HOW TO APPLY THIS GEAR TO AMERICAN LOCOMOTIVES.
To apply this gear, the valve and steam-chest are placed, as is usually the case in American locomotives, over the cylinders; the valve-stem center being, however, in the same vertical plane as the cylinder center line, immediately over it. All the valve-motion is thus arranged on this plane,—perfectly central,—and there are no crooked or side strains. To a point A on diagram, about two-fifths along the connecting rod from the piston end, a small hook-link is pinned. From the lower end of this at D is jointed a lever E, which, of course, moves with the connecting rod both backward and forward, and up and down; the point D, in fact, moving in a very irregular ellipse, hereafter explained. The fulcrum F of the lever E is carried in a block which slides in a slot-link JK, and from the upper end of this lever E the valve-stem rod G is carried to the valve. This slot-link JK is centered so as to be able to be inclined from the vertical either way. When standing in the vertical position, the engine is in mid-gear, and the valve will only be opened for lead; but this will be exact for each end, and exact also on either side of the center line of the connecting rod. When the slot-link is inclined forward to the front of the engine, the engine is in full gear forward; and, when inclined backwards, it is in full gear for going back. Placed in any intermediate position, the cut-off is regulated for any required degree of expansion; the front and back of the piston receiving equal cut-off, or equal amounts of steam.