Valves Vacuum. 



73 



14. The upper valve removes the air from 

 the pump, and immedi- 

 ately the water is pressed 

 up and flows out at the 

 spout. 



1 5. The valves are so 

 made that the water and 

 air by pressing upwards 

 open them and rise 

 above them, but by 

 pressing downward, 

 close them ; therefore, 

 the valves prevent the 

 return of the water 

 through the pump into 

 the well. 



1 6. When the upper 

 valve goes down, it is 



Bod coming up Upper Valve opened by the TUSh of 

 closed Lower Valve open. . 



air upward, but when it 



rises it is closed by the pressure of the air above 

 it; a few strokes in this way remove the air 

 from within the pump, and the consequence is 

 that the air in the well, but outside of the pump, 

 forces the water upward to fill the vac'-u-um. 



17. Any space which contains nothing not even air 

 is called a vacuum. 



