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DIFFERENCES BETWEEN DOUBLE VS. TRIPLE ECCENTRIC BUTTERFLY VALVE

Double Eccentric (Double Offset) and Triple Eccentric (Triple Offset) Butterfly Valves are advanced designs of butterfly valves used in critical applications. Here are the key differences between them:

1. Eccentricity (Offset Design)

  • Double Eccentric (2-offset):

    • 1st Offset: The shaft is positioned behind the seat (offset from the centerline of the disc).

    • 2nd Offset: The shaft is offset from the pipe centerline (radial offset).

    • Reduces friction during operation but still has some contact between disc and seat.

  • Triple Eccentric (3-offset):

    • 1st & 2nd Offsets: Same as double eccentric.

    • 3rd Offset: The seating surface is conical/angled (eccentric taper), ensuring zero friction during operation.

    • Eliminates rubbing between disc and seat, enhancing durability.

2. Sealing Mechanism

  • Double Eccentric:

    • Uses a soft seat (PTFE, elastomeric) or metal-to-metal seal.

    • Requires some contact between disc and seat for sealing.

    • Suitable for moderate temperatures and pressures.

  • Triple Eccentric:

    • Uses metal-to-metal sealing (often with a layered or laminated seat).

    • Bubble-tight shut-off even in high-pressure/temperature applications.

    • Ideal for extreme conditions (cryogenic, high-pressure steam, corrosive fluids).

3. Applications

  • Double Eccentric:

    • Water treatment, HVAC, general industrial processes.

    • Moderate pressure/temperature conditions.

  • Triple Eccentric:

    • Oil & gas, petrochemical, power plants, LNG, high-pressure steam.

    • Critical services requiring zero leakage and high durability.

4. Pressure & Temperature Ratings

  • Double Eccentric:

    • Typically up to Class 600 (PN 100).

    • Max temperature limited by seat material (usually up to 200°C with soft seats).

  • Triple Eccentric:

    • Can handle Class 1500+ (PN 250+).

    • Operates up to 1000°C (with metal seats).

5. Maintenance & Lifespan

  • Double Eccentric:

    • Requires occasional maintenance due to seat wear.

  • Triple Eccentric:

    • Longer lifespan due to no friction wear.

    • Minimal maintenance needed.

6. Cost

  • Double Eccentric:

    • More economical, suitable for less demanding applications.

  • Triple Eccentric:

    • Higher initial cost but cost-effective in critical services.

Summary Table

Feature Double Eccentric Butterfly Valve Triple Eccentric Butterfly Valve
Eccentricity 2 offsets (shaft & radial) 3 offsets (shaft, radial, conical taper)
Sealing Type Soft or metal-assisted seal Metal-to-metal (bubble-tight)
Friction Some contact during operation Zero friction (no rubbing)
Max Pressure Up to Class 600 Up to Class 2500+
Max Temperature ~200°C (soft seat) Up to 1000°C (metal seat)
Applications Water, HVAC, general industry Oil & gas, power plants, steam
Cost Lower Higher (justified for critical use)

Conclusion

  • Choose Double Eccentric for cost-effective, moderate-duty applications.

  • Choose Triple Eccentric for high-pressure, high-temperature, or zero-leakage requirements.

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