then open main throttle valve, when the steam from
steam chest will blow back through the choke plug, clearing it of any
obstruction.

84. Q. What is superheated steam?

A. It is the saturated steam separated from the water from which it is
generated with more heat added, increasing its temperature from 100
degrees to 250 degrees Fahrenheit above the saturated steam temperature.

85. Q. What is the advantage of superheating or increasing the
temperature of the steam?

A. By increasing the temperature of the steam the volume of a given
weight of steam is increased and all losses due to cylinder condensation
are eliminated, which result in a reduced steam consumption, a saving in
coal and water and increased boiler capacity.

86. Q. How is the increased temperature obtained by the use of the
superheater?

A. By admitting the saturated steam into a partitioned receiver which
has a number of 1-1/2-inch pipes attached to it. These are located in
and extend nearly the full length of the large flues, the steam having
to pass through these 1-1/2-inch pipes on its way back to the receiver,
absorbs the heat from the gases passing through the large tubes, causing
its temperature to rise, or in other words, become superheated.

87. Q. How much is the volume of steam increased by superheating?

A. For each 100 degrees of superheat added to saturated steam, at
temperatures ordinarily used in locomotive practice, the volume of a
given weight is increased roughly from sixteen to seventeen per cent.

88. Q. Why is the superheated steam so much more economical on coal and
water than the saturated steam?

A. Because for a given amount of water evaporated you can increase the
volume of steam 33 per cent. by superheating. It is readily seen that
the coal does not have to be burned if the steam used has 33 per cent.
more volume for filling space, or in other words, only so much steam can
be admitted to the cylinders for every movement of the valve, and what
can not be used must remain in the boiler, so if the engine can not use
all of the steam that the boiler is capable of generating, the saving
must show in coal and water. If you can not use all of the steam you do
not have to burn coal to make it.

89. Q. Which is the better practice, to close the feed valves or water
valve while waiting on sidings, etc.?

A. Close the feed valves; the water valve may leak.

90. Q. How can you tell if equalizer tubes become stopped up or br