Ball Valves: Floating vs Trunnion, Types & Selection Guide

Quick Answer

A ball valve is a quarter-turn isolation valve using a spherical closure element with a bore through it: rotate the ball 90° and the bore aligns with the pipe (open) or sits perpendicular to it (closed). Ball valves give fast operation, tight bubble-tight shutoff, and very low pressure drop when full bore, which is why they dominate isolation duty in oil and gas, chemical, and general process piping. The primary design distinction is floating vs trunnion mounted: in a floating ball valve the ball is held only by the two seats, and line pressure pushes it downstream against the outlet seat to create the seal — simple, economical, and standard up to roughly NPS 6 and Class 600. In a trunnion mounted valve the ball is fixed by upper and lower shafts (trunnions) and spring-loaded seats press against it, so line pressure does not transfer to the seat — this keeps operating torque low and makes trunnion the choice for large sizes and high pressures, and enables double block and bleed (DBB) functionality. Bore choice matters too: full bore (same ID as the pipe, allows pigging, minimal pressure drop) versus reduced bore (one size smaller, cheaper and lighter, slight pressure drop). Governing standards are API 6D (pipeline valves), API 608 (metal ball valves, flanged/threaded/welding end), ASME B16.34 (pressure-temperature), with API 607/API 6FA for fire-safe and ISO 15848 for fugitive emissions.

Ask any piping engineer which valve they specify most for on/off isolation and the answer will usually be the ball valve. It closes in a quarter turn instead of dozens of handwheel rotations. It seals bubble-tight where a gate valve merely seals well. When full bore, it presents essentially no restriction to flow. It is compact, light for its capacity, and easy to automate. For isolating a line quickly and completely, nothing else combines those qualities as economically.

But "ball valve" covers a wide range of designs that behave very differently, and the wrong choice shows up as high operating torque, seat damage, or a valve that cannot be safely maintained. A floating ball valve specified in a large high-pressure line becomes almost impossible to turn and destroys its seats. A soft-seated valve installed on hot service melts its seats. A valve without fire-safe certification fails open in a fire, feeding it. A reduced-bore valve on a line that must be pigged blocks the pig.

For piping engineers, pipeline operators, and procurement teams — this guide covers ball valves: the floating and trunnion designs, bore and body configurations, seat materials, the certification requirements that matter for hydrocarbon service, and how to select.

For comparisons with other valve families, see Gate Valve vs Ball Valve, Ball vs Butterfly Valve, and Industrial Valves Guide.

How a Ball Valve Works

A spherical ball with a cylindrical bore sits between two seats inside the body. The stem connects the ball to the operator (lever, gear, or actuator).

• Open: the bore is aligned with the pipe axis — flow passes straight through
• Closed: the ball is rotated 90° so the solid face blocks the flow and presses against the seats

The quarter-turn action means opening and closing is fast, and lever position gives immediate visual indication of valve state — a practical safety advantage.

Because the closure element is not in the flow path when open, a full-bore ball valve has almost no pressure drop.

Important: ball valves are isolation valves. They are not designed for throttling — a partially open ball concentrates flow across a small crescent, causing high velocity, seat erosion, and cavitation. For modulating duty use a control valve or a purpose-built V-port ball control valve (see Control Valves & Actuators).

Floating vs Trunnion Mounted

This is the central design decision.

Floating Ball Valve

The ball is not fixed. It is suspended between two seats, held by the stem only at the top, with a small amount of freedom to move.

How it seals: line pressure pushes the ball downstream against the outlet seat, and that force creates the seal. The higher the pressure, the harder the ball presses — self-energising sealing.

• Simple, fewer parts, lower cost
• Typically used up to around NPS 6 and Class 600
• Usually single-seated sealing (downstream seat does the work)
• Operating torque rises with pressure and size — because all the line thrust bears on the seat, torque climbs quickly in large or high-pressure applications
• Seats carry the full ball thrust, so seat wear is higher in demanding service

Use for: general isolation, utilities, smaller lines, moderate pressures, cost-sensitive applications.

Trunnion Mounted Ball Valve

The ball is anchored by an upper stem and a lower trunnion shaft, so it cannot move downstream. Instead, spring-loaded seats are pushed against the ball, assisted by line pressure acting behind the seat ring.

