What is the difference between hard seal and soft seal? In what situations are they applied respectively?

I. The main structural differences between soft seals and hard seals are as follows: 1. Temperature resistance: Soft seals are used in normal temperature environments. Rigid seals can be used in environments with low temperatures, normal temperatures, and high temperatures. 2. Pressure: Soft-seal for low to normal pressure; hard-seal can also be used in medium and high pressure applications. 3. Soft-sealed designs often use rubber rings, while hard-sealed designs rely directly on structural elements for sealing, such as labyrinth or conical surfaces. II. Soft seals and hard seals each have their advantages and disadvantages: 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. Advantages of soft seals: The sealing performance can reach level 6, and the valve seat is easy to maintain and replace. The valve has low torque, which helps to reduce the cost of actuators. Low manufacturing costs, inexpensive processing, and short delivery times. It is generally used for relatively clean liquids and gases with low viscosity. The disadvantages are: it cannot withstand high temperatures and is not wear-resistant. Advantages of hard-sealing: Various combinations of valve cores and seats are available, and the use of surface spraying techniques enables the valves to perform well in conditions involving wear resistance, high temperatures, and corrosion, resulting in a long service life. Disadvantages: High manufacturing cost; maintenance and replacement of the valve core and seat usually require full grinding, making on-site maintenance inconvenient. The valve torque is also relatively high. III. Applications: A soft seal refers to a sealing pair in which one side is made of a metallic material, while the other side is made of an 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. Hard sealing refers to a sealing pair in which both sides are made of metallic materials or other harder materials, which is known as \"hard sealing\". This type of seal has poor sealing performance, but it is resistant to high temperatures, wear, and has good mechanical properties. The soft-seal seat is made of non-metallic materials with certain strength, hardness, and temperature resistance, offering good sealing performance that can achieve zero leakage; however, it has a shorter lifespan and limited adaptability to temperature changes. Rigid seals are made of metal, resulting in relatively poor sealing performance. Soft seals cannot meet the process requirements for some corrosive materials, while 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 today hard seals also offer sealing quality that meets the required standards.