Trunnion Ball Valve vs Floating Ball Valve: Key Differences
Pipe designers, maintenance leads, and control engineers all ask the same question when selecting quarter-turn isolation: should the ball be allowed to float or should it be anchored by a trunnion support system? That design choice shapes everything from torque and actuator size to how trunnion ball valves seal under changing pressure, how they behave during a fire test, and how expensive they will be to keep running.
A clear comparison cuts through brand naming and marketing claims. It starts with how the ball is supported and moves into sealing behavior, class and size ranges, actuation, and field realities like cavity relief and maintenance windows.
Industrial valve systems in operation
What actually moves inside floating ball valve vs trunnion ball valve
A floating ball valve supports the ball by the seats and the stem. Line pressure pushes the ball downstream to energize the downstream seat. That small axial movement creates the seal.
A trunnion ball valve pins the ball in place using a stem on top and a trunnion shaft underneath. The seats move instead, typically with springs behind each seat that push them toward the ball. Line pressure helps those springs and can energize one or both seats depending on the design.
Two different kinematics, two different torque profiles and sealing modes.
-
Floating ball
- The ball shifts slightly downstream under differential pressure.
- Seat load is driven by line pressure plus any seat preload.
- Simpler body designs are common: two-piece or three-piece.
-
Trunnion ball valve type
- The ball is held by bearings and a lower trunnion; it does not shift axially.
- Seats move, often with spring packs providing initial load.
- Larger bodies, side-entry split body or top-entry styles, often with welded or bolted construction.
One more practical note: because the floating ball must move to seal, dimensioning the seat clearances and finish becomes critical. For trunnions, the bearing alignment and seat springing dominate performance.
Ball valve internal mechanism detail
How sealing changes with pressure direction
The most important behavior difference appears when pressure reverses. It affects isolation performance, safety, and testing outcomes.
Floating ball sealing
- Under forward flow, the ball pushes downstream and seals on the downstream seat.
- If pressure reverses, the ball moves the other way and seals on the new downstream side.
- The upstream seat can unseat under high differential pressure and may not carry a reliable seal unless designed for bi-directional performance.
- Good low-pressure shutoff as the preload and ball movement generate contact stress even at low differential pressure.
Trunnion sealing
- The ball stays centered, supported by a robust sealing mechanism. Each seat can be designed as single piston effect or double piston effect.
- Single piston effect: line pressure pushes the seat toward the ball from the pressurized side. The seat can also self-relieve the cavity if pressure builds there.
- Double piston effect: pressure on either side forces the seat into tighter contact. This improves isolation but traps cavity pressure, so a relief path is needed.
- Consistent sealing under pressure reversal without relying on ball movement.
For many pipelines and compressor stations, that difference decides the spec. Some operators want true bi-directional isolation without relying on ball travel. Others value simplicity and the self-energizing effect of a floating ball.
Torque, actuation, and size envelope
Torque drives actuator size. Actuator size drives footprint and cost. The linkage from internal geometry to capex is straightforward.
- Floating ball torque rises rapidly with differential pressure because the ball must be forced off both seats before it rotates, then it drags across the downstream seat as it reseats. The moment arm and seat friction become significant once diameters grow.
- Trunnion ball torque stays lower and more predictable because the ball is supported and the seat loads are spring and pressure assisted. The ball turns in bearings; friction is mainly at the seat interfaces.
This is why floating ball valves are popular in smaller sizes and moderate pressures where a manual gear or compact actuator will suffice. Trunnions dominate at larger diameters or higher classes where torque penalties would otherwise explode.
A practical rule: for 6 inches and above at Class 600 and up, trunnion torque savings over floating designs often offset the higher body cost through a much smaller actuator.
Pressure class and size sweet spots
Both designs cover a wide span, yet each has a home turf.
Floating ball sweet spots
- 0.5 to 6 inches is common, with many offerings up to 8 or 10 inches.
- Class 150 to 300 for general service, sometimes Class 600 with careful material and seat selection.
- Process utilities, clean fluids, gas distribution skids, HVAC, water, steam at moderate pressure with the right seats.
Trunnion sweet spots
- 4 inches and up to very large diameters in pipeline service.
- Class 600 to 2500 and API 2000 to 15000 psi designs for upstream and transmission service.
- High differential pressure, sour service, ILTA pipeline valves, piggable full-bore designs, LNG, and CNG.
