In industrial piping systems, ball valves play a crucial role in controlling fluid flow with precision and reliability. Among various types, the Fixed Ball Valve and Trunnion Ball Valve are two of the most commonly used designs. While both serve the same purpose—to start, stop, or regulate flow—their internal mechanisms, performance, and applications differ significantly. Understanding these differences helps engineers and buyers choose the right valve for their systems. In this article, we’ll break down the 10 key differences between Fixed Ball Valves and Trunnion Ball Valves, explore their structures, and highlight why leading trunnion ball valve manufacturers like GOTEB are setting new standards in quality and innovation.
A Trunnion Ball Valve features a ball that is supported by trunnions (metal shafts) at both the top and bottom. These trunnions act as anchors, holding the ball firmly in place within the valve body while allowing it to rotate smoothly when the valve opens or closes.
This trunnion-mounted design reduces the load on the valve seats and lowers the operating torque, making it ideal for high-pressure and large-diameter applications. In other words, the trunnion meaning refers to the mechanical support structure that stabilizes the ball during operation.
The term Fixed Ball Valve often refers to a Floating Ball Valve or a ball valve with a stationary ball design—meaning the ball is not supported by trunnions but held in place by the valve seats. When pressure is applied, the ball slightly moves downstream to press against the seat, ensuring a tight seal.
Fixed Ball Valves (or non-trunnion ball valves) are simpler in structure, smaller in size, and best suited for low to medium pressure applications.
In a Trunnion Ball Valve, the ball is supported by trunnions at both ends, reducing seat load. In contrast, a Fixed Ball Valve relies on floating seat rings to center the ball, which can increase wear under high pressure.
The Trunnion Ball Valve’s ball stays fixed in position and only rotates on its axis. A Fixed Ball Valve’s ball moves slightly downstream when pressure is applied, pressing against the seat for sealing.
The trunnion mounted ball valve uses spring-loaded seats that maintain consistent sealing regardless of pressure fluctuations. Meanwhile, Fixed Ball Valves depend on line pressure for sealing performance, which may decline in low-pressure conditions.
Because of the trunnion ball valve design, torque requirements are significantly lower. The trunnions absorb the pressure load, minimizing seat friction. Fixed Ball Valves require more torque, especially in high-pressure environments.
Trunnion Ball Valves are designed for high-pressure systems, often rated up to Class 2500 or higher. Fixed Ball Valves, on the other hand, are typically limited to Class 300 or 600, depending on materials and configuration.
Trunnion designs accommodate larger diameters (DN100–DN2000), making them suitable for heavy-duty pipelines. Fixed or floating ball valves are generally used for smaller sizes (DN15–DN200).
Due to their complex structure and higher manufacturing precision, Trunnion Ball Valves are more expensive than Fixed Ball Valves. However, they offer longer service life and reduced maintenance costs in demanding applications.
Trunnion valves are built for long-term durability and allow easier seat replacement without removing the valve from the pipeline. Fixed Ball Valves are simpler, but may require full removal for internal maintenance.
Thanks to dual-seat and trunnion support systems, Trunnion Ball Valves provide tighter shutoff and better leakage control under high pressure. Fixed Ball Valves can achieve reliable sealing, but are more susceptible to wear and seat deformation over time.
