SCIENCE OF THRESHING 109 



Sometimes high speed pumps with long inlet pipes 

 work better with an air chamber just outside the 

 inlet valve, communicating with the inlet pipe to give 

 the column of water flowing into the pump a more 

 uniform motion. 



If there is any air admitted to the pump it expands, 

 and reduces the vacuum caused by the withdrawal of 

 the piston, thereby diminishing the pressure of the 

 outer air on the water at the feed pipe mouth, and to 

 that extent impeding the inflow of water. If the 

 water is too hot, so as to steam, the vapor fills the 

 cylinder instead of the fluid, and so interferes with 

 its working. 



INJECTORS. 



Injectors make use of a jet of steam to force the 

 feed water into the boiler. Although there are 

 many makes and kinds, they all work on the same 

 general plan. 



The injector consists in general of a suction 

 chamber, a condensing tube, and an overflow valve. 

 Live steam is taken from the boiler directly through 

 a pipe to the injector. As it is forced through the 

 condensing tube, it forms a vacuum therein so 

 that the water is lifted and enters the condensing 

 tube, intermingling with the steam. The water 

 being cold, this condenses the steam and greatly re- 

 duces its bulk, so that the combined columns of water 

 and steam, as thus condensed, are smaller than the 

 column of steam alone as it comes from the boiler; 

 so there is a less volume or bulk of water entering 



