WATER OR LIQUID PUMPS 219 



Much of the water used for irrigating arid lands is ele- 

 vated a few feet for that purpose by centrifugal pumps. 

 When caissons of any kind are sunk in a river for con- 

 struction work, such as the building of abutments for 

 bridges or laying pipe lines across a river, the centrifugal 

 pump is used to remove the water. Swamp lands also 

 can easily be drained by this pump. Sand and other 



*&* \ 



LARGEST CENTRIFUGAL PUMP IN THE WORLD 

 It can deliver 100,000,000 gallons in 24 hours. (Pittsburgh City Water.) 



foreign matter do not injure the centrifugal pump as 

 they do the valves of the force or lift-pump. 



149. Wells and How to Get Water from Them. Wells 

 are sometimes made by digging a round hole about six 

 feet in diameter and deep enough to reach sufficient 

 water. The well is then walled with stone, leaving an 

 opening in the center about three feet in diameter. The 

 water usually comes from an underground stream called 

 a vein. Wells sixty or more feet deep are drilled by 

 machinery, and a large pipe casing is put down for the 

 wall. Wells which are not very deep are usually drilled, 