| Type | Typical Applications |
|---|---|
| Trunnion Ball Valve | Oil & gas pipelines, petrochemical plants, power generation, offshore platforms |
| Fixed Ball Valve | Water supply systems, HVAC, low-pressure chemical and food industries |
| Aspect | Fixed Ball Valve | Trunnion Ball Valve (Trunnion Mounted Ball Valve) |
|---|---|---|
| 1. Ball Support Structure | The ball is held in position by the valve seats only. There are no trunnions or mechanical supports; the ball “floats” slightly downstream under pressure. | The ball is supported by trunnions (mechanical shafts) at both the top and bottom. These trunnions fix the ball in place while allowing it to rotate smoothly. |
| 2. Movement of the Ball | The ball can move slightly along the flow direction when pressure is applied. This movement presses the ball against the downstream seat for sealing. | The ball does not move axially. It only rotates on its axis because the trunnion support holds it firmly in place. |
| 3. Sealing Mechanism | Sealing depends on line pressure pushing the ball against the seat. Sealing effectiveness may decrease in low-pressure systems. | Uses spring-loaded seats that maintain constant contact with the ball. Provides reliable sealing performance even under varying pressure conditions. |
| 4. Operating Torque | Requires higher operating torque because the entire pressure load acts on the ball and seat contact area. | Lower torque required since trunnions absorb the pressure load, reducing friction between the ball and seats. |
| 5. Pressure Rating | Typically suitable for low to medium pressure applications, such as Class 150–600. | Designed for high-pressure systems; can handle Class 900–2500 and even higher in special designs. |
| 6. Valve Size Range | Commonly used for small to medium sizes (DN15–DN200). | Preferred for large diameters (DN100–DN2000) and critical applications. |
| 7. Construction Complexity | Simple structure, fewer parts, easier to manufacture and install. | More complex design with multiple components, including trunnions, bearings, and pressure-balanced seats. |
| 8. Cost | More economical due to simpler construction and fewer materials. Ideal for budget-sensitive applications. | More expensive because of its robust structure, precision machining, and enhanced performance under extreme conditions. |
| 9. Maintenance and Serviceability | Easier to install but often requires complete removal from the pipeline for seat or seal replacement. | Designed for in-line maintenance; seat rings and seals can be replaced without removing the valve from the line. |
| 10. Leakage Resistance | Good sealing performance at moderate pressures but can suffer from seat deformation over time. | Excellent leakage resistance; dual-seat design and trunnion support ensure tight shutoff under high pressure. |
| 11. Durability | Suitable for normal service conditions; wear increases with pressure and frequency of operation. | Extremely durable and long-lasting; suitable for continuous high-pressure, high-cycle service. |
| 12. Flow Control Performance | Provides decent flow control but limited stability under fluctuating pressure. | Offers stable and precise flow control even under high-pressure or high-flow conditions. |
| 13. Weight | Lightweight and compact. | Heavier and bulkier due to trunnion assembly and reinforced body structure. |
| 14. Typical Applications | Water treatment systems, HVAC, general industrial lines, low-pressure chemical systems. | Oil & gas pipelines, petrochemical plants, power generation, offshore drilling platforms. |
| 15. Common Pressure Classes | 150LB, 300LB, 600LB | 900LB, 1500LB, 2500LB |
| 16. Suitable Mediums | Clean liquids, gases, and low-viscosity fluids. | Suitable for high-temperature, high-pressure, or corrosive media (e.g., oil, gas, slurry). |
| 17. Trunnion Meaning | Not applicable — this design doesn’t include a trunnion. | “Trunnion” refers to the support shaft that holds the ball in position, reducing load on the valve seats. |
| 18. Maintenance Frequency | Higher maintenance frequency due to seat wear in high-pressure use. | Longer maintenance intervals; seats and seals are protected from pressure-induced damage. |
| 19. Design Standard Examples | API 608, ISO 5211 (for general use) | API 6D, ISO 14313 (for pipeline and industrial use) |
| 20. Example Manufacturer | Available from general-purpose valve suppliers. | GOTEB trunnion ball valves — precision-engineered according to international standards for high-performance applications. |
Both Fixed Ball Valves and Trunnion Ball Valves play vital roles in fluid control systems. The Trunnion Ball Valve provides better sealing, durability, and pressure resistance for demanding industries, while the Fixed Ball Valve offers a simple and cost-effective solution for smaller systems.GOTEB is a trusted trunnion ball valve manufacturer, specializing in high-precision valve spheres. Since 2016, GOTEB has served clients in over 40 countries with a strong reputation for quality, innovation, and reliability.
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