What is the difference between hard sealing and soft sealing for the sealing of valve stems and seat rings?

Maybe the original poster didn’t express themselves clearly, or there are spelling mistakes

As the name implies, a soft seal refers to a sealing pair in which one side is made of a material with relatively low hardness. Generally, the soft seal seat is constructed from non-metallic materials that possess certain strength, hardness, and temperature resistance; it provides good sealing performance and can achieve zero leakage, but its lifespan and tolerance to temperature are relatively poor. A hard seal, on the other hand, is made of metal, and its sealing performance is relatively inferior, although some manufacturers claim it can also achieve zero leakage.

One additional point: soft seals cannot meet the process requirements for certain 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 nowadays hard seals also have sealing capabilities that meet the required standards!

It seems to be related to the medium as well as the frequency of use. The gas valves and valve cores used in gas generators employ hard sealing, as the gas contains dust. Moreover, these valves need to be opened once every 1–2 minutes, which is quite frequent! Soft seals simply can’t do it! Reduce maintenance costs!

For both types of hard-sealed valves, cemented carbide is used for cladding; they are more commonly used in high-pressure valves. Soft-sealed valves have harder valve heads and are the most common type: lol

One more thing: in addition to what LS has mentioned, for valves of the same pressure rating, specifications, and model, those with hard seals cost significantly more than those with soft seals! :lol

The internal sealing of a valve is achieved through the sealing pair between the valve stem and the valve seat. When both sides of the sealing pair are made of metallic materials or other hard materials, it is referred to as a \"hard seal.\" This type of seal offers poor sealing performance, but it is resistant to high temperatures, wear, and has good mechanical properties. Examples include steel+steel; steel+copper; steel+graphite; steel+alloy steel (where the steel can also be cast iron or cast steel, and the alloy can be one that has been welded on or sprayed on). When one side of the sealing pair is a metallic material while the other side is an elastic non-metallic material, it is called a \"soft seal.\" This type of seal provides better sealing performance, but it is not resistant to high temperatures, is prone to wear, and has poor mechanical properties. Examples include steel+rubber; steel+tetrafluoroethylene, etc.

Soft seals and hard seals differ in terms of the sealing material used; generally, hard seals are made by welding other alloys onto stainless steel, which gives them greater hardness. Their sealing performance is not as good as that of soft seals, but hard seals offer better corrosion and wear resistance. They should be used in media containing solid particles

Upstairs, for media containing solid particles, a soft seal should be used.