Understanding Trunnion Ball Valves: A Comprehensive Guide

WKM 370 Series Trunnion Mounted​ Ball Valve Photo.

Trunnion mounted ball valves are essential components in fluid control systems, offering precise regulation and secure sealing in various industries. Understanding the intricacies of trunnion ball valves is crucial for engineers and operators to make informed decisions when selecting valves for specific applications. This comprehensive guide delves into the workings, differences, components, materials, applications, advantages, disadvantages, and selection criteria of trunnion ball valves.

What is a Trunnion Ball Valve?

Trunnion ball valves are quarter-turn valves designed to control the flow of media within pipelines. Unlike other ball valves, trunnion ball valves feature a fixed ball connected to a shaft called the trunnion on one end, ensuring the ball is securely held in place. This design offers stability and precise control, making trunnion ball valves suitable for high-pressure applications.

How Does a Trunnion Ball Valve Work?

The functionality of a trunnion ball valve is relatively straightforward. Here’s a breakdown of the process:

  • Closed Position: In the closed position, the hollow center of the ball is perpendicular to the flow path, blocking the passage of the fluid.
  • Opening the Valve: By rotating the handle connected to the stem, the ball rotates 90 degrees. Now, the hollow center aligns with the flow path, allowing the fluid to pass through unrestricted.
  • Sealing: The tight shut-off is ensured by resilient seats located around the ball’s opening. These seats compress against the ball, creating a leak-proof seal.

The trunnion plays a critical role in this process. By absorbing the pressure from the fluid, it reduces the load on the ball and seats, enabling smooth operation and minimizing wear and tear, even in high-pressure environments.

Differences Between Trunnion Ball Valves and Floating Ball Valves

The key distinction between trunnion ball valves and floating ball valves lies in their design and functionality.

  • Trunnion ball valves are ideal for high-pressure applications due to their fixed ball design, which provides better sealing on both sides and requires less torque to operate. Trunnion ball valves’ cost is higher than floating ball valves.
  • Floating ball valves have a floating ball that moves slightly downstream against the seat ring, creating a seal on one side and increasing stem torque. This design is simpler and more cost-effective, but it limits the pressure rating due to the stress placed directly on the ball and seats.

Components of a Trunnion Ball Valve

WKM 370D5 Trunnion Mounted Ball Valves Details

Trunnion ball valves consist of essential components such as the ball, stem, trunnion, bearings, seats, and body. The trunnion supports the ball, ensuring stability and controlled rotation. Bearings reduce friction, while seats provide sealing against pressure. The body construction can be side entry or top entry, allowing for maintenance without removing the valve from the pipeline.

Materials of Trunnion Ball Valves

The materials used in trunnion ball valves play a critical role in their performance and longevity. Common materials include steel for the ball, polymers like PTFE or metals for the seats, and high-quality gaskets for reliable tightness and low-emission performance. The choice of materials depends on factors such as pressure, temperature, and the nature of the fluid being controlled.

Trunnion Ball Valve Applications

Trunnion ball valves find extensive applications in industries such as oil refineries, petrochemical plants, power generation facilities, water treatment plants, and hydrocarbon industries. Their ability to provide precise fluid control, secure sealing, and reliable performance makes them suitable for a wide range of demanding environments where efficient flow regulation is essential.

Advantages of Trunnion Ball Valves

  • High-Pressure Rating: The trunnion design allows them to handle significantly higher pressures compared to floating ball valves.
  • Reliable Shut-Off: The positive sealing mechanism ensures a leak-proof closure, which is critical for applications where safety and environmental concerns are paramount.
  • Durability: The robust construction with superior materials makes them resistant to wear and tear, ensuring a long service life.
  • Low Maintenance: Trunnion ball valves generally require minimal maintenance due to their simple design and high-quality components.
  • Quick Operation: The quarter-turn operation allows for rapid opening and closing of the valve, which is essential for emergency shut-off situations.
  • Versatility: Trunnion ball valves are available in a wide range of sizes and materials, making them suitable for diverse applications.

Disadvantages of Trunnion Ball Valves

While offering numerous benefits, trunnion ball valves also have some drawbacks:

  • Higher Cost: Due to their complex design and use of high-quality materials, trunnion ball valves are generally more expensive than floating ball valves.
  • Larger Size and Weight: The robust construction makes them larger and heavier compared to floating ball valves, which may limit their use in space-constrained applications.
  • Higher Operating Torque: Opening and closing a trunnion ball valve, particularly in larger sizes, may require more torque due to the pressure load on the ball. 
  • Limited Throttling Capability: Trunnion ball valves are primarily designed for on/off flow control and are not ideal for precise flow regulation applications.

How to Choose the Right Trunnion Ball Valves

Selecting the appropriate trunnion ball valve involves considering several factors:

  • Application: Identify the specific application and the fluid characteristics (pressure, temperature, corrosivity).
  • Pressure Rating: Choose a valve with a pressure rating exceeding the maximum operating pressure in your system.
  • Material Compatibility: Select materials compatible with the fluid being handled to ensure corrosion resistance and long-term performance.
  • Size and Weight: Consider the available space and piping layout when selecting valve size. Weight may be a factor for overhead installations.
  • Standards and Regulations: Ensure the valve complies with relevant industry standards and safety regulations.
  • Manufacturer Reputation: Select a reputable manufacturer known for quality products and reliable after-sales support.

By carefully considering these factors, you can ensure that the chosen trunnion ball valve effectively meets your application requirements and delivers optimal performance and value throughout its service life.

In conclusion, trunnion ball valves are indispensable components in fluid control systems, offering precise regulation, secure sealing, and reliable performance in various industries. Understanding their design, functionality, components, materials, applications, advantages, disadvantages, and selection criteria is essential for engineers and operators to optimize fluid control operations and enhance system efficiency.