Single Eccentric vs. Double vs. Triple Eccentric Butterfly Valves: The Differences

1. Introduction to Eccentric Butterfly Valves

Eccentric butterfly valves are a significant type of butterfly valves, a critical part of fluid control systems. They are available in different designs according to different operation requirements.

Single eccentric butterfly valves, double eccentric butterfly valves, and triple eccentric butterfly valves are three broad types of eccentric butterfly valves.The aim here in this guide is to give a brief summary of the main differences between these valve types and assist you in making a choice about which is best for your application.

2. Definition of Eccentricity of Butterfly Valves

Eccentricity of the butterfly valve is the condition where the axis of rotation of the valve disc is not in the center of the valve body. The major function of eccentricity is to reduce wear and friction, seal maximally, and reduce operating torque. The quantity and amount of offset decide the kind of eccentric butterfly valve and the length it can be utilized for various applications.

3. Single Eccentric Butterfly Valves

3.1. Design and Function

Single eccentric butterfly valves consist of one offset and consequently mean that axis deviation of the disc from center of the valve body. This design reduces extrusion between the disc and seat. However, it can still susceptible to scraping in opening and closure between seat and disc. The single offset minimizes and manages extrusion between the seat and disc.

3.2. Merits and Constraints

The single eccentric butterfly valve has the benefit of reducing wear and tear than the non-eccentric. However, there is scrapping between disc and seat. Its applications are limited, especially at high temperature and pressure.

4. Double Eccentric Butterfly Valves

4.1. Design and Working

Double eccentric butterfly valves contain two offsets: one is the disc axis is offset from the valve body center, while the other offset is offsetting the stem to the rear of the disc and to the side of the disc center. In this way, the disc is able to be pulled off the seat when the valve begins to open up. Double offset design further decreases the friction, producing a cam effect between seat and disc to reduce the torque required to shift the valve.

4.2. Advantage and Limitation

Double eccentric butterfly valves are pressure proof compared to single offset valves and typically have ANSI Class ratings of up to 600. The valves are made of materials like Hastelloy, stainless steel, and carbon steel with seats typically being Polytetrafluoroethylene (PTFE) or Teflon. The valves close more securely by rubbing against the seat through the utilization of only 1° to 3° of a 90° turn. This design relies on line pressure against the disc to create an appropriate bubble-tight seal. Double eccentric butterfly valves may be applied in process on/off and throttling service. They are sensitive to pressure and temperature, though, more than triple offset valves.

5. Triple Eccentric Butterfly Valves

5.1. Design and Operation

Triple eccentric butterfly valves use three offsets to eliminate seat and sealing ring friction. The valve is created by the seat surface shape and hence creates a cone shape of the disc and seat. The cone angle along with the two shaft offsets provides the disc the ability to seal against the seat with zero friction. This type of configuration is often called a torsion seal in the sense that it seals solely with the pressure of seat contact face and does not deform the elastic valve seat.

5.2. Advantages and Limitations

Advantages:

Balanced Sealing and Tight Shut-Off Contact: Ensures reliable sealing with minimal leakage, especially in metal seat construction.

Low Seat Friction: Reduces wear and extends the life of the valve.

Durability and Versatility: Long seat life, especially in metal seat construction. Besides, it is suitable for handling abrasive and corrosive media.

Limitations:

Material Limitations: Elastomeric or graphite on stainless steel seat are not typically used for very abrasive or high-temperature media.

Specific Applications:Triple eccentric butterfly valves are not typically used for very abrasive or high temperature media.

6. Key Differences Summarized

To clarify the differences, here is a summary table:

7. Applications of Different Eccentric Butterfly Valves

The different forms of eccentric butterfly valves have their usage in different applications. Double eccentric butterfly valves are primarily employed in heavy underground water applications, where they are primarily employed in conjunction with gate valves. They are capable of providing high tightness. Triple eccentric butterfly valves find application in heavy applications like oil and gas refining and processing, petrochemical and chemical usage, and power generation. They are most utilized to control steam above 150 psi, pure gas pressure, or liquids. The valves are also applied in pulp and paper manufacturing, offshore operations.

8. Selecting the Proper Eccentric Butterfly Valve

Selecting the proper eccentric butterfly valve involves taking into account numerous factors:

Application: Determine the requirements of the fluid system, for example, pressures, temperatures, and flow rates.

Type of Media: What kind of fluid is being worked with. Something unique will be present in the abrasive or corrosive fluid.

Sealing Needs: High sealing requirement or no high sealing requirement. Double or triple eccentric will work best for bubble-tight seal.

Condition of Operations: Whether for on/off, throttling, or for on both.

Expenses: Initial expenditure vs. greater duration operating necessity and maintenance cost.

9. Conclusion

Single eccentric butterfly valves are somewhat better than concentric valves but less versatile regarding application. Double eccentric butterfly valves are sealable and versatile for most of the applications like water management and other industrial processes. Even in the toughest application such as high pressure, high and low temperature, and corrosive liquids, triple eccentric butterfly valves are applied due to their rugged design and efficient sealing capabilities.

FLUIDO offers better butterfly valves from double offset to triple offset to fulfill different applications in a safe manner. Always install valves made by reputed firms like FLUIDO in order to achieve optimum performance and longevity.