link, but the link block can be moved from one end of the link to the
other to reverse the engine; or part way toward the center of the link
to change the cut-off. A radius rod connects the link block to the valve
stem. There are two motions given to the valve stem, one from the link
block which regulates the travel of the valve for the cut-off and
reversing; the other motion is from a connection with the cross-head
which gives the valve a positive motion to take care of the lap and
lead. To give this motion there is used a combination lever or a lap and
lead lever connected to a cross-head arm by the union link.

2. Q. Is the Walschaert gear direct or indirect?

A. It is direct when the link block is below the center of the link; it
is indirect when the link block is above the center of the link.

3. Q. What are the principal differences in the location of the
Stephenson and Walschaert gears, and what advantages does this give the
Walschaert?

A. The Stephenson gear is placed between the main frames and employs two
eccentrics, with straps and rods on each side of the locomotive; one
for forward and one for backward motion. The Walschaert gear is placed
outside the driving wheels and frame, has but one eccentric, which is a
simple arm connected to the outside end of the crank pin for both
forward and back motion. The links are set above the wheels on a level
with the steam chest, the combination lever next to the cross-head. This
gives it an advantage of a better chance to inspect all parts, the
eccentric connections are much lighter and direct, which makes them less
liable to wear or breakdown, and the valve has a constant lead.