Trunnion Ball Valve: Structure, Function, and Applications

A trunnion ball valve is a type of industrial valve used to control the flow of liquids or gases through a pipeline. Unlike traditional floating ball valves, the ball in a trunnion ball valve is fixed and supported by trunnions, which help absorb pressure from the pipeline and reduce wear on the valve seat. This design is especially suitable for high-pressure, large-diameter applications and ensures reliable sealing and long-term performance.

What is a Trunnion Ball Valve?

In a trunnion ball valve, the ball is held in place by both an upper and lower trunnion (shaft-like supports), which restrict the ball’s movement. The valve seats are spring-loaded and move slightly toward the ball to create a tight seal when the valve is closed. This reduces the torque required to operate the valve and helps ensure a more consistent seal even under fluctuating pressure or temperature conditions.

Key Features of Trunnion Ball Valves

• Fixed Ball Support: The ball is mounted on trunnions, which eliminates lateral movement and enhances valve stability.
• Low Operating Torque: Because the seats move toward the ball, less torque is needed to rotate the ball, making it easier to operate manually or with an actuator.
• Double Block and Bleed (DBB): Trunnion valves often offer DBB capabilities, allowing isolation on both sides of the valve and the release of trapped pressure through a bleed valve.
• Anti-blowout Stem: The stem design prevents it from being expelled under pressure, adding an extra layer of safety.
• Fire-safe Design: Many trunnion ball valves include a fire-safe mechanism that maintains a secondary seal even after soft seat materials are damaged by fire.

Materials Used

Trunnion ball valves can be made from a variety of materials based on application needs. Common materials include:

• Stainless steel
• Carbon steel
• Alloy steel
• Duplex stainless steel
• Inconel and other exotic alloys for aggressive environments

Seat materials may include PTFE, reinforced Teflon, or metal for high-temperature or abrasive applications.

Types of Trunnion Ball Valves

1. Side-entry Trunnion Ball Valve: Assembled from the side, these are common in many pipeline systems and are easy to inspect and maintain.
2. Top-entry Trunnion Ball Valve: The top-entry design allows access to internal parts without removing the valve from the pipeline, ideal for systems requiring regular maintenance.
3. Fully Welded Trunnion Ball Valve: Designed for underground or buried service, offering high integrity with minimal maintenance.

Applications of Trunnion Ball Valves

Trunnion ball valves are used in industries and systems where high performance, safety, and reliability are critical. These include:

• Oil and Gas Industry: Used in upstream, midstream, and downstream operations for isolation and flow control of crude oil, natural gas, and refined products.
• Petrochemical Plants: Handles aggressive chemicals and high-pressure steam.
• Power Plants: Controls flow in high-temperature, high-pressure steam systems.
• Water Treatment Facilities: Used for flow isolation and control in large-diameter water pipelines.
• Marine and Offshore Platforms: Suitable for harsh environments where corrosion resistance and reliability are crucial.

Advantages of Trunnion Ball Valves

• Excellent performance under high pressure and large bore sizes
• Lower operating torque and energy costs
• Effective sealing even in harsh service conditions
• Long operational life and minimal maintenance
• Enhanced safety with DBB and fire-safe features

Disadvantages

• Higher cost compared to floating ball valves
• Heavier and bulkier, requiring more installation space
• More complex internal components, requiring experienced maintenance technicians

Maintenance and Inspection

Although trunnion ball valves are durable, periodic inspection is recommended to ensure optimal performance. Maintenance may include:

• Lubrication of stem and trunnion bearings
• Inspection of seats and seals
• Checking for corrosion or wear on the ball surface
• Verification of valve actuation mechanism. Visit our website https://www.bjmvalves.com/  for more details.

Conclusion

Trunnion ball valves offer a robust and efficient solution for managing the flow of fluids and gases under demanding conditions. With their fixed ball support, low operating torque, and safety features, these valves are widely used in critical applications across multiple industries. Though they are more expensive than floating ball valves, their durability and long-term performance often justify the investment, especially in high-pressure or hazardous environments.