Pipeline valve installation in industrial setting
Side by side comparison
| Feature | Floating Ball | Trunnion Ball |
|---|---|---|
| Ball support | Held by seats and stem, ball moves slightly | Anchored by stem and lower trunnion, seats move |
| Typical size range | 0.5 to 6 inches, sometimes 8 to 10 | 4 inches to 60 inches and beyond |
| Pressure classes | ASME 150 to 300 common | ASME 600 to 2500, API high-pressure |
| Torque trend | Rises steeply with differential pressure and size | Lower and more stable across pressure range |
| Seat energizing | Line pressure pushes ball into downstream seat | Springs plus line pressure load one or both seats |
| Bi-directional shutoff | Depends on design; often seals on downstream side only | Readily engineered for dual sealing; DBB or DIB options |
| Cavity relief | Inherent relief via ball movement on many designs | Requires self-relieving seats or external relief if DIB |
| Actuation | Smaller actuators on small sizes; manual common | Pneumatic or hydraulic actuators favored on large sizes |
| Body styles | Two-piece, three-piece, often threaded or socket-weld ends | Side-entry split body, top-entry, welded body for pipelines |
| Cost profile | Lower initial valve cost, actuation cost rises with size | Higher valve cost, actuation and life-cycle savings at scale |
| Maintenance access | Remove from line for two or three-piece designs | Top-entry styles allow in-line service on many models |
| Applications | Utilities, plant air, water, chemicals, low to medium pressure | Pipelines, oil and gas, LNG, high pressure, piggable lines |
Seats, materials, temperature window, and fire testing
Both types can be built to meet the same materials and testing standards. The differences in valve type show up in seat options and how they behave across temperature and media.
Seat materials
- Soft seats: PTFE, reinforced PTFE (RPTFE), PEEK, UHMWPE. Great leakage performance, limited by temperature and chemical compatibility.
- Metal seats: Stellite or other hardfacing on the ball and seat. Handles abrasive or high temperature service with higher allowable leakage classes.
- Hybrid: soft primary with metal backup for fire-safe compliance.
Temperature ranges
- PTFE variants commonly up to 400 to 450 F, PEEK higher, UHMWPE lower.
- Metal seated designs can exceed 1000 F depending on body and trim materials.
- Cryogenic service needs extended stems and carefully engineered seat shrink clearances. Trunnion designs are often chosen for cryo duty in LNG because of stable sealing with low torque.
Fire-safe and emissions
- Fire-safe certification per API 607 or API 6FA is achievable for both designs. Expect a metal-to-metal backup path in case soft seats char.
- Low fugitive emissions rely on stem packing technology. API 641 or ISO 15848 ratings are common requirements. Trunnion stems often include bearings, anti-static devices, and blowout-proof features.
Seat scrubbing behavior differs as well. Floating balls rely on the ball wiping across the downstream seat during closing, which can clear minor contaminants but can also wear soft seats faster under abrasive service. Trunnions can be tuned with seat springs and differential piston effects to reduce seat scrubbing.
DBB and DIB: isolation philosophies that matter
DBB means double block and bleed. DIB means double isolation and bleed. They sound similar, yet the safety and cavity pressure story is different.
DBB
One valve provides shutoff against pressure from both sides with a bleed in the body cavity. Seats are usually single piston effect. If cavity pressure rises above line pressure on either side, the seat self-relieves into that line. This protects the cavity from overpressure without an external relief device.
DIB
Both seats seal from both directions using double piston effect. This tightens isolation, but it traps pressure in the cavity. Thermal gain or leakage can spike cavity pressure. A dedicated cavity relief valve or self-relieving insert is then essential.
Many trunnion valves can be configured either way by changing seat ring geometry. Floating ball valves will often act like DBB because the ball can move to relieve cavity pressure, though that depends on the specific seat design and spring preload.
Advanced valve control and monitoring system
Cavity pressure and thermal expansion
Trapped liquids expand rapidly with heat. A sealed cavity with no relief can generate dangerous pressure even at ambient swings.
- When DIB is required for tight isolation under testing, include a cavity relief path to a safe location or to one side of the line.
- For hydrocarbon gases or two-phase service, consider how flashing and condensables will behave across temperature cycles.
- High temperature service with soft seats requires clear thermal relief logic to avoid seat extrusion or body distortion-induced leaks.
Simple checklist:
- Is the valve DIB or DBB by seat design?
- Is the media compressible or not?
- Where does cavity pressure go during abnormal conditions?
- Does the spec require a monitored bleed?
Maintenance and lifecycle cost
Upfront cost tilts toward floating ball valves. Lifecycle can favor trunnion designs as sizes and pressures go up.
Floating ball
- Lower initial price, especially in threaded or socket-weld end connections.
- Seat wear rises with differential pressure and cyclic use.
- Removal from the line is common for overhaul unless a three-piece body with swing-out center is installed.
Trunnion ball
- Higher initial price and heavier weight.
- Lower torque means smaller actuators and lower actuation energy costs.
- Top-entry styles allow in-line seat and stem servicing, a significant advantage in busy units and pipelines.
Smart buyers look at actuator cost and maintenance windows over the expected duty cycle. On a 24-inch Class 600 line with frequent operations, the actuator size difference alone can justify a trunnion design.
Installation and piping loads
Real-world installations do not align perfectly. Loads from misaligned piping can warp bodies and bind balls.
Floating ball valves are more tolerant of minor misalignment because the ball can reposition slightly. Excessive piping load still risks seat damage or stem packing leaks.
Trunnion valves are sensitive to bending loads that misalign the trunnion bearings. Pipe support placement and hot-cold alignment planning prevent costly torque spikes.
Good practices:
- Set and verify pipe supports before makeup.
