US Patent 7451959 Plug valve having a seal boss

A fluid control valve utilizes a rotatable plug valve member mounted in a fluid passage to control the flow of fluids. Two segments are placed on each side of the plug valve member within a recess located between the plug valve member and the body of the fluid passage. The outer surface of the segments includes an elastomeric seal and metal annular boss, which acts as a stop to limit deformation of the seal when the valve is closed and under pressure.