Joy Valve Gear

Mechanism for the valves of steam engines, recently much used for marine engines. A short rod is attached by a pin to a point on the connecting rod of the engine, the other end of the short rod being pivoted to a radius arm attached to the frame of the engine. The first end therefore moves in an ellipse or oval. A second rod is pinned to the first at an intermediate point, for reduction of the amplitude of throw and to diminish the eccentricity of the curve of motion of this end, while the valve stem is pinned to the other extremity. This second rod vibrates upon a pin in a slide block in a groove, the groove being capable of having its angular position adjusted on one side or the other of a mean position, and at varying angles with it. The throw of the valve is thus varied, and hence the cut-off is adjusted, or the distribution of steam reversed. See RADIAL VALVE GEARS and LINK MOTIONS.