magnetically driven pumps – especially due to the fact that it generates no eddy current losses and considering economic factors. Different applications sometimes lead to the development of special design series as a result of product improvements; vortex pumps are capable of transporting smaller flow rates at higher head pressures. These pumps provide accurate adjustment between the impeller and ring channels. Eddy current pumps feature an enlarged pump chamber and a special impeller geometry; they are the ideal choice when it is necessary to transport very large particles or long fiber particles, or when the particle content is high, or when the gas content in the medium exceeds 5% by volume. Suction pumps have proven to be successful in discharge applications in chemical containers/pools at low levels, and they are also suitable for higher back pressures. What experience have pump designers and operators gained over the years regarding available plastics? (See Figure 3, Table 1) Figure 3: The lining materials for magnetically driven pumps, polypropylene (PP) and polyethylene (PE), can be used as pump linings due to their low thermal resistance and chemical resistance. Polyethylene has much greater wear resistance than polypropylene, while polyvinylidene fluoride (PVDF) has relatively good chemical resistance. Polytetrafluoroethylene (PTFE) and perfluoroalkoxy (PFA) possess excellent chemical resistance. These materials can also be made into conductive materials using additives, and they meet FDA standards. Table 1: Materials for plastic pumps. Since 1970, fluoroplastic linings have been used as a substitute for high-alloy metals in devices such as pumps, valves, control valves, and containers. At the same wall thickness, due to its microstructure, PFA generally exhibits a permeability that is significantly lower than that of PTFE (Figure 4), but they possess the same chemical resistance and thermal resistance. Even the excellent barrier properties of pure PFA are sometimes insufficient to ensure a satisfactory service life in media with particularly high permeability, such as chlorine or bromine compounds. Figure 4: Permeability comparison. For compound PFA-P (“P” stands for “permeation”), a thermoplastically treated variant of PFA exhibits a higher permeation resistance, but the same chemical and thermal resistance. Long-term tests conducted in the laboratory and in field conditions show that, across all operating ranges, the permeability of compound PFA-P is reduced by at least half. Silicon carbide (SiC) is a material known as an engineering ceramic, and it serves as an important material for pump sliding bearings due to its hardness and heat resistance. Shaft sleeves made of silicon carbide are, as the name suggests, used to protect rotating shafts from chemical erosion. Sintered silicon carbide (SSiC) possesses extremely high hardness and comprehensive chemical resistance. Here, this sentence also applies: Perfection is the enemy of excellence: for magnetically driven pumps equipped with traditional uncoated SSiC sliding bearings, any dry operation is unacceptable. Even checking the rotation direction in the absence of a medium can cause the bearing temperature to rise suddenly to several hundred degrees Celsius, leading to damage to the pump. SAFEGLIDE®Plus bearings are much more stable: they have an additional layer of amorphous carbon only a few micrometers thick, featuring a diamond-like microstructure. The properties of the coating are as follows: amorphous structure, isotropy, good adhesion, high hardness (HV0.05 = 4000 to 6000), good elasticity, high wear resistance, excellent surface quality, good thermal conductivity, a heat resistance of up to 300°C, and general chemical resistance – it is not corroded by chemicals. SAFEGLIDE®Plus reduces the friction coefficient of sliding bearings, thereby minimizing friction and temperature rise in such bearings. Due to this effect, pump damage caused by brief dry running can be avoided. Ricite’s magnetic pump features a metal-free dual shielding system: the inner shield is made of corrosion-resistant plastic, while the outer shield is made of carbon fiber reinforced plastic, which can absorb pressure. Carbon fiber reinforced plastic refers to a fiber plastic composite material in which carbon fibers are embedded in a plastic synthetic resin matrix for reinforcement. The shielding cover used in these pumps (Figure 5) is characterized in that the rotating magnet does not generate any eddy currents in the metal-free shielding cover, and therefore no heat is produced. Figure 5: External isolation shield; thus, no driving energy is wasted by introducing heat into the medium. The driving power is 15 – 20% higher than that of a metal shield. For example, using 50-32-160 sizes in a three-shift operation can save over 1,000 euros in energy costs per year. Another advantage is that media with temperatures close to the vaporization point can also be transported safely. Figure 6: Energy density of permanent magnet. The outer magnetic cylinder operates outside the dual shielding enclosures, which serve as barriers between the medium and the surrounding area, while the inner magnetic cylinder rotates inside the dual shielding enclosures. Permanent magnets with the highest energy density are used as materials (Figures 6, 7), such as neodymium-iron-boron magnets (NdFeB) and samarium-cobalt magnets (SmCo). SmCo magnets belong to the rare earths. They provide a high energy density, as well as a very high coercive field strength Hc. Figure 7: The Curie temperature (limiting operating temperature) of permanent magnets, Hc, is an indicator for measuring a magnet’s ability to retain its magnetism. This enables the design of magnet systems to be compacted, allowing them to be used in high temperatures up to +300°C and in strong reverse magnetic fields. Neodymium-iron-boron possesses excellent properties due to the combination of the rare earth element neodymium and iron. Currently, neodymium-iron-boron magnets are widely used in applications that require a strong magnetic field in a compact size.