2O4 



PUMPS AND THEIR VALUE TO MAN 



Figure 147 shows men at work on a bridge foundation. 



Workmen, tools, and sup- 

 plies are lowered in baskets 

 through a central tube BC 

 provided with an air chamber 

 Z, having air-tight gates at 

 A and A'. The gate A' is 

 opened and workmen enter 

 the air chamber. The gate 

 A' is then closed and the 

 gate A is opened slowly to 

 give the men time to get 

 accustomed to the high pres- 

 sure in B, and then the men 

 Excavated earth is removed in 



FIG. 146. The principle of work under 

 water. 



are lowered to the bottom, 

 a similar manner. Air 

 is supplied through a 

 tube DD. Such an 

 arrangement for work 

 under water is called a 

 caisson. It is held in 

 position by a mass of 

 concrete EE. 



In many cases men 

 work in diving suits 

 rather than in caissons ; 

 these suits are made of 

 rubber except for the 

 head piece, which is of 

 metal provided with 

 transparent eyepieces. 



FlG. 147. Showing how men can work under 

 water. 



Air is supplied through 



a flexible tube by a compression pump. The diver sometimes 



