Butterfly Valves: Choosing Between Hard and Soft Seals

In the realm of industrial valves, butterfly valves play a crucial role in regulating the flow of fluids within pipelines. One key aspect to consider when selecting a butterfly valve is the type of seal it employs, with options falling into two main categories: hard seal and soft seal. In the following parts, we will mainly talk about the differences between hard seal butterfly valve and soft seal butterfly valve, in terms of the materials, strcutures and applications. 
Hard Seal Butterfly Valves
Hard seal butterfly valves feature sealing surfaces on both sides made of metal or other hard materials. These seals, often referred to as "hard seals," exhibit lower sealing performance but boast high-temperature resistance, wear resistance, and excellent mechanical properties. Examples include steel-to-steel, steel-to-copper, steel-to-graphite, and steel-to-alloy steel connections. It's important to note that the term "steel" here can encompass cast iron, cast steel, alloy steel, or even deposited and sprayed alloys.
Soft Seal Butterfly Valves
On the other hand, soft seal butterfly valves employ a sealing surface with one side made of metal and the other side utilizing an elastic non-metal material, termed a "soft seal." These seals provide better sealing performance but are less resistant to high temperatures, prone to wear, and exhibit inferior mechanical properties. Examples include steel-to-rubber and steel-to-polytetrafluoroethylene (PTFE). Soft seal seats are crafted from non-metal materials with specific strength, hardness, and temperature resistance, ensuring excellent sealing performance and minimal leakage. However, they tend to have a shorter lifespan and lower temperature adaptability.
Structural Differences: Hard Seal Butterfly Valves vs. Soft Seal Butterfly Valves
The structural disparities between hard and soft seal butterfly valves are notable:
1. Structural Types: Soft seal butterfly valves are predominantly of the centerline type, while hard seal valves are commonly single eccentric, double eccentric, or triple eccentric.
2. Temperature Resistance: Soft seal valves are suitable for ambient temperature conditions, while hard seal valves can operate in low, ambient, and high-temperature environments.
3. Pressure Range: Soft seal butterfly valves are designed for low to ambient pressure, whereas hard seal valves can handle medium to high-pressure conditions.
4. Sealing Performance: Both soft and hard seal butterfly valves offer good sealing performance. Soft seal valves maintain excellent sealing even in high-pressure and high-temperature environments.
Application Considerations
Considering these characteristics, soft seal butterfly valves are well-suited for applications such as bidirectional opening and closing in ventilation and dust removal pipelines, as well as in industries like water treatment, light industry, petroleum, and chemicals. On the other hand, hard seal butterfly valves find their place in environments dealing with heating, gas supply, as well as gases, oils, acids, and bases.
In conclusion, the choice between hard and soft seal butterfly valves depends on the specific operational conditions and requirements of the application. Understanding the advantages and limitations of each type is essential for ensuring optimal valve performance in diverse industrial scenarios.

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