VAPOUR JETS 



seventeen-hundredth part of the volume that 

 it occupies as steam. This means that a jet 

 of steam suddenly condensed will have its 

 diameter reduced to less than one-fortieth of 

 what it was before. All its moving energy is, 

 therefore, concentrated into this small jet of 

 water from the condensed steam. That means 

 that over this small area 

 the jet has seventeen 

 hundred times as much 

 energy as before con- 

 densation, supposing the 

 change of conditions to 

 be realised with theo- 

 retical completeness. 

 Allowing a large margin 

 for imperfection in prac- 

 tice, the increase of 

 energy is sufficient to 

 enable the smaller jet of 

 what is now condensed 

 steam or water easily to overcome the boiler- 

 pressure, and re-enter the boiler, carrying with 

 it the water which condensed it. 



The diagram in Fig. 37, in order to make the 

 general nature of the operation clearer, has 

 some of the details which are necessary in prac- 

 tice omitted altogether, and others exaggerated 

 in their proportions, for the assistance of those 

 who have no acquaintance with the injector 

 at all. 



163 



FlG. 37. PRINCIPLE OF THE 

 STEAM INJECTOR. 



