Double Offset Butterfly Valve:A Complete Guide for Industrial Use

What Is a Double Offset Butterfly Valve?

A double offset butterfly valve incorporates two structural offsets between the disc, shaft, and pipeline centerline. These offsets reduce seat wear, minimize friction, and allow the valve to provide bi-directional sealing with longer service life.

The two offsets include:

1. First Offset:
   The stem (shaft) is placed behind the centerline of the valve seat.
2. Second Offset:
   The stem is also positioned slightly off the centerline of the pipeline.

These two offsets ensure that the disc moves away from the seat quickly during opening, significantly reducing contact and friction.

Double offset butterfly valves are referred to as "high-performance" because they offer better sealing, durability, and temperature capability compared with concentric designs.

How Does a Double Offset Butterfly Valve Work?

In a double offset butterfly valve, the disc rotates around an eccentrically positioned shaft. During operation:

• The disc contacts the seat only at the final closing moment.
• When opening, the disc immediately lifts off the seat, eliminating sliding friction.
• The valve achieves reliable Class VI or bubble-tight shutoff with soft-seated designs.
• Metal seats are also available for higher pressure and temperature applications.

This offset geometry enhances both performance and longevity, making it suitable for demanding industrial systems.

Key Features of Double Offset Butterfly Valves

1. Improved Sealing Performance

Double offset designs deliver tighter shutoff than concentric butterfly valves, especially under high pressure.

2. Reduced Wear and Longer Service Life

Because contact occurs only at the final degree of closing, seat wear is minimized.

3. High-Performance Soft Seat and Metal Seat Options

• Soft seat: Excellent for low leakage and clean media.
• Metal seat: Suitable for high temperatures and corrosive media.

4. Higher Pressure and Temperature Ratings

Typically used for:

• Pressure Class 150–300
• Temperatures up to 400°C (depending on materials)

5. Lower Operating Torque

Offset geometry reduces torque requirements, making the valve suitable for electric, pneumatic, or hydraulic actuators.

6. Versatile End Connections

Available in wafer, lug, and flanged types to match different pipeline standards.

Materials Commonly Used in Double Offset Butterfly Valves

Double offset butterfly valves can be manufactured using:

• Body materials:
  Carbon steel, stainless steel, duplex stainless steel, aluminum bronze, cast iron, ductile iron
• Disc materials:
  Stainless steel, duplex, nickel alloy, aluminum bronze
• Seat materials:
  EPDM, NBR, PTFE, reinforced PTFE, metal seat alloy
• Stem materials:
  High-strength stainless steel or alloy steel

Material selection depends on temperature, media, corrosion level, and pressure requirements.

Advantages of Double Offset Butterfly Valves

Applications of Double Offset Butterfly Valves

Double offset butterfly valves are widely used across many industries due to their reliability and efficiency.

1. Oil & Gas and Petrochemical

Used in refined products, pipelines, tank farms, and general process control.

2. Chemical Processing

Reliable for corrosive or abrasive fluids when combined with the right seat material.

3. Water Treatment and Desalination

Offer smooth flow control and excellent corrosion resistance.

4. HVAC and Building Systems

Provide efficient control for chilled water, heating, and ventilation systems.

5. Power Generation

Used for cooling water systems, steam support lines, and auxiliary systems.

6. Marine and Offshore

Resistant to seawater corrosion and harsh marine environments.

Double Offset vs. Triple Offset Butterfly Valves

For most general industrial applications, the double offset design provides an excellent balance between performance and cost.

How to Select the Right Double Offset Butterfly Valve

To choose the appropriate valve, consider:

• Pipe size (DN / NPS)
• Pressure class (PN / ASME)
• Temperature range
• Media type (clean water, chemical, slurry, gas, etc.)
• Soft seat or metal seat requirement
• End connection type (wafer, lug, flanged)
• Compatibility with actuators
• Required standards (API, ASME, ISO, EN)

Proper selection ensures optimal flow control, long service life, and maximum reliability.

Conclusion

A double offset butterfly valve is a high-performance industrial valve known for improved sealing, reduced friction, and long-term durability. It provides a cost-effective solution for medium-pressure and medium-temperature applications across water treatment, chemical processing, oil & gas, HVAC, and marine industries.