868 



THE COMMON PUMP. 



Sen. The principle of the diving bell is applied in div- 

 ing dresses. The diver is clothed in a water-tight dress 

 fitted with a helmet, and is supplied with air by means of a 

 pump. There is an escape valve by which the circulation 

 of fresh air is maintained. The diver may be weighted up 

 to 200 Ibs., but on closing the escape valve, he can rise at 

 once to the surface in virtue of the buoyancy due to the 

 increased displacement of water by the enclosed air. 



143. The Common Pump (Suction Pump). Any 



machine* used for raising water from one level to a higher, 

 in which the agency of atmospheric pressure is employed, is 

 called a pump. Pumps are either suction, forcing, or lift- 

 ing pumps. 



The pump most commonly in use is a 

 suction pump, of which Fig. 73 is a ver- 

 tical section. AB and BC are two cylin- 

 ders connected together having a common 

 axis; the former is called the barrel of the 

 pump and the latter the suction pipe; M 

 is a piston accurately fitting the barrel, 

 and movable up and down through the 

 space AB by means of a vertical rod EV, 

 connected with a handle or lever EF, 

 which turns on a fulcrum ; in the piston 

 is a valve V which opens upwards, and at 

 the top of the suction pipe BO is another 

 valve V, which likewise opens upwards. 

 S is a spout a little above A, and C is 

 the surface of the water in which the lower part of the 

 pump is immersed. 



To explain the action of the suction pump, suppose the 

 piston M to be at B, the pump filled with ordinary atmos- 



* Machines for raising water have been known from very early ages, and the 

 invention of the common pump is generally ascribed to Ctesibius, teacher of the 

 celebrated Hero of Alexandria ; but the true theory of its action was not under- 

 stood till the time of Galileo and Torricelli. (See Dcschanel's Nat. Phil., p. 215.) 



Fig. 73 