• Line pressure is carried by the trunnions, not transferred into the seats
• Operating torque stays low even at large sizes and high pressures
• Suits large diameters and high pressure classes (NPS 8+ and Class 600–2500 routinely)
• Usually double-seated — both upstream and downstream seats seal
• Enables double block and bleed (DBB): both seats seal and the body cavity can be vented/drained through a bleed valve to prove isolation
• More parts, higher cost

Use for: pipelines, large-bore isolation, high-pressure hydrocarbon service, ESD applications, anywhere DBB is required.

Comparison

Bore: Full vs Reduced

Full bore (full port): the ball bore equals the pipe internal diameter.

• Minimal pressure drop
• Allows pigging — essential for pipelines
• Larger, heavier, more expensive

Reduced bore (standard port): the bore is typically one nominal size smaller than the line.

• Slight pressure drop and a small velocity increase
• Lighter, more compact, lower cost
• Cannot be pigged

Rule: specify full bore for pipelines, pigging, slurries, and low-pressure-drop-critical lines; reduced bore is acceptable and economical for general isolation where a small pressure drop is tolerable. Bore and line size interact with pipe schedule — see Pipe Schedule Chart.

Body Configurations

One-piece — body machined from a single casting/forging. Cannot be dismantled; usually reduced bore, small sizes, economical, non-repairable.

Two-piece — body plus one end cap. Common, economical, can be dismantled but requires removal from the line.

Three-piece — central body with two end caps held by bolts. The centre section can be removed for maintenance without disturbing the pipework — favoured for hygienic, chemical, and frequently-serviced applications.

Side-entry (split body) — the standard construction for most trunnion valves; the body splits perpendicular to the flow axis.

Top-entry — the bonnet lifts off to allow in-line maintenance without removing the valve from the pipeline. Used in critical pipeline and subsea service where removal is impractical; higher cost.

Welded body — fully welded for buried pipeline service where leakage paths must be eliminated.

Seats and Seals

The seat material sets the temperature limit and often the service life.

Soft seats give the tightest shutoff but limit temperature. Metal seats handle heat, abrasives, and coke-forming service but require higher torque and generally achieve a lower leakage class.

Body seals, stem seals and packing are typically PTFE, graphite (for fire-safe and high temperature), or elastomer O-rings selected against the fluid.

Standards and Certifications

API 6D — Specification for Pipeline and Piping Valves. The dominant pipeline standard, covering ball, gate, check and plug valves; includes requirements for DBB/DIB configurations.

API 608 — Metal Ball Valves, flanged, threaded and welding end. Covers general refinery and process service.

ASME B16.34 — pressure-temperature ratings and body wall thickness.

API 607 / API 6FA — fire-safe testing. A fire-safe valve maintains a defined level of sealing after exposure to fire, once soft seats have burned away, using secondary metal seats and graphite seals. Mandatory for hydrocarbon service.

ISO 15848 — fugitive emissions testing (stem sealing performance), increasingly specified for environmental compliance.

Anti-static device — a spring or contact providing electrical continuity between ball, stem and body, preventing static build-up from ignition. Standard requirement for flammable service.

NACE MR0175 / ISO 15156 — sour service (H₂S) material requirements.

Other Configurations

Multi-port (3-way / 4-way) — L-port for diverting between two outlets; T-port for mixing or diverting with a common position. Used for tank switching and sampling.

Double block and bleed (DBB) vs double isolation and bleed (DIB) — DBB provides sealing from both sides of a single valve with a bleed between; DIB provides independent sealing from each seat. Specify per API 6D definitions — these terms are frequently confused in enquiries.

Cryogenic — extended bonnet to keep packing above the cold zone, for LNG and industrial gas service.

Jacketed — steam or hot-oil jacket for products that solidify (bitumen, sulphur, polymer).

V-port — a shaped notch in the ball giving a controllable characteristic for modulating duty.

Selection Process

1. Size and pressure class — from the line list
2. Floating or trunnion — floating for small/moderate, trunnion for large or high pressure or where DBB is needed
3. Bore — full bore if pigging or minimal pressure drop is required; otherwise reduced
4. Body style — three-piece for maintenance in place, top-entry for in-line pipeline maintenance, welded for buried
5. Seat material — from maximum temperature and fluid; soft for tight shutoff, metal for heat and abrasion
6. Body/trim materials — WCB, CF8M, LCC, duplex, or alloy per fluid and temperature
7. End connection — flanged (RF/RTJ), butt weld, socket weld, threaded
8. Certifications — fire-safe (API 607/6FA), anti-static, NACE, ISO 15848, as service requires
9. Operation — lever, gearbox (usually required above NPS 6 or higher classes), pneumatic/electric actuator, ESD requirements, locking device

Common Specification Mistakes

After 15+ years supplying valves to oil & gas, process, and industrial projects:

Mistake 1: Floating Ball Valve Too Large or Too High Pressure

Floating design specified for a large high-pressure line. Operating torque becomes excessive, the gearbox strains, and seats wear rapidly.

