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Valve Comparison Guide

Trunnion vs Floating Ball Valve — Which Design Do You Need?

Trunnion-mounted vs floating ball valve: size boundary, seat load, fire-safe design, DBB capability explained. API 6D selection guide for oil & gas, chemical and pipeline service.

Overview

Trunnion-Mounted Ball Valve

In a trunnion ball valve, the ball is supported at top and bottom by fixed trunnion bearings. The upstream pressure acts on the seats (which are spring-loaded against the ball), not on the ball itself. This design is standard for large bore (DN100+) and high-pressure pipeline isolation.

DN50–DN600, Class 150–2500, A216 WCB / A351 CF8M / A890 Duplex, API 6D

Floating Ball Valve

In a floating ball valve, the ball is not fixed — it 'floats' between the two seats, held only by the seats themselves. Upstream pressure pushes the ball against the downstream seat to achieve shut-off. This simple design is cost-effective for small bore and lower pressure applications.

DN15–DN150, Class 150–600, A216 WCB / SS 316 / A182 F51, ASME B16.34

Pros & Cons

Trunnion-Mounted Ball Valve

Low operating torque regardless of pressure — bearings take the load
DBB (Double Block and Bleed) inherent design
Suitable for large bore and high pressure (Class 150–2500)
Fire-safe design easily achieved — seats absorb pressure automatically
API 6D standard design for pipeline service
Better for automated/actuated applications — lower torque means smaller actuator
More complex and expensive than floating ball
Overkill for small bore (DN15–DN50) and low pressure applications
Larger physical size and weight vs. floating at same DN

Floating Ball Valve

Simple, cost-effective design — fewer components
Excellent for small bore (DN15–DN80) applications
Lightweight and compact
Widely available in stainless steel, alloy, and exotic materials
Adequate shut-off for most utility and instrument service
High seat load at high pressure — limits operating torque and cycle life
Not suitable for large bore or high pressure (above Class 600 / DN150+)
DBB not inherent — requires special design
Fire-safe design more complex (seats must seal under fire conditions)
Actuated valves need oversized actuator due to high torque

Trunnion-Mounted Ball Valve vs Floating Ball Valve — Specification Comparison

ParameterTrunnion-Mounted Ball ValveFloating Ball Valve
Ball SupportFixed trunnion bearings (top and bottom)Floats between seats
Seat LoadSpring-loaded seats push against ballLine pressure pushes ball against downstream seat
Operating TorqueLow — independent of line pressureIncreases with line pressure (high at DN100+)
Typical Size RangeDN50–DN600 (up to DN1200 special)DN15–DN150 (rarely above DN200)
Typical PressureClass 150–2500Class 150–600 (Class 900 special)
DBB CapabilityInherent — standard trunnion designSpecial design required
Fire SafeAPI 607 / API 6FA — easier to achieveAPI 607 — requires additional back-up seats
API 6DStandard for pipeline serviceOnly small bore pipeline valves
CostHigher — more componentsLower — simpler design
Actuated UseIdeal — small actuator due to low torqueRequires large actuator at high pressure

When to Use Each

Use Trunnion-Mounted Ball Valve when:

Oil & gas pipelines (API 6D) — DN100 and above
High-pressure applications (Class 600, 900, 1500, 2500)
DBB skids and metering station isolation
ESD (Emergency Shut-Down) actuated valves
Any automated ball valve where actuator torque is a constraint

Use Floating Ball Valve when:

Small bore instrument isolation (DN15–DN50)
Utility water and air systems (Class 150–300)
Chemical injection and metering connections
General purpose plant isolation below DN100
Cost-sensitive applications where actuated operation is not required

Decision Guide

Use a trunnion ball valve for DN100 and above, for any Class 600+ pressure application, for ESD or automated service requiring low actuator torque, or for API 6D pipeline isolation where DBB capability is required. Use a floating ball valve for DN15–DN80 general purpose isolation, instrument connections, utility services at Class 150–300, and any cost-sensitive application where automated operation at high pressure is not needed.

Frequently Asked Questions

At what size do I switch from floating to trunnion ball valve?
The industry rule of thumb is: use floating ball valves for DN50 (2") and below at Class 150–300, and trunnion-mounted ball valves for DN100 (4") and above, or for any size above Class 300. At DN80 (3") and Class 600+, trunnion is preferred. For API 6D pipeline service, trunnion design is standard from DN50 upward.
What is DBB in a ball valve?
DBB stands for Double Block and Bleed. A trunnion ball valve has inherent DBB capability: when closed, both the upstream seat (spring-loaded against ball) and the downstream seat (pressure-energised) independently block the line pressure. A bleed port in the body cavity allows trapped pressure to be vented safely. DBB is required for metering skids, chemical injection, and instrument isolation where safe maintenance isolation is critical.
Are trunnion ball valves always fire-safe?
Trunnion ball valves are designed for fire-safe compliance per API 607 or API 6FA. In the event of a fire that destroys the soft polymer seats, the spring-loaded seat rings make metal-to-metal contact with the ball, maintaining a secondary seal. This fire-safe design must be explicitly tested and certified — always request API 607 fire-test certification for hydrocarbon service.

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