June. 24, 2026
Reading volume: 6
Ball valves are widely used across oil and gas, petrochemical, power generation, water treatment, and industrial processing systems. Their simple operation, reliable sealing, and fast shutoff capability make them one of the most common valve types for pipeline isolation and flow control.
Among the various ball valve designs, two configurations dominate industrial applications: the floating ball valve and the trunnion mounted ball valve. Although both operate using a rotating ball with a bore through its center, their internal structures, pressure-handling capabilities, and sealing mechanisms differ significantly.
Understanding the differences between these two designs helps engineers select the right valve for operating conditions, pressure ratings, maintenance requirements, and project budgets.
A floating ball valve uses a ball that is not mechanically anchored at the top and bottom. The ball is held in place by the valve seats and stem connection.
When line pressure enters the valve, the pressure pushes the ball toward the downstream seat, creating a tight seal. This pressure-assisted sealing principle is one of the defining characteristics of a floating ball valve.
This design works well in low- to medium-pressure applications and smaller valve sizes.
A trunnion mounted ball valve features a ball that is mechanically supported by trunnions at both the top and bottom. Instead of moving under pressure, the ball remains fixed while the seats move toward the ball to achieve sealing.
This trunnion design significantly reduces operating torque and improves performance in high-pressure applications.
In a trunnion mounted design:
Because the ball remains stable, operating forces are much lower than those found in comparable floating ball valves.
| Feature | Floating Ball Valve | Trunnion Mounted Ball Valve |
|---|---|---|
| Ball Support | Supported by seats | Supported by trunnions |
| Ball Movement | Ball floats slightly | Ball remains fixed |
| Sealing Method | Pressure pushes ball against downstream seat | Seats move toward ball |
| Operating Torque | Higher | Lower |
| Valve Size Range | Small to medium | Medium to large |
| Pressure Capability | Moderate | High pressure |
| Cost | Lower | Higher |
| Maintenance | Simpler | More complex |
| API 6D Availability | Available | Commonly specified |
| Double Block and Bleed | Limited | Common |
The defining feature of a trunnion mounted ball valve is the trunnion design itself.
A trunnion is a mechanical anchoring shaft that supports the ball from above and below. This support prevents the ball from shifting under line pressure.
As valve size increases, the force acting on the ball also increases. Without trunnion support, operating torque can become excessive. By stabilizing the ball, the trunnion design allows manufacturers to produce large-diameter valves that remain practical to operate.
This design is commonly used in:
The downstream seat plays an important role in both valve types.
Pressure pushes the floating ball against the downstream seat. The downstream seat becomes the primary sealing surface.
The higher the pressure, the greater the sealing force applied to the seat.
The ball remains stationary. Instead, spring-loaded seats move toward the ball to create sealing contact.
The downstream seat still contributes to sealing performance, but the sealing mechanism differs significantly from the floating ball design.
The flow path inside both valve types is generally straight and unrestricted when fully open.
Benefits include:
Because the bore aligns with the pipeline, fluids can pass through with minimal resistance.
For this reason, ball valves are widely selected for applications requiring reliable isolation without significantly affecting system flow efficiency.
One of the largest distinctions between floating and trunnion ball valves is behavior under high pressure.
As pressure rises:
Under identical conditions:
For high pressure transmission systems, engineers frequently choose trunnion mounted ball valves because they offer more predictable performance.
Many pipeline operators specify compliance with API 6D, the industry standard for pipeline valves.
API 6D covers:
Trunnion mounted ball valves used in oil and gas transmission pipelines are commonly manufactured according to API 6D specifications.
While floating ball valves can also meet API 6D requirements, trunnion designs are more frequently selected for large pipeline projects.
One major advantage of many trunnion mounted ball valves is their ability to provide double block and bleed (DBB) functionality.
Double block and bleed means:
This arrangement allows operators to verify isolation before performing maintenance.
Double block and bleed capability is particularly valuable in oil and gas operations where system isolation must be confirmed before equipment servicing.
Floating ball valves are commonly used in:
They are often selected when:
Trunnion mounted ball valves are widely used in:
They are preferred when:
The choice depends on operating conditions.
Choose a floating ball valve when:
Choose a trunnion mounted ball valve when:
A floating ball valve uses a ball that moves slightly under pressure and seals against the downstream seat. A trunnion mounted ball valve uses a ball anchored by trunnions, while the seats move toward the ball to create the seal.
The trunnion design supports the ball and reduces the forces transmitted to the seats. This results in lower operating torque and improved performance under high pressure conditions.
The downstream seat is the seat located on the outlet side of the valve. In floating ball valves, it often serves as the primary sealing surface because pressure pushes the ball against it.
Quarter turn means the valve moves from fully open to fully closed with a 90-degree rotation of the stem and ball.
Double block and bleed is a valve configuration that provides sealing from both upstream and downstream seats while allowing the cavity between them to be vented or drained for isolation verification.
Many trunnion mounted ball valves are designed and tested according to API 6D standards, making them suitable for pipeline service in the oil and gas industry.
While ball valves can provide basic flow control, they are primarily designed for on/off service. For precise throttling applications, other valve types may be more suitable.
Service life depends on operating conditions, materials, maintenance practices, and media characteristics. In demanding high-pressure environments, trunnion mounted ball valves often experience lower seat loading and may provide longer operational life.
Both floating ball valves and trunnion mounted ball valves offer reliable shutoff performance and efficient flow paths. The floating ball design provides a cost-effective solution for smaller, moderate-pressure systems, while the trunnion design delivers enhanced stability, lower operating torque, and dependable sealing for large-diameter and high-pressure applications.
When selecting a ball valve design, engineers should evaluate line pressure, valve size, sealing requirements, operating frequency, and industry standards such as API 6D. Matching the valve design to the application helps achieve dependable performance over long periods of operation while minimizing maintenance requirements.
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