A trunnion-type ball valve is a type of valve that uses a rotating ball as its core control element. The opening and closing of the medium is controlled by the contact or separation of the ball and the valve seat. The "trunnion" in its name originates from the support shaft structure located on both sides of the ball. This design gives it unique advantages in high-pressure, large-diameter, and complex operating conditions, making it a key piece of equipment in the field of industrial fluid control.
Structural Features and Core Components
The structural design of imported trunnion-type ball valves revolves around "stability" and "sealing." Its core components include the ball, trunnion, valve seat, valve stem, and valve body:
Ball: The ball surface is machined with a circular through-hole, the diameter of which matches the inner diameter of the pipe, ensuring minimal fluid resistance when fully open. The ball material is typically stainless steel, carbon steel, or a corrosion-resistant alloy to adapt to different media requirements.
Truncusion: The symmetrically arranged support shafts (trunnions) on both sides of the ball are connected to the valve body via bearings, forming a fixed structure. The trunnion not only restricts the axial displacement of the ball but also reduces operating torque through rigid support, allowing the valve to open and close easily even under high pressure.
Valve Seat: The valve seat employs a spring-loaded design, automatically compensating for wear and maintaining sealing pressure. Some high-end models feature a lubrication port around the valve seat, allowing lubricant injection to reduce friction during closure and extend service life.
Valve Stem: The valve stem is keyed to the trunnion, transmitting the rotational torque of the drive unit (manual, pneumatic, or electric). The valve stem seal utilizes a stuffing box structure, combined with a spring-loaded design, effectively preventing media leakage.
Valve Body: The valve body is typically a one-piece cast or forged structure, with material matching the ball to ensure pressure resistance. Its internal flow channel design is optimized to reduce fluid turbulence and lower pressure drop.
Working Principle and Operating Mode
The operation of an imported trunnion-type ball valve consists of two stages: opening and closing.
Closed State: The ball's through-hole is perpendicular to the valve body's flow channel. Under spring force, the valve seat is tightly pressed against the ball surface, forming a metal-to-metal or soft seal (such as PTFE) sealing structure, preventing media flow.
Opening Process: The drive unit rotates the ball 90° via the valve stem, aligning the through-hole with the flow channel, allowing for smooth media flow. Due to the support of the trunnion, the ball remains stable during rotation, with no axial displacement, ensuring uniform stress on the sealing surface.
Bidirectional Sealing: The fixed ball design of the imported trunnion-type ball valve provides bidirectional sealing capability, meaning that regardless of the media flow direction, the valve seat automatically compensates for pressure changes, maintaining seal integrity. This characteristic is particularly important in multi-port valves or operating conditions where the media flow direction frequently changes.
Technical Advantages and Application Scenarios
The imported trunnion-type ball valve exhibits significant advantages in several dimensions thanks to its unique design:
- High Pressure Adaptability: The trunnion support structure effectively distributes the stress on the ball, allowing it to withstand pressures up to 6000 psig (413 bar) or even higher, far exceeding the pressure range of floating ball valves.
- Large Diameter Capability: The trunnion design reduces operating torque, allowing valve sizes to be extended to 60 inches (DN1500) and above, meeting the needs of large pipeline systems.
- Low-torque operation: Trunnion bearings reduce friction during ball rotation, lowering the operating torque by 30%-50% compared to floating ball valves, making them particularly suitable for frequent opening and closing conditions.
- Wear resistance and long service life: Spring-loaded valve seats automatically compensate for wear, and the lubrication port design significantly extends valve life and reduces maintenance costs.
- Fire-safe design: Some models have passed API 607 or 6FA fire resistance tests, maintaining a seal even under extreme conditions such as fires, preventing secondary disasters caused by media leakage.
Typical applications include:
- Oil and gas industry: Used in oil pipelines, refining units, and natural gas processing systems, withstanding high pressure and corrosive media.
- Power industry: Ensures reliable control of high-temperature and high-pressure fluids in boiler feedwater, steam pipelines, and cooling water systems.
- Chemical industry: Handles corrosive media such as acids, alkalis, and solvents, requiring valves with chemical corrosion resistance and sealing stability.
- Water treatment: Controls water flow and chemical additives; its sanitary design meets the needs of the food and beverage industry.
- Cryogenic Engineering: By selecting cryogenic materials (such as LCB steel) and special seals (such as cryogenic nitrile rubber O-rings), it is suitable for cryogenic media such as liquefied natural gas (LNG).
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