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What is the difference between soft seal gate valve and hard seal gate valve?

2023-11-10 11:26:49

Soft seal gate valves and hard seal gate valves are commonly used devices for regulating and shutting off the flow. Both have good sealing performance and are widely used. They are one of the products purchased by Wesdom customers in large quantities. Some new purchasers may be curious.

They are both gate valves. What are the specific differences between them?

Soft seal is the seal between metal and non-metal, and hard seal is the seal between metal and metal. Both soft seal gate valves and hard seal gate valves are made of sealing materials. The hard seal is precision machined from the valve seat material to ensure the accuracy of matching with the valve core (ball), usually stainless steel and copper. Soft seal means that the sealing material embedded on the valve seat is non-metallic material. Since the soft sealing material has a certain elasticity, the processing accuracy requirements will be lower than that of a hard seal.

Let’s take a look at the differences between soft seal gate valves and hard seal gate valves from five aspects.

1. Sealing materials:

① The sealing materials of the two are different:

Soft seal gate valves are usually made of materials such as rubber or polytetrafluoroethylene. Hard seal gate valves use metals such as stainless steel.

② Soft seal:

One side of the two sides of the sealing pair is made of metal material, and the other side is made of elastic non-metallic material, which is called “soft seal”. This type of gate valve has good sealing effect, but is not resistant to high temperatures, is prone to wear, and has poor mechanical properties. Such as: steel + rubber; steel + PTFE, etc.

Soft seal gate valve

③ Hard seal:

The sealing pair of the hard seal is made of metal material or other harder materials on both sides. This type of gate valve has poor sealing performance, but is resistant to high temperatures, wear and tear, and has good mechanical properties. Such as steel + steel; steel + copper; steel + graphite; steel + alloy steel; (cast iron, alloy steel, spray-painted alloy, etc. can also be used).

Hard seal gate valve

2. Construction technology

The working environment of the machinery industry is complex, many of which are ultra-low temperature and low pressure, with large medium resistance and strong corrosiveness. Nowadays, technological advancement has made hard-sealed gate valves popular.

The hardness relationship between metals must be considered. In fact, hard-sealed gate valves are the same as soft-sealed valves. The valve body needs to be hardened, and the valve plate and valve seat must be continuously ground to achieve sealing. The production cycle of hard-sealed gate valves is longer.

3. Conditions of use

① The soft seal can achieve zero leakage, while the hard seal can be adjusted in height according to requirements;

② Soft seals may leak at high temperatures, so pay attention to fire prevention; while hard seals will not leak at high temperatures. The hard seal of the emergency shut-off valve can be used under high pressure, but the soft seal cannot be used.

③ For some corrosive media, soft seals cannot be used and hard seals can be used;

④ At ultra-low temperatures, soft seal materials may leak, while hard seals do not have such problems.

4. Equipment selection

The sealing level of both can reach level six. The appropriate gate valve is usually selected based on the process medium, temperature and pressure. Generally, it is best to choose a hard seal when the medium contains solid particles or is worn, or when the temperature exceeds 200 degrees. If the shut-off valve has a large torque, a fixed hard-sealed gate valve should be selected.

5. Differences in service life

The advantage of soft seal is good sealing performance, but the disadvantage is that it is easy to age, wear and have a short life. Hard seals have a longer service life, but their sealing performance is worse than soft seals. The two can complement each other.

WESDOM Group specializes in pipeline fluid systems: R&D, production and sales of valves, pipe fittings, water meters, flow meters, etc. The products cover cast iron, cast steel, stainless steel, copper, plastics and other materials, which are widely used in hydropower stations, heat, buildings, Water supply and drainage, petroleum, chemical industry, electric power, medical and other fields.


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