Soft and hard seal are able to complement each other. The seal ability of soft one is better than hard one, however, hard seal now can also meet some requirements.
Soft seal has better sealing ability, but can easily age, wear and has a short lifespan. Hard seal can be used longer, but has poorer sealing ability.
Characters of Soft Seal
Valves
Soft seal: one side of the seal is metal, while another the other side is elastic nonmetallic materials. This is “soft seal”. It has great sealing ability, but can difficultly resist wear and high temperature with bad mechanical properties, For example, such as steel+rubber; steel+Polyethylene tetrafluoride, etc.
One side of soft seal is made of low-hardness materials. Generally speaking, the seat of soft seal should be made from nonmetallic materials of relatively strong, hard and resisting high temperature. Therefore, its sealing ability can be so good and even has no leakage, but the life span and adaptability to temperature are terrible. Hard seal is made of metal materials so its sealing is not so good, although some manufacturers declare that theirs have no leakage. Soft seal cannot be able to resist some caustic materials, while the hard one can deal with that.
Hard Seal: the seal whose both sides are made of metal or other harder materials is called “hard seal”. Its seal ability is poor, while its wear and high temperature resistance as well as mechanical capacity are good, such as steel+steel, steel+copper, steel+graphite, steel+alloy steel; (Steel here can be cast iron or cast steel, and the alloy steel can be welded or spraying alloy).
