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Floating vs Trunnion Ball Valve Selector

Ball Valve Selection - EEMUA 182 / API 6D
Floating vs Trunnion Ball Valve Selector

Answer a few quick questions about your duty and this tool tells you whether a floating or trunnion-mounted ball valve fits, and explains why, using size, pressure class, automation and torque.

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When should you use a trunnion ball valve instead of a floating one?

The choice between a floating and a trunnion-mounted ball valve comes down to how the ball is supported and how much the seats are loaded. Floating designs suit small-to-medium sizes at lower pressure classes, while trunnion designs take over as size and pressure rise, commonly from Class 600 upwards and in larger bores.

Floating ball valve - the ball is held only by the two seats. Line pressure pushes the ball onto the downstream seat to seal. Simple, economical, inherently bidirectional, but operating torque climbs with pressure and roughly the square of the ball diameter.
Trunnion-mounted ball valve - the ball is fixed on upper and lower trunnions (bearings) and the spring-loaded seats are pushed against it. The trunnions absorb the pressure load so torque stays low and stable. The right answer at high pressure, large bore, and for automation.

Why floating torque rises so fast

In a floating valve the entire differential pressure acts across the ball and presses it into the downstream seat. The resulting friction scales with pressure and the square of the seal diameter, which is why large or high-pressure floating valves become impractical.

The automation angle

Because trunnion valves keep torque low and predictable, they need smaller, cheaper actuators and tolerate frequent cycling better. They are also the usual platform for double block and bleed (DBB) and double isolation and bleed (DIB) seat arrangements.

Frequently asked questions

What is the difference between a floating and trunnion-mounted ball valve?
In a floating ball valve the ball is held only by the two seats and line pressure pushes it against the downstream seat to seal. In a trunnion-mounted valve the ball is fixed on bearings and the spring-loaded seats press against it, so the trunnions take the pressure load, giving lower, more stable torque at high pressure and large sizes.
When should I use a trunnion ball valve instead of a floating one?
As size and pressure rise. Consider trunnion from around Class 600 and in larger bores (roughly above NPS 4 to 6). Always check EEMUA 182, the manufacturer torque data and the project specification.
Why does a floating ball valve need more torque?
Line pressure forces the whole ball against the downstream seat, so torque rises with pressure and roughly the square of the seal diameter. A trunnion ball is carried by its bearings so torque stays lower and more predictable.
Are both designs bidirectional?
A floating ball valve is inherently bidirectional. Trunnion valves are also commonly bidirectional and form the platform for DBB and DIB isolation.
Is a trunnion ball valve better than a floating one?
Neither is universally better. Trunnion handles high pressure and large bores at lower torque and suits automation, but costs more. Floating is simpler, cheaper and fine for small-to-medium, lower-pressure service.