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Difference Between Floating and Trunnion Ball Valves

 

Some of the ball valves we offer have a trunnion mounted ball design, but most have a floating ball design; the most applicable design for your application depends upon your design criteria.

 

The floating ball valve design is most common, especially for smaller size pipelines, due to its relatively inexpensive cost when compared to a trunnion style valve.  The ball is sandwiched between concave shaped "seats", forming a tight seal between the inlet and outlet ports of the ball and the valve body.  These seats are fixed in-place, meaning they do not move and the actuation shaft is not rigidly attached to the ball, thus it pivots as the axis of the ball is rotated and presses against the seat opposite the pressurized port.  Stem packing prevents leakage via the stem and bonnet interface.

 

What makes a trunnion style ball valve different are the seats, which instead of being fixed are spring loaded, thus actively pushing against the ball to form a seal; therefore there's no need for the ball to pivot for sealing.  The trunnion design is more complex, requiring both a top and bottom shaft to properly position the ball.

 

Therefore the primary functional difference between the two designs involves the operating pressure characteristics, with floating ball valve styles having better sealing for low pressure applications because they are not relying on system pressure to aid with sealing.  Trunnion style valves also offer operational advantages for large diameter pipelines and high pressures, namely extended valve seat life.

 

As might be expected, more stringent performance requirements often translate into more complex designs where the trunnion mounted ball design is advantageous.