TESTS OF DRAINAGE PUMPING PLANTS. 3 



CENTRIFUGAL PUMPS. 



The centrifugal pump in some of its various forms has proved to 

 be a favorite for drainage work, where large volumes of water must 

 be elevated only a few feet. There are many reasons for the popu- 

 larity of the centrifugal pump, among which might be mentioned 

 first cost, reliability of operation, simplicity of construction, and its 

 ability, when forced, to develop a capacity much greater than the 

 rated capacity. It is efficient if properly designed for the condi- 

 tions under which it is operated. 



A cheap but fairly efficient form of centrifugal pump that was much 

 used a few years ago is the vertical-shaft, wooden-box pump. Many 

 are still in use, but of late they have given way to more substantial 

 pumps made entirely of metal. The older pumps usually were 

 driven by belt or rope drive, while the modern plants often have 

 pumps and engines direct connected. 



HORIZONTAL CENTRIFUGAL PUMPS. 



Centrifugal drainage pumps with horizontal shafts ususally have 

 double suction pipes. The suction and discharge pipes with the 

 pump form a siphon, with the pump at the top at a convenient 

 height for examination and for repair. Variations in level of the 

 suction and discharge sides do not affect the pump, and the lift is 

 always equal to the actual difference of level while the head the 

 pump must develop is the lift plus the various friction losses in the 

 pump and piping. These pumps are made by many firms and differ 

 considerably in minor details. Their popularity is shown by the 

 fact that a large majority of all the drainage plants installed during 

 the last 10 years are of this type. 



SCREW PUMPS. 



Screw pumps range from 3 to 12 feet in diameter, the largest hav- 

 ing a capacity of 700 cubic feet per second. The lift ranges up to 

 10 feet or more. 



A combination centrifugal screw pump has been developed that is 

 especially suited to electric motor drive or internal-combustion 

 engines. The blades of this type of pump are so designed that the 

 load is practically constant from a minimum to a maximum lift 

 when running at a constant speed. 



SUCTION AND DISCHARGE PIPES. 



In drainage installations, where the lift is usually between 4 and 

 10 feet, the Losses at the entrance of suction pipes and the kinetic 

 energy thrown away at the end of the discharge pipe together make 

 up a lar<_'e perecnl.a^e, of the energy used. These losses increase with 

 the square of the velocity of the water at entrance and discharge, 



