End seal for chemical pumps designed for transferring nitric acid

When pumping nitrous acid (HNO₂) through chemical pumps, the use of mechanical seals is required, which have high resistance to corrosion and chemical attacks. Nitrous acid is a strong oxidizing acid that can be aggressive to most materials, and its pumping requires the selection of specially designed seals.Key requirements for mechanical seals for pumping nitrous acid:1. Seal materials:Nitrous acid is a corrosive substance that can corrode many materials, so it is important to choose components resistant to chemical attacks and high levels of corrosion.Seal faces:Ceramic (silicon carbide, aluminum oxide) - a material with high wear resistance and corrosion resistance. Ceramic is suitable for aggressive chemicals, such as nitrous acid.Graphite (with protective coatings, such as metallic layers) - graphite has good resistance to acids, but additional processing is often used to protect against wear and damage.Stainless steel (e.g. 316 or 904L) - resistant to oxidants, such as nitrous acid, especially at low acidity, but additional coatings are better for high concentrations.PTFE (Teflon) - a material with excellent chemical resistance to acids, including nitrous acid. However, its mechanical strength is limited, and it can be used as sealing rings or components.Elastomers:FKM (fluoroelastomer, Viton) - often used for seals in the chemical industry due to good resistance to acids and a high temperature range. However, it should be noted that FKM may not always be resistant to highly oxidizing acids, such as nitrous acid.PTFE - resistant to chemicals, including nitrous acid, and can be used for various types of seals, such as rings and protective elements.EPDM - can be used when working with diluted solutions of nitrous acid, but is not an ideal choice for concentrated acids.2. Types of seals:Mechanical seals - the most suitable type of seals for chemical pumps pumping nitrous acid. Mechanical seals create a tight seal, preventing leakage of chemicals.Wet seals - for pumps where cooling or protection from overheating is necessary. This can be important when pumping nitrous acid, as oxidative reactions can lead to increased wear.Dry seals - possible when cooling is not necessary, but it is important to ensure high tightness.3. Design and additional mechanisms:Dust caps and protective rings - prevent particles and contaminants from entering the sealing area, which is important for extending the service life and maintaining tightness.Lubrication and cooling systems - in some cases, a special system may be required for lubricating or cooling the seals to avoid overheating and wear due to the high chemical activity of the acid.Overheat protection - due to the high oxidizing properties of nitrous acid, it is important to provide cooling or overheat protection systems.4. Operating conditions:Temperature: Nitrous acid can operate in a temperature range from -20°C to 100–120°C depending on the concentration. The seal must be resistant to these temperatures.Acid concentration: With higher concentrations of nitrous acid, the requirements for seal materials increase. In such cases, it is important to use more corrosion and wear-resistant materials.Pressure: Depending on the operating conditions, the seal must withstand the working pressure. Nitrous acid can be pumped at high pressures in some cases, requiring a reliable seal.5. Recommendations:Use ceramic, PTFE, or graphite seals for seal faces. These materials provide resistance to oxidative and chemical properties of nitrous acid.Stainless steel (e.g. 316 or 904L) can be used for metallic seal parts if the acid concentration is low.For elastomers, it is preferable to choose FKM or PTFE to ensure resistance to acid exposure and prevent leaks.Wet seals or cooling systems will help prevent overheating and wear of seals when working with concentrated solutions of nitrous acid.Conclusion:Careful selection of materials for mechanical seals is required for pumping nitrous acid, focusing on resistance to oxidative and aggressive effects. The use of ceramics, PTFE, graphite, and fluoroelastomers will provide reliable sealing and extend the equipment's service life.