Floating Ball Valve vs Trunnion Mounted Ball Valve Selection Guide

Ball valves come in two fundamental designs: floating ball and trunnion mounted. Understanding the differences helps engineers select the right design for each service condition.

Floating Ball Valve Design

In a floating ball valve, the ball is held in place only by seat rings. Line pressure pushes the ball against the downstream seat to create a seal. This simple design works well at moderate pressures and smaller sizes.

• Pressure range: Best suited below Class 600 and NPS 6

• Sealing mechanism: Differential pressure creates seat contact force

• Zero pressure sealing: Poor; ball not held against seat without line pressure

• Construction: Fewer components; lower cost than trunnion design

Trunnion Mounted Ball Valve Design

Trunnion valves have the ball mechanically fixed by upper and lower trunnion bearings. Spring-loaded seats are pushed against the fixed ball, providing sealing independent of line pressure.

• Pressure range: Preferred above Class 600 or NPS 6 and larger

• Low torque: Ball does not transfer pressure load to seats; easier to operate

• Zero pressure sealing: Spring-loaded seats maintain contact at all times

• Cavity relief: Double block and bleed possible; automatic cavity pressure venting

When to Choose Floating Ball Valves

Floating ball valves are economical for standard service within their pressure and size limits. They are reliable and require minimal maintenance in clean, moderate-temperature service.

• Budget-sensitive projects with moderate pressure and temperature

• NPS 2 through NPS 6, Class 150 to Class 300

• Non-critical services where temporary high-torque operation is acceptable

• High cycle applications where low cost replacement is preferred

When to Choose Trunnion Ball Valves

Use trunnion valves for high pressure, large bore, or safety-critical applications. Their mechanical stability, low operating torque, and consistent sealing make them the preferred choice for demanding service.

• High pressure above Class 600 regardless of size

• Large bore above NPS 8 in any pressure class

• Fire-safe and safety-critical isolation valves

• Automated valves where consistent torque is required for actuator sizing