The core difference between trunnion ball valves and floating ball valves lies in their structure: In a floating ball valve, the ball is "floating," relying on medium pressure to press the valve seat for a single-sided seal, suitable for low to medium pressure. In a trunnion ball valve, the ball is fixed by upper and lower shafts, sealing through a floating valve seat, capable of withstanding high pressure and large-diameter conditions, offering a more stable seal.
Floating ball valves have a simple structure and low cost. The ball is connected only by the upper valve stem and can slightly shift under medium pressure, forming a seal against the outlet valve seat-a single-sided forced seal. This design results in lower operating torque, suitable for smaller diameters and lower pressures (e.g., ≤100mm, ≤1.6MPa). However, because all the load on the ball is transferred to the valve seat, it is prone to seal failure under large diameters or high pressures, and the opening and closing torque increases significantly.
In contrast, the ball in a trunnion ball valve is fixed by support shafts on both the upper and lower sides. The ball itself cannot float; the seal relies on a spring or medium pressure to push the valve seat against the ball, resulting in a double-sided seal structure that effectively distributes stress.
This design significantly reduces operating torque, improving the reliability and lifespan of the valve under high pressure, large diameter (up to 60 inches), and harsh operating conditions, and is widely used in critical systems such as long-distance pipelines and oil refining and chemical industries. Furthermore, trunnion ball valves typically feature automatic pressure relief, enhancing safety.
Budget vs. Performance: When Should You Choose a Floating Ball Valve? Get the Selection Guide.
Core Mechanical & Operational Features
| Parameter | Floating Ball Valve | Trunnion Mounted Ball Valve |
| Ball Support | The ball is suspended by the stem and supported only by two valve seats. | The ball is fixed by a top stem and a bottom trunnion (fixed shaft). |
| Sealing Mechanism | Ball moves to the seat. Media pressure pushes the ball against the downstream seat to create a seal. | Seat moves to the ball. The ball remains fixed; spring-loaded seats are pushed against the ball by media pressure. |
| Sealing Type | Typically Downstream Sealing only. | Bidirectional Sealing (Often features Double Block and Bleed - DBB). |
| Operating Torque | High. Due to the friction caused by the ball pressing against the seat. | Low. The ball is supported by bearings, resulting in minimal friction. |
| Seat Design | Static seats, usually soft-seated. | Floating, spring-loaded seats; can be soft, metal, or primary-metal secondary-soft. |
| Cavity Relief | Difficult (requires special seat grooves). | Automatic Self-Relieving. Seats push away automatically if cavity overpressure occurs. |
Technical Specifications & Limitations
| Parameter | Floating Ball Valve | Trunnion Mounted Ball Valve |
| Size Range | Small Bore (Typically ≤ DN150 / 6") | Full Range (DN50 - DN1500+ / 2" - 60") |
| Pressure Class | Low to Medium (Typically ≤ Class 300/600) | All Classes (Class 150 - 2500+) |
| Opening Speed | Fast. | Medium (Usually requires gearbox or actuator). |
| Manufacturing Cost | Lower. Simple structure with fewer parts. | Higher. Complex structure requiring precision machining for the trunnion and seats. |
| Maintenance | Relatively Easy. | Complex (Many heavy internal components). |
| Weight | Lightweight and compact. | Heavy and robust. |
Advanced Functional Features
| Feature | Floating Ball Valve | Trunnion Mounted Ball Valve |
| DBB (Double Block & Bleed) | Not Available. | Standard Feature. |
| Emergency Sealant Injection | Rarely Available. | Standard Feature (At seats and stem). |
| Anti-Static Design | Requires additional components. | Inherently easier to implement. |
| Fire-Safe Design | Standard Option (API 607 / 6FA). | Standard Option (API 607 / 6FA). |
| Cavity Pressure Relief | Relieves to the downstream side. | Relieves to the upstream or downstream pipeline. |
Typical Applications
| Requirement | Recommended Type | Reason |
| Residential Gas/Water | Floating | Low cost, small diameter, and low pressure. |
| High-Pressure Gas Pipelines | Trunnion | Requires DBB, sealant injection, and low torque under high pressure. |
| Chemical Process Lines | Floating | Simple structure is easier to maintain in corrosive environments. |
| Large Oil Terminals | Trunnion | Ensures absolute sealing and downstream protection at high pressures. |
| High Cycle Automation | Trunnion | Low torque design reduces wear on actuators. |
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FAQ
When to use a trunnion mounted ball valve?
Trunnion mounted ball valves are perfect for a wide range of applications among several oil and gas industries. Examples of oil and gas industries that utilize trunnion mounted ball valves include gas feed lines, field gas plants, industrial gas processing plants, oil refinery feedstock lines, and crude oil plants.
What is the purpose of a floating ball valve?
Floating ball valves are commonly used in filtration systems to control the flow of fluids during the filtration process. They play a crucial role in isolating and directing the flow of fluids through different stages of the filtration system.
What is a trunnion ball valve?
Trunnion ball valves are quarter-turn valves used to control the flow of media in a pipeline. Unlike the more common "free floating" ball valve design, trunnion ball valves have a unique configuration.