Sealing Materials
Material Types
Soft-Sealing Gate Valves: Use non-metallic materials like rubber or polytetrafluoroethylene (PTFE) for sealing. These materials offer flexibility and good sealing performance but are less durable under extreme conditions.
Hard-Sealing Gate Valves: Utilize metallic materials such as stainless steel, copper, or alloy steels. These materials ensure high durability and are suitable for more demanding environments.
Soft Sealing
Involves one metal component and one non-metallic, elastic component.
Offers excellent sealing performance, but the non-metallic part is not suitable for high-temperature applications.
Common combinations include steel with rubber or steel with PTFE.
Hard Sealing
Both sides of the sealing pair are made from metal or other hard materials.
Provides good resistance to high temperatures and wear but typically does not offer as tight a seal as soft-sealing.
Examples include steel with steel, steel with copper, or steel with alloy materials like graphite.
Construction Process
The construction and manufacturing process for hard-sealing gate valves is more intricate due to the need for precise machining and alignment of the metal components. The valve body often undergoes hardening, and continuous grinding is necessary to achieve a proper seal.
Soft-sealing gate valves are easier and faster to manufacture because the non-metallic sealing material does not require the same level of machining precision.
Conditions of Use
Sealing Performance
Soft Sealing: Can achieve zero leakage at moderate temperatures and pressures.
Hard Sealing: Typically allows for some minor leakage but can be used in high-temperature and high-pressure environments without degradation.
Temperature Resistance
Soft Sealing: May fail or degrade at high temperatures, necessitating additional fire protection measures.
Hard Sealing: Can withstand high temperatures without leaking or degrading.
Corrosive Media
Soft Sealing: Not suitable for highly corrosive media due to the potential for material degradation.
Hard Sealing: Preferred in corrosive environments as metals like stainless steel or copper offer better resistance to chemical attack.
Low Temperature
Soft Sealing: Elastic materials may become brittle and leak at ultra-low temperatures.
Hard Sealing: Remains effective at very low temperatures, ensuring reliable sealing.
Equipment Selection
Application Considerations
Soft-Sealing Gate Valves: Suitable for applications requiring a perfect seal at moderate temperatures and pressures, and where the medium is not abrasive or corrosive.
Hard-Sealing Gate Valves: Ideal for high-temperature, high-pressure environments or when dealing with abrasive or corrosive media. They are also the choice for applications where the fluid may contain solid particles.
Difference in Service Life
Soft-Sealing Valves
Generally have a shorter lifespan due to material wear and aging.
Require periodic maintenance or replacement to maintain optimal sealing performance.
Hard-Sealing Valves
Offer a longer service life because of the durability of metal components.
May have lower initial sealing performance but maintain functionality over a longer period, even in harsh conditions.
Conclusion
The choice between soft-sealing and hard-sealing gate valves depends on the specific application requirements. Soft-sealing valves are preferable for low-temperature and non-corrosive environments where a perfect seal is crucial. In contrast, hard-sealing valves are better suited for high-pressure, high-temperature, and corrosive applications where durability and long service life are essential.By understanding these differences, you can make informed decisions about which type of gate valve is best suited for your needs.
