Drainage by Steam Power. 



53 



are efficient machines and the best where there is a large 

 amount of debris, and that they have the further advantage 

 that they can be easily repaired by ordinary workmen. The 

 motors for moving them may be of common types, but cannot 

 be used to the best advantage, owing to the difficulty of 

 adapting them to the slow velocity required for the wheel. 

 That they further labour under the disadvantage, as compared 

 to centrifugals, of requiring stronger foundations ; with a 

 high lift the wheel must have a large diameter, the sill must 

 have a low level, and this necessitates massive and deep 

 masonry. That when there is a liability of a permanent lower- 

 ing of the low-water level, wheels would require costly altera- 

 tion, whereas with centrifugals additional lengths can always 

 be added to the piping, and the only difference is that the 

 consumption of steam will be greater. That in regard to the 

 separation between internal and external water, the easiest 

 and safest arrangement is that of pumps which discharge the 

 water through pipes carried over the banks or inserted in 

 masonry walls of sufficient thickness, thus avoiding the sluices 

 which are required for wheels or screws. That the system of 

 direct action between engine and pump is one that is most 

 economical in fuel ; and that the centrifugal pump lends itself 

 most readily for action with this kind of motor. 



As regards expense, Signor Cuppari gives a table showing 

 the cost of the pumping stations in Holland during the pre- 

 vious ten years, from which it appears that the average cost 

 per horse-power of water lifted is as follows : — 



Scoop wheels .. 

 Screw pumps .. 

 Centrifugal pumps ,. 

 Piston pumps .. 



Building. 



46*14 

 34-20 



Machinery* 



£ 



46*28 



36*80 



Total. 



£ 

 92-42 



94 

 72 



Statistics given of the drainage stations erected in the seven 

 years 1875-81 show that centrifugal pumps are steadily making 



