The role of hard seal in butterfly valve is mainly reflected in the following aspects, especially in harsh working conditions:

1. High temperature and high pressure resistance

- High temperature stability: Hard seal materials (such as stainless steel, alloy or surface welded carbide) can maintain structural stability at high temperature, avoiding the sealing failure caused by softening or decomposition of soft seal materials (such as rubber, PTFE) at high temperature.

- High pressure adaptability: The rigid structure of the metal sealing surface can withstand higher pressure to prevent deformation or crushing of the sealing surface.

2. Wear resistance and particle erosion resistance

- In media containing solid particles or high flow rate, the hard seal surface reduces wear through high hardness materials (such as tungsten carbide) and extends the life of the valve. It is especially suitable for impurity-containing fluids such as coal chemical industry and mining.

3. Corrosion resistance

- Using corrosion-resistant alloys (such as Hastelloy, Monel) or surface coating technology, hard seals can resist corrosive media such as strong acids and alkalis, and avoid chemical erosion of soft sealing materials.

4. Long life and low maintenance

- The hard seal structure wears slowly under frequent opening and closing or harsh working conditions, reducing the replacement frequency and maintenance cost, and is suitable for fields with high reliability requirements such as nuclear power and petrochemicals.

5. Wide temperature range adaptability

- The thermal expansion coefficient of metal materials is controllable, and can maintain sealing performance in the range of -196℃ (deep cold) to 600℃ (high temperature), which is suitable for LNG or high-temperature steam systems.

6. Special structural design to enhance sealing

- Multi-layer hard seals (such as metal + graphite gaskets) or eccentric designs can compensate for processing errors, improve the sealing level (such as reaching ANSI VI level), and take into account rigid sealing and slight elastic deformation.

Compared with the limitations of soft seals:

Although soft seals have better sealing performance at room temperature and low pressure (can reach zero leakage), they are limited by the material's temperature resistance (usually ≤200℃) and anti-aging ability, and are prone to rapid failure in high temperature, particle-containing or corrosive media.

Conclusion: The hard-sealed butterfly valve is designed for extreme working conditions through material and structure optimization, balancing sealing reliability and durability. It is an irreplaceable key component in the fields of energy, heavy industry, etc.