VALVE MOVEMENT
The valves are actuated by two motions,—one taken from a single eccentric, the other derived from a connection with the cross-head. The single eccentric is used to give both forward and backward motion, and is set in the proper angle to the crank to produce motion in either direction. For reversing the motion of the valve, a curved rocker-arm R ([Fig. 27]) is used, on which moves a sliding-block r. Attached to the sliding-block is the link H, which connects with the lap-and-lead lever D. The lower end of this lever is attached by the link d to the cross-head, from which the lever receives an oscillating motion. This lever is suspended by a hanger from any convenient part of the engine. Projecting from one side of the lap-and-lead lever are two pins, to which are connected the valve-stem rods m and n. These pins are set upon the lever at points between 90 and 180 degrees apart, so as to give a differential movement to the valve, which can not be obtained when the pins are set opposite on the lever.