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.
67. Q. Then why not heat the feed water to the boiling point (212 degrees)?
A. If the feed water is heated much above 100 degrees it will not condense enough steam in the injector to cause it to work properly. Some injectors will work hotter water than others. It would also spoil the paint on the tank if heated to a much higher temperature.
68. Q. At 200 pounds pressure per square inch, what is the pressure per square foot on the sheets of a boiler?
A. About fifteen tons.
69. Q. What is the total pressure on the fire-box of a large locomotive?