64. Q. How is the greatest injury done to a boiler when cleaning or
knocking the fire?

A. By excessive use of the blower drawing cold air through the fire-box
and flues.

65. Q. Why does putting a large quantity of cold water into a boiler
when the throttle is closed cause the flues to leak? When is this most
serious?

A. When steam is not being used there is not much circulation of water
in the boiler, and the water entering the boiler at about 150 degrees
temperature is heavier than the water in the boiler. The cooler water
will go to the bottom and reduce the temperature in that part of the
boiler and causing the flues to contract in length as well as in
diameter and this has a tendency to pull them out of the sheet. This
will loosen them and cause them to leak. After the fire has been knocked
this tendency is much greater, and for that reason cold water should not
be put into a boiler after the fire has been knocked out. Always fill
the boiler before the fire is knocked out.

66. Q. Is warm water in the tank of any advantage in making steam
rapidly?

A. Yes; careful experiments have shown that a locomotive will generate
one per cent. more steam for every eleven degrees that the tank water is
heated; thus by heating the feed water in the tank from 39 degrees to 94
would effect a saving of five per cent.