The Difference Between Floating and Trunnion Metal Seated Ball Valves

In industrial process industries where fluid control is critical, the choice of valve technology can significantly impact performance, safety, and operational cost. Among the most widely used types of valves in demanding applications are metal seated ball valves. These valves are designed to provide robust sealing and long service life under extreme conditions such as high temperatures, abrasive media, and high pressure. The two primary types of metal seated ball valves available are floating ball valves and trunnion ball valves. This article will comprehensively explore the differences between these two designs, their construction, operating principles, typical applications, and maintenance considerations to aid industry professionals in making the best valve choice.

What Is a Metal Seated Ball Valve?

A metal seated ball valve is a quarter-turn valve where both the ball and seat rings are made from hardened metal alloys rather than soft plastics or elastomers. This composition gives the valve exceptional wear resistance and the ability to function reliably in applications involving abrasive slurries, high-temperature steam, or corrosive fluids. The metal-to-metal sealing ensures durability, extended valve life, and tighter shut-off compared to soft-seated valves. Metal seated ball valves are critical components in oil and gas upstream, midstream, and downstream operations, seawater desalination plants, offshore drilling platforms, and petrochemical processing.

Structural Differences Between Floating and Trunnion Metal Seated Ball Valves

Floating Metal Seated Ball Valves

In floating metal seated ball valves, the ball is not fixed within the valve body. Instead, it "floats" between two metal seats and is held in sealing contact by the line pressure pushing it downstream. This slight lateral movement allows the ball to press firmly against the downstream seat to create a tight seal. The seats are pushed inward by springs or body pressure to maintain contact with the ball.

Key attributes of floating ball valves include:

- The ball is free to move within the cavity.

- Sealing is achieved by the pressure-driven lateral movement of the ball.

- Typically smaller valve sizes are designed in this configuration.

- A simpler design with fewer internal parts, resulting in easy maintenance.

- Generally used in applications with low to medium pressure ranges.

Trunnion Metal Seated Ball Valves

Trunnion metal seated ball valves feature a ball that is rigidly supported by shaft-like trunnions fixed to the valve body at the top and bottom. This firm anchoring keeps the ball from moving laterally, instead, the seats are designed to move or are spring-loaded to press against the ball to achieve sealing.

Main features of trunnion ball valves:

- Fixed ball supported by upper and lower trunnions.

- The seats are floating or spring-loaded for effective sealing.

- Can handle much larger valve sizes and higher pressures.

- Reduced operating torque due to fixed ball.

- More complex internal design but superior performance in severe service.

Operating Principles

Floating Ball Valves

The floating ball valve's sealing is primarily accomplished by fluid pressure pushing the ball against the downstream seat. When the valve closes, the pressure forces the ball to press down on the seat to form a tight metal-to-metal seal. Due to the floating nature, the ball can move slightly inside the cavity to accommodate pressure variations and maintain sealing integrity. The valve opens by rotating the ball 90 degrees to allow flow through the bore.

Trunnion Ball Valves

In trunnion valves, the ball remains fixed due to the trunnions, which reduces the lateral movement seen in floating designs. Instead, the seats move or compress via springs or body pressure to seal against the ball. This configuration lowers the torque needed to operate the valve, especially at larger sizes or higher pressures. The anchored ball design is well-suited to tough service conditions with high differential pressures or large diameter pipelines.

Performance Comparison and Applications

Floating Ball Valves

Floating metal seated ball valves are commonly selected for:

- Medium pressure applications, typically up to 600 psi.

- Smaller valve sizes, generally under 10 inches in diameter.

- Applications requiring a simple, affordable valve with effectiveness.

- Water treatment, HVAC, general chemical lines, and gas distribution systems.

Advantages:

- Cost-effective manufacturing and maintenance.

- Tight sealing through dynamic pressure assistance.

- Fewer parts reduce risk of component failure.

Limitations:

- Higher torque required to operate due to the floating ball movement.

- Not ideal for very large or ultra-high-pressure pipelines.

- Seal integrity may be affected under fluctuating pressure conditions.

Trunnion Ball Valves

Trunnion metal seated ball valves are favored in:

- High pressure and large diameter pipelines, capable of handling pressures beyond 2500 psi.

- Oil and gas industry, offshore oil platforms, refineries, and petrochemical plants.

- Applications demanding low torque operation and high reliability.

- Situations requiring double block and bleed capabilities or fire-safe design features.

Advantages:

- Lower torque requirements due to fixed ball and seat mechanism.

- Superior ability to handle severe pressures and large valve sizes.

- Enhanced durability with robust internal components.

- Consistent sealing unaffected by pressure fluctuations.

Limitations:

- Higher cost due to complex internal assembly.

