What Is a Trunnion Ball Valve?
Ball valves fall into two basic designs depending on how the ball is supported. In a floating ball design the ball sits freely between two seats, and line pressure pushes it against the downstream seat to seal. In a trunnion design the ball is supported by upper and lower shafts; the ball axis is fixed and the pressure load is carried by bearings rather than seals.
In control valves, trunnion mounting keeps the ball on the same axis in every position. This makes the contact between ball and seal predictable during throttling, helps the seal wear evenly and allows actuator motion to reach the ball without loss. Heavy-duty trunnions are designed to reduce maintenance time and cost in demanding applications that require long service life.
The trunnion-mounted ball control valves covered here come in two families: a segmented family with a non-clogging V-notch ball, and a full-bore family with noise and cavitation attenuator options. Both use splined shaft connections. The family is chosen according to solids or fiber content, line size and the need to reduce noise or cavitation.
How Does Trunnion Mounting Work?
With trunnion mounting, the ball is carried by shafts turning in bearings placed in the body. When the actuator rotates the ball, the ball axis does not move; the contact geometry between seal and ball is therefore kept throughout rotation and control behavior stays predictable.
1. Supporting the ball: The ball sits in bearings in the body through the drive shaft and the follower shaft (or trunnion) on the opposite side. The force of process pressure on the ball is taken by these bearings.
2. Loading the seal: The seal is pressed against the ball with a controlled spring or pressure force. The seal's task is sealing; it does not carry the ball.
3. Transferring motion: Splined shaft connections and double power-end bushings transfer actuator motion to the ball without play.
4. Control and shutoff: In intermediate positions the ball throttles flow; in the closed position the seal rests on the ball surface and provides shutoff to the selected class.
Trunnion vs floating ball
The floating design uses line pressure to create the seal; its simple construction and metal-seated severe service versions make it popular for on-off duty. In a trunnion design the pressure load goes into the bearings, so seal and ball contact surfaces are less stressed and the ball position stays more stable in control service.
Effect on control performance
A fixed ball axis makes the flow area repeatable during throttling. Trunnion guiding, together with splined ball-to-shaft and shaft-to-actuator connections, improves dynamic control performance. In the full-bore family the ball seal can be replaced without removing the actuator; in the segmented family the seal assembly is renewed at the valve inlet without taking the ball out of the body.
Key Features
· Wear-resistant support: The trunnion-mounted ball is designed for long service life and high wear resistance.
· Heavy-duty trunnions: Ball trunnions sized to reduce maintenance time and cost in demanding applications.
· Splined connections: Splined ball-to-shaft and shaft-to-actuator connections reduce lost motion.
· Two valve families: Trunnion-mounted segmented V-notch (1–24 in) and full-bore (6–24 in) families.
· Flexible seal options: Composition and metal seals; single, dual and double block-and-bleed arrangements in the full-bore family.
· Noise and cavitation trims: Attenuator and special trim options for gas and liquid service in both families.
· Easy maintenance: Seals can be replaced without removing the actuator or taking the ball out of the body.
Technical Specifications
Key configuration data of the trunnion-mounted ball control valve families:
Parameter | Technical data |
Ball support | Trunnion (shaft-supported), fixed ball axis |
Segmented family – size | 1–24 in (DN25–600) |
Segmented family – connection | CL150, CL300 flanged; CL600 flangeless (flanged in 2–8 in); EN 1092-1 options |
Segmented family – characteristic | Modified equal percentage |
Segmented family – shutoff | Composition seal Class VI; Class IV or III depending on metal seal option |
Full-bore family – size | 6, 8, 10, 12, 16, 20 and 24 in |
Full-bore family – connection | CL150, CL300, CL600 RF flanges (ASME B16.5); optional CL900 and RTJ |
Full-bore family – shutoff | Class IV standard, Class VI optional; double block-and-bleed option |
Full-bore family – max. shutoff pressure drop (38 °C) | CL150: 20 bar; CL300: 51 bar; CL600: 103 bar |
Rotation | Up to 90 degrees |
Shaft connection | Splined |
Sour service | Optional materials under NACE MR0175 (both families) |
Values vary with valve family, seal type and material; confirm per project.
Key Advantages
· Longer seal life: Because the bearings carry the pressure load, the seal only has to seal.
