How to select a chemical pump?

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I. Corrosion resistance issues: 1. Sulfuric acid: As one of the highly corrosive substances, sulfuric acid is an important industrial 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 (0Crl18Ni9) and 316 (0Cr18Ni12Mo2Ti) also have limited utility in sulfuric acid media. Therefore, pump valves 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 fluorine-lined pumps (F46) a more economical option. The company’s applicable products include the fluoroplastic alloy pump series: CQBF type fluoroplastic alloy magnetic pump (CQBF fluoropolymer alloy magnetic pump), VYF type fluoroplastic reinforced alloy submersible pump (VYF pump), VFS type fluoroplastic reinforced alloy centrifugal pump (VFS fluoropolymer alloy pump), and IHF type fluoroplastic reinforced alloy centrifugal pump (IHF pump). 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. The fluoroplastic alloy pump series is suitable for use with nitric acid: Most metals are rapidly corroded and damaged by nitric acid, while 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 typically used, as well as fluoroplastic alloy pump series. 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 harsh conditions such as high-temperature, high-concentration acetic acid or the presence of other corrosive substances, high-alloy stainless steel or fluoroplastic pumps can be used. 5. Bases (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 100°C and concentrations below 75%; although corrosion increases, it remains cost-effective. Compared to cast iron, ordinary stainless steel does not offer any significant advantage in terms of corrosion resistance to alkaline solutions; stainless steel is recommended as long as a small amount of iron can be tolerated in the medium. For high-temperature alkaline solutions, titanium and titanium alloys or super austenitic stainless steels are commonly used. Ordinary cast iron pumps can be used for alkalis at normal temperature and low concentration; for special requirements, various stainless steel pumps or fluoroplastic pumps can be employed. 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. Many of our corrosion-resistant chemical pumps are suitable for use in 7. Saltwater (seawater): Ordinary steel does not suffer high rates of corrosion in sodium chloride solutions, seawater, or brackish water; coating protection is generally required ； Various types of stainless steel also have very low uniform corrosion rates, but local corrosion may occur due to chloride ions; therefore, 316 stainless steel is generally the better choice. 8. Alcohols, alkanes, esters, ethers: Common alcohol-based media include methanol, ethanol, ethylene glycol, propanol, etc.; alkanes include propane, butane, etc.; ester-based media include various methyl esters, ethyl esters, etc. Ether-based media include dimethyl ether, diethyl ether, butyl ether, etc. They are virtually non-corrosive, and common materials can be used for them; however, a reasonable choice should be made based on the properties of the medium and relevant requirements. It is also worth noting that ketones and ester ethers are soluble in various rubbers, which helps to avoid mistakes when selecting sealing materials. II. Sealing issues: 1. Sealing types: For static sealing, there are usually only two types – gaskets and seals, with seals being 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. Single-face mechanical seals are suitable for sealing high-pressure media (typically those with a pressure greater than 1.0 MPa), while double-face mechanical seals are used 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 seal chamber using double-face mechanical seals, with its pressure generally being 0.07–0.1 MPa higher than that of the medium. 2. Sealing material: Fluororubber is generally used as the static sealing material for chemical pumps, with polytetrafluoroethylene being 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 the appropriate materials based on the characteristics of the medium being handled. III. Viscosity issue: 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 optimal operating conditions decrease, while power consumption increases, resulting in reduced efficiency. The parameters on the standard sample represent the performance when transporting clean water; a conversion is 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 or rotor pumps.