- More challenging maintenance compared to floating designs.

- Larger physical size and weight.

Materials, Construction, and Technical Specifications

Metal seated ball valves are typically constructed of high-grade stainless steels or alloys to withstand corrosive and abrasive environments. Common body materials include carbon steel, forged steel, and stainless steel (such as 316SS or CF8M). The ball and seat surfaces may be coated with wear-resistant alloys like chromium carbide or tungsten carbide through processes like High Velocity Oxy-Fuel (HVOF) coating to enhance durability and reduce friction.

Standard design features include:

- Fire-safe design compliant with API 607 and API 608 standards.

- ISO 5211 mounting pads for actuator installation.

- Blowout-proof stems for safety.

- Bi-directional tight shutoff meeting ANSI FCI 70-2 Class V or VI.

- Sizes ranging from 1/2 inch up to 24 inches or larger depending on valve type.

- Pressure ratings from ANSI Class 150 to Class 2500 or above.

- End connection types such as flanged RF & RTJ, butt weld, socket weld, threaded NPT or BSP.

Some valves incorporate advanced seat designs such as spring-loaded upstream and downstream metal seats to maintain optimal sealing pressure regardless of thermal expansion or wear. Graphite or flexible graphite packings are utilized to ensure low fugitive emissions around the stem.

Maintenance and Operational Considerations

Floating ball valves, with fewer moving parts and simpler internal design, offer ease of maintenance and are suitable for processes with moderate pressure and less abrasive media. Maintenance usually involves seat replacement or ball machining, which can often be done without removing the valve from the pipeline.

Trunnion ball valves require more attentive maintenance due to the complexity of the trunnion shafts and spring-loaded seats. However, their robust design extends service intervals and enhances reliability in continuous high-stress conditions. Regular inspection and lubrication of moving parts, along with seat and seat seal replacement, ensure continued performance. Many manufacturers offer modular designs enabling easier maintenance in the field with minimal downtime.

Choosing Between Floating and Trunnion Metal Seated Ball Valves

The decision depends on several factors including:

- Operating pressure and temperature.

- Valve size and pipeline diameter.

- Media abrasiveness and corrosion potential.

- Required frequency of operation and maintenance capability.

- Cost constraints and valve lifecycle expectations.

For smaller pipelines with moderate pressure and less severe conditions, floating metal seated ball valves provide a practical, cost-effective solution with reliable sealing. For larger, high-pressure pipelines, especially in upstream/downstream oil & gas and offshore platforms, trunnion valves deliver superior performance, lower operational torque, and enhanced safety.

Conclusion

Metal seated ball valves are essential for critical flow control applications where durability, tight sealing, and resistance to harsh environments are mandated. Understanding the operational differences between floating and trunnion metal seated ball valves enables better selection tailored to specific industrial requirements. Floating valves offer simple, efficient sealing for moderate pressures and smaller sizes, while trunnion valves provide superior handling of large sizes, high pressure, and severe service conditions.

As a dedicated manufacturer specializing in designing, developing, and producing high-quality floating, trunnion, and top-entry metal seated ball valves, we provide OEM services to meet the precise needs of global brands, wholesalers, and manufacturers. Our valves serve diverse sectors including petroleum, natural gas, seawater desalination, and offshore drilling platforms with uncompromising quality and reliability.

Contact us today to consult with our experts and discover how our metal seated ball valves can optimize your system's performance, safety, and longevity. Explore our extensive valve portfolio tailored to your process challenges.

Frequently Asked Questions (FAQ)

1. What is the primary operational difference between floating and trunnion metal seated ball valves?

The floating valve's ball moves slightly inside the body, sealing by pressing against the downstream seat due to line pressure, while the trunnion valve's ball is fixed by trunnions, and the seats move or compress against the ball to seal.

2. Which metal seated ball valve type is recommended for very high-pressure applications?

Trunnion metal seated ball valves are recommended for very high-pressure and large-diameter applications because of their anchored design and lower operating torque.

3. Are metal seated ball valves suitable for abrasive and corrosive media?

Yes, with their hardened metal seats and specialized coatings such as chromium or tungsten carbide, metal seated ball valves resist wear and corrosion in abrasive and harsh chemical environments.

4. How do the maintenance requirements differ between floating and trunnion ball valves?

Floating ball valves require simpler maintenance due to fewer parts and easier access, whereas trunnion valves, although more robust, need more detailed maintenance occasionally, especially of the trunnion shafts and seat springs.

5. Can metal seated ball valves be used in fire-safe applications?

Yes, many metal seated ball valves are designed and certified to conform to fire-safe standards like API 607 and API 608, ensuring valve integrity during and after fire exposure.

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