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Hard seal butterfly valve means that both sides of the sealing pair are metal materials or harder other materials, which are called "hard seals". The sealing performance of the butterfly valve hard seal is poor, but it is resistant to high temperature, wear resistance and has good mechanical properties. Such as: 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 and sprayed alloys).

Both sides of the soft seal butterfly valve sealing pair are metal materials on one side and elastic non-metallic materials on the other side are called "soft seals". This kind of seal has good sealing performance, but it is not resistant to high temperature, easy to wear, and has poor mechanical properties. Such as: steel + rubber; Steel + tetrafluoropolyethylene; The soft seal seat is made of non-metallic materials with certain strength, hardness and temperature resistance, with good sealing performance and zero leakage, but the life and adaptability to temperature are relatively poor.

Hard seals are made of metal, and the sealing performance is relatively poor, although some valve manufacturers claim to be able to make zero-leakage butterfly valves. Soft seal for some corrosive materials can not meet the process requirements, hard seal disc valve can be solved. These two seals can complement each other, soft seals are relatively good in terms of sealing, but now the tightness of hard seals can also meet the corresponding requirements.

The advantage of soft seal disc valve is good sealing performance, and the disadvantage is easy aging, wear and short service life.

Hard seal disc valves have a long service life, but the tightness is relatively worse than that of soft seal butterfly valves.

Structural differences between hard seal butterfly valve and soft seal butterfly valve:

1. Structural differences: soft seal butterfly valves are mostly medium-line butterfly valves, and hard seals are mostly single eccentric butterfly valves, double eccentric butterfly valves, and triple eccentric butterfly valves.

2. Temperature resistance: soft seal is used in normal temperature environment. Hard seals 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 and other working conditions.

4. Sealing performance: soft seal butterfly valve and three-eccentric hard seal butterfly valve have better sealing performance, and three-eccentric butterfly valve can maintain good sealing in high pressure and high temperature environment.

In view of the above characteristics, the soft seal butterfly valve is suitable for the two-way opening and closing and adjustment of ventilation and dust removal pipelines, water treatment, light industry, petroleum, chemical and other industries. Hard seal butterfly valves are mostly used in heating, gas, and gas, oil, acid and alkali environments. With the widespread use of butterfly valve, its characteristics of easy installation, convenient maintenance and simple structure are obvious. Electric soft seal butterfly valve, pneumatic soft seal butterfly valve, hard seal butterfly valve, etc. have begun to replace electric gate valves, globe valves, etc. in more and more occasions.