"Double eccentric" refers to the two intentional offsets in the position of the valve stem (shaft):

First Offset (Axial Eccentricity): The centerline of the valve shaft is offset from the centerline of the valve seat (sealing surface). The purpose is to prevent continuous friction between the disc and the seat during opening and closing.

Second Offset (Radial Eccentricity): The centerline of the valve shaft is also offset from the centerline of the pipeline/valve body. This offset allows the disc to detach from the seat instantly upon opening, and to wedge tightly into the seat upon closing, ensuring an excellent seal.

How Does It Work?

When Opening: The moment you rotate the valve stem, the disc immediately "detaches" from the seat. Unlike standard butterfly valves where the disc scrapes against the seat throughout the rotation, the double eccentric butterfly valve experiences almost zero friction, making the rotation extremely smooth.

When Closing: As the disc rotates into place, it utilizes the "wedging" effect of the second offset to smoothly and tightly press against the seat.

This structure of "detaching upon rotation, contacting only upon closure" significantly extends the service life of the rubber or PTFE valve seat.

Advantages of Double Eccentric Butterfly Valves

Ultra-Long Service Life: Because friction is minimal during opening and closing, the valve seat is highly resistant to wear and scratches.

Excellent Bi-directional Sealing: It achieves "zero leakage" and can even be used in medium-to-high pressure conditions.

Low Torque: Compared to standard butterfly valves, it requires less force (or lower actuator power) to open and close.

Wide Material Selection: The valve seat can be configured as a soft seal (PTFE/rubber for conventional media) or a metal hard seal (for high-temperature and high-pressure applications).

Where Is It Commonly Used?

While standard concentric butterfly valves are typically limited to low-pressure, ambient-temperature water systems, double eccentric butterfly valves are upgraded to an industrial grade and are widely used in:

Water supply, drainage, and urban heating systems,Chemical, petroleum, and natural gas pipeline networks,Power plant circulating water systems,Wastewater treatment and the transport of certain corrosive media

In short, when you need a valve that is more durable and seals better than a standard butterfly valve, yet remains lighter and more space-saving than a gate valve or ball valve, the double eccentric butterfly valve is often a highly cost-effective choice.