THE LOCOMOTIVE 



249 



Water gauge. The boiler has attached to it a water gauge, 

 a steam gauge, a safety valve, and an injector. The water 

 gauge is a glass tube placed on the outside of the boiler, so 

 that the height of water may be determined by looking at 

 this gauge. 



Steam gauge. The steam gauge is a device for recording 

 the pressure of the steam in pounds. It is so arranged that 

 as the pressure increases, a hand on a dial rotates, much like 

 the hands on a clock; and the pressure is read from the 

 figure to which the hand points. 



Safety valve. The safety valve is a device for allowing 

 the steam to escape when a certain pressure is reached, so 



Throtl/e Va/ve 



Backward Rod 



f-brword Rod 



Courtesy of Harper & Brothers 

 FIG. 92. Parts of a locomotive. 



as to prevent the possibility of an explosion occurring in 

 the boiler. This valve fits into a hole in the boiler ; it con- 

 sists of a tight-fitting plug, which is kept in place either 

 by a spring or by a lever with a weight attached to it. The 

 tension of the spring or the weight can be adjusted to allow 

 the steam to escape at any desired pressure. 



The injector is a device which fills the boiler with water ; 

 this is operated by steam pressure. 



Fuels. Coal is the fuel generally used. The draft is 

 increased by allowing the exhaust steam to pass into the 

 smoke box; and as this is under considerable pressure, it 

 rushes out of the box, creating a partial vacuum. As a result, 



