Floating vs Trunnion Ball Valves: Structure, Application and Cost Compared

The first structural decision in any ball valve requisition is barely visible on the datasheet, yet it drives sealing performance, operating torque, actuator sizing and total cost more than almost any other line item: is the ball floating or trunnion-mounted?

Both designs shut off flow with a quarter-turn of a bored ball. Under the hood, they are two different machines. This guide compares the two constructions across the parameters that matter to project engineers, and closes with selection rules you can apply directly.

The Floating Ball Valve: Simple, Self-Energizing, Economical

In a floating design, the ball is not fixed to the body. It is held between two seats and free to "float" along the line of flow. When the valve closes, upstream pressure pushes the ball against the downstream seat, compressing it to form the seal.

This is elegant engineering, because the very pressure the valve is holding provides the sealing force:

• Fewer parts: no trunnion, no bearings, no seat springs — simpler bodies, easier maintenance

• Tight shutoff at low and medium pressure: the seal improves as line pressure rises

• Lower purchase costfor the same size and class

The limitations are just as physical. All the pressure load lands on one downstream seat, so:

• Sealing force — and turning torque — grow with line pressure

• The downstream seat and bearing areas wear faster on high-cycle duty

• Above roughly NPS 4"–6" (DN100–DN150) or Class 600, the seat loads and torque become impractical

Floating design dominates small-bore, low-to-medium pressure isolation: utilities, water treatment, chemical dosing, instrument isolation, process lines to Class 300 or 600 depending on size.

The Trunnion-Mounted Ball Valve: Engineered for High Load

In a trunnion design, the ball is pinned to the body by upper and lower trunnions running in bearings. The ball no longer moves with pressure. Sealing is achieved by spring-loaded seats that push against the ball from both sides, independent of line pressure.

The consequences cascade positively under high load:

• Both seats seal, both directions— and each seat is typically self-relieving against cavity overpressure

• Low, stable operating torque: pressure pushes the seats into the ball, not the ball into a seat, so torque does not climb with pressure — smaller actuators, less wear

• Double Block and Bleed (DBB): with both seats sealing independently, the cavity between them can be vented through a body bleed valve — the configuration pipeline and EPC specifications call for on isolation points

• Double Piston Effect (DPE) seatscan be specified so either seat alone holds full differential pressure

• Suitable for large bore and high class: NPS 6" and above, Class 600 and 900+, pipeline and EPC service

What you pay for: more parts, more machining, higher purchase price — and a body geometry that is nearly always flanged or welded, rarely threaded.

Side-by-Side Comparison

Selection Rules You Can Apply Today

1. Default to floatingfor NPS 2" and below at Class 300 and under — the economics are unbeatable and the physics is on your side.

2. Move to trunnionat NPS 4"–6" and above, at Class 600 and above, or wherever the specification demands DBB isolation.

3. Choose trunnion for actuated valvesin continuous duty: the flat torque curve lets you size a smaller, cheaper actuator — often repaying the valve price premium within the actuator budget.

4. Specify trunnion for high-cycle service: the symmetric seat loading extends seat life where floating designs wear one seat prematurely.

5. Fire-safe and pipeline service: API 608 / API 6D trunnion designs with fire-tested (API 607) seats are the standard answer for hydrocarbon lines.

The Cost Question, Honestly

On purchase price, floating wins, always. But procurement engineers should price three life-cycle lines instead:

• Actuation: a floating Class 600 valve may need an actuator two sizes larger than the trunnion equivalent — erasing the valve saving

• Seat replacement: one compressed downstream seat replaced twice as often is hidden cost

• Downtime risk: on isolation-critical EPC points, DBB capability is not a feature, it is the requirement

Where Both Designs Come From One Supplier

Wenzhou Linkv Valve Co., Ltd. manufactures both families from its own casting and machining facilities in Wenzhou: two-piece and three-piece floating stainless steel ball valves in CF8 and CF8M for process isolation, and trunnion-mounted ball valves for higher-pressure project service, with anti-static and fire-safe construction per API 607 testing where specified. Seat materials span PTFE, R-PTFE and metal for temperature-extended duties, and every valve ships with ISO 5208 pressure test reports. For help matching a construction to your specification, request a quotation or browse our trunnion ball valve range and flanged ball valves. To vet the factory behind both designs, see our guide to verifying a ball valve manufacturer.

FAQ

Q1: Why is it called a floating ball valve?

Because the ball is not fixed to the valve body — it "floats" between two seats and is pressed against the downstream seat by line pressure to seal.

Q2: Can a floating ball valve seal in both directions?

It seals in both directions for shutoff, but the effective sealing seat is the downstream one — upstream pressure defines which side is downstream. Trunnion designs seal symmetrically on both seats.

Q3: When must I use a trunnion ball valve?

At large bore (NPS 4"–6" and above), Class 600 and above, for double block and bleed isolation, or for actuated high-cycle service where torque stability matters.

Q4: What is Double Block and Bleed (DBB)?

With both trunnion seats sealing independently, the cavity between them can be vented via a body bleed valve — allowing verified zero-pressure isolation of a downstream work zone from both directions.

Q5: Do trunnion valves cost much more?

Purchase price is typically 1.5–3× the floating equivalent, but actuator sizing, seat life and DBB capability often repay the difference over the valve's life cycle.