LAND DRAINAGE BY MEANS OF PUMPS. 45 



One arrangement of pipe which is much used is to place the suction 

 pipe on a uniform slope from the pump to its lower end in the suction 

 pit. This slope should be flat enough to allow of the pipe being sup- 

 ported rigidly. The end of the pipe can be cut horizontally, making 

 an oblong opening, or the end of the pipe can be turned down in an 

 elbow of large radius; such an arrangement is used on the plant of 

 the Louisa-Des Moines Drainage District No. 4. (See fig. 2.) Again, 

 the pipe can be curved until it is horizontal and the end cut vertically. 

 Another arrangement is to bring the suction pit directly under the 

 pumps and have a short vertical pipe with an expanded horizontal end. 

 Especially if there are two or more pumps close together, the area of 

 the suction basin will be rather limited and a great many cross 

 currents will be set up. When such pumps are in operation this 

 turbulent condition of the water in the suction pit is very noticeable. 

 The efficiency of the centrifugal pump is seriously affected if the 

 water approaches the impeller in this condition. Riveted steel pipes 

 are universally used for the above-mentioned designs. The metal in 

 the pipes should be special low-carbon steel, so that it will better 

 resist corrosion. After erection the pipes should be heavily coated 

 with an asphalt paint. 



The use of reinforced concrete for suction pipes is just commencing. 

 Figure 3 shows the plan of the pumphig plant bemg constructed on 

 the Muscatine-Louisa Levee and Drainage District, which has con- 

 crete suction pipes built into the foundation. As the suction elbows 

 on the pumps, and the yoke which connects them with the concrete 

 pipe, are of cast iron, this construction of suction pipe should be 

 permanent, with very little if any depreciation. Figure 2 of Plate VIII 

 shows the forms for these concrete pipes. It will be noted from 

 figure 3 that these pipes do not extend into the suction pit; conse- 

 quently the water, as it approaches the entrance to the pipes, has no 

 chance to pass the edge on the outside of the pipe and cause eddies. 

 As the edges of the entrance are rounded the water that approaches 

 along the wall or bottom of the suction pit does not have to turn a 

 sharp angle. The entrance losses for these pipes should be less than 

 in any of the others described and the water should approach the 

 impeller of the pump in a condition favorable to the best pump 

 efficiency. 



The discharge pipe also should be strong enough to resist any suction 

 pressure that may be put upon it. It should be gradually expanded, 

 immediately after leaving the pump, so as to reduce the velocity to as 

 near 5 feel per second as seems practicable. It must be remembered, 

 however, that in expanding the cross section of a stream so as to re- 

 duce its velocity the changes must he very gradual; otherwise there 

 will be Loss of energy due. to the impact of the rapidly moving stream 

 against the more slowly moving mass of water. 



