ir pressure.

44. Q. Can and should steam pressure be used?

A. Yes. However, steam should never be used except in an emergency when
air is not available.

45. Q. What precaution should be taken regarding steam check and
throttle?

A. That they are tight and check working properly, to insure that steam
is kept from entering main reservoir, for if it should do so it would
burn out the gaskets in the air brake equipment, allow moisture to
accumulate, which would result in freezing and bursting of equipment as
well as being dangerous.

46. Q. What would cause the gear to fail to hold links in intended
cut-off, and allow them to raise and lower without operating valve in
the cab being changed?

A. Leaks in main valve and piston packing.

=WALSCHAERT AND BAKER-PILLIOD VALVE GEARS=

1. Q. Give a brief explanation of the Walschaert valve gear.

A. The Walschaert gear has an eccentric crank attached to the end of the
main pin on each side of the locomotive, with an eccentric rod from this
pin to the connection at the bottom end of the link. This eccentric is
located so it serves for both forward and back motion. The link swings
on a center trunnion and cannot be moved up and down as the Stephenson
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 eccentri