44 
ever to rise high enough to interfere with its operation. In a certain 
district on the Illinois River it became necessary to protect with a 
levee the pumping plant and its immediate grounds from the remain- 
der of the district. 
There are various arrangements of pipes for taking the water from 
the suction pit to the pumps, but there are a number of features in 
addition to those already mentioned which apply to most of the 
designs. The suction pipe should be perfectly air-tight and so strong 
as not to collapse under the greatest suction that will be put upon it. 
The entrance should be expanded so as to provide for a gradual con- 
traction of the stream of entering water. The curvature of the 
expanded end may be relatively abrupt, but should be smooth, so 
that the water shall not flow swiftly past any sharp edge or angle. 
In general, in contracting a stream there is no loss of head, even if 
the reduction in cross section be comparatively sudden, so long as 
the surfaces are smooth and without sharp angles. If the entrance 
end of the pipe is cut horizontally, the edge must be at least as low 
as the lowest level to which the water in the suction pit is to be 
reduced, and it would be better if it were a foot lower. Below this 
edge there should be a clear distance to the bottom of the pit equal 
to one or one and one-half times the diameter of the suction pipe. 
If the entrance of the suction pipe is expanded to such a degree that 
the velocity of the incoming water is not more than 2 feet per second, 
the water level can be drawn down to the end of the suction pipe 
without trouble from sucking air. Without such expansion, while the 
level of the water is still considerably above the end of the pipe, much 
air will be drawn into the pump, with a consequent loss of efficiency 
and danger of losing the priming. Neglect to provide ample water- 
way around the entrance to the suction pipe has been a source of 
much annoyance to pumping plants. If the end of the suction pipe 
is cut vertically the lower side of the pipe should be at or near the 
bottom of the pit. As the water can not be lowered to a level very 
near the top of the pipe without the latter sucking air, the entrance 
should be oblong in shape, with its greatest diameter horizontal. 
Small whirlpools will often form over such pipes and allow air to 
enter. This condition is likely to give the most trouble as the water 
nears the top of the pipe but before there is any appreciable velocity 
of the water in the suction pit toward the pipe. When the water is 
low enough in the pit to have an appreciable velocity toward the 
pipe the small whirlpools will be swept into the pipe before they are 
of sufficient size to admit air. Where these whirlpools cause the 
pumps to lose their priming a remedy has been to place a large raft 
of timbers in the pit in such a manner that whirls can not form 
directly over the end of the pipe. 
