Q. What is the most economical pressure to carry on high
pressure engine?
A. From 90 to 110 pounds.
Q. Why is high pressure more economical than low pressure? A. Because the loss is greater in low pressure owing to the atmospheric pressure. With 45 pounds steam the pressure from the atmosphere is 15 pounds, or 1/3, leaving only 30 pounds of effective power; while with 90 pounds the atmospheric pressure is only 1-6 of the boiler pressure.
Q. Does it require any more fuel to carry I00 pounds than it does to carry 60 pounds? A. It don't require quite as much.
Q. If that is the case why not increase the pressure beyond this and save more fuel? A. Because we would soon pass the point of safety in a boiler, and the result would be the loss of life and property.
Q. What do you consider a safe working pressure on a boiler? A. That depends entirely on its diameter. While a boiler of 30 inches in diameter 3/8 inch iron would carry I40 pounds, a boiler of the same thickness 80 inches in diameter would have a safe working pressure of only 50 pounds, which shows that the safe working pressure decreases very rapidly as we increase the diameter of boiler. This is the safe working pressure for single riveted boilers of this diameter. To find the safe working pressure of a double riveted boiler of same diameter multiply the safe pressure of the single riveted by 70, and divide by 56, will give a safe pressure of a double riveted boiler.
Q. Why is a steel boiler superior to an iron boiler?
A. Because it is much lighter and stronger.
Q. Does boiler plate become stronger or weaker as it becomes heated? A. It becomes tougher or stronger as it is heated, till it reaches a temperature Of 550 degrees when it rapidly decreases its power of resistance as it is heated beyond this temperature.
Q. How do you account for this? A. Because after you pass the maximum temperature of 550 degrees, the more you raise the temperature the nearer you approach its fusing point when its tenacity or resisting power is nothing.
Q. What is the degree of heat necessary to fuse iron?
A. 2912 degrees.
Q. Steel?
A. 2532 degrees.