HYDRAULICS. 183 



that the air is sometimes lighter than 33 feet of 

 water ; and whenever that was the case, the pump 

 would fail in its performance. 



The sucking-pump is an engine both pneumatic 

 and hydraulic. It consists of a pipe open at both 

 ends (Plate 9. %. 1.), in which is a moveable cy- 

 linder or piston, as big as the bore of the pipe in 

 that part wherein it works ; and contrived by 

 leathers or other means to fit the bore exactly, so 

 as not to allow any air to get between it and the 

 sides of the pipe where it acts. In the piston of 

 the common sucking-pump, there is a valve open- 

 ing upwards, like a trap-door, to allow the air and 

 water readily to ascend through it, but to prevent 

 either of them from descending. This piston is 

 then called the bucket. It is moved up and down 

 in the pipe by a rod fastened to a handle or lever, 

 or such parts of machinery as are intended to work 

 it. The pipe A B usually consists of two parts ; 

 of which the first, A D, is called the barrel, or the 

 working barrel, and is wider, to contain the piston ; 

 and the other, D B, is called the suction-pipe, 

 which is of a smaller diameter. 



At the joining of the working-barrel with the 

 suction-pipe, there is a fixed valve also opening 

 upwards, D. Lastly, the lower end of the suction- 

 pipe is immersed in water, which is admitted into 

 it through small holes, to prevent the entrance of 

 dirt; and at the top of the working-barrel is a 

 wide head, A, and a pipe, E, for the delivery of 

 the water which is raised. 



Having thus mentioned the principal parts of 

 the sucking-pump, we shall next describe its mode 

 of operation. 



Let the piston C be close down upon the fixed 

 valve D ; both the valves remaining shut by their 



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