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A “soft seal” refers to a seal pair in which one side is made of metal material and the other side is made of elastic non-metallic material. This type of seal has good sealing performance, but it is not resistant to high temperatures, is prone to wear, and has poor mechanical properties. e.g.: Steel + rubber ； Steel + PTFE, etc. The soft-seal seat is made of non-metallic materials with certain strength, hardness, and temperature resistance, offering good sealing performance and the ability to achieve zero leakage; however, its lifespan and adaptability to temperature are relatively poor. Hard seal: A sealing pair in which both sides are made of metal materials or other harder materials is referred to as a “hard seal”. This type of seal has poor sealing performance, but it is resistant to high temperatures, wear, and has good mechanical properties. For example: steel + steel ； Steel + Copper ； Steel + Graphite ； Steel + alloy steel ； (The steel here could also be cast iron, cast steel, or alloy steel; it might also be an alloy applied through surfacing or spraying.) Rigid seals are made of metal, and their sealing performance is relatively poor, although manufacturers claim to be able to achieve zero leakage. Soft seals cannot meet the process requirements for some corrosive materials, but hard seals can solve this issue! These two types of seals can complement each other; in terms of sealing performance, soft seals are relatively better, but nowadays hard seals also have sealing capabilities that meet the required standards! The advantage of soft seals is their good sealing performance, while the disadvantages are that they tend to age and wear out easily, resulting in a short service life. Rigid seals have a long service life, but their sealing performance is relatively inferior to that of soft seals. The main structural differences are as follows: 1. Structural differences: Soft-sealed butterfly valves are usually of the centerline type, while hard-sealed ones are typically single-eccentric, double-eccentric, or triple-eccentric butterfly valves. 2. Temperature resistance: Soft seals are suitable for use in normal temperature environments. Hard seals can be used in environments with low temperatures, normal temperatures, and high temperatures. 3. Pressure: Soft seals are suitable for low to normal pressure conditions, while hard seals can also be used in medium to high pressure applications. 4. Sealing performance: Both soft seals and triple-eccentric hard seal butterfly valves offer good sealing performance; triple-eccentric butterfly valves can maintain effective sealing in high pressure and high temperature conditions.