Butterfly valve hard seal means that the sides of the seal pair are made of metal material or other hard materials. It is called "hard seal". This seal has poor sealing performance, but it is resistant to high temperature, abrasion and mechanical properties. : steel + steel; steel + copper; steel + graphite; steel + alloy steel; (the steel here may also be cast iron, cast steel, alloy steel may also be surfacing, sprayed alloy). Soft seal : the side of the seal pair is made of metal material, and the other side is made of elastic non-metallic material. It is called "soft seal". This seal has good sealing performance, but it is not resistant to high temperature and easy to wear. Poor mechanical properties. For example: steel + rubber; steel + PTFE [wiki] polyethylene [/ wiki]; etc. The soft seal seat is made of non-metallic materials with certain strength, hardness and temperature resistance, and the sealing performance is good. Zero leakage can be made, but life and temperature are less adaptable. The hard seal is made of metal and the sealing performance is relatively poor, although some manufacturers claim to be able to make zero leakage. Soft seals can not meet the process requirements for a part of corrosive materials, hard seals can be solved! These two seals can complement each other, and the soft seal is relatively good in terms of sealing, but now the seal of the hard seal can meet the corresponding requirements! The advantage of the soft seal is that the sealing performance is good, and the disadvantage is that it is easy to age, wear, and has a short service life. The hard seal has a long service life, but the seal is relatively inferior to the soft seal. The structural differences are mainly as follows: 1. Structural difference: soft seal butterfly valves are mostly medium-line type hard seals, mostly single eccentric, double eccentric, triple eccentric butterfly valve 2, temperature resistance: soft seal for normal temperature environment. Hard seal can be used in low temperature, normal temperature, high temperature and other environments 3, pressure: soft seal low pressure - normal pressure , hard seal can also be used in medium and high pressure conditions 4, sealing performance: soft seal and three eccentric hard seal butterfly valve sealing performance is better, three eccentric butterfly valve can maintain a good seal in high pressure and high temperature environment. In view of the above characteristics, the soft sealing butterfly valve is suitable for two-way opening and closing and regulation of ventilation and dust removal pipelines, water treatment, light industry, petroleum, chemical industry and other industries. Hard-sealed butterfly valves are mostly used for heating, gas supply, and gas, oil, acid and alkali environments. With the wide use of butterfly valves , the features of convenient installation, convenient maintenance and simple structure are becoming more and more obvious. Electric soft sealing butterfly valves, pneumatic soft sealing butterfly valves, hard sealing butterfly valves, etc. have begun to replace electric gate valves and globe valves in more and more occasions.