CHAPTER VIII 



THE BOILER 



THE function of the boiler is to heat water suffi- 

 ciently to change it into steam, for use in an 

 engine, or for other purposes. The supply of 

 water for the boiler has been treated under "The Feed 

 Water" in Chapter II, and the management of the fire 

 with various fuels under "Firing" in Chapter III. 



Boiler Fittings. The fittings necessary for the opera- 

 tion of a boiler, are the feeder ( for supplying the water) , 

 glass gage and gage cocks (for indicating the water level), 

 a steam gage (for indicating the pressure), a pop or 

 safety valve (to prevent the pressure from reaching a 

 dangerous height), and a "blow-off" valve (for draining 

 the boiler) . A boiler is usually fitted also with a whistle 

 for signaling, a fusible plug and a blower for forcing the 

 draft. The water feeders, water glass and gage cocks 

 have been treated under "Feed Water" in Chapter II. 



The Steam Gage. The steam gage indicates the steam 

 pressure in the boiler in pounds per square inch. The cut 

 shows the interior of the gage used on "Case" engines. 

 The curved tube or Bourdon spring has an oval cross sec- 

 tion, and when exposed to pressure from the inside, tends 



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