- Use spreader bars or lifting points provided by the manufacturer to prevent body distortion during hoisting.
- Recheck breakaway torque after installation, not just at the bench.
Typical applications and selection tips
When to go with floating ball:
- Plant utilities and chemical skids up to 6 inches.
- Low to medium pressure water, air, nitrogen, inert gases.
- Clean liquids where soft-seat shutoff is desired.
- Manual operation or small electric actuators.
When to go with trunnion ball valves:
- Transmission pipelines, gathering systems, meter stations.
- High differential pressure or frequent cycling under large load.
- Cryogenic natural gas or LNG process duty.
- Large-bore pumps and compressors with high surge pressures.
- Double block and bleed with certified valve isolation.
Extra selection notes:
- Full-bore trunnion designs allow pigging and reduce pressure drop.
- Reduced-bore floating designs cut cost and weight where Cv targets are modest.
- Sour service needs NACE-compliant materials and coatings for both valve types.
Common failure modes and what they look like
Floating ball
- Seat erosion from solids affects the sealing mechanism, leading to leakage at low differential pressure first, then under all conditions.
- High torque on closing points to extrusion or swelling of soft seats or to debris packed at the seat interface.
- Stem packing leaks after thermal cycling if packing relaxation is not managed with live-loading.
Trunnion ball
- Rising torque due to misaligned supports or thermal bow that loads trunnion bearings.
- Cavity overpressure signs when DIB seats lack proper relief, including blowdown through cavity relief if present.
- Leakage under reverse pressure if seat design depends on single piston effect and the wrong seat faces the pressure.
In both cases, a clean barrier fluid during commissioning and strainers upstream of small-bore valves extend life.
Standards, testing, and certification to look for
- Design and pressure-temperature rating: ASME B16.34
- Pipeline valves: API 6D with end-to-end testing provisions and DBB/DIB definitions
- Fire test: API 607 or API 6FA
- Fugitive emissions: API 641 or ISO 15848
- Antistatic and blowout-proof stems: common design features that should be specified in datasheets
- Inspection and NDE: MSS SP-55 for visual, API 598 or ISO 5208 for pressure testing acceptance criteria
Ask for torque curves across differential pressure, not just a single breakaway number. For actuated packages, request an AOV sizing sheet that includes worst-case service factors, temperature, and safety margins.
A short sizing reality check
Engineers sometimes try to compare costs using a single torque value. Better to use trends:
Floating ball:
Breakaway torque is usually highest and sensitive to differential pressure, media lubricity, and temperature. Running torque may drop compared to breakaway.
Trunnion ball:
Breakaway and running torques are closer to each other, with flatter response across pressure.
If you need a quick screen:
- For gas service at high differential pressure, assume the floating option will require a much larger actuator than the trunnion.
- For clean low-pressure water or air at small sizes, the floating option will usually win on both valve and actuator cost compared to trunnion ball valves.
Materials and trim choices that save headaches later
Seat choice
- • PTFE for clean, moderate temperature service.
- • RPTFE or PEEK where permeation and temperature push PTFE limits.
- • Metal seated where solids or high temperature make soft seats short-lived.
Ball and seat coatings
- • Hard chrome or tungsten carbide for abrasion resistance.
- • Corrosion resistant overlays for sour or chloride-laden media.
Body material
- • WCB or LCB for standard or low temperature carbon steel service.
- • CF8M or stainless or duplex stainless for chloride-rich or corrosive environments.
Stems and bearings
- • Bearings in trunnion valves should match the temperature and media. Dry gas often benefits from low-friction composite bearings.
Field checklist for a confident selection
- What differential pressure and cycle frequency will the valve see across its life?
- Does isolation need DBB or DIB, and how will cavity pressure be relieved?
- Is the line piggable, and do you need full bore?
- What are the torque implications across temperature and media, not just at ambient water?
- Which emissions standard is required, and is the packing certified?
- How will piping loads be managed and verified at installation?
- What maintenance access is realistic at that location, and do you want top-entry serviceability?
Quick Q&A
Can a floating ball valve be bi-directional?
A: Yes, many are. The seal depends on the ball moving toward the downstream seat. Verify test orientation and certification if true bi-directional isolation is required.
Do all trunnion valves trap cavity pressure?
A: No. Seat geometry determines that. Single piston effect seats allow self-relief. Double piston effect seats provide tighter isolation but trap pressure unless a relief path is provided.
Why do some trunnion valves use top-entry bodies?
A: To allow in-line maintenance of seats and stem seals, and to simplify inspection in critical service without cutting the valve out of the line.
When should metal seats be considered?
A: Abrasive media, high temperature, steam, coking, slurry service, or where soft seats have shown rapid wear in similar duty.
Are floating ball valves suitable for steam?
A: They can be with appropriate seats and body materials, but temperature limits of soft seats and thermal cycling must be respected. Metal seats or trunnions may be more robust at higher pressures and temperatures.
With a clear view of how the internals move and seal, the choice aligns with service needs rather than brand habits. The right selection trims torque, improves isolation behavior during pressure swings, and cuts downtime when the calendar says it is time to service the valve.
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