CREAMERY MECHANICS 277 



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 

 injector is dependent upon the completeness with which 

 the steam condenses. This is clearly proved 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. 



Care of Injector. An injector will become coated 

 with sediment or scale the same as the boiler and must, 

 therefore, be frequently cleaned. This is best done by 

 immersing it in a solution of one part muriatic acid and 

 ten parts water. Allow to remain in this solution until 

 the scale becomes soft enough to permit washing out. A 

 clean injector rarely causes trouble but if trouble does 

 occur it may be due to: (i) low steam pressure; (2) too 

 hot water; (3) leaks in pipes and injector; (4) clogging 

 of water pipe; (5) wet steam; (6) poor working condi- 

 tion of check and overflow valves; (7) clogging of feed 

 pipe where it enters the boiler. 



The injector is commonly used to feed water into the 

 boiler because it is cheap and simple, and occupies little 

 space. 



Pumps. There are two kinds: (i) those run with 



