Comparing Floating and Trunnion Ball Valves Key Design Differences

In complex industrial pipeline systems where various media flow continuously, ball valves serve as diligent "gatekeepers," controlling the opening and closing of media flow. While these valves might appear simple at first glance, they contain sophisticated design variations. Floating and trunnion (fixed) ball valves, as two mainstream designs, each have distinct advantages in principle, performance, and application scenarios. This article provides an in-depth analysis of these two types of ball valves, examining their working principles, design characteristics, and selection criteria to help professionals make informed choices in practical applications.

Among various valve types, ball valves stand out for their compact structure, durability, and quick operation, making them indispensable components in industrial pipeline systems. The core component of a ball valve is a sphere with a through-hole (called the bore), which controls media flow by rotating 90 degrees. When the bore aligns with the valve body channel, media flows freely; when rotated to the closed position, the bore becomes perpendicular to the flow path, stopping media movement.

All ball valve designs rely on two seats to secure and seal the ball. These seats are typically made of materials like polytetrafluoroethylene (PTFE), which tightly conform to the ball surface to prevent leakage. Based on how the ball is secured, ball valves are classified into two main types: floating ball valves and trunnion ball valves.

Floating ball valves are the most common type in industrial pipeline systems. Their design features a ball that isn't fixed within the valve body but instead "floats." When the seats begin to wear, the media pressure pushes the ball against the downstream seat, maintaining a tight seal. This design gives floating ball valves excellent self-sealing properties.

Unlike floating designs, trunnion ball valves have their balls fixed with bearings within the valve body, restricting downstream movement. To maintain sealing after seat wear, trunnion ball valves typically use spring-loaded seat mechanisms. This design makes them more reliable in high-pressure applications.

Before examining floating ball valve specifics, let's review the main components of ball valves:

• Valve body: The outer shell containing valve mechanisms, typically made of steel, iron, brass, bronze, or PVC, depending on media characteristics, temperature, and pressure.
• Ball: The core rotating sphere with a through-hole, connected to the body via a stem.
• Bore: The central through-hole controlling media flow, with size directly affecting flow characteristics.
• Packing: Flexible seals around the stem preventing media leakage, requiring corrosion and heat resistance.
• Seat: Ring-shaped components between ball and body creating seals, usually made of thermoplastic materials like PTFE for self-lubrication and wear resistance.
• Stem: The shaft connecting the ball to external operators, controlling rotation for opening/closing.
• Actuator: External devices rotating the stem, including manual levers/gears or electric/pneumatic/hydraulic actuators, selected based on valve size, operation frequency, and automation needs.

Most ball valves use floating designs. The floating ball is supported by cup-shaped seats that form tight seals between ball and body. The ball remains suspended in media, held in place by thermoplastic seats. These seats create bidirectional sealing, allowing the ball to move freely and block media flow in either direction. Floating valves are lightweight, economical, and versatile, widely used in oil, gas, water, steam, and petrochemical applications.

Floating ball valves operate via a stem connected to the ball's top, rotating 90 degrees (quarter-turn). As the ball rotates, the bore becomes covered or exposed by the valve body wall, controlling media flow. The stem-ball connection is loose enough that media pressure pushes the ball against the downstream seat when rotating, creating a tight seal. However, in extremely low-pressure applications with seat wear, floating valves may not seal effectively due to insufficient pressure. In most applications though, downstream pressure maintains sealing long after initial seat wear.

Trunnion ball valves function similarly to floating designs, but feature a second stem opposite the operating stem that fixes the ball. This second stem and bearing assembly is called the trunnion .

Unlike floating valves, trunnion valve stems rigidly connect to balls, restricting all movement except rotation. Since balls don't "float" downstream with media pressure, trunnion valves maintain proper sealing on both sides simultaneously. This proves especially important for multi-port valves and extremely low-pressure applications where media flow can't push balls against seats.

Trunnion valves work effectively in both low- and high-pressure applications and require less operating torque than floating valves. However, pipeline designers should note that trunnion designs are generally more expensive than floating alternatives.

Trunnion valves are commonly found in these industries:

• Chemical
• Power generation
• Oil and gas
• Pipelines
• Hydrocarbon processing

In both valve types, stem-to-environment seals endure the most wear over time, making valve packing crucial for preventing media escape. Designers should consider spring-loaded packing designs to compensate for inevitable wear and prevent stem seal leakage.

While floating and trunnion ball valves function similarly in practice, pipeline designers must understand each type's advantages and limitations. Professional valve suppliers can help determine the optimal ball valve type based on specific applications and budgets.

For clearer understanding of their differences, we compare key characteristics:

When choosing between floating and trunnion ball valves, consider these factors:

• Working pressure: For high pressures, trunnion valves ensure reliable sealing.
• Pipe size: Trunnion valves suit large-diameter pipes better due to lower torque requirements.
• Operation frequency: Trunnion valves offer greater durability for frequent operation.
• Media characteristics: Corrosive media require valves with corrosion-resistant materials.
• Budget: Floating valves typically cost less than trunnion alternatives.

Both floating and trunnion ball valves have distinct advantages suited for different applications. Professionals should evaluate specific working conditions and requirements when selecting valve types, considering all relevant factors to make optimal decisions for their systems.