The floating ball valve vs the trunnion mounted ball valve

Understanding the differences between floating ball valves and trunnion mounted ball valves is essential for selecting the right type for your application. Both designs serve unique purposes and function based on various requirements.

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Key Differences

The primary distinction between these two designs lies in the construction of the ball and how it is mounted inside the valve body. In a trunnion ball valve, the ball is anchored at the top and bottom through a valve stem and a trunnion, respectively. In contrast, a floating ball valve is secured only through the valve stem, which allows the ball to "float" within the valve seats.

Torque Requirements

In a floating ball design, the ball moves against the downstream seat thanks to the inline pressure, which ensures a tight seal. When transitioning from the closed to the open position, the ball must overcome both the inline pressure and the friction from the seats. Therefore, the torque required to operate the valve is significantly affected by the inline pressure and the valve size, especially with metal-seated valves, which demand greater force.

Conversely, a trunnion ball valve is held securely by the trunnion. The inline pressure presses the seats against the ball to create a seal, meaning the ball only needs to combat the pressure from the seats during operation. This crucial difference typically means that the torque required for a trunnion mounted ball valve is lower than that of a floating ball valve. For example, a DN200 metal-seated floating ball valve may need a larger actuator compared to a DN200 trunnion valve, often resulting in lower overall costs for the trunnion setup.

Applications and Advantages

The trunnion-mounted ball valve is generally better suited for high-pressure situations and larger dimensions when compared to floating ball valves. One additional benefit of the trunnion design is the inclusion of drain or bleed connections, which enhance its function as a dual-safe device. In the event the central cavity pressure exceeds the seat spring force, the seat springs will automatically relieve to drain excess pressure back into the main line. For this reason, trunnion designs are often the preferred choice in offshore and oil & gas applications, where extreme conditions prevail.

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Cost Considerations

One notable disadvantage of trunnion mounted ball valves compared to floating designs is the higher cost associated with them. Trunnions are typically utilized only when absolutely necessary due to these increased expenses.

Our specialists at Xiangyu can assist you in determining the right ball valve design tailored to your application's specific needs.