Floating vs Trunnion-Mounted Ball Valve: Which to Specify?

When sourcing ball valves for an industrial project, the floating vs trunnion ball valve choice drives pressure rating, actuator sizing, cost and long-term reliability — yet it is often glossed over on datasheets. As a sourcing engineer, I treat it as a first-pass filter: once the medium, line size and pressure class are fixed, the correct construction is usually obvious. This guide lays out the engineering and commercial trade-offs so your RFQ goes to the right design the first time.

How Ball Fixing Differs: Floating vs Trunnion Design

In a floating ball valve, the ball is not anchored at top or bottom; it is free to translate slightly along the line axis. The stem engages a slot in the top of the ball, and the ball floats between two seat rings. In a trunnion-mounted ball valve, the ball is pinned at the top stem and at a bottom trunnion that carries the line load; the ball does not shift under pressure, and both the upstream and downstream seats are engineered to seal against it.

That single mechanical difference cascades into everything else — sealing behavior, torque curve, maximum size and service strategy.

Sealing Principle: Pressure-Assisted vs Dual-Seat

A floating ball seals because line pressure pushes the ball against the downstream seat. This pressure-assisted action is self-energizing: the higher the pressure, the tighter the seal on the downstream side. The trade-off is that the ball and downstream seat carry the full pressure load, and the stem sees a reaction load that grows with line pressure.

A trunnion valve works differently. Because the trunnion anchors the ball, both seats are spring-loaded or pressure-activated and press against the ball faces. This gives genuine double-block-and-bleed capability in many designs, and seal integrity no longer depends on the ball deflecting under full line pressure. For low-pressure or vacuum service, where a floating ball would lose its pressure assist, trunnion sealing is far more predictable.

Size and Pressure Boundaries

Most catalog floating ball valves top out around DN 200 (8") and Class 150 / PN 16 to PN 40, sometimes Class 300 in forged bodies. Beyond that, seat load becomes excessive and actuator torque climbs rapidly. The PrimeFlow (sample) floating range sits in the small-to-medium band — the 3-piece SS316 ball valve PF-BV-3PC-316-DN50, for example, covers DN15–100 at PN16 / 1000 WOG / Class 150, which is representative for water, HVAC, light process and utility duties (parameters per the PrimeFlow data sheet).

Trunnion-mounted ball valves start where floating valves stop. They are routinely supplied from DN 50 (2") up to DN 900 (36") and beyond, and from Class 150 up to Class 900, 1500 and 2500. For large-diameter, high-pressure lines, trunnion is the only practical construction.

Torque, Actuation and Cost Implications

Because the floating ball transmits line pressure into the seat and stem, seating torque scales with pressure. For a DN 50 valve that is manageable; at DN 200 and Class 300, the actuator must overcome a large breakaway torque, and manual gearing quickly becomes the limiting factor.

Trunnion valves decouple line load from seat load, so operating torque is lower and more stable across the pressure range. This is the reason an automated DN 300 trunnion valve can be actuated with a comparatively compact pneumatic or electric actuator, where an equivalent floating valve would need a much larger one — if it could be sourced at all.

Cost-wise, trunnion valves are more expensive per unit: they carry machined seats, top and bottom trunnion bearings, and often a side-entry or top-entry body that eases in-line maintenance. Floating valves are commodity items in the DN 15–100 band, where economies of scale dominate. The right comparison is not unit price but total cost of ownership for the line size and pressure involved.

Typical Applications: When Trunnion Wins

For oil, gas and petrochemical service — pipeline isolation, main process lines, EPC packages — trunnion-mounted ball valves are the default, frequently specified to API 6D with double-block-and-bleed and metal-seated options for abrasive or high-temperature media. If your project references API 6D, offshore service, or sour service under NACE MR0175, expect trunnion almost by default above DN 50.

Floating ball valves are the better fit for utility water, HVAC, light chemicals, compressed air and instrumentation isolation — the dense, low-pressure distribution network behind the main process. They are inexpensive, well-stocked and straightforward to automate in the smaller sizes.

Comparison at a Glance

Selection Summary

• Use floating for small-to-medium bore, low-to-medium pressure, and utility or general service.
• Use trunnion for large bore, high pressure, oil and gas, and any line requiring DBB, metal seats or API 6D compliance.
• When the spec sits at the boundary (say DN 200, Class 150), let torque, actuation and the maintenance plan decide — not the sticker price.

For a broader walk-through of body styles and end connections, see our ball valve selection guide, and if you are weighing ball against other isolating valves, the ball valve vs gate valve comparison covers the next decision upstream. For full product specifications, open the PF-BV-3PC-316-DN50 product page, or browse API-spec and trunnion options inside the Oil, Gas & Petrochemical solution.

Frequently Asked Questions