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.
4. Q. How is the lead affected by movement of the reverse lever with the
two gears?
A. With the Stephenson gear the lead increases as the reverse lever is
hooked toward the center in both forward and back motion. With the
Walschaert gear the lead is the same in all positions of the lever, so
that the lever is used to reverse the engine or adjust the cut-off.
5. Q. In reversing, how do the two gears differ as to the movement of
the link and link block?
A. With the Stephenson gear, when reversing, the link is raised and
lowered, bringing the block which is not moved by the reverse lever
under control of either the forward or back-up eccentric as is desired
to move the engine the proper way. With the Walschaert gear the link is
not moved by the reverse lever, but the link block is raised and lowered
in the link; the position of the block above or below the center of the
link controlling the direction of motion.
6. Q. What would you disconnect if the eccentric crank, eccentric rod,
or the arm at the bottom of the link should break?
A. Would remove the broken parts, disconnect the link lifter from the
radius rod and block the link block in the center of the link; the
combination lever would then move the valve twice the amount of its lap
and lead, which would be sufficient to provide for lubricating the
cylinder.