Views: 0 Author: Site Editor Publish Time: 2025-09-01 Origin: Site
In industrial fluid control systems, valves play an essential role in regulating, directing, and isolating the flow of liquids or gases. Among the most widely used are ball valves, which rely on a rotating spherical closure element (the ball) with a hole through its center. When the hole aligns with the pipeline, fluid flows freely; when it is turned perpendicular, flow stops.
Two major designs dominate the ball valve category—trunnion ball valves and floating ball valves. At first glance, they may appear quite similar. Both use the same basic principle of a ball inside a valve body and offer reliable shut-off capabilities. However, their internal structure, mechanical support, sealing method, and best-use scenarios differ significantly. Understanding these differences helps engineers, operators, and procurement managers make informed choices for specific applications.
This article takes an in-depth look at trunnion ball valves and floating ball valves, comparing their construction, operation, strengths, limitations, and common uses in industrial environments.
Before diving into the differences, it is useful to briefly review how each design functions.
In a floating ball valve, the ball is held in place only by the compression of two elastomeric or metal seats, one on the upstream side and one on the downstream side. The ball is not physically fixed to the valve body; instead, it “floats” slightly between the seats. The stem is connected to the top of the ball, allowing rotation for opening or closing.
When fluid pressure comes from the upstream side, it pushes the ball against the downstream seat, creating a tight seal. This design is mechanically simpler, with fewer internal supports, and works well for smaller valves and moderate pressures.
A trunnion ball valve features additional mechanical anchoring of the ball. The ball is fixed in position by trunnion supports—one at the top (connected to the stem) and one at the bottom. These trunnions keep the ball from moving sideways within the valve body.
Instead of relying on upstream fluid pressure to push the ball into the downstream seat, the sealing is achieved through spring-loaded or pressure-assisted seats that move toward the ball. This design is better suited for larger valve sizes, higher pressures, and more demanding applications.
The most fundamental distinction lies in how the ball is supported inside the valve.
Floating Ball Valve: The ball is free to move slightly downstream under pressure. This movement helps create a seal but means the seats must absorb both the sealing force and the full load from the fluid pressure. The stem is the only rigid connection to the ball.
Trunnion Ball Valve: The ball is mounted on shafts (trunnions) at the top and bottom, which hold it firmly in place. The seats move toward the ball to form the seal, and the trunnion bearings absorb much of the operating torque and pressure load.
This difference in support greatly affects performance, sealing behavior, torque requirements, and suitable size/pressure ranges.
One of the biggest operational differences is the torque required to open or close the valve.
Floating Ball Valve: Since the ball must be pushed into the downstream seat to form a seal, the contact area between the seat and ball can be high under pressure. This increases friction and requires higher torque to operate—especially at high pressure or in large sizes.
Trunnion Ball Valve: Because the ball is fixed and the seats move toward it, the sealing pressure does not significantly increase operating torque. This results in smoother operation and the ability to use smaller, less expensive actuators.
For manual operation, lower torque can mean easier handling. For automated systems, it can reduce power consumption and actuator costs.
Floating ball valves are generally best for smaller sizes and lower pressures, while trunnion ball valves excel in large-diameter, high-pressure applications.
Floating Ball Valve: Commonly used in sizes up to about 6 inches (150 mm) and pressure classes up to ANSI 600 (PN 100). Beyond that, the forces on the ball and seats can become too great for practical operation.
Trunnion Ball Valve: Suitable for much larger diameters—up to 60 inches (1500 mm) or more—and for very high pressures, including ANSI 1500 and above. They are a common choice for oil and gas transmission pipelines and other heavy-duty services.
In floating ball valves, the upstream pressure pushes the ball into the downstream seat, creating a primary seal. This is a straightforward approach but depends heavily on the condition of the seat material and the precise alignment of components.
In trunnion ball valves, the seats are spring-loaded or use differential pressure to push toward the ball, creating seals on both upstream and downstream sides regardless of pressure direction. This is particularly advantageous for bidirectional sealing and for situations where pressure changes direction or where reliable sealing is required in both flow directions.
Both designs can achieve very tight shut-off (often rated as “bubble-tight”), but trunnion ball valves can maintain sealing performance more consistently under high pressure and in large sizes. The controlled seat movement also allows better sealing with a variety of seat materials, including metal seats for abrasive or high-temperature service.
The maintenance profile of each valve type is influenced by its design.
Floating Ball Valve: With fewer parts and simpler construction, these valves are easier to disassemble, inspect, and repair. However, because the seats bear the full brunt of pressure and sealing force, they may wear faster in high-pressure or abrasive services.
Trunnion Ball Valve: More complex internally, with additional bearings and seat mechanisms, which may require specialized maintenance. But because the load is distributed through trunnions and seats are spring-loaded, wear can be reduced, leading to longer service life in heavy-duty applications.
The choice between floating and trunnion ball valves often comes down to matching the valve to the service conditions.
Floating Ball Valves are well-suited for:
Low to medium pressure systems
Smaller line sizes
General-purpose shut-off in water, air, and non-corrosive fluids
Applications where simplicity and cost-effectiveness are priorities
Trunnion Ball Valves are better for:
Large-diameter pipelines
High-pressure applications
Oil and gas transmission
Petrochemical plants
Power generation and offshore platforms
Systems requiring low operating torque for automation
Generally, floating ball valves are less expensive in smaller sizes because they require fewer parts and simpler machining. Trunnion ball valves are more costly, particularly in smaller sizes, because of the additional components and precision manufacturing required. However, for large sizes and high pressures, trunnion ball valves often provide better long-term value due to reduced operating costs, lower maintenance needs, and longer service life.
Trunnion ball valves often include additional safety features such as double block-and-bleed capability. This allows isolation and venting between the two seats, which is valuable in hazardous applications for ensuring no fluid remains in the valve cavity.
Floating ball valves can be designed with similar features, but this is less common in standard designs.
In industries like oil and gas, petrochemicals, LNG, and high-pressure water transmission, trunnion ball valves are the clear choice due to their performance advantages under extreme conditions.
In general industrial plants, HVAC systems, municipal water treatment, and light chemical service, floating ball valves remain a popular option thanks to their simplicity, low cost, and proven reliability in less demanding environments.
While both valve types share the core concept of a rotating ball with a through-hole for fluid control, their differences in ball support, sealing mechanism, torque requirements, and capacity for pressure and size lead to distinct strengths and weaknesses.
Floating ball valves are simple, cost-effective, and ideal for small to medium sizes and pressures.
Trunnion ball valves are engineered for strength, low torque, and durability in large, high-pressure applications.
Choosing between them requires careful evaluation of service conditions, budget, maintenance capability, and safety requirements.
Selecting the right ball valve design is not just a matter of cost or availability—it directly affects system reliability, safety, and long-term operating costs. Floating ball valves offer simplicity, affordability, and effective sealing for smaller-scale, moderate-pressure uses. Trunnion ball valves, with their fixed ball and spring-loaded seats, excel in heavy-duty service, offering lower torque, higher pressure capability, and robust performance over time.
By understanding the key differences and benefits of each type, decision-makers can match the valve design to the specific needs of their system, ensuring efficiency, safety, and longevity. As industries continue to demand more from their equipment, the right choice between trunnion and floating ball valves will remain a vital factor in the success of fluid control systems.