Prevention: Use trunnion mounted designs for large sizes and high pressures — typically above NPS 6 or Class 600.

Mistake 2: Using a Ball Valve for Throttling

Ball valve left partially open to regulate flow. High velocity across the partial opening erodes the seat and ball; the valve then fails to seal when closed.

Prevention: Ball valves are isolation devices. For modulation use a control valve or a purpose-designed V-port ball control valve.

Mistake 3: No Fire-Safe Certification on Hydrocarbon Service

Standard soft-seated valve used in a hydrocarbon line. In a fire the PTFE seats burn out and the valve leaks, feeding the fire.

Prevention: Specify API 607 or API 6FA fire-safe certified valves for all flammable service, with graphite secondary seals and anti-static devices.

Mistake 4: Reduced Bore on a Pigged Line

Reduced-bore valve installed in a pipeline that must be pigged. The pig jams.

Prevention: Specify full bore wherever pigging is required, and confirm the actual bore diameter rather than assuming from the nominal size.

Mistake 5: Soft Seat Above Its Temperature Limit

PTFE-seated valve specified for service above roughly 200°C. The seats deform and the valve leaks.

Prevention: Match seat material to maximum operating (and upset) temperature — RPTFE, PEEK, or metal seats as required.

Mistake 6: Confusing DBB and DIB

Enquiry asks for "double block and bleed" when the process actually requires double isolation. The valve supplied does not do what the process needs.

Prevention: Use API 6D definitions explicitly and state which sealing behaviour is required from each seat.

Mistake 7: Trapped Cavity Pressure

Valve closed with liquid trapped in the body cavity; thermal expansion over-pressures the body.

Prevention: Specify self-relieving seats or a cavity relief provision (vented ball or body relief) for liquid service, especially cryogenic and hydrocarbon duties.

Supply from Kasko Makine

Kasko Makine supplies ball valves for oil & gas, pipeline, petrochemical, power, and general industrial applications:

Valve types:

• Floating ball valves — one-piece, two-piece, three-piece
• Trunnion mounted ball valves — side-entry and top-entry
• Fully welded body ball valves for buried pipeline
• Multi-port (3-way L-port and T-port, 4-way)
• Cryogenic ball valves with extended bonnet
• Jacketed ball valves
• V-port control ball valves
• Double block and bleed configurations

Sizes and ratings: NPS ½" to 56", Class 150 through 2500

Bore: full bore and reduced bore

Materials:

• Body: A216 WCB, A351 CF8M/CF3M, LCC/LCB low temperature, duplex and super duplex, Inconel/Monel
• Ball and stem: 316, 316 with ENP or hard chrome, duplex, hardened for abrasive service
• Seats: PTFE, RPTFE, PEEK, Devlon, metal seated (Stellite / tungsten carbide)

End connections: flanged RF and RTJ, butt weld, socket weld, threaded, hub

Certifications: API 6D, API 608, ASME B16.34, fire-safe per API 607 / API 6FA, anti-static device, NACE MR0175 / ISO 15156, ISO 15848 fugitive emissions, PED, EN 10204 Type 3.1/3.2

Operation: lever, gear operator, pneumatic and electric actuators, ESD packages, locking devices, stem extensions for buried service

Engineering support:

• Floating vs trunnion selection for size and pressure
• Torque calculation and actuator sizing
• Seat material selection for temperature and fluid
• DBB / DIB clarification per API 6D
• Fire-safe and emissions compliance review
• Cavity relief specification

Logistics: Ball valves shipped from Istanbul to projects across Africa, the Middle East, Central Asia, and beyond. Standard valves 6-10 weeks; trunnion, large bore and special materials 12-22 weeks.

Need ball valves? Send us the size and pressure class, service fluid and temperature, bore requirement (full or reduced), end connection, required certifications (fire-safe, NACE, ISO 15848), and operation type to info@kaskomakine.com or WhatsApp +90 (537) 521 1399. We'll recommend floating or trunnion design, select seat and body materials, size the operator, and provide a quotation with certification within 48 hours.

