An adjustable trunnion valve includes an obturator, a valve stem, at least one valve seal, and a trunnion. The trunnion and obturator are configured to translate the obturator along a longitudinal axis extending through the trunnion and the obturator upon rotation of the valve stem beyond one or both of its open position and its closed position. A method of operating an adjustable trunnion valve having an obturator coupled to a trunnion and a valve stem includes passing a fluid through the adjustable trunnion valve and rotating the valve stem to rotate the obturator about an axis of rotation and to simultaneously translate the obturator in a direction along the axis of rotation while the obturator is supported by the trunnion and while the fluid flows through the adjustable trunnion valve.