Metal Seated And Soft Seated Butterfly valve

Hard-sealed and soft seated butterfly valve are two main categories of butterfly valves used in industrial pipeline systems. They are classified based on sealing materials and structural design, each suited for different pressure, temperature, and media conditions. These valves are widely applied in municipal, chemical, power generation, and metallurgical industries, serving as essential devices for flow isolation and regulation.

Structure and Sealing Principles
Both valve types operate by rotating the disc through 0°–90° to open or close the flow path. The primary difference lies in the sealing materials and contact mechanisms.

Soft-Seated Butterfly Valves
Soft-seated butterfly valves use flexible sealing materials such as rubber (EPDM, NBR) or polytetrafluoroethylene (PTFE) for the valve seat, with discs typically made of stainless steel. During closing, the disc compresses the flexible seat, creating elastic deformation that forms a tight seal. This elastic sealing structure is usually centerline-designed, offering symmetrical flow paths and low flow resistance.

Metal-Seated Butterfly Valves
Metal-seated butterfly valves feature both disc and seat made of metal materials, such as stainless steel, tungsten carbide, or Stellite alloys. These valves are commonly designed with single-, double-, or triple-eccentric structures. During operation, the disc disengages from the seat through eccentric movement, preventing friction and wear. Upon closing, the eccentric torque generates forced sealing pressure, forming a rigid metal-to-metal seal suitable for high-temperature and high-pressure conditions.

Performance and Application Suitability

Sealing Performance and Leakage Rating
Soft-seated butterfly valves offer excellent sealing performance, achieving leakage ratings up to API 6D Class VI (bubble-tight), making them ideal for water, wastewater, and mildly corrosive media where tight sealing is critical. Metal-seated butterfly valves typically meet ISO 15848 Class B leakage standards, with high-performance designs reaching Class A, ensuring reliable isolation in industrial processes.

Temperature, Pressure, and Media Compatibility
Soft-seated butterfly valves are limited by seal material temperature resistance, generally operating between -20°C and 150°C with pressure ratings from PN10 to PN40. They are not suitable for high-temperature, highly corrosive, or particulate-laden media. In contrast, metal-seated butterfly valves operate across a wide temperature range from -40°C to 650°C and pressure classes from PN10 to PN420. They are well suited for steam, flue gas, slurry, acids, alkalis, and other severe service conditions.

Operation and Maintenance Characteristics
Soft-seated butterfly valves require low operating torque, are easy to operate, and are cost-effective; however, flexible seats are prone to aging and wear, resulting in shorter service life and the need for periodic replacement. Metal-seated butterfly valves offer high structural strength and mechanical life exceeding 50,000 cycles. They support online maintenance and perform reliably under high-pressure and high-wear conditions, though they typically require higher operating torque, with large-diameter valves often equipped with worm gear actuators.

Typical Applications
Soft-seated butterfly valves are commonly used in municipal water supply and drainage systems, HVAC water circuits, and food and beverage pipelines. Metal-seated butterfly valves are preferred for thermal power plant steam pipelines, metallurgical blast furnace gas transport, and chemical reactor process control, where high temperature, high pressure, and abrasive conditions are present.