What is an eccentric butterfly valve?
Eccentricity in a butterfly valve refers to the intentional offset between the valve disc's rotational axis (stem) and the valve body's centerline or sealing surface. While the stem of a traditional centerline butterfly valve coincides with the valve body's center, an eccentric butterfly valve uses an offset structure to reduce friction between the valve disc and the sealing ring, thereby improving sealing performance and service life. Based on the direction and amount of offset, butterfly valves can be divided into the following three categories:
1. Single-Eccentric Butterfly Valve: The stem center is offset from the valve body's centerline but centered on the sealing surface. This offset is typically 5%-10% of the valve disc's thickness and is suitable for low-pressure, normal-temperature applications, such as water supply systems.
2. Double-Eccentric Butterfly Valve: The stem is offset from both the valve body's centerline and the sealing surface's center, resulting in a double offset. This design allows the disc to quickly clear the sealing surface during opening, reducing wear. It is commonly used in the petroleum and chemical industries.
3. Triple eccentric butterfly valve: Based on the double eccentric valve, the valve seat sealing surface has a cone angle offset (usually 8°-12°), achieving zero metal seal friction. It is resistant to high temperatures and high pressures (up to 600°C/PN100, according to API 609 standard) and is mostly used in power plants or harsh working conditions.
What is a centerline butterfly valve
The centerline butterfly valve is an industrial valve used for on/off switching and flow control in pipeline systems, widely used in the petroleum, chemical, metallurgical, and hydropower industries. Its core structural feature is the coaxial alignment of the stem axis, disc center, and body center, resulting in simple manufacturing and balanced opening and closing torque.
This valve achieves flow control by rotating the disc between 0° and 90°. Traditional designs suffer from poor sealing material temperature resistance and wear on the disc and seat. High-performance, improved models utilize a soft T-shaped sealing ring combined with multiple layers of stainless steel sheets, combined with an oblique tapered sealing surface welded with a high-temperature-resistant alloy, achieving the dual advantages of both hard and soft metal sealing. A spring mechanism compensates for tolerances and elastic deformation, making it suitable for high-temperature, high-pressure environments and bidirectional media transport. The valve is available in various structural types, including center seal and eccentric seal. Sealing materials include soft seals (such as EPDM rubber and PTFE) and hard metal seals. Actuation options include manual, electric, and pneumatic. Ensure flange alignment during installation. Periodic opening and closing of the valve for extended periods of closure should be prevented from sticking. Its improved design has gradually expanded to large-scale valve applications, and has spawned dedicated testing equipment and patented optimization solutions.
What is the difference between eccentric butterfly valve and concentric butterfly valve
I. Structural Design
Center Butterfly Valve (Centerline Butterfly Valve)
The valve stem axis, disc center, and valve body center completely coincide.
The disc contacts and rubs against the valve seat throughout the opening and closing process, causing rapid wear.
Eccentric Butterfly Valve
Single Eccentric: The valve stem is offset from the disc center, reducing extrusion but still causing friction.
Double Eccentric: The valve stem is offset from both the disc center and the body center, allowing the disc to quickly disengage from the seat during opening and closing, reducing friction by 90%.
Triple Eccentric: Based on the double eccentric design, the sealing surface adopts a tapered design to achieve a zero-friction torque seal.
II. Sealing Performance and Materials
Center Butterfly Valve
Relies on soft sealing materials such as rubber/PTFE, which achieve a seal through elastic deformation.
Poor temperature resistance (usually ≤80°C) and poor resistance to high pressure.
Eccentric Butterfly Valve
Double Eccentric: A metal seat can be used, improving temperature resistance, but this seal is in line contact and prone to leakage under high pressure. Triple-eccentric: Metal seal, contact surface pressure increases with medium pressure, achieving zero leakage at high temperatures and high pressures.
III. Applications
Center Butterfly Valve:
Normal temperature and pressure environments (such as fire water pipes and general industrial water supply).
Advantages: Simple structure and low cost.
Eccentric Butterfly Valve:
Double-eccentric: Medium temperature and medium pressure systems (such as steam pipelines and circulating water).
Triple-eccentric: High temperature and high pressure harsh conditions (such as power plant flue gas and high-pressure natural gas).
Advantages: Long life, wear resistance, and wide application range.
