TESTS OF DEAINAGE PUMPING PLANTS. 6 
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 large percentage of the energy used. These losses increase with 
the square of the velocity of the water at entrance and discharge, 
