1. Definition and Classification
An eccentric butterfly valve is a valve that optimizes sealing performance and operating efficiency by adjusting the center position offset (i.e. "eccentricity") between the valve stem, butterfly plate and valve body. Its core feature is the axis design that deviates from the center line. According to the difference in eccentric structure, it is mainly divided into the following types:
Single eccentricity: Only the axis of the valve stem deviates from the center of the butterfly plate to alleviate the excessive extrusion of the butterfly plate and the valve seat when closing; Double eccentricity (double offset): The axis of the valve stem deviates from the center of the butterfly plate and the center of the valve body at the same time, which significantly reduces the friction between the butterfly plate and the valve seat and prolongs the sealing life; Triple eccentricity: On the basis of double eccentricity, the axis of the sealing surface is further tilted to achieve 360° zero friction sealing, which is suitable for high temperature and high pressure conditions; Variable eccentricity: Dynamically adjust the eccentricity to adapt to the pressure requirements of different working conditions.
2. Core structural features
Sealing design:
Double eccentric and triple eccentric butterfly valves use an oblique conical sealing surface. When closed, the butterfly plate and the valve seat quickly separate to reduce wear;
Some models are equipped with flexible composite seals (such as the double seal design in the patent), which adapt to high and low pressure requirements through different deformation amounts.
Material optimization:
Metal valve seats (such as stainless steel and alloys) are preferred in high-temperature scenarios, and the temperature resistance can reach above 425°C;
Polytetrafluoroethylene (PTFE) or nitrile rubber sealing rings are suitable for low-pressure or corrosive media.
Drive mode:
Large-diameter high-pressure valves are often equipped with pneumatic/hydraulic actuators to ensure high torque output;
Manual operation is suitable for low-pressure and small-diameter scenarios.
3. Typical application scenarios
Heating network: Double eccentric butterfly valve is used for steam pipeline, which is heat-resistant and has stable sealing;
Chemical system: Triple eccentric butterfly valve is suitable for high-pressure control of highly corrosive media (such as acid and alkali);
Energy transportation: Variable eccentric butterfly valve is used in oil and gas pipelines to dynamically adapt to pressure fluctuations.
4. Technical advantages
Low operating torque: The eccentric structure enables the butterfly plate to quickly detach from the valve seat, reducing the opening and closing resistance (40%~60% less than the concentric butterfly valve);
High sealing performance: The triple eccentric design achieves zero friction contact, and the leakage rate is ≤0.01%;
Long service life: Reduce the wear of the sealing surface, and the metal hard seal type can reach more than 100,000 times. V. Selection and use precautions
Seal pressure adaptation: Single eccentric or double eccentric + soft seal can be selected for low pressure scenarios, and triple eccentric or double seal design is required for high pressure;
Installation accuracy requirements: Double eccentric valves must strictly calibrate the pipeline coaxiality to avoid eccentric wear of the butterfly plate;
Maintenance focus: Regularly check the wear depth of the sealing surface (recommended threshold ≤0.1mm) and the lubrication status of the actuator.
Summary
The eccentric butterfly valve optimizes the sealing performance and operating efficiency through the axis deviation design. The type selection needs to be combined with the working pressure, temperature and medium characteristics. Double eccentric and triple eccentric structures are most widely used in the industrial field, especially suitable for high pressure, high temperature and high wear scenarios, and flexible sealing technology (such as patented double seal) further expands its scope of application.