Key Takeaways

• A floating ball valve suspends the ball between two seats and relies on line pressure to energise the downstream seat, making it well suited to small and mid-sized, low to medium pressure isolation work.
• A trunnion ball valve supports the ball top and bottom on fixed pins, so the seats carry the load instead of the ball. This is the go-to design for large bore, high pressure, and critical shutoff service.
• The call between a trunnion ball valve and a floating ball valve usually comes down to size, pressure class, torque, cycle frequency, and whether double block and bleed is required.
• Fox Global stocks both floating and trunnion ball valves across a full range of materials, sizes, and pressure classes, with Australia-wide delivery and technical support to help you specify the right valve for the job.

Ball valves sit at the heart of countless pipelines, whether it is a small fuel depot in regional Queensland or a large gas processing plant on the North West Shelf. They are simple, reliable, and quick to operate, which is why they remain the default isolation choice across oil and gas, water treatment, mining, food and beverage, and general industrial service.

But ball valves are not all built the same way. The two most common types, the floating ball valve and the trunnion ball valve, each handle line pressure very differently, and picking the wrong one for your service conditions can mean leaks, excessive torque, or premature failure.

This guide breaks down how each design works, where each one shines, and how to match the right ball valve to your application.

Whether you are specifying a quarter-turn valve for a small chemical dosing line or a large bore shutoff for a high pressure gas trunkline, understanding the mechanical differences between a trunnion ball valve and a floating ball valve will save you time, money, and a lot of potential headaches down the track.

How a Floating Ball Valve Works

A floating ball valve is the simpler of the two designs. The ball is located between two seats, typically soft seats made from PTFE or reinforced PTFE, with the stem or shaft passing through the top of the ball to connect to a handle, lever, or actuator.

The ball has no other fixed support. It literally floats between the two seats, and a through hole drilled across its centre creates the flow path when the valve is open.

When the ball rotates into the closed position, line pressure pushes the ball against the downstream seat, squeezing it into the seating surface and creating a bubble-tight seal. This pressure-assisted sealing is what gives a floating ball valve its strong shutoff performance across low to medium pressure service. The higher the differential pressure, the harder the ball presses into the seat, and the tighter the seal becomes.

The trade-off is that all the load from the line pressure transfers directly through the ball into the downstream seat.

In small valve sizes and moderate pressure classes this is not an issue. But as valve size and pressure climb, the load on the seat climbs with it. That translates to higher operating torque, faster seat wear, and a practical upper limit on where a floating ball valve makes sense.

Typical applications for floating ball valves include general water, air, and steam isolation up to Class 150 or Class 300, fuel and lubricant fluid lines, instrument air systems, small bore chemical and utility services, and quarter-turn stem operation on pumps, tanks, and process skids. They are a workhorse design that covers most everyday isolation work across the Australian industry, from commercial piping to marine settings.

How a Trunnion Ball Valve Works

A trunnion ball valve, also known as a trunnion mounted ball valve, adds two fixed pins, the upper and lower trunnions, that hold the ball in place top and bottom.

These pins are the key components that set this design apart. With the ball supported on the trunnions, line pressure no longer pushes the ball into the downstream seat. Instead, the seats are spring-loaded and energised against the ball from both sides, which creates a reliable shutoff regardless of line pressure.

This changes the way the valve behaves under pressure. Because the ball does not shift, the load on the seats stays consistent regardless of line pressure.

Operating torque is far lower than an equivalent floating ball valve, with noticeably less torque on the stem and attached drive train, which means smaller actuators, smaller gearboxes, and easier manual operation. It also means the seats wear more evenly and last longer in high cycle service.

Most trunnion ball valve designs include double block and bleed capability, where each seat seals independently and the body cavity between them can be vented or drained. That is a significant safety and maintenance advantage in hazardous and critical service, particularly across the oil and gas industry, where positive isolation, leakage containment, and cavity monitoring are often mandatory for operator safety.

Trunnion mounted ball valves are the right call for large bore service, typically 6 inch and above, high pressure applications across classes (Class 600, 900, 1500, and 2500), cryogenic and high temperature duties, pipeline isolation on oil, gas, and LNG trunklines, and any application that demands the benefits of low torque, reliable cycling, and double block and bleed performance.

