134 ROUGH-AND-TUMBLE ENMNKKRIN* 



lapse than one of small diameter? 



A. Yes. 



Q. Why? 



A. Because its power of : much 1e^ ihan 



a tuhe of a small diameter. 



Q. Is the pressure on the shell of a hniirr the .<,ame as 

 on the tubes? 



A. No. 



Q. What is the difference? 



A. The shell of a boiler has a tearing or internal pres- 

 sure while the tubes have a crushing or external pressure. 



Q. What causes an explosion ? 



A. An explosion occurs generally from low water, 

 allowing the iron to become overheated and thereby weak- 

 ened and unable to withstand the pressure. 



Q. What is a "burst?" 



A. It is that which occurs when through any defect 

 the water and steam are allowed to escape freely without 

 further injury to boiler. 



Q. What is the best way to prevent an explosion ? 



A. (i) Never go beyond the safe working pressure. 

 (2) Keep the boiler clean and in good repair. (3) 

 Keep the safety valves in good shape and the water at 

 its proper height. 



O. What is the first thing to do on going to your 

 engine in the morning? 



A. See that the water is at its proper level. 



