l$2 KOI -TUMBLE ENGINEERING 



Q. \\"hat do you consider a safe working pressure 

 a bo: 



A. in;.! depends entirely on its diameter. While 

 a boiler of 30 inches in diameter ^ inch iron would carry 

 pounds, a boiler of the same thickness So inches 

 in diameter would have a safe working pressure of only 

 50 pounds, which shows that the safe working pre 

 decreases very rapidly as we increase the diameter of the 

 r. This is the safe working pressure for single riv- 

 eted boilers of this diameter. To find the safe 

 pressure of a double riveted boiler of the same din: 



safe pressure of the single riveted 1>\ 

 divide by 56, this will give a safe pressure of a double riv- 

 eted boiler. 



O. Why is a steel boiler superior to an iron boiler ? 

 A. Because it is much lighter and stronger. 



Does boiler plate become stronger or weaker as 

 comes heated? 



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 if it is heated beyond this 

 temperature. 



O. How do you account for this? 

 A. Because after you pass the maximum temperature 

 of ^Q decrees, the more you raise the temperature the 

 nearer you approach its fusing point, when its tenacity or 

 resisting power is nothing. 