Key Differences Between Trunnion and Floating Ball Valves

Unlike many valve comparisons, the easiest way to compare these two is to look at how each design handles the three things that matter most in ball valve selection: sealing, torque, and size-to-pressure range.

• Sealing: A floating ball valve relies on line pressure to energise the downstream seat, so it performs best when there is enough differential pressure to push the ball firmly into the seating surface. A trunnion valve uses spring-loaded seats that stay in constant contact with the ball, delivering consistent, bubble-tight sealing from low pressure right through to very high pressure applications.
• Torque: A floating ball valve has to overcome the friction of the ball pressing into the downstream seat every time it is cycled. That torque rises sharply with valve size and pressure. A trunnion ball valve keeps the ball fixed on its pins, so the only friction the stem has to fight as the ball rotates is at the seat-to-ball interface, allowing fluid to flow freely through the port, and that value stays essentially constant. For the same size and pressure class, a trunnion ball valve typically needs about half the operating torque of an equivalent floating design, making it suitable for valve stem automation on larger actuators.
• Size and pressure: Floating ball valves are economical and reliable up to mid-range sizes, generally up to around 6 to 8 inch, and moderate pressure classes from Class 150 to Class 300. Beyond those thresholds the torque, wear and tear, and seat loading climb to the point where a trunnion design becomes the only practical choice. Trunnion ball valves scale comfortably into the largest pipeline and process applications without the same penalties.
• Cost: A floating ball valve is almost always cheaper up front because the design is simpler and uses fewer parts. For small bore utility and isolation work that cost difference is hard to beat. For large bore or high pressure duty, however, the reduced torque, longer service life, and double block and bleed capability of a trunnion mounted ball valve deliver better total cost of ownership over the life of the valve.
• Maintenance: Trunnion designs with bolted body construction are generally easier to service in place, with seats, stem assemblies, stem packing, and seals replaceable without removing the valve from the pipeline. Floating ball valves, particularly one-piece and two-piece welded body types, are typically treated as replace-in-kind once the seats eventually wear out.

Which Ball Valve Should You Specify?

Choosing between a trunnion and floating ball valve starts with answering a handful of simple questions about the service conditions.

• What is the pipe size? As a rule of thumb, a floating ball valve covers sizes up to around 6 to 8 inch comfortably in both full port and reduced port configurations. Anything larger is almost always better served by a trunnion mounted ball valve.
• What is the pressure class? Class 150 and Class 300 services sit squarely in floating ball valve territory. Class 600 and above, especially for gas and hydrocarbon service, is where a trunnion ball valve earns its place.
• How often will the valve cycle? For high cycle service where the valve is opened and closed frequently, a trunnion ball valve offers longer seat life and lower wear thanks to its spring-loaded seat contact.
• Do you need double block and bleed? If positive isolation of hazardous media or cavity venting is required, specify a trunnion ball valve with DBB. A floating ball valve is not designed for this duty.
• What fluid are you handling? Abrasive, slurry, or dirty media tend to be harder on soft seats regardless of valve design. For these services, specify metal-seated ball valves, whether floating or trunnion, with attention paid to seat materials and clearances.What about fugitive emissions? For volatile hydrocarbon, chemical, and gas service, look for ball valves that prevent stem and seat leakage by meeting international fugitive emission standards such as ISO 15848 and API 641.

If you are unsure which type is the better specification for your application, our experienced team can walk you through it based on the operating conditions of your system.

Materials, Trims, and Standards

Both floating and trunnion ball valves are manufactured from a range of body materials to suit different service conditions.

Common options include bronze, brass, and ductile iron for lighter utility and marine service, carbon steel (typically A105 or WCB) for general-purpose oil, gas, and industrial service, stainless steel (304, 316, and duplex grades) for corrosion resistance in corrosive, marine, and hygienic applications, and exotic alloys such as Inconel, Monel, and Hastelloy for highly aggressive chemical duty.

Seat material matters as much as the body material. Soft seats made from PTFE, reinforced PTFE, PEEK, or Devlon handle most general service and provide bubble-tight shutoff at moderate temperatures. Metal seats, sometimes with stellited or tungsten carbide facings, are specified for abrasive media, high temperature service, and fire-safe applications.

