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 1½-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 1½-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.?