Trunnion Mounted Ball Valve VS Floating Ball Valve

The floating ball valves and trunnion ball valves are both quarter-turn valves, providing a bubble-tight seal for bi-directional sealing for both low and high pressure. However, they have advantages and disadvantages when compared to floating and trunnion-mounted ball valves.

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Floating and Trunnion Ball Valve Comparation

  Floating Ball Valve Trunnion Ball Valve Construction Without "trunnion", the ball will move towards the seat when the flow pressure pushes it, while the seat will not move. The &#;trunnion&#; makes the ball not move, while the seat will move towards the ball when flow pressure pushes it. Working Principal The flow pressure pushes the ball to the seat to seal. The flow pressure pushes the seat to the ball to seal. Function On/off, self relieving seat On/off, double block and bleed, DIB, self relieving seat Open Speed Quarter turn, fast operation Quarter turn, fast operation Suitable Fluid Oil, gas, petrochemical, wast water etc, hydraulic power Oil, gas, petrochemical, wast water etc, hydraulic power Suitable Pressure & Size Class 150-300, 1/2&#;-6&#;;
Class 600, 1/2&#;-3&#;;
Class 900, 1/2&#;-2&#;;
Class , 1/2&#;-1&#; Class 150-300, 3&#; and larger;
Class 600-90, 2&#; and larger;
Class -, 1-1/2&#; and larger Flow Direction Bi-direction, single direction Bi-direction, single direction Torque Higher Lower Seat Material Soft, metal Seat Soft, metal Seat Suitable Temperature -196~625&#; -196~625&#; Design Standard API 6D, API 608, BS API 6D, API 608 Price Lower Higher

Floating Ball Valve

A floating ball valve gets its name from the ball. It is a sphere that "floats" freely inside the valve&#;s body, which is compressed between two flexible seats while suspended in liquid. What a floating ball valve normally does during operation is float slightly downstream, which causes the seating mechanism to compress under the ball. Should the seat disintegrate, the ball floats to the metal stem to seal it. This provides a failsafe within the design.

As the most common valve type in the piping industry, floating ball valves play an important role in regulating flow through pipelines and other piping systems in the gas, oil, water and other industries. They create a bi-directional seal and can even be customized for high pressure operations, though normally they are only used in pipelines with low to medium pressure. Available in different configurations and sizes, they feature a ball-shaped disk that&#;s hollow and perforated so that liquids can pass through it when open.

As the nominal bore size of the ball increases, the weight of the ball also increases, and the area subjected to the line pressure also increases. This has the overall effect of increasing the load (force) acting on the ball. There comes a point where it is no longer possible for the seats to support the ball and it is necessary to look at a different design. This is where the trunnion-mounted ball design comes into play.

Advantages:

1. Cost-effectiveness
2. Fewer valve parts make maintenance easier.
3. Reduced manufacturing time

Disadvantages:

1. Complete reliance on the downstream seat when carrying a medium load
2. Bigger torque at the same size and operating conditions
3. Seating directly absorbs the ball&#;s gravity, so it is unable to reliably withstand higher pressures or larger balls.
 

Trunnion Mounted Ball Valve

As described above, there comes a point where, owing to the high value of the loading forces on the ball, it becomes no longer possible for the seats to support the ball and an alternative design is required.

A trunnion mounted ball valve means that the ball is constrained by bearings and is only allowed to rotate. The majority of the hydraulic load is supported by the system constraints, resulting in low bearing pressure and no shaft fatigue.
In effect, the trunnion mounted ball design in effect addresses this problem, where in effect the shaft, ball, and trunnion act as a single assembly that supports the ball instead of the seats, and the seats become "floating" in a kind of reversal of the "floating ball" design. Similarly, a trunnion-mounted ball design is also capable of bi-directional sealing.

Advantages:

1. Low torque
This is particularly advantageous when the ball valve is actuated because it reduces the size of the actuator and, hence, the overall cost of the valve actuation package. Obviously, this distinction becomes significant as the pressure class and valve size increase.

2. It can withstand higher pressures or larger balls on a consistent basis.

Disadvantages:

1. Expensive
2. It is not suitable for very small sizes, typically 1-1/2" and below.

 

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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

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.

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