Acetic acid (CH₃COOH) transfer through chemical pumps requires the selection of mechanical seals that will provide tightness and reliability when working with organic acid. Acetic acid is a weak organic acid, but it requires materials resistant to its effects, especially at high concentrations or under conditions of elevated temperatures.
1. Seal materials:
Mechanical seal faces:
Ceramic (silicon carbide, aluminum oxide): Ceramic materials have excellent wear resistance and chemical resistance, including organic acids such as acetic acid. Ceramics work well at high pressures and temperatures, providing durability.
Graphite: Graphite can be used for sealing surfaces due to its resistance to acetic acid. However, graphite is brittle and needs to be protected from mechanical wear, for example, with additional coatings.
PTFE (Teflon): PTFE has high chemical resistance to acetic acid and can be used for mechanical seals, as well as for various sealing rings and components that come into direct contact with the liquid.
Stainless steel (316, 904L): Stainless steel, especially in the 316 or 904L variant, is a good choice for metallic seal parts, as it is resistant to corrosion caused by acetic acid and can work at moderate temperatures and pressures.
Elastomers:
FKM (fluoroelastomer, Viton): This material has good resistance to organic acids, including acetic acid, and works well at high temperatures.
EPDM (ethylene propylene diene monomer): EPDM can be used for seals in case of lower concentrations of acetic acid. It is resistant to weak acids and is used at lower temperatures.
PTFE: PTFE-based elastomers can be used for sealing rings, as this material has excellent chemical resistance and good wear resistance.
2. Types of seals:
Mechanical seals: Mechanical sealing is the preferred choice for chemical pumps transferring acetic acid. It provides tightness and prevents liquid leakage, which is critical when working with chemical liquids.
Wet seals: This solution is used for cooling and preventing overheating of seals. In the case of transferring acetic acid at high temperatures, a cooling system may be required.
Dry seals: In some cases, dry seals are possible, especially if the temperature and pressure in the system are controlled, and liquid leakage is not a problem.
3. Design and additional mechanisms:
Dust seals and protective rings: These elements protect seals from contamination, helping to reduce wear and increase durability.
Lubrication and cooling systems: In some cases, a lubrication or cooling system is required to prevent overheating and increase the service life of the seals.
Seal condition monitoring: Using sensors to monitor the condition of the seals allows timely detection of wear and prevention of leaks.
4. Operating conditions:
Temperature: Acetic acid is used at temperatures ranging from -10°C to 60°C, depending on the concentration. The seal must be resistant to these temperature conditions.
Acid concentration: Acetic acid can be used in diluted or concentrated form. For high concentrations, more resistant materials need to be selected.
Pressure: The seal must be designed for the operating pressure at which acetic acid is transferred. The pressure is usually moderate, but it is important for the seal to withstand the loads.
5. Recommendations:
Ceramic, PTFE, or graphite are good materials for sealing faces, as they are resistant to acetic acid.
FKM (Viton) or EPDM can be used for sealing rings at lower acid concentrations.
Stainless steel (316L or 904L) is a suitable choice for metallic seal parts at moderate concentrations of acetic acid.
Conclusion:
For transferring acetic acid, optimal materials for mechanical seals are ceramic, PTFE, graphite, and stainless steel. FKM and EPDM can be used for sealing rings depending on the acid concentration. It is important to choose the right materials to ensure tightness, durability, and safety of pump equipment operation.