Butterfly valve hard seal means that both sides of the sealing pair are made of metal or other hard materials, which is called "hard seal". The sealing performance of this kind of seal is poor, but it has high temperature resistance, wear resistance and good mechanical performance. Soft seal refers to the sealing pair with metal material on one side and elastic non-metal material on the other side, which is called "soft seal". This kind of seal has good sealing performance, but it is not resistant to high temperature, easy to wear and has poor mechanical property.

The soft seal seat is made of non-metallic materials with certain strength, hardness and temperature resistance. It has good sealing performance and can achieve zero leakage, but its service life and adaptability to temperature are relatively poor. The hard seal is made of metal and its sealing performance is relatively poor, although some manufacturers claim that it can achieve zero leakage. Soft seal can not meet the process requirements for some corrosive materials. Hard seal can solve this problem! These two kinds of seals can complement each other. As far as the sealing performance is concerned, the soft seal is relatively good, but now the sealing performance of the hard seal can also meet the corresponding requirements. The advantages of soft seal are good sealing performance, and the disadvantages are easy aging, wear and short service life. The service life of hard seal is long, but the sealing performance is relatively worse than that of soft seal.

The structural differences are as follows:

1. Difference in structure: most of the soft seal butterfly valves are medium type hard seal butterfly valves with single eccentricity, double eccentricity and three eccentricity

2. Temperature resistance: soft seal is used in normal temperature environment. Hard seal can be used in low temperature, normal temperature, high temperature and other environments

3. Pressure: soft seal low pressure atmospheric pressure, hard seal can also be used in medium and high pressure pneumatic soft seal butterfly valve

4. Sealing performance: soft sealing and three eccentric hard sealing butterfly valves have better sealing performance, and three eccentric butterfly valves can keep good sealing under high pressure and high temperature environment.

In view of the above characteristics, the hard seal butterfly valve has been widely used in many fields, such as petroleum, chemical industry, metallurgy, hydropower and so on, as a component to realize on-off and flow control of pipeline system. The soft sealing butterfly valve is suitable for two-way opening and closing and regulating of ventilation and dust removal pipeline, water treatment, light industry, petroleum, chemical industry and other industries. Hard seal butterfly valve is mainly used for heating, gas supply, gas, oil, acid and alkali environment.