The core differences between trunnion ball valves and floating ball valves are mainly reflected in three aspects: structural design, sealing principle and applicable scenarios:
1. Structural differences
Ball support method
Floating ball valve: The ball is connected only by a single-side valve stem (usually the lower valve stem), and the ball can be slightly displaced axially with the medium pressure.
Trunnion ball valve: The ball is fixed by the upper and lower double valve stems to form a stable rotation axis, and the ball cannot be displaced.
Valve seat design
The floating ball valve adopts a double valve seat structure, and the outlet valve seat bears the main sealing load;
The trunnion ball valve is equipped with a floating valve seat, which pushes the valve seat against the ball through spring preload or medium pressure.
2. Sealing principle
Self-sealing dependent on medium pressure: When closed, the fluid pressure pushes the ball to press the outlet valve seat. The greater the pressure, the tighter the seal (the sealing may be insufficient due to the weight of the ball at low pressure).
Trunnion ball valve:
Bidirectional active seal:
Spring preload provides initial seal;
The medium pressure pushes the valve seat to press the ball to form a double seal, which is not affected by pressure fluctuations.
The valve seat can automatically compensate after wear, extending the seal life.
3. Performance and applicable scenarios
Pressure bearing capacity
Floating ball valve: Applicable to medium and low pressure systems ≤PN40 (the outlet valve seat is easily crushed by the ball under high pressure);
Trunnion ball valve: Can withstand ultra-high pressure (≥Class 300) and large diameter (DN＞250mm) working conditions.
Operational characteristics
The operating torque of the floating ball valve increases significantly with the increase of pressure (the friction between the ball and the valve seat increases);
The torque of the trunnion ball valve is stable (the ball is supported by the bearing and the friction is small).
Special function
The trunnion ball valve can achieve double cut-off relief (DBB): automatically release pressure to the pipeline when the middle cavity is overpressured;
Floating ball valves are generally one-way seals and have no pressure relief function.
Applicable media
Floating ball valve: clean media (water, natural gas, etc.);
Trunnion ball valve: containing particles/slurry, high temperature/ultra-low temperature (-196℃ LNG), corrosive media.
Selection summary
Choose floating ball valve: DN≤250mm, PN≤40 clean media system, pursuing low cost and light weight;
Choose trunnion ball valve: high pressure/ultra-low temperature, impurity-containing media, large-diameter pipelines or safety systems that require double cut-off and release.