298 



CONSTRUCTION OF PUMP 



downward pressure presses it close against the sides of the tut 

 and nothing is allowed to pass out ; while upward pressure separat 

 it from the sides, and allows water and air to pass between; the india- 

 rubber tube thus acts by its elasticity like a valve, and no other 

 valve is required in the piston. 



A 





B 





FIG. 198 (A, % real size ; 5 and C, real size}. 



The top of the suction-tube is shown at C separately. It consis 

 of a sheet of metal Z> ft, to which are fixed two short tubes, one at tlj 

 upper side, and another, somewhat narrower, at the lower sid 



