What Is a Floating Ball Valve?
In a floating ball design, the ball is not fixed to the body by upper and lower trunnions. The shaft that turns the ball only transmits torque, and the ball has limited axial freedom between the upstream and downstream seats. When the valve closes, upstream pressure pushes the ball toward the downstream seat, and this force supports the seal.
This way of working keeps the valve structurally simple and robust. In severe service versions of this design, the preferred seat is formed directly in the end adapter, then coated and lapped together with the ball. With no separate seat part, a potential leak path between seat and body disappears and the valve better withstands high pressure, high temperature and erosive conditions.
Floating ball and trunnion-mounted designs serve different needs. In a trunnion design the ball is supported by shafts and the pressure load is carried by bearings; this approach stands out for large control valves. The floating design is a strong option for isolation and on-off services that require metal-seated tight shutoff.
How Does a Floating Ball Seal?
This type of valve opens and closes by rotating up to 90 degrees. The key factor that creates the seal is line pressure acting on the ball in the closed position.
1. Open position: The ball bore is aligned with the flow and the fluid passes through the ball.
2. Closing movement: A lever or actuator turns the ball a quarter turn through the shaft. Machined stops on the lock plate prevent over-rotation and preserve alignment.
3. Pressure-assisted seating: In the closed position upstream pressure pushes the floating ball onto the downstream seat, and the seal is supported by this force.
4. Maintaining seat load: Belleville springs keep the seat loaded; in small-bore welded and threaded constructions a seat holder protects the spring against back pressure.
Metal-seated floating ball
In severe service floating ball valves, ball and seat surfaces are coated with chrome carbide or tungsten carbide using the high-velocity oxy-fuel (HVOF) process. These coatings create a very hard, dense layer on the base metal and resist wear, corrosion and erosion. Lapping ball and seat to each other secures the seal.
Bidirectional sealing
In the standard design the preferred flow direction is forward into the integral seat. For applications that need sealing in the reverse direction too, a bidirectional sealing option is available and must be specified at order; reverse-flow sealing is then defined as Class V, Type B per ANSI/FCI 70-2.
Key Features
· Simple two-piece construction: A two-piece floating ball design with a small number of parts.
· Integral metal seat: Seat formed in the end adapter, then coated and lapped with the ball; no additional leak path.
· Hard-coated ball: Chrome carbide (standard) or tungsten carbide HVOF coating; spray-and-fuse coating options.
· Blowout-proof shaft: One-piece, surface-hardened and polished shaft without pins.
· Live-loaded packing: Belleville-spring packing stays energized through temperature swings and is easy to adjust.
· Metal body gasket: A self-energizing metal gasket helps prevent leakage during thermal transients.
· Side-mounted bracket: Prevents side load on shaft and packing box and gives easy access to the packing gland nuts.
· Machined stops: A 90-degree lock plate prevents over-rotation and keeps critical alignment.
Technical Specifications
The values below belong to a metal-seated, two-piece floating ball severe service valve family.
Parameter | Technical data |
Design | Two-piece floating ball; integral metal seat |
Sizes | From 1/2 in up to 36 in |
Pressure classes | From ASME CL150 up to CL4500 (depending on size and connection) |
Connections | Buttweld, socketweld, threaded (FNPT), RF and RTJ flanged |
Body materials | Carbon steel, F22, F91, F316 and F316H |
Shutoff test | Tested to API 598 in the preferred flow direction |
Reverse flow (optional) | Class V, Type B per ANSI/FCI 70-2 in the bidirectional design |
Upper temperature (welded/threaded ends) | Carbon steel 427 °C; F22 593 °C; F91 649 °C; F316 538 °C; F316H 760 °C |
Lower temperature | Carbon steel -29 °C; stainless steel -40 °C |
Coating | HVOF chrome carbide (standard), HVOF tungsten carbide, spray-and-fuse nickel-boron |
Packing | Wire-reinforced graphite; Belleville live loading |
Rotation | Up to 90 degrees |
Options | Reduced port, expanded outlet, scraper seats, high-cycle constructions, lockouts |
Upper temperature limits are lower for flanged connections; see the Severe Service Ball Valves page for details. Values are confirmed per project.
Key Advantages
· Strong shutoff: Line pressure supports the seal, and the lapped metal seat gives tight shutoff.
