Sep.19.2024
Soft sealing refers to the sealing between metal and non-metal, while hard sealing is the sealing between metal and metal. Both soft-sealing gate valves and hard-sealing gate valves are sealing materials. Hard sealing is achieved through precision machining of valve seat materials to ensure the accuracy of the fit with the valve core (ball), usually made of stainless steel or copper. Soft sealing refers to the non-metallic sealing material embedded in the valve seat. Due to the elasticity of the soft sealing material, the requirement for machining accuracy is relatively lower compared to hard sealing. Let's delve into the differences between soft sealing gate valves and hard sealing gate valves.
I. Sealing Materials
1. The sealing materials used in the two differ. Soft-sealing gate valves typically use materials such as rubber or polytetrafluoroethylene (PTFE), while hard-sealing gate valves use metals like stainless steel.
2. Soft Sealing: One side of the sealing pair is metal, and the other side is elastic non-metallic material, referred to as "soft sealing." Such gate valves offer good sealing effects but are not resistant to high temperatures, prone to wear, and have poorer mechanical performance. Examples include steel + rubber; steel + PTFE, etc.
3. Hard Sealing: Both sides of the sealing pair in hard sealing are made of metal or other harder materials. Such gate valves have poorer sealing performance but are resistant to high temperatures, wear, and have good mechanical performance. Examples include steel + steel; steel + copper; steel + graphite; steel + alloy steel; (cast iron, alloy steel, spray-coated alloy, etc., can also be used).
II. Construction Process
The task environment in the mechanical industry is complex, often involving ultra-low temperatures, low pressures, high media resistance, and strong corrosion. Technological advancements have led to the widespread adoption of hard-sealing gate valves.
Consideration must be given to the hardness relationship between metals. In reality, both hard-sealing and soft-sealing gate valves require hardening of the valve body, and continuous grinding between the valve plate and the valve seat is necessary to achieve sealing. The production cycle for hard-sealing gate valves is longer due to the need for hard sealing.
III. Conditions of Use
1. Soft sealing can achieve zero leakage, while hard sealing can be adjusted according to requirements.
2. Soft sealing may leak at high temperatures and requires fire prevention measures, while hard sealing does not leak at high temperatures. Hard-sealing emergency shutdown valves can be used under high pressure, while soft sealing cannot.
3. For corrosive media, soft sealing cannot be used, and hard sealing should be employed.
4. At ultra-low temperatures, soft sealing materials may leak, while hard sealing does not have such issues.
IV. Equipment Selection
Both types of sealing can achieve level six sealing, usually chosen based on the differences in process media, temperature, and pressure. Hard sealing is preferred when the medium contains solid particles or is prone to wear, or when the temperature exceeds 200 degrees Celsius. If the torque of the shut-off valve is high, a fixed hard-sealing gate valve should be selected.
V. Difference in Service Life
The advantage of soft sealing lies in its good sealing performance, but it is prone to aging, wear, and has a shorter service life. Hard-sealing valves have a longer service life but poorer sealing performance compared to soft sealing. They can complement each other.
The above are the differences between soft-sealing gate valves and hard-sealing gate valves. Hopefully, this knowledge sharing will be helpful in your procurement work.
