CHAPTER XXXI. 



CREAMERY MECHANICS. 

 THE STEAM BOILER. 



There are three principal types of boilers in use at the 

 present time : (i) water tube boilers ; (2) internally fired, 

 or marine, boilers; and (3) fire tube boilers. 



In the water tube boiler the water circulates through 

 tubes which receive the heat directly from the furnace. 

 These tubes communicate with an iron cylinder, placed 

 directly over them, which serves the purpose of a steam 

 reservoir. Boilers of this type are rapidly gaining favor 

 as economical steam generators. They occupy somewhat 

 more space, however, than the other types of boilers. 



In the marine boiler, the firing is done in the shell, the 

 entire fire box being surrounded by water. The return 

 heat passes through a series of tubes which nearly sur- 

 round the upper half of the fire box. The entire boiler 

 consists of a round iron cylinder supported on short legs. 

 It is heavily covered with asbestos which dispenses with 

 the brick work necessary with the fire tube boilers. 



The marine boiler is neat and attractive and has grown 

 much in popularity in recent years. As its name implies 

 this type of boiler has been mostly used on the sea, but 

 is now to be seen nearly everywhere in power plants. 



The common form of creamery boiler belongs to the 

 fire tube kind. Fig. 75 illustrates this boiler partly laid 

 in brick. The grates, or iron bars, upon which the fire is 

 placed are seen in the front half of the brick work. The 



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