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 pumping plant being 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 feet 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 be 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. 
