Double Eccentric vs. Triple Eccentric Butterfly Valve

In modern industrial sectors, fluid control is a critical task. Butterfly valves, as key components in fluid control systems, are widely used across numerous industries due to their unique structure and excellent performance. Among them, double eccentric and triple eccentric butterfly valves play irreplaceable roles in different application scenarios due to their respective advantages. This article will explore the design principles, structural characteristics, performance advantages, and application fields of these two types of butterfly valves, helping readers better understand them and providing reference for the correct selection and application of appropriate butterfly valves.

Among various types of butterfly valves, the double eccentric butterfly valve, with its unique structural design and outstanding performance, has become an ideal choice for medium and low pressure fluid control. Its double eccentric structure not only effectively solves the sealing problem of traditional butterfly valves but also significantly reduces operating torque and extends service life. It is widely used in water supply and drainage systems, wastewater treatment, and air conditioning systems where frequent opening and closing are required.

The design concept of the double eccentric butterfly valve stems from the optimization of traditional butterfly valve performance. Its distinctive double eccentric structure is the core feature that distinguishes it from other butterfly valve types. The first eccentricity refers to the valve stem axis deviating from the center of the sealing surface, i.e., the valve stem axis is located behind the disc surface. This design cleverly makes the contact surface between the disc and seat become the sealing surface, fundamentally solving the inherent defects of the concentric butterfly valve and effectively preventing internal leakage at the intersection between the valve stem axis and the sealing surface seat, greatly improving the sealing performance.

The second eccentricity refers to the offset between the center of the valve body's flow passage and the valve stem axis, which causes the valve stem axis to divide the disc into two unequal parts. This eccentric structure allows the disc to quickly disengage from or approach the seat during opening and closing, significantly reducing friction travel between the disc and sealing surface, decreasing wear, lowering closing torque, and thereby extending the service life of the seat.

The disc periphery and sealing surface of the double eccentric butterfly valve are machined into spherical shapes. Tight shutoff is achieved through the elastic deformation generated by the disc's external spherical surface pressing against the inner spherical sealing surface. In terms of sealing material, PTFE (polytetrafluoroethylene) is commonly used for the valve seat due to its excellent corrosion resistance and sealing performance, meeting the needs of most medium and low-pressure fluid control. To expand its application in high-temperature environments, metal sealing seats can also be used. However, it's important to note that the metal seat in a double eccentric butterfly valve still relies on position sealing—meaning the sealing surface between the disc and seat is a line contact. Therefore, its high-pressure resistance is relatively poor, and when used in high-pressure systems, it may result in significant leakage. Hence, in systems with extremely strict sealing requirements under high pressure, double eccentric butterfly valves with metal seats should be avoided.

The main performance advantages of the double eccentric butterfly valve include:

Reliable Sealing Performance: The unique double eccentric structure effectively resolves sealing issues of traditional butterfly valves, significantly reducing internal leakage and improving system reliability.

Flexible and Labor-Saving Operation: The disc can quickly disengage or approach the seat during opening and closing, reducing travel friction and significantly lowering operating torque.

Long Service Life: The eccentric structure reduces wear between the disc and sealing surface, extending seat life and reducing maintenance costs.

Wide Applicability: Suitable for medium and low pressure fluid control, featuring simple structure and flexible operation, especially ideal for frequently operated systems like water supply, wastewater treatment, and HVAC.

Double eccentric butterfly valves are widely used in many industries, particularly where certain sealing requirements exist but system pressure is relatively low. For example, in water supply systems, they can effectively control water flow to ensure normal system operation; in wastewater treatment, their good sealing and corrosion resistance make them an ideal valve choice; in air conditioning systems, they can precisely regulate refrigerant flow to ensure efficient system operation. Additionally, they are widely used in the food processing industry for controlling various liquids and semi-fluid materials, meeting strict hygiene and sealing requirements.

When facing high pressure, high temperature, and corrosive media, the triple eccentric butterfly valve, with its unique design and outstanding performance, becomes a key choice in industrial fluid control. By adding a third eccentric axis, triple eccentric butterfly valves achieve zero leakage sealing, greatly reduce friction resistance, and increase service life, meeting the high standards of industries such as petroleum, chemical, natural gas, and thermal power.

The triple eccentric butterfly valve is an optimized upgrade of the double eccentric design. Its most significant feature is the addition of a third eccentric axis—angular eccentricity. This design creates a conical sealing surface: the outer edge of the disc is machined into an outer conical surface, while the inner sealing surface of the seat is machined into an inner conical surface. As a result, the sealing cross-section of the butterfly valve becomes elliptical, and the sealing surface of the disc is asymmetrical top and bottom.

In triple eccentric butterfly valves, the larger side of the disc presses upward toward the seat along the large sloped surface, and the smaller side presses downward along the small sloped surface. Unlike double eccentric valves, triple eccentric valves do not rely on the elastic deformation of the seat for sealing. Instead, sealing is achieved entirely through tight contact between sealing surfaces. This allows the valve to achieve zero leakage when closed, and as closing pressure increases, sealing performance improves—the tighter it closes, the better it seals.

Triple eccentric butterfly valves typically use metal hard-sealing seats, which provide excellent high-temperature resistance. Around the disc edge, multi-layer sealing rings are embedded, composed of alternating stainless steel and graphite sheets. This sealing structure combines the advantages of both metal hard seals and elastic soft seals, allowing the valve to withstand high temperatures and pressures while effectively preventing leakage, further enhancing sealing performance and reliability.

The performance advantages of triple eccentric butterfly valves are evident in the following aspects.

Outstanding Sealing Performance: Relying purely on tight contact of sealing surfaces, triple eccentric butterfly valves can achieve zero leakage. Even under high pressure and high temperature, they maintain excellent sealing, significantly improving system reliability and safety.

Extremely Low Friction Resistance: As the disc completely disengages from the seat during opening and closing, the operation is nearly frictionless, resulting in more flexible and energy-saving operation with reduced torque and energy consumption.

Exceptional Service Life: The optimized sealing structure minimizes wear, enabling repeated open-close cycles with a long service life, reducing maintenance and replacement costs.

Strong Pressure and Temperature Resistance: With metal hard-sealing seats, these valves can withstand high pressure and temperature, making them suitable for harsh environments involving corrosive or high-temperature media.

Thanks to its excellent performance, the triple eccentric butterfly valve is widely applied in many high-pressure and harsh environments. In the petroleum industry, it is used to control the transport and distribution of oil, ensuring safety and reliability in oil transfer processes; in the chemical industry, it effectively controls corrosive media flow, meeting stringent valve performance requirements; in the natural gas sector, it regulates and conveys natural gas, withstanding high pressure and low temperatures to ensure system stability; in thermal power plants, it manages steam and hot water flow, withstanding high temperature and pressure to ensure efficient operation. It is also suitable for high-temperature media control in food processing and high-pressure water flow control in water treatment.

Double eccentric butterfly valves and triple eccentric butterfly valves each have their own strengths and optimal application scenarios. Double eccentric butterfly valves offer reliable sealing, easy operation, and cost-effectiveness for medium and low pressure fluid control systems such as water treatment, HVAC, and general industrial processes. Triple eccentric butterfly valves excel in demanding conditions requiring high pressure, high temperature, zero leakage, and durability, making them indispensable in industries such as petroleum, chemical, natural gas, and thermal power. Choosing the appropriate butterfly valve depends on specific system requirements including pressure, temperature, media characteristics, sealing demands, and budget considerations. Understanding the structural and functional differences between double and triple eccentric butterfly valves ensures optimal valve performance, system safety, and operational efficiency.