What Is A Double Block And Bleed (DBB) Trunnion Ball Valve?

In high-risk industrial applications such as oil & gas, petrochemical, and pipeline transportation systems, safety and isolation reliability are critical. One valve design widely recognized for meeting these stringent requirements is the Double Block and Bleed (DBB) Trunnion Ball Valve. This article provides a professional and in-depth technical explanation of what a DBB trunnion ball valve is, how it works, and why it is essential for critical flow control systems.

Definition of a Double Block and Bleed (DBB) Trunnion Ball Valve

A Double Block and Bleed (DBB) Trunnion Ball Valve is a valve that incorporates two independent sealing surfaces (double block) and a bleed mechanism to safely isolate a section of the pipeline and verify sealing integrity.

When the valve is in the closed position:

• The upstream and downstream seats simultaneously block the process media.

• A bleed valve or drain port between the two seats allows trapped pressure to be safely vented.

This design ensures positive isolation, prevents pressure buildup in the valve cavity, and allows operators to confirm that both sealing seats are functioning correctly.

How a DBB Trunnion Ball Valve Works

The DBB function is achieved through the trunnion-mounted ball design combined with self-energizing seats.

Operating Principle

1. Valve Closure
   The trunnion-supported ball rotates 90 degrees to the closed position.

2. Double Blocking

• The upstream seat blocks incoming pressure.

• The downstream seat blocks reverse pressure.
  Both seats seal independently against the ball.

3. Bleed Operation
   The cavity pressure trapped between the seats is released through a bleed or drain valve, ensuring:

• Zero internal pressure

• Verification of tight shut-off performance

This configuration significantly enhances operational safety compared to standard single-seated valves.

Key Components of a DBB Trunnion Ball Valve

1. Trunnion-Mounted Ball

• Supported at both top and bottom by trunnions

• Minimizes operating torque

• Ensures stable sealing under high pressure and large diameters

2. Dual Independent Seats

• Typically spring-loaded or pressure-energized

• Seal against both upstream and downstream pressure

• Enable true double block isolation

3. Valve Body and Cavity

• Designed to safely manage cavity pressure

• Often includes automatic pressure relief features

4. Bleed / Drain Port

• Located between the two seats

• Allows safe venting of trapped fluid or gas

• Enables leak detection and seal verification

5. Stem and Actuation System

• Compatible with manual, pneumatic, electric, or hydraulic actuators

• Designed for smooth and reliable quarter-turn operation

DBB vs DIB: Understanding the Difference

A DBB trunnion ball valve is often compared with a Double Isolation and Bleed (DIB) valve:

DBB valves are preferred where simple verification of sealing and safe cavity venting are required.

Advantages of DBB Trunnion Ball Valves

• Enhanced safety through double isolation

• Prevention of cavity overpressure

• Reduced leakage risk

• Lower operating torque compared to floating ball valves

• Reliable sealing for high-pressure and large-diameter pipelines

• Easy maintenance and inspection

Typical Applications

DBB trunnion ball valves are widely used in:

• Oil and gas transmission pipelines

• Offshore platforms

• Refineries and petrochemical plants

• LNG and gas processing facilities

• High-pressure process isolation systems

These valves are especially suitable where zero leakage and safe maintenance isolation are mandatory.

Relevant Standards and Certifications

DBB trunnion ball valves are commonly manufactured in compliance with:

• API 6D – Pipeline valves

• API 608 – Metal ball valves

• ASME B16.34

• Fire-safe and fugitive emission standards (API 607)

Compliance with these standards ensures reliable performance in demanding environments.

Conclusion

A Double Block and Bleed (DBB) Trunnion Ball Valve is a critical solution for safe and efficient pipeline isolation in high-risk industries. By combining trunnion-mounted ball support, dual independent sealing seats, and a bleed function, this valve design delivers superior safety, pressure control, and operational reliability.

For applications requiring proven isolation, pressure verification, and long-term durability, DBB trunnion ball valves remain one of the most trusted choices in modern flow control systems.