Southern valve gear

Southern valve gear was briefly popular on steam locomotives in the United States.

As with those systems it used a return crank on a driver (instead of the eccentrics used by the Stephenson valve gear).

This pivot attached to the end of the radius hanger, the other end of which attached to a link block which slid back and forth in a track curved in the same manner as the expansion link of a Walschaerts gear.

In this system, however, the track was fixed in place; sliding the link block back and forth controlled reversing and cutoff.

As link block moves back and forth, the angle of the radius hanger changes, and the up and down motion of the transmission yoke in response to the back and forth motion of the eccentric rod is increased or decreased.