Core Differences Between Resilient Seals and Metal Seals in Valves

In numerous fields such as industrial fluid control, water supply and drainage, and petrochemicals, valves serve as critical "switches." Among these, sealing performance is the key indicator of valve quality. Based on the materials used for sealing surfaces, valves are primarily divided into two major categories: resilient-sealed valves and hard-sealed valves. Understanding their differences and selecting the appropriate type is essential to ensuring safe, stable, and economical system operation.

The fundamental difference lies in the hardness of the material used on the sealing surface where the valve seat contacts the closing element—such as the disc, ball, or plug.

resilient-Sealed Valves  

Sealing Material: One side of the sealing pair typically uses non-metallic, resilient materials, such as:  

- Rubber (e.g., Nitrile Butadiene Rubber NBR, Ethylene Propylene Diene Monomer EPDM, Fluorocarbon Rubber FKM)  

- Plastics (e.g., Polytetrafluoroethylene PTFE, Reinforced PTFE RPTFE, Nylon, PEEK)  

Working Principle: The elasticity of the resilient material allows it to conform to microscopic irregularities on the sealing surface, creating a tight fit that achieves zero leakage or extremely high-level sealing.  

Advantages:  

- Excellent sealing performance: Can achieve zero leakage with outstanding shut-off capability.  

- Low sealing torque: Due to the resilientness of the material, minimal force is required to deform it and create a seal, enabling smooth and easy operation.  

- Tolerance for particulates: Small impurities may become embedded within the resilient material without compromising the seal.  

- Lower cost: resilient-sealed seats are generally less expensive to manufacture and replace.  

Disadvantages:  

- Poor temperature resistance: Non-metallic materials cannot withstand high temperatures; typical operating ranges are -20°C to 180°C (depending on specific material—PTFE can handle slightly higher temperatures, while rubber types have lower limits).  

- Limited wear and erosion resistance: High-speed fluids or media containing hard particles can quickly cut or erode the resilient sealing surface, leading to seal failure.  

- Limited corrosion resistance: Although PTFE exhibits excellent chemical resistance, rubber materials require careful selection based on the medium.  

- Susceptible to aging: Rubber-based materials may degrade and become brittle under exposure to ultraviolet light or ozone.  

Metal-Sealed Valves  

Sealing Material: Both sides of the sealing pair use metal materials, or combinations of metal with hard non-metallic materials.  

Working Principle: Relies on the inherent hardness of metal, its extremely smooth surface finish, and precise geometric configurations (such as line contact or spherical contact) to achieve sealing. Typically requires significantly greater closing force than resilient seals to tightly compress two rigid surfaces together.  

Advantages:  

- High-temperature tolerance: Suitable for high-temperature applications (above 600°C or even higher), such as steam and thermal oil systems.  

- Exceptional wear and erosion resistance: Ideal for handling abrasive media like particulates, powders, and slurries.  

- High-pressure capability: Offers high mechanical strength, making it suitable for high-pressure conditions.  

- Long service life and anti-aging properties: Metal materials are chemically stable and resistant to aging, often outlasting resilient seals under harsh conditions.  

Disadvantages:  

- Higher relative leakage rate: Due to the rigidity of metal, achieving perfect 100% contact is difficult, making zero leakage challenging (though high-performance metal seals, after precision grinding, can reach very high standards).  

- High operating torque: Greater force is needed to press two hard surfaces together, requiring larger actuators.  

- High manufacturing requirements: To ensure proper sealing, extreme precision in surface finishing, smoothness, and strict heat treatment processes for mating materials are required.  

• Higher cost: Especially when using special alloys or ceramics, metal-sealed valves tend to be more expensive.