Trunnion vs Floating Ball Valve — Size, Class & Torque
Floating and trunnion ball valves both provide quarter-turn isolation, but how the ball is supported changes seat load, torque, and suitability for large bore or high pressure. Specifying the wrong type drives oversized actuators and seal wear.
Quick selection
Floating for smaller sizes and lower classes where line pressure pushes the ball into the downstream seat. Trunnion for larger bore and higher class (often ≥6" or Class 600+) where the ball is shaft-supported and seats are spring-loaded — lower torque, better for pipeline and DBB duty.
Comparison table
| Factor | Floating ball | Trunnion-mounted |
|---|---|---|
| Ball support | Free-floating between seats | Fixed on top and bottom trunnions |
| Seat sealing | Upstream pressure loads ball into downstream seat | Spring / pressure-energised seats to ball |
| Typical size band | 1/2"–6" (project-dependent) | 4"–48"+ common on pipelines |
| Pressure classes | 150–600 common; higher possible in small bore | 150–2500 / API 6D pipeline classes |
| Operating torque | Rises with size and differential pressure | Lower relative torque at large size/high DP |
| DBB / DIB | Limited; special designs exist | Common with cavity relief / DIB options |
| Actuation | Manual / compact actuator often enough | Gear or actuator sized for breakaway |
When floating is enough
- Utility and process lines in smaller sizes and Class 150/300.
- Soft-seated (PTFE/RPTFE) on/off duty with moderate differential.
- Cost-sensitive packages where pipeline features are not required.
When trunnion is preferred
- Pipeline and large-bore isolation (API 6D style service).
- High differential pressure where floating seat load would spike torque.
- Double block and bleed or double isolation and bleed requirements.
- Fire-safe metal-seat or high-integrity applications with gear operators.
RFQ checklist
- Floating or trunnion — state explicitly on each BOQ line.
- Full bore vs reduced bore, soft vs metal seat, fire-safe if required.
- Ends (RF/RTJ/BW), class, MOC, gear/actuator, limit switches.
- DBB/DIB, anti-static, stem extension, and cavity relief notes.
FAQ
At what size should I switch to trunnion?
Many plants move to trunnion around 6"–8" or earlier at Class 600+. Confirm with torque curves and the piping class — there is no single universal cutover.
Is trunnion always API 6D?
Trunnion construction is common under API 6D for pipelines, but process plants also buy trunnion ball valves to ASME B16.34. State the design standard on the RFQ.
Does trunnion cost more?
Usually yes at the same size, because of bearings, seat springs, and body complexity. The trade-off is lower torque and longer seat life under high DP.
Can floating valves be fire-safe?
Yes. Fire-safe floating designs exist; confirm API 607 / API 6FA test basis and seat type on the inquiry.
Related RFQs and hubs
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