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APPLIED SCIENCE 



out at least once a day, and sometimes three or four times, 

 depending upon the quality of the feed water. The gauge 

 cocks should be opened after blowing out the water column 

 to see that the level in the glass coincides with the level indi- 

 cated by the gauge cocks. The water has to be kept at about 

 the same height all the time, and the engineer can tell 

 whether it is right or not by opening the gauge cocks. One 

 of these is below the water line, and one is above it. If the 



FIG. 167. Cross-Section of a Boiler Pump. 



water in the boiler is right, steam will come out of the upper 

 one and water out of the lower one ; if it is too low, steam 

 will come out of both. 



355. Boiler Pumps and Injectors. A boiler should have 

 at least two means of feeding water, because one might fail 

 to work. The water inside a boiler is usually kept at a proper 

 level by either pumps or injectors. Steam pumps (Fig. 167) 

 are most commbnly used on stationary and marine boilers, 

 and may be classified as boiler-feeders, general surface 

 pumps, tank pumps, or water-work pumps. 



