SPRAY IRRIGATION. 35 



general estimating purposes. Small plants under 100 gallons per 

 minute, especially in the case of centrifugal pumps, are apt to re- 

 quire a greater horsepower than given, while the larger plants should 

 require somewhat less, due to the greater efficiencies. In every case. 

 however, the actual horsepower to use should be determined by the 

 manufacturers furnishing the pump. 



OUTLINE OF PROCEDURE FOR INSTALLING SPRAY IRRIGATION 



SYSTEMS. 



This outline is for the installation of an overhead spray plant, but 

 by substituting underground laterals and nozzle risers for nozzle 

 lines and posts it will apply to the stationary, circular nozzle type of 

 system. 



First, excavate a trench for the main feed pipe. Second, lay the 

 main feed pipe. Third, screw nozzle line risers into main feed pipe. 

 Fourth, install posts for nozzle lines. Fifth, assemble and tap nozzle 

 lines for nozzles. Sixth, install pumping equipment and house. 

 Seventh, pump water thorugh distribution system to flush out dirt. 

 Eighth, install nozzles in nozzle lines. 



INSTALLING THE MAIN FEED PIPE. 



The main feed pipes are expensive items and therefore should be 

 carefully designed and located. Usually the main pipes should be 

 made as short as possible and yet intersect the nozzle lines at inter- 

 vals so that their length will not exceed 600 feet ; otherwise the sizes 

 of the nozzle lines become large enough to offset any saving in cost 

 from the use of fewer mains. The field to be irrigated should be 

 divided into irrigation units, each unit having an area to correspond 

 to the capacity of the main and pumping plant. The main feed pipe 

 should be given sufficient size to carry the water for one unit at a time 

 without excessive friction loss. (See Table 2, p. 30.) When the most 

 distant unit is reached the main can be decreased in size gradually to 

 correspond to the amount of water taken out by each nozzle line, 

 unless the full capacity is needed for extension or another type of 

 irrigation in an adjoining field. All pipe over 2 inches in diameter 

 should be cut in the shop to fit the spacing of nozzle lines. Straight 

 mains of the larger sizes should be equipped with expansion joints 

 near the pumps to absorb the contraction and expansion of the pipe 

 due to changes of temperature. Easy bends should be used where it 

 is necessary to change the course of the main. All angles retard the 

 flow of water by friction. 



The main feed pipe should be laid underground below the depth of 

 cultivation and on a grade so it can be drained at convenient places, 

 especially in regions where freezing occurs. The main should be 