· Simple, robust design: A low part count simplifies maintenance and spare parts management.
· Resistance to harsh conditions: Hard coatings and metal seats give long life in high-temperature and erosive services.
· Safety-oriented details: Blowout-proof shaft, machined stops and metal body gasket.
· Wide size and pressure range: Options from 1/2 in to 36 in and from CL150 to CL4500.
Applications
Metal-seated valves of this design are used across industries at points that need tight shutoff under high temperature, high pressure and erosive conditions.
High-temperature and high-pressure services
Isolation and on-off duty on high-temperature lines with alloy steel body options.
Erosive fluids
Tight shutoff in solids-laden or erosive fluids thanks to hard-coated ball and seat.
Sour service
Sour liquid and gas applications with materials compliant with NACE MR0103.
Floating Ball Valve Selection Criteria
Success in service depends on correctly defining service conditions and operating mode.
Service conditions
· Design pressure and temperature
· Solids content and erosion risk
· Possibility of back pressure or reverse flow
· Sour service requirement
Construction and connection
· Size and port type (full or reduced)
· Welded, threaded or flanged connection
· Body material and coating type
Operation
· Cycling frequency (need for a high-cycle design)
· Lever or actuator operation
· Lockout requirement
· Where continuous throttling is required, evaluation of a control-type ball design
Standards
Main standards applicable to floating ball severe service valves:
Standard / approval | Scope and description |
ASME B16.34 | Pressure-temperature classes (CL150–CL4500). |
API 598 | Shutoff test in the preferred flow direction. |
ANSI/FCI 70-2 | Class V Type B reverse-flow sealing in the bidirectional design. |
NACE MR0103 | Material requirements for sour service. |
Other shutoff requirements are evaluated per project.
The TLY Enerji Approach
This design may look simple on paper, but its success in high-temperature and erosive services depends on the right evaluation of body material, coating, connection type and back-pressure scenarios. TLY Enerji performs this evaluation using process data and failure history.
For on-off and isolation points, we report with technical justification whether a floating ball design is suitable, or whether control-type ball valves are more appropriate where continuous throttling is needed. Once body material, temperature limit and options are defined, quotation and documentation are prepared, and installation and commissioning support are planned within the project scope. For high-cycle services, maintenance intervals and spare parts needs are also forecast and shared with the operations team.
· Service condition and failure analysis
· Material and coating selection
· Connection and pressure class definition
· Quotation and documentation
· Site support coordination
Frequently Asked Questions
How does a floating ball valve seal?
When the valve is closed, upstream pressure pushes the ball toward the downstream seat. Because the ball is not held by trunnions, this force is transferred directly to the seat contact surface and supports the seal. In metal-seated designs, ball and seat are lapped to each other to secure tightness.
What is the difference between a floating ball valve and a trunnion ball valve?
In a floating ball valve the ball sits free between two seats and the pressure load is transferred to the seat. In a trunnion valve the ball is supported by upper and lower shafts, bearings carry the pressure load and the ball axis stays fixed. The floating design suits on-off duties needing tight shutoff, while the trunnion design stands out in control and large-bore applications.
Does a floating ball valve seal against reverse flow?
In the standard design the preferred flow direction is into the integral seat, and the shutoff test is carried out in this direction to API 598. If sealing is also needed in the reverse direction, the bidirectional sealing option must be specified at order; reverse-flow sealing is then defined as Class V, Type B per ANSI/FCI 70-2.
What temperatures can metal-seated floating ball valves handle?
The temperature limit depends on body material and connection type. With welded and threaded ends the upper limits are 427 °C for carbon steel, 649 °C for F91 and 760 °C for F316H; the lower limit is -29 °C for carbon steel and -40 °C for stainless steel. Upper limits are lower for flanged connections.
Can a floating ball valve be used for control (throttling)?
Metal-seated floating ball valves are designed primarily for isolation and on-off services that need tight shutoff. For points that require continuous flow control, control-type ball valves with a characterized ball and low lost motion, or globe control valves, are the more suitable choice.
Why do ball and seat coatings matter?
High temperature, solids-laden fluids and frequent cycling cause rapid wear on metal surfaces. Chrome carbide or tungsten carbide coatings applied by HVOF form a hard, dense layer strongly bonded to the base metal; wear, corrosion and erosion resistance increase and sealing life is extended.