Trunnion Mounted Ball Valve: A Comprehensive Overview
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A Trunnion Mounted Ball Valve is a specialized quarter-turn valve designed to control the flow of fluids in pipelines. Distinguished by its unique design, this valve type offers increased stability, durability, and precise control, making it ideal for high-pressure, high-flow applications. Unlike traditional ball valves, which feature a floating ball, a trunnion ball valve incorporates a fixed ball that is supported by a trunnion (a shaft-like support) on both the top and bottom of the ball. This design offers significant advantages, particularly in terms of stability and performance under high-pressure and high-flow conditions. In this article, we will dive into the features, benefits, and applications of trunnion mounted ball valves, as well as the innovative technologies that enhance their safety and reliability.
The trunnion design provides several key advantages:
What is a Trunnion Mounted Ball Valve?
A trunnion mounted ball valve is a type of ball valve designed to operate in larger pipelines and systems with higher pressure and flow requirements. It differs from traditional floating ball valves in that the ball is securely fixed within the valve body using two trunnions (upper and lower shafts). This fixed ball design minimizes ball movement, reducing wear on the seats and ensuring consistent sealing performance throughout the valve's service life.The trunnion design provides several key advantages:
Enhanced stability
The ball is firmly supported at both ends, preventing axial float or unwanted movement during operation, which increases the valve's performance under high-pressure conditions.
Reduced torque
With the ball fixed in place, the torque required to operate the valve is lower than that of traditional floating ball valves, reducing actuator size and operational costs.
Precise control
The fixed ball allows for more precise flow control, making these valves ideal for applications that require accuracy, such as in the oil and gas, chemical, and petrochemical industries.
Key Features of Trunnion Mounted Ball Valves
1. Emergency Seat Sealant Injection
One of the critical features of trunnion ball valves is the optional emergency seat sealant injection system. This system allows for the injection of sealant into the valve’s end connections, helping to create a positive seal if there is seat leakage caused by service impurities or unplanned pressure spikes. This feature ensures that the valve remains functional in extreme conditions, preventing unwanted leaks and improving the reliability of the valve in emergency situations.
2. Drain and Vent Ports
Trunnion mounted ball valves are equipped with drain and vent ports, which are essential for safety and maintenance. Drain ports, typically located at the bottom of the valve, allow trapped fluid to be released from the body cavity of the valve. Similarly, vent ports at the top of the body cavity are designed to expel any gas that might be trapped when the valve is in the closed position. These ports play an integral role in double block and bleed (DBB) and double isolation and bleed (DIB) configurations, where the goal is to isolate sections of the pipeline while safely removing trapped fluids or gases. This ensures that the system remains safe even during maintenance or emergencies.
3. Double Block and Bleed
In critical applications, a double block and bleed configuration is essential for preventing pressure build-up within the valve body. This feature is designed to isolate the pipeline from both sides of the valve and safely vent any trapped pressure, even while the valve is fully closed. This helps prevent dangerous situations where high-pressure fluids might accumulate in the valve body, improving the safety of the overall system.
4. Firesafe Design
Trunnion ball valves can be equipped with a firesafe design that complies with industry standards such as API 607. This design includes secondary metal seats that provide a fire-safe shutoff in the event of a fire, ensuring that the valve seals properly even under extreme temperatures. Additionally, flexible graphite packing and secondary graphite body seals prevent leakage through body joints and the stuffing box during a fire, enhancing the valve's performance in hazardous situations.
5. Internal Trunnion Design
The internal trunnion design of these valves features upper and lower bearing plates that hold the ball in place and prevent axial float. This design helps prevent excessive stress on the valve seats, thereby extending the life of the valve and ensuring reliable operation in high-pressure applications. Some valve models also offer an external trunnion design for certain sizes, providing flexibility in system configurations.
6. Pressure Energized Stem Packing
Trunnion mounted ball valves are equipped with pressure-energized stem packing, which is a key feature that enhances sealing performance. This proprietary design includes an energizer ring located above the primary O-ring stem seal. In the event that the O-ring is damaged or compromised, the media pressure helps create an upward compressive force on the packing, increasing the net compressive force on the seal. This results in a more reliable seal and prevents leaks, even under high-pressure conditions.
7. Double Seals on Body Joints
Trunnion ball valves incorporate double seals on body joints, which ensure zero leakage under standard operating conditions. The primary elastomeric seals provide an effective seal under normal conditions, while secondary graphite seals are used to handle extreme temperature changes or fires, as per API 607 requirements. This dual-seal design guarantees optimal sealing performance in a wide range of operational scenarios.
8. Anti-Static Devices
To prevent the risk of sparks or static discharge, trunnion mounted ball valves come with anti-static devices as a standard feature. These devices ensure electrical continuity between the ball, stem, and body, eliminating the possibility of static charge accumulation and reducing the risk of sparks that could lead to safety hazards in flammable environments.
9. Valve Position Indication
Clear markings are provided on the valve’s mounting flange to indicate the open or closed position of the valve. This valve position indication helps operators quickly identify the status of the valve, based on the orientation of the stem key, improving safety and reducing the chance of errors during operation.
10. Blowout-Proof Stem Design
The valve design incorporates a blowout-proof stem, which prevents the stem from being ejected under line pressure. This design ensures that the valve remains secure and safe under high-pressure conditions, preventing potential accidents or failures in the system.
Applications of Trunnion Mounted Ball Valves
Trunnion mounted ball valves are widely used in industries that require robust, reliable, and safe flow control under high-pressure and high-flow conditions. Key applications include:
Oil and Gas
These valves are ideal for controlling the flow of crude oil, natural gas, and refined products in pipelines, especially in offshore and subsea operations where high pressure and safety are critical.
Petrochemical and Chemical Plants
Trunnion ball valves are used to control the flow of various chemicals and gases, ensuring precise and reliable operation in demanding environments.
Power Generation
These valves are essential for controlling steam and water flow in power plants, where high pressure and temperature conditions are the norm.
Water Treatment
Trunnion ball valves are used in water treatment facilities to regulate the flow of water and chemicals, providing consistent performance over long periods.
Conclusion
The trunnion mounted ball valve is a versatile, reliable, and safe solution for controlling fluid flow in high-pressure applications. With features such as emergency seat sealant injection, drain and vent ports, firesafe design, and pressure-energized stem packing, these valves offer excellent sealing performance, safety, and durability. Whether for oil and gas, chemical processing, or power generation, trunnion ball valves are essential components in systems that demand precision, reliability, and safety. Their innovative design and advanced features make them a top choice for industries that rely on efficient, high-performance valves.
