48 BULLETIN 304, U. S. DEPARTMENT OF AGRICULTURE. 
will be of use principally when the water in the river is high. Some 
arrangement should also be made for continually exhausting the air 
from the highest point in the discharge pipe; otherwise air will 
collect, the pipe will not run full, and the perfect siphon action will 
be interfered with. By connecting the top of the pipe with a large 
receiver under vacuum, equipped with a water-gauge glass, the con- 
dition of the pipe can always be easily observed and pumping of air 
will be only necessary at intervals. 
Others prefer to carry the discharge pipe through the levee on a 
level. This necessitates the installation of a gate valve in the pipe 
next to the pump. If the pipe is not over 2 feet in diameter, a flap 
valve might be used on its outer end; but such a valve is never en- 
tirely reliable and certain in its operation, and its use is not recom- 
mended. A gate valve must be of the slow-closing type, as it is 
dangerous to the plant to close such a valve quickly. If the pipe is 
carried through the levee, all the precautions that were mentioned in 
the section on gravity sluiceways should be used to prevent seepage 
along the pipe. The outlet end of the pipe must have adequate pro- 
tection against river wash and against undercutting by the water dis- 
charged by the pump. 
Attention has already been called to the plans of the Louisa- 
Des Moines and the Muscatine-Louisa pumping plants (figs. 2 and 3). 
Plate VI and figure 1 of Plate VIII are views of the Louisa-Des Moines 
pumping plant. Figure 1 of Plate VI is a view from outside the levee, 
showing the front of the building and the discharge bay. Figure 2 
of the same plate is a view of the engine room, giving a good idea of 
the size of the 50-inch centrifugal pumps, each of which is direct-con- 
nected with a tandem compound condensing engine of 250 horsepower. 
Figure 1 of Plate VI1T is a view of the rear of the building, showing the 
levee beyond and the enlarged ends of the suction pipes. 
Plate III, figure 2, and Plate VII are two views of the Lazwell plant 
of the Des Moines County Levee and Drainage District No. 1. Plate 
III, figure 2, is a view of the suction side of the plant, showing concrete 
suction basin, steel screen across the portion of the pit where the 
water goes into the pumps, and the discharge pipes curving out of the 
building, over the levee, and downward. Plate VII is a closer view of 
the discharge pipes as they turn down through the top of the levee 
to the river channel to the left. These views illustrate the easy curves 
used in such pipes. In Plate VII the small pipes connected to the top 
of the discharge pipes are used in priming the pumps and also in 
exhausting the air that collects in the top of the pipes while the 
pumps are operating. 
