1. Soft seal:

One side of the sealing pair is made of metal materials and the other side is made of elastic non-metallic materials, which is called "soft seal". The sealing performance of the seal is good, but it is not resistant to high temperature, easy to wear and poor mechanical performance. Such as: rubber; Tetrafluoropolyethylene, etc. The soft seal seat is made of non-metallic materials and has certain strength, hardness and temperature resistance. Good sealing performance, zero leakage can be achieved, but poor service life and temperature adaptability.

2. Hard seal:

Both sides of the sealing pair are metal materials or other hard materials, which is called "hard seal". The sealing performance of this seal is poor, but it has good high temperature resistance, wear resistance and mechanical properties. Such as copper; Graphite; Alloy steel（ The steel here can also be cast iron, cast steel, alloy steel, surfacing and spraying alloy).

Hard seals are made of metal and have relatively poor sealing performance, although some manufacturers claim to achieve zero leakage. The soft seal can not meet the process requirements for some corrosive materials, and the hard seal can be solved. The two seals can complement each other. Soft seal is relatively good in sealing, but now the hard seal can also meet the corresponding requirements. The advantages of soft seal are good sealing performance, while the disadvantages are easy aging, wear and short service life. The service life of hard seal is long, but the sealing performance is worse than that of soft seal.

The main structural differences are as follows:

1. Structural difference: most soft seal butterfly valves are linear hard seal, and most are single eccentric, double eccentric and triple eccentric butterfly valves.

2. Temperature resistance: soft sealing at room temperature. 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 under high pressure and other conditions.

4. Sealing performance: the soft sealing and three eccentric hard sealing butterfly valves have good sealing performance. The three eccentric butterfly valve can maintain good sealing performance under high pressure and high temperature environment.

As the butterfly valve has the characteristics of convenient installation, maintenance and simple structure, it replaces gate valve and stop valve in more and more occasions.