What is a Double Eccentric Butterfly Valve?

Double eccentric butterfly valves, also known as double-offset butterfly valves, are essential components in modern pipeline systems. These valves are widely used in water supply applications, particularly below ground, as a reliable and cost-effective alternative to gate valves. Their design offers advantages such as a reduced bury depth requirement and lower overall costs, especially for larger diameters.

This article explores the double eccentric butterfly valve, its design, functionality, and applications, while comparing it to other types of butterfly valves. Additionally, we discuss its advantages, features, and the various models available to suit different industrial needs.

Key Differences Between Centric and Double Eccentric Butterfly Valves

Butterfly valves come in different configurations to meet specific performance requirements. Two common designs are the centric (concentric) and double eccentric butterfly valves.

Centric Butterfly Valves

In a centric butterfly valve, the stem is located at the center of the disc, which itself is centrally positioned in the valve bore. This configuration ensures that the disc is always in contact with the seat, providing a simple and cost-effective sealing mechanism. However, constant contact increases wear, making centric valves less ideal for high-pressure or high-cycle applications.

Double Eccentric Butterfly Valves

In contrast, double eccentric butterfly valves feature an advanced design where the stem is offset from the center in two directions: laterally from the disc's center and axially from the bore's center. This dual offset reduces contact between the disc and the seat during operation, enhancing the valve’s efficiency, durability, and sealing performance. This design is particularly suitable for high-pressure and high-temperature applications.

How Does a Double Eccentric Butterfly Valve Work?

Double eccentric butterfly valves operate using a straightforward yet efficient mechanism. Their primary function is to control the flow of fluid in a pipeline by using a circular disc as the closing and opening element. The term "double eccentric" refers to the disc's offset positioning in two dimensions:

Lateral Offset

The disc’s axis is offset laterally from the valve bore’s centerline.

Axial Offset

The disc’s rotation axis is offset from the valve’s body centerline.

This eccentric arrangement ensures that the disc disengages from the seat as soon as the valve begins to open. As the valve closes, the disc rotates back to form a tight seal with the seat, minimizing potential leakage. This design not only enhances the sealing efficiency but also reduces the torque required for operation, resulting in less wear on the valve components and extending its operational lifespan.

Advantages of Double Eccentric Butterfly Valves

Double eccentric butterfly valves offer several benefits, making them a preferred choice for various industrial and water supply applications:

Reduced Leakage

The eccentric design ensures minimal contact between the disc and the seat during operation, reducing the likelihood of wear and potential leakage. The tight seal achieved upon closure provides reliable performance in critical systems.

High Pressure-Bearing Capacity

These valves are capable of withstanding high-pressure conditions, making them suitable for demanding applications in industries such as oil and gas, water treatment, and power generation.

High-Temperature Resistance

Double eccentric butterfly valves are designed to operate efficiently in high-temperature environments, offering exceptional thermal resistance and maintaining performance under extreme conditions.

Long Service Life

Reduced wear and tear, coupled with robust materials used in construction, ensure a longer service life. This durability lowers maintenance costs and enhances the valve’s overall cost-effectiveness.

Applications of Double Eccentric Butterfly Valves

Double eccentric butterfly valves are versatile and can be used across various industries, including:

Water Supply and Distribution

Ideal for underground installations, where reduced bury depth and reliable operation are crucial.

Oil and Gas

Suitable for high-pressure and high-temperature applications, ensuring efficient flow control and sealing.

Power Plants

Used in cooling and steam systems due to their ability to handle extreme temperatures and pressures.

Chemical Processing

Their resistance to aggressive media makes them suitable for chemical handling and processing systems.

Types of Double Eccentric Butterfly Valves

To cater to diverse operational needs, double eccentric butterfly valves are available in different designs:

Full Cone Disc Model

This model features a cone-shaped disc that improves fluid dynamics and reduces flow resistance. It is particularly suited for high-flow applications.

Slice Disc Model

The slice disc design is lightweight and offers reduced torque requirements. It is commonly used in systems where operational efficiency is a priority.

Built-in Resilient Seat Ring Model

This model incorporates a resilient seat ring within the valve body, enhancing sealing performance and accommodating slight misalignments during installation.

Key Features of Double Eccentric Butterfly Valves

Compact Design

These valves require less space for installation compared to gate valves, making them ideal for confined spaces.

Ease of Operation

The reduced torque requirement ensures smooth operation, either manually or via an actuator.

Versatile Materials

Double eccentric butterfly valves are available in various materials, including ductile iron, stainless steel, and aluminum bronze, to suit different applications and environmental conditions.

Cost-Effective

Their durability and low maintenance requirements translate into reduced lifecycle costs, making them an economical choice for many projects.

Comparison with Triple Offset Butterfly Valves

While double eccentric butterfly valves are efficient for most applications, triple offset butterfly valves provide an additional level of sealing performance. The triple offset design introduces a conical sealing element, eliminating all friction between the disc and seat during operation. This makes them ideal for applications requiring zero leakage or where metal-to-metal sealing is essential.

Selecting the Right Double Eccentric Butterfly Valve

When choosing a double eccentric butterfly valve, consider the following factors:

Application Requirements

Evaluate the operating pressure, temperature, and type of fluid to ensure compatibility with the valve’s design and materials.

Valve Size

Select the appropriate size to match pipeline specifications and flow requirements.

End Connection Type

Double eccentric butterfly valves are available with wafer, lug, and flanged end connections. Choose the one that best suits your installation needs.

Operation Method

Determine whether manual, electric, or pneumatic actuation is required for your system.

Conclusion

Double eccentric butterfly valves are indispensable in modern industrial and water supply systems. Their innovative design, combining efficiency, durability, and cost-effectiveness, makes them a superior choice over traditional valves such as gate valves. With advancements in materials and sealing technology, these valves continue to provide reliable performance in demanding applications.

Whether you're working in water supply, oil and gas, or chemical processing, the double eccentric butterfly valve offers a versatile and dependable solution for fluid control. By understanding their operation, advantages, and available models, you can make informed decisions to optimize your system’s performance and longevity.