What is the difference between butterfly valve soft seal and hard seal

The difference between soft seal butterfly valve and hard seal butterfly valve:

Soft seal butterfly valve: the two sides of the seal pair are metal material, the other side is elastic non-metallic material is called soft seal, the sealing performance is better, but not high temperature resistance, easy wear, mechanical poor. Soft sealing surface, in the use of soft sealing, the contact of the two sealing surface can be alone, or can all use soft materials, such as plastic and rubber. But the soft sealing material is easy to deform, fill the uneven sealing surface, soft sealing can achieve a high degree of medium sealing performance.

Hard seal butterfly valve, both sides of the seal pair are metal materials or hard other materials known as hard seal, the sealing performance of the seal is poor, but high temperature resistance, wear resistance, mechanical performance is good. Hard seal is made of metal, the sealing performance is relatively poor, soft seal on some corrosive materials can not meet the process requirements, hard seal can be solved. On the other hand, the hard sealing surface is generally made of metal, so it is also known as the metal sealing surface, the metal sealing surface is susceptible to the influence of the medium and the particles in the deformation, the two sealing methods can learn from each other's strengths and weaknesses, in terms of sealing, soft sealing is relatively better, but now the hard sealing sealing can also meet the corresponding requirements, the advantage of soft sealing is good sealing performance, Disadvantages are easy to aging, wear, short service life. The service life of hard seal is long, but the tightness is worse than that of soft seal.