METHODS OF RAISING WATER 121 



at the bottom which permits the entrance of water when the 

 bucket is lowered, but which shuts and prevents its escape on 

 being lifted. Its use is confined almost entirely to wood-curbed, 

 bored and punched wells. The diameter is just enough smaller 

 than the inside diameter of the curbing to permit it to be raised 

 and lowered without undue friction. There is nothing inherently 

 objectionable in the bucket itself, though the open top and. the 

 wooden curb with which it is associated are to be condemned. 



Chain pumps. - - The so-called chain pump consists of an end- 

 less chain passing over a sprocket wheel at the top, and running 

 through a wooden tube. The chain is equipped at short intervals 

 with rubber or metal disks. On turning the handle attached to 

 the sprocket, it is made to revolve, the water being lifted by 

 the tightly fitting disks as they pass upward through the tube. 

 Much has been claimed of this type of pump because of the 

 aeration of the water produced by the descending disks, but it is 

 very doubtful if the slight aeration brought about is of any 

 material importance. The pumps of this type are commonly en- 

 closed, so that their use is attended by relatively little risk of 

 pollution, provided the well is otherwise properly protected. 

 They are best adapted to shallow wells and cisterns, since the 

 weight of the water in the tube in the deeper wells is consider- 

 able. Their cost with w r ooden curbs varies from $2.50 to #3.50, 

 according to the depth of the well; with steel curbs the costs 

 average 50 per cent more. 



Suction Pumps. - - There are several forms of suction pumps, 

 the most common of which is the familiar "pitcher pump," so 

 named from the resemblance to a pitcher suggested by its shape 

 (Figs. 51, 52). Theoretically it will lift a column of water equal in 

 weight to the atmospheric pressure, or about 32 feet, but in prac- 

 tice it is difficult to lift water by a pump of this type if it lies 

 more than 25 feet below the cylinder. Its effective range can be in- 

 creased, however, by sinking the pump cylinder below the surface 

 of the ground. When the depth of the water is only 30 or 35 

 feet from the surface the cylinder is often placed at the bottom of 



