There are many differences between hard-seal and soft-seal butterfly valves in terms of sealing materials, structural features, performance, application scenarios, and maintenance costs. These differences are as follows:
1. Sealing Materials
Hard-seal butterfly valves: Both sides of the sealing pair are made of metal or a combination of metal and hard materials such as carbide, such as stainless steel, alloy steel, or tungsten-cobalt alloy. These materials offer high hardness, strength, and wear resistance, and can withstand high temperatures and pressures.
Soft-seal butterfly valves: One side of the sealing pair is made of a soft material such as rubber or tetrafluoroethylene, while the other side is made of metal. Soft materials have excellent elasticity and flexibility, and can compensate for unevenness and deformation of the sealing surface to a certain extent.
2. Structural Features
Hard-seal butterfly valves: These typically utilize a metal-to-metal direct contact seal. The sealing surfaces of the butterfly disc and valve body require high machining precision to ensure sealing performance under harsh operating conditions such as high temperatures and high pressures. To enhance sealing effectiveness, a multi-layered sealing structure or the addition of sealing gaskets is sometimes used.
Soft-seal butterfly valves: These rely on the elastic deformation of the soft sealing material to achieve sealing, and their structure is relatively simple. Soft sealing material is typically embedded in or coated onto the butterfly disc or valve body to form a sealing surface. This structure ensures closer contact between the sealing surfaces when the soft-seal butterfly valve is closed, resulting in a superior seal.
3. Performance
Hard-Seal Butterfly Valve
High-Temperature and High-Pressure Resistance: Able to withstand high temperatures, generally exceeding 425°C, with some special materials capable of withstanding even higher temperatures. It can operate at higher pressures, typically exceeding 1.6 MPa, and even exceeding 10 MPa.
Wear Resistance: Because the sealing surface is made of hard material, it exhibits excellent wear resistance under frequent opening and closing conditions and when the medium contains particles and other impurities, resulting in a longer service life.
Relatively Low Sealing Performance: Minor leakage may occur under some extreme operating conditions, but the hard sealing structure ensures a high degree of sealing reliability under harsh conditions such as high temperature, high pressure, and high wear.
Soft-Seal Butterfly Valve
Excellent Sealing Performance: The soft sealing material adheres tightly to the sealing surface, achieving zero or extremely low leakage rates, making it particularly suitable for applications with stringent sealing requirements.
Good low-temperature adaptability: Soft sealing materials maintain good elasticity and flexibility in low-temperature environments, are less susceptible to brittle cracking, and can operate normally.
Not resistant to high temperatures and high pressures: Generally, operating temperatures are below 120°C, with some applications reaching around 150°C. They can withstand relatively low pressures, typically below 1.6 MPa. Beyond a certain pressure and temperature range, soft materials are prone to deformation, aging, and damage, resulting in a decrease in sealing performance.
4. Application Scenarios
Hard-seal butterfly valves: Widely used in piping systems involving high temperatures, high pressures, and particulate matter in the power, metallurgy, petrochemical, and cement industries. Examples include high-temperature steam pipelines in thermal power plants, blast furnace gas pipelines in the metallurgical industry, and heavy oil pipelines in the petrochemical industry.
Soft-seal butterfly valves: Commonly used in water supply and drainage, sewage treatment, food and beverage, pharmaceutical, and air conditioning applications where sealing performance is critical and medium temperatures and pressures are relatively low. Examples include urban water supply pipelines, aeration pipelines in sewage treatment plants, and material conveying pipelines in food processing plants.
5. Maintenance Cost
Hard-Seal Butterfly Valve: Because the sealing surface and valve body of a hard-seal butterfly valve are made of relatively durable materials, maintenance costs are relatively low under normal use. However, if the sealing surface becomes worn or damaged, repair is more difficult and may require specialized equipment and technicians, resulting in higher repair costs.
Soft-Seal Butterfly Valve: The soft sealing material of a soft-seal butterfly valve is easily affected by the media and environment, requiring regular inspection and replacement of the seals. This results in relatively high maintenance costs. However, seal replacement is relatively simple and inexpensive.
