How to Choose Optimal Packing Material for Industrial Valves

The sealing packing of a valve stem is a crucial component for ensuring the valve operates properly in high-pressure, high-temperature, or corrosive environments. The choice of packing material directly impacts the sealing performance, durability, and maintenance costs of industrial valves. Packing materials are generally categorized into three main types: non-metallic, semi-metallic, and metallic, each with distinct performance characteristics and suitable applications. Below is a detailed introduction to these packing materials for industrial valves and their selection criteria.

Non-Metallic Packing

 
Non-metallic packing materials are widely used in valve sealing applications and include graphite, plastics (such as PTFE), asbestos fibers, and carbon fiber. Each material has unique properties and suitable conditions.

1. Graphite Packing

 
Advantages: Graphite packing offers excellent high-temperature resistance, corrosion resistance, and self-lubrication. It is suitable for sealing high-pressure steam, water, and oil, and maintains stability under extreme conditions.
Usage Conditions: Suitable for temperatures ranging from -200°C to 600°C and nominal pressures up to 32 MPa. Graphite packing can withstand most media except for strong oxidizing agents like fuming sulfuric acid and concentrated nitric acid. Its superior high-temperature and corrosion resistance make it ideal for demanding sealing applications.

2. Plastic Packing

 
Types: Mainly includes PTFE (Polytetrafluoroethylene) and PTFE-impregnated packing.
Advantages: This packing material has excellent corrosion resistance, making it particularly suitable for sealing gases and highly flowing liquids. PTFE's chemical stability allows it to resist most chemical substances.
Usage Conditions: Suitable for temperatures ranging from -200°C to 200°C and nominal pressures up to 32 MPa. Due to its excellent chemical stability, PTFE packing performs exceptionally well in handling corrosive gases and liquids.

3. Asbestos Fiber Packing

 
Advantages: Asbestos fiber packing has good heat resistance, able to withstand temperatures up to 480°C, and exhibits good resistance to weak acids and strong alkalis. The high strength and adsorptive properties of asbestos fibers are notable.
Disadvantages: Asbestos fiber has poor resistance to strong acids, high friction coefficients, and relatively poor thermal conductivity. To improve these shortcomings, asbestos fibers are often impregnated with PTFE emulsion or lubricating grease, or combined with metal wires to reduce friction coefficients and enhance wear and heat resistance.

4. Carbon Fiber Packing

 
Advantages: Carbon fiber packing features high strength, high-temperature resistance, and wear resistance, with relatively low density. The elasticity and flexibility of carbon fibers make them excel in dynamic sealing environments.
Usage Conditions: Suitable for temperatures ranging from -120°C to 350°C and pressures up to 32 MPa. Due to its excellent self-lubrication properties, carbon fiber packing can reliably operate under many harsh conditions.

Semi-Metallic Packing

 
Semi-metallic packing combines the properties of both metals and non-metals and is commonly used in high-temperature, high-pressure, and erosion-resistant applications. Below are several common semi-metallic packings and their characteristics.

1. Metal Foil Wrapped Packing

 
Advantages: Metal foil wrapped packing offers excellent high-temperature resistance, erosion resistance, wear resistance, high strength, and good thermal conductivity. It is suitable for high-temperature and high-pressure conditions, such as those found in the petrochemical and power industries.
Usage Conditions: Capable of withstanding extreme temperature and pressure conditions, suitable for demanding industrial environments.

2. Metal Foil Laminated Packing

 
Advantages: This packing provides similar benefits to metal foil wrapped packing, suitable for high-temperature and high-pressure environments, and performs well in high-impact and corrosive environments.
Usage Conditions: Commonly used under stringent temperature and pressure conditions, providing stable sealing performance.

3. Metal Corrugated Packing

 
Advantages: Metal corrugated packing performs well under high-temperature and high-pressure conditions, offering good elasticity and sealing performance. The corrugated design effectively handles pressure fluctuations and temperature variations.
Usage Conditions: Suitable for high-temperature and high-pressure applications, widely used in energy, chemical, and other fields.

4. Lead Wire Twisted Packing

 
Advantages: Mainly used in strong oxidizing media such as concentrated sulfuric acid at temperatures not exceeding 90°C. Lead wire packing has good adaptability to acidic media.
Usage Conditions: Suitable for acidic and oxidizing environments, effectively resisting chemical corrosion.

5. Lead Ring Packing

 
Advantages: Used in conjunction with asbestos packing, suitable for oil media at temperatures not exceeding 550°C. Lead ring packing offers good high-temperature and corrosion resistance.
Usage Conditions: Mainly used for sealing oil media, capable of withstanding higher temperatures and pressures.

Metallic Packing

 
Metallic packing is used in sealing applications that require high temperature, high pressure, and durability. The primary types are as follows.

1. Metal Wire Packing

 
Advantages: Composed primarily of metal wire, often combined with other materials to enhance high-temperature, wear resistance, and corrosion resistance. Metal wire packing has high mechanical strength and excellent thermal conductivity.
Usage Conditions: Suitable for high-temperature and high-pressure conditions, particularly in industries such as petroleum, chemical, and power, for handling high-temperature gases and liquids. Its main advantages include good erosion resistance and long-term stability.

2. Metal Strip Packing

 
Advantages: Made from rolled metal strips, this packing offers high temperature and pressure resistance. Its design effectively reduces leakage and withstands higher pressure fluctuations.
Usage Conditions: Suitable for high-temperature and high-pressure conditions, especially where extremely high sealing performance is required. Metal strip packing is widely used for sealing high-temperature gases, such as in gas turbines and petrochemical equipment.
 
Choosing the right packing material is crucial in valve design and maintenance. Each type of packing material—whether non-metallic, semi-metallic, or metallic—has unique performance characteristics and application ranges, directly impacting the valve's sealing performance, durability, and overall operational efficiency. By understanding the advantages and limitations of different packing types and their suitable conditions, one can select the most appropriate packing for specific operational needs, thereby enhancing the reliability and long-term stability of the valve system.