2O2 



PUMPS AND THEIR VALUE TO MAN 



portant class of pump is that known as the compression 

 type; in these, air or any other gas is compressed rather 

 than rarefied. 



Air brakes and self-opening and self-closing doors on cars 

 are operated by means of compression pumps. The laying 

 of bridge and pier foundations, in fact all work which must 

 be done under water, is possible only through the agency of 

 compression pumps. Those who have visited mines, and 

 have gone into the heart of the under-ground labyrinth, 

 know how difficult it is for fresh air to make its way to the 

 miners. Compression pumps have eliminated this difficulty, 

 and to-day fresh air is constantly pumped into the mines to 

 supply the laborers there. Agricultural methods also have 

 been modified by the compression pump. The spraying of 



trees (Fig. 143), 

 formerly done 

 slowly and labo- 

 riously, is now 

 a relatively 

 simple matter. 



190. The Bi- 

 cycle Pump. 

 The bicy c le 

 pump is the 

 best known of 

 all compression 

 pumps. Here, 

 as in other 

 pumps of its 



type, the valves open inward rather than outward. When 

 the piston is lowered, compressed air is driven through 

 the rubber tubing, pushes open an inward-opening valve 

 in the tire, and thus enters the tire. When the piston is 



FIG. 143. Spraying trees by means of a compression pump. 



