The steam is admitted through a piston value operated by a species of link motion, as shown.
The link motion of an American locomotive is shown in Figs. 3329 and 3330.
The parts usually case hardened are the link motion, and other light working parts that are of wrought iron.
One form of valve-gear is the link motion invented by Stephenson.
I was much like the rest of the boys until I commenced to try to get up a substitute for the link motion.
link motion for locomotives—George Stephenson, England, 1833.
The advantage of the link motion is its simplicity and durability.
This latter plan is also adopted for forms not easily ground out in a machine, as, for example, a die in a link of a link motion.
When there is no link motion, a Joy valve gear, a Marshall valve gear, or a loose eccentric may be used.
Other forms of link motion have been devised, but the Stephenson form has become almost universal.