CHAP. III.] 



PUMPS. 



vacuum behind them by pressing the water forward, thus acting as so 

 many pistons. 



Behrens' rotatory pump (Fig. 40) 

 which works also as a steam-engine 

 (see chapter devoted to steam-engines), 

 is a much more simple construction. 

 Any motive power, steam for instance, 

 puts in motion an arbor which, by a 

 system of cogged wheels, moves in con- 

 trary directions the axes c, c' of two 

 pistons. These turn in the interior, a 

 drum communicating with the suction- 

 tube B and the ejection-tube D. Each 

 piston E, E', has the form of a portion 

 of a massive crown which leaves free a 

 circular space a, a. When this space 

 falls opposite the suction orifice, the 



piston E by its movement increases more and more the free space 

 behind it ; a vacuum is gradually developed, and a certain quantity of 

 water fills it. 



FIG. 39. Stoltz's rotative pump. 



Fio. 40. Belirtus' rotatory pump : phases of the rotatory movement.. 



