Link'-mō'tion, n.

n. (Steam-eng.) A valve gear consisting of two eccentrics and their rods, connected by an adjustable piece, called the link, to the valve, in such a way as to produce a variable cut-off, and to reverse the steam when the engine is in motion.

Let C represent the center of the shaft, C D the engine crank, C A the fore-eccentric (which is the equivalent of a crank), C B the back-eccentric, and E and F the eccentric-rods, taking hold of the link a, which is a plane slotted bar capable of being moved up and down with the eccentric-rods by the hand-lever H, on a fixed (as to vertical motion) block, to which the valve-rod I is attached. The valve-rod and valve will then receive the motion of the fore-eccentric A when in the position shown, and the motion of the back-eccentric when the link is moved up so as to bring C F I in line, or a compound motion derived from both of them, when the link is in intermediate positions. This compound motion, in virtue of the lap, lead, and advance (relative angles and proportions), produces a variable cut-off, remarkable for the complexity of its motions and the simplicity of its parts. It is used almost exclusively on locomotive and screw-propeller engines. Its forms are various, such as stationary-link, shifting-link, &c.