Link 2 is a shutter and turns about fixed axis F. Rod 5 reciprocates in fixed guide q. Cam c turns about fixed axis G. When crank 1 rotates about fixed axis A, shutter 2 is oscillated by rod 5 whose pin d slides along slot e of the shutter. This opens and closes the port through which steam is admitted to the engine cylinder. Motion is transmitted from crank 1 to rod 5 by four-bar linkage ABCD through rocker arm 4 and spring 3 when rod 5 moves to the right. Reverse motion is transmitted to rod 5 through lever 6 which oscillates about axis E and has lug a which, by the action of spring 7, engages lug b on rod 5. Lever 6 is disengaged from lug b by governor 9 whose weights are either forced outward or inward upon changes in speed of the governor spindle. This moves sleeve 8 either upward or downward. The length of time during which lever 6 remains engaged to lug b depends upon the position of sleeve 8 and the shape of cam c.
$1708$LC,G$