BOILER AND MANAGEMENT 161 



tampered with. Both' can be set to blow off at different 

 pressures. 



Water Feed Apparatus. There are two ways ot 

 feeding water into a boiler, namely, with injectors and 

 with pumps. 



Injector. This important boiler accessory is attached 

 to the side of the boiler. It utilizes the steam 

 directly from the boiler for- forcing water into it 

 against a pressure as great as that which sends it forth. 

 The principle which makes this possible may be stated 

 as follows: Steam issuing from a boiler under 70 pounds 

 pressure has a velocity of 1,700 feet per second. When 

 steam with this high velocity strikes the combining tube 

 it produces suction which in turn induces a flow of 

 water. As soon as the water enters the combining tube 

 it is given motion by the high velocity of the steam, 

 which immediately condenses and moves with the water 

 into the boiler at a comparatively low velocity. The 

 energy, therefore, by which steam can force water into the 

 boiler against its own pressure is the latent heat resulting 

 from the condensation of the steam in the combining tube. 



From this it must be evident that the efficiency of the 

 injeqtor is dependent upon the completeness with which 

 the steam condenses. This is clearly proven by every 

 day practical experience. When, for instance, the feed 

 water is too hot, the steam pressure too high, or the 

 steam is wet, the injector fails to work properly because 

 the steam does not sufficiently condense when it strikes 

 the feed water. 



Starting the Injector. This is done by opening the 

 supply water valve one or two turns, then the steam valve 

 wide. . If steam issues from the overflow admit a little 

 more water ; if water overflows admit less. 



