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 broken?

A. If they were stopped up the equalization would be destroyed, and when the steam-chest pressure was less than the boiler pressure the feed would work too fast, the oil would enter the feed glass in a stream instead of forming into drops.  If they were broken, the lubricator could not be used.  The auxiliary oilers would have to be used to lubricate the cylinders.

=Air brake questions=

1.  Q. Explain how an air compressor should be started.

A. A compressor should be started slowly, with the drain cocks open to allow the water of condensation to escape; and as no provision is made in the steam end to cushion the pistons at the end of their stroke, it should be allowed to work slowly until a pressure of thirty or forty pounds has accumulated in the main reservoir; the piston, having to work against this pressure, will be cushioned at the end of each stroke.  After the compressor is warm, the drain cocks should be closed and the throttle opened sufficiently to run the compressor at the proper speed.  The lubricator should then be started and allowed to feed freely until eight or ten drops have passed, when the feed should be reduced to an amount sufficient for proper lubrication.

2.  Q. What kind of oil should be used to lubricate both the steam and air cylinders of the compressor?

A. Valve oil.

3.  Q. Where does the main reservoir pressure begin and end?

A. Begins at the discharge valves in the compressor and ends at the engineer’s brake valve.

4.  Q. Where does the brake pipe pressure begin and end?

A. The brake pipe pressure begins at the feed valve and ends at the brake pipe side of the triple piston, conductor’s valve and at the rear angle cock.