44 BULLETIN 304, U. S. DEPARTMENT OF AGRICULTURE. 



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 siifhcient 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. 



