How A Trunnion Ball Valve Works & A Buying Guide

A ball valve is a shut off valve that makes use of a rotating ball with a bore. In a trunnion ball valve, the ball has small protruding shafts at the top and bottom that are mechanically supported. This makes it suitable for higher pressures and larger diameters. The majority of ball valves in the world don’t have a trunnion design, they are called floating ball valves. In this design, the ball is held into place by the compression of the seat rings on both sides. The ball has some freedom of movement. During use, the ball floats slightly downstream against the seat ring and creates a sealing. When the loads on the ball get very high, the seat rings are not able to support the ball and this is the point where the trunnion design offers a solution. In the trunnion design, the ball is not floating anymore and instead the seat rings are floating. An advantage of this solution is that the operating torque is lower than with floating ball valves. A lower operating torque can reduce the cost of the complete system, taking into account the cost of an actuator that delivers lower torque. The trunnion ball valve itself however, will in general have a higher cost. 

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