Look for ball valves that conform to recognised design standards such as API 6D for pipeline service, API 608 for steel valves, BS EN ISO 17292 for general industrial use, and API 607 or API 6FA for fire-safe qualification.

Ratings to ASME B16.34 cover the pressure-temperature curves for the valve body and housing, while end connection standards (ASME B16.5 for flanges, ASME B16.11 for socket weld and threaded ends, and ASME B16.25 for butt weld ends) keep the valve connected and compatible with your piping system.

Source Your Ball Valves from Fox Global

Fox Global is an established Australian importer, manufacturer, and distributor of industrial valves, fittings, and flow control products. Our ball valve range covers both floating and trunnion designs in a wide choice of materials, sizes, and pressure classes, backed by the technical experience to help you specify the right valve the first time.

Whether you need a compact floating ball valve for pump isolation on a small process skid, or a large bore trunnion mounted ball valve with double block and bleed for a high pressure gas trunkline, we’ve got the range and the local knowledge to get you sorted.

With Australia-wide delivery, competitive pricing, and a team that understands the real-world conditions these valves have to perform in, we make it simple to source the right ball valve without delays or unnecessary runaround.

Contact the Fox Global team on 1300 852 795 to request a quote, or get technical advice on the right specification for your application or view the full ball valve range today.

Ball Valves FAQs

Can a floating ball valve be used for natural gas service?

Yes, a floating ball valve is commonly used for natural gas service at lower pressure classes, typically up to Class 300, in smaller bore sizes. The key considerations are the working pressure, the size of the valve, and whether fugitive emission standards apply.

For high pressure natural gas trunklines, LNG, and hydrocarbon service above Class 300, trunnion ball valves are almost always specified because of their lower torque, longer seat life, and compatibility with double block and bleed requirements.

For lower pressure instrument gas, fuel gas trains on small equipment, and utility gas services, a fire-safe rated floating ball valve with a graphite stem seal and stem packing is often the most practical and economical choice.

What is a fire-safe ball valve and do I need one?

A fire-safe ball valve is a design that maintains a defined level of tightness and a proper seal after its soft seats and seals have been partially destroyed by fire. The valve incorporates secondary metal-to-metal seating surfaces and graphite body and stem seals that provide shutoff once the primary PTFE seats melt away.

Fire-safe ball valves are qualified to standards such as API 607 for quarter-turn valves and API 6FA for pipeline valves.

If your service involves flammable hydrocarbons, fuels, or other combustible media, or if local code requires fire-safe isolation for operator safety, specify a fire-safe rated valve regardless of whether the design is floating or trunnion.

What is the difference between a one-piece, two-piece, and three-piece floating ball valve body?

These terms refer to how the valve body is constructed. A one-piece body is machined from a single forging or casting and is the most compact and cost-effective option, but cannot be disassembled for in-line service.

A two-piece body splits into a main body and an end cap, which provides easier access to internal components than a one-piece design.

A three-piece body has two end caps that can be removed while the centre section stays bolted into the pipeline, which makes it the easiest design to service, repair, or clean in place.

Three-piece floating ball valves are particularly popular in food, beverage, and pharmaceutical systems where frequent cleaning or swab testing is standard practice.

Are trunnion ball valves always side-entry?

No, trunnion ball valves are manufactured in both side-entry (also called split-body) and top-entry configurations.

Side-entry is the most common type. The body splits vertically and bolts together around the ball assembly, which keeps manufacturing costs down and makes the valve easier to assemble and replace as a unit.

Top-entry trunnion ball valves have a one-piece body with a removable bonnet, allowing seats, seals, and the ball itself to be inspected or replaced without breaking the pipeline. Top-entry designs are common on welded pipelines and in applications where removing the valve body for maintenance is impractical.

How often should ball valves be cycled during normal service?

Even when a ball valve is left in a fixed position for long periods, it should be cycled periodically to stop the ball and seats sticking, allow fluid to flow through the port, and flush any build-up out of the seat area.

For critical and infrequently operated isolation valves, a partial-turn or full-turn exercise every 6 to 12 months is good practice, particularly in services carrying sediment, scale, or polymerising fluids.

For automated valves on process trains, the control system usually handles cycling as part of normal operation.

If a valve has been out of service for an extended period, it is worth inspecting the stem, stem seal, and stem packing, and confirming smooth travel before putting it back into duty.