Continue Reading: Valve Guides

• Industrial Valves Guide — All valve types and how to choose
• Gate Valve vs Ball Valve — Isolation valve comparison
• Ball vs Butterfly Valve — Quarter-turn comparison
• Globe Valve vs Gate Valve — Throttling vs isolation
• Control Valves & Actuators — V-port ball control valves

Frequently Asked Questions

Q: What is the difference between a floating and trunnion mounted ball valve?
A: In a floating ball valve the ball is held only by the two seats and the stem, with freedom to move slightly — line pressure pushes the ball downstream against the outlet seat, and that force creates the seal. This is simple and economical but means operating torque and seat loading rise steeply with size and pressure, so floating designs are typically limited to around NPS 6 and Class 600. In a trunnion mounted ball valve the ball is anchored by an upper stem and a lower trunnion shaft so it cannot move downstream; spring-loaded seats press against the fixed ball instead. Line pressure is carried by the trunnions rather than the seats, keeping operating torque low even at large sizes and high pressures, and enabling double block and bleed functionality.

Q: What is the difference between full bore and reduced bore ball valves?
A: A full bore (full port) ball valve has a ball bore equal to the pipe internal diameter, so there is essentially no flow restriction, minimal pressure drop, and pigs can pass through — making it essential for pipelines and pigged systems. It is larger, heavier, and more expensive. A reduced bore (standard port) valve has a bore typically one nominal size smaller than the line, causing a slight pressure drop and local velocity increase, but is more compact, lighter, and lower cost. Reduced bore is perfectly acceptable for general isolation duty where a small pressure drop is tolerable. Always specify full bore where pigging is required, and verify the actual bore diameter rather than assuming it from the nominal valve size.

Q: Can a ball valve be used for throttling?
A: Standard ball valves should not be used for throttling. They are isolation devices designed to be fully open or fully closed. When held partially open, flow is concentrated through a small crescent-shaped opening, creating high local velocity that erodes the ball and seat, and potentially causing cavitation in liquid service. The damaged seat then fails to seal when the valve is closed. For modulating duty, use a purpose-designed control valve — either a globe control valve or a V-port ball control valve, which has a shaped notch in the ball giving a controllable flow characteristic and hardened trim suited to continuous throttling.

Q: What is a fire-safe ball valve?
A: A fire-safe ball valve is designed and tested to maintain a defined level of sealing after exposure to fire, once the soft (PTFE) seats have burned away. Secondary metal seats and graphite body and stem seals take over sealing duty, limiting leakage so the valve does not feed the fire. Certification is to API 607 or API 6FA, which specify the burn test conditions and allowable leakage before, during, and after fire exposure. Fire-safe certification is mandatory for hydrocarbon and flammable service. Fire-safe valves are normally supplied together with an anti-static device — a spring or contact providing electrical continuity between ball, stem and body to prevent static discharge igniting the medium.

Q: What standards apply to ball valves?
A: Several standards apply depending on service. API 6D (Specification for Pipeline and Piping Valves) is the dominant pipeline standard and includes double block and bleed definitions. API 608 covers metal ball valves with flanged, threaded, and welding ends for general refinery and process service. ASME B16.34 governs pressure-temperature ratings and body wall thickness. API 607 and API 6FA cover fire-safe testing, mandatory for hydrocarbon service. ISO 15848 covers fugitive emissions testing of stem sealing, increasingly specified for environmental compliance. NACE MR0175 / ISO 15156 applies to sour service in H₂S environments. Material certification typically follows EN 10204 Type 3.1 or 3.2.

Q: What seat material should a ball valve have?
A: Seat material sets the temperature limit and shutoff performance. PTFE is the standard soft seat, giving bubble-tight shutoff and excellent chemical resistance up to roughly 200°C. Reinforced PTFE (glass or carbon filled) extends this to around 230°C with better creep resistance. PEEK handles 260°C and above with high strength and abrasion resistance. Devlon and nylon suit hydrocarbons to around 150°C. Metal seats, hard-faced with Stellite or tungsten carbide, handle 400°C and above plus abrasive and erosive service, but require higher operating torque and do not achieve the same leakage tightness as soft seats. Select from maximum operating and upset temperature, fluid chemistry, and required shutoff class.