HARMONY OF WORKING-PARTS.
Hitherto we have regarded the link as merely performing the functions of transmitting the motion of the eccentrics to the valves, with the additional capability of reducing the travel at the will of the engineer. Otherwise, the motion of the link is intensely complex; and its movements are susceptible to a multitude of influences, which improve or disturb its action on the valve. A good valve-motion is planned according to certain dimensions of all the working-parts; and any change in their arrangement will almost invariably entail irregularities upon the link’s movement, which will radically affect the distribution of steam. A link-motion schemed for an eccentric throw of 4½ inches will not work properly if the throw be increased to five inches: a link with a radius of 57 inches can not be changed with impunity for one of 60 inches. Any change in the position of the tumbling-shaft or rocker-arms distorts the whole motion, and any alteration in the length of the rods or hangers has a similar effect. That the link may perform its functions properly, all its connections must remain in harmony.