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1 Electrochemical corrosion: To prevent electrochemical reactions in the medium, the same material is generally used for the flow channels of horizontal multi-stage centrifugal pumps. 2. Temperature of the medium: The material requirements for water pumps vary depending on whether they are used in high-temperature or low-temperature environments. Creep occurs at high temperatures, while materials become brittle at very low temperatures. A material that is resistant to corrosion at normal temperatures may not necessarily possess such resistance or heat tolerance at high temperatures; therefore, the material properties must meet the requirements dictated by the temperature of the medium being transported. 3. For pumps with very high single-stage head, the liquid flow velocity is extremely high; therefore, the components that handle this flow must have strong cavitation resistance and good erosion resistance. 4 Wear resistance of solid particles When the medium contains abrasive solid particles, it is necessary to choose materials with high wear resistance. 5 Interference between materials For parts that move relative to each other, such as shaft sleeves, bolts and nuts, impeller sealing rings and pump body sealing rings, etc., the hardness of the materials of these two parts should be different when selecting materials, in order to prevent them from interfering with or scratching each other during installation, removal, and operation. 6. The magnitude of temperature differences on the same component: When there are large temperature differences on the same component during operation, for example when a pump cover is cooled while transporting high-temperature liquids, the area in contact with the medium experiences high temperatures and thus greater expansion, while the area in contact with the cooling water has lower temperatures and therefore less expansion. In such cases, it is advisable to use materials with good plasticity to prevent cracks from forming due to these differing expansions during operation. 7 Parts that require welding Parts that need to be rewelded during casting, processing, or use should be made of materials with good weldability; for example, low-carbon steel has better weldability than high-carbon steel. 8. Cost-effectiveness Different materials result in different performance characteristics, and consequently different prices for the products. Therefore, when several materials can meet the requirements, it is advisable to choose the one with a relatively lower price, provided that its components have good manufacturing quality and standards. 9 Corrosivity of media Different materials have varying corrosion resistance; for example, 1Cr18Ni9 can resist corrosion from nitric acid and organic acids at moderate to high concentrations, but it is not resistant to corrosion by dilute sulfuric acid or hydrochloric acid. Fluoroplastic materials can withstand acids and alkalis of various strengths.