60 MISC. PUBLICATION 4 3 4, U. S. DEPARTMENT OF AGRICULTURE 



The horizontal centrifugal pump is also well adapted to pumping 

 from open water in lakes or streams. In such cases the suction pipe 

 is fitted with a strainer foot valve at the intake, to screen out trash 

 and facilitate priming. Where the water-bearing material is of a 

 fine texture, it has been found advisable to have the well points or 

 screens gravel-packed to allow a more rapid inflow of water and to 

 reduce possibility of partially clogging up the well screens or points 

 by fine particles of sand. 



By gravel packing is meant surrounding the well screen or per- 

 forated casing with gravel. A 16- to 24-inch blank casing is sunk to 

 15 or 25 feet (or to the depth of the well) below the surface of the water; 



Figure 12. — A centrifugal pump drawing water from three 3-inch sand points. 

 Capacity is 200 gallons per minute at 40 pounds pressure. An economical unit 

 in pumping from open bodies of water or from shallow water-table areas under- 

 lain by sand or gravel. The effective lift of such pumps is generally 10 to 

 20 feet. 



all the sand or silty material inside the casing is cleaned out with a 

 sand bucket as the casing is sunk; an intake pipe with a smaller- 

 sized perforated casing or a well screen attached is inserted in the 

 center of the casing; and graded gravel from one-fourth to one inch 

 in diameter is packed between the well screen and the casing. The 

 blank casing should be 12 to 20 inches larger in diameter than the 

 well screen or perforated casing. As packing proceeds, the outer 

 casing is gradually withdrawn. The gravel filling is kept a foot or 

 two higher than the bottom of the blank casing. The outer casing is 

 completely removed after the gravel packing has been completed. 



A cheaper method, used extensively in Nebraska, consists of digging 

 a hole to the water table, setting the casing in the hole, and sinking it 

 by weighting. A sand bucket is used to remove the material inside 

 the casing below the water table. Gravel is poured between the 

 casing and the sides of the hole in the upper portion of the well, and 

 as the casing sinks, the gravel works downward along the side of the 

 casing and leaves a gravel pack around the perforated lower part. 



