THE BICYCLE PUMP 



331 



be done under water, is possible only through the use of com- 

 pression pumps. Those who have visited mines, and have gone 

 into the heart of 

 the underground 

 labyrinth, know 

 how difficult it is 

 for fresh air to 

 make its way to 

 the miners. Com- 

 pression pumps 

 have eliminated 

 this difficulty, 

 and to-day fresh 

 air is constantly 

 pumped into the 



mines to supply ^ IG- 20 - Spraying trees by means of a compression 



pump. 



the laborers there. 



Agricultural methods also have been modified by the com- 

 pression pump. The spraying of trees formerly done slowly 

 and laboriously, is now done very 

 simply by pumps (Fig. 200). 



The bicycle pump. The bicycle 

 pump is the best known of all com- 

 pression pumps. Here, as in all 

 compression pumps, the valves open in- 

 ward rather than outward. When the 

 piston (p) is lowered, compressed air is 

 driven through the rubber tubing, 

 pushes open an inward-opening valve in 

 the tire, and enters the tire. When the 

 piston is raised, the lower valve closes, 

 the upper valve is opened by atmos- 



FIG. 201. The bicycle foot r . ' 



pump. phenc pressure, and air from outside 