· Stable control: A fixed ball axis and splined connections increase throttling accuracy.
· Suitable for large bores: The bearing-supported design works reliably on large-diameter lines.
· Lower maintenance cost: Heavy-duty trunnions and easy seal replacement shorten downtime.
· Adaptable to the application: Attenuator, seal and trim options for gas, liquid and slurry services.
Applications
Trunnion-mounted ball control valves are used where control accuracy and mechanical strength are both required.
Large-bore gas and liquid lines
Attenuated full-bore designs at large control points with noise or cavitation risk.
Pump bypass and pipeline take-off
Bypass and take-off points where cavitation is limited with the liquid-attenuator full-bore design.
Slurry and difficult fluids
Non-clogging control of fibrous and solids-laden fluids with the segmented V-notch ball.
Trunnion Ball Valve Selection Criteria
For trunnion-mounted valves, selection is made through the family and seal arrangement.
Valve family
· Segmented V-notch family for services needing non-clogging control
· Full-bore family for low flow resistance and large bore
· Attenuated design for noise or cavitation
Seal and shutoff
· Required shutoff class
· One- or two-directional shutoff, double block-and-bleed
· Seal material suitable for process temperature
Mechanical requirements
· Pressure class and flange type
· Body material and sour service
· Actuator torque capacity and mounting side
Standards
Main standards applicable to trunnion-mounted ball control valves:
Standard / approval | Scope and description |
ASME B16.34 | Pressure-temperature classes. |
ASME B16.5 and EN 1092-1 | Flange connections. |
ANSI/FCI 70-2 / IEC 60534-4 | Shutoff leakage classes. |
NACE MR0175 | Material requirements for sour service. |
Applicable standards vary with the selected family
TLY Enerji Support Scope
Selecting a trunnion-mounted ball valve should be based on understanding the process conditions rather than browsing a catalog, and it is often a family decision: a non-clogging segmented ball, or an attenuated full-bore ball? TLY Enerji makes this decision based on fluid character, line size, pressure drop and shutoff requirement.
Our engineers evaluate seal arrangement, trim needs and actuator size together with control and safety requirements, and also point out on-off services where a floating ball design may be more appropriate. Alternatives are compared with their technical justification at quotation stage, and commissioning and site support are planned according to project scope. Which seal and trim parts can be shared between families is also reported as part of the maintenance strategy.
· Family and configuration selection
· Seal and trim evaluation
· Actuator sizing
· Technical comparison and quotation
· Site support coordination
Frequently Asked Questions
What is the difference between a trunnion ball valve and a floating ball valve?
In a floating ball valve the ball sits free between two seats and line pressure pushes it onto the downstream seat. In a trunnion ball valve the ball is supported by upper and lower shafts; bearings, not seals, carry the pressure load. Seal load is therefore more controlled in the trunnion design and the ball axis stays fixed.
Why is trunnion mounting preferred in control valves?
In control service the ball works continuously in intermediate positions. Trunnion mounting keeps the ball axis fixed so the flow area is repeatable, reduces seal wear and, together with splined connections, transfers actuator motion to the ball without loss.
Which sizes are available for trunnion-mounted ball control valves?
The trunnion-mounted segmented V-notch family is available in 1–24 in (DN25–600), and the full-bore family with attenuator options from 6 to 24 in (6 through 12, plus 16, 20 and 24). The right size is determined by sizing for the required flow capacity and rangeability.
How is maintenance carried out on trunnion ball valves?
In the segmented family the seal assembly can be replaced at the valve inlet without removing the actuator or taking the ball out of the body. In the full-bore family the ball seal can also be renewed without removing the actuator. Heavy-duty trunnions are designed for long service life and reduced maintenance time.
Do trunnion ball valves provide bidirectional shutoff?
In the full-bore family, bidirectional shutoff and double block-and-bleed are possible with the dual-seal design. In the segmented family the heavy-duty metal seal gives Class IV shutoff in bidirectional flow, while composition seals provide Class VI in the forward flow direction.
Can trunnion ball valves reduce noise and cavitation?
Yes. The full-bore family offers drilled attenuators integrated into the ball: aerodynamic noise is reduced in gas service, and cavitation and the resulting vibration in liquid service. The segmented family offers a rotary attenuator, anti-cavitation trim and noise trim. The right trim is chosen through analysis of pressure drop and fluid properties.
