30 



lU'I.I.KTIX 4II."», V. S. DRIWRTMKXT OF AGRICULTURE. 



The distribution system should be laid out to use the minimum 



amount of large pipe for both distributaries and main feed pipe. The 

 Laterals or nozzle lines should run in a direction which will give the 

 least amount of obstruction to the cultivation of the field in the most 

 efficient manner. The field should be laid off in irrigation blocks or 

 units, a unit representing the area to be irrigated at one time. The 

 unit should be of a desirable length for the kind of orops to be 

 irrigated. Where possible, it is advisable to divide the field by the 

 irrigation system into blocks which will make the estimating of acre- 

 ages easy when arriving at the amount of seed and fertilizer re- 

 quired or determining yields. This is done usually by having a con- 

 venient fraction of an acre under each spray line or by having the 

 crop rows a length which will make each rod or yard in width a 

 known fraction of an acre. 



To keep the cost of a spray distribution system as low as pos- 

 sible, yet obtain a good uniform pressure and distribution of water, 

 the sizes of pipes must be proportioned properly. Each lateral or 

 nozzle line must be proportioned in size according to the number 

 and capacity of the nozzles used. The main feed pipe must be pro- 

 portioned to carry the total amount of water to the most distant 

 irrigation unit and then be reduced in size as the water is de- 

 creased by each nozzle line within the irrigation unit. ■ The water 

 required to run an irrigation unit determines the capacity of the 

 pumping equipment. 



There is a resistance to water flowing in pipe which has been 

 determined by experiments and is called " friction head." This 

 friction is in proportion to the roughness of the inside surface of 

 the pipe and varies with the velocity of the water and the length 

 and diameter of the pipe line. The greater the friction of the 

 water in the pipe the more power is required to pump the water; 

 therefore, there is a logical size of pipe to use for each quantity of 

 water and set of conditions to keep this frictional factor within rea- 

 sonable limits. Table 2 shows the quantities of water which should be 

 cari'ied in different sizes of iron pipe. 



Table 2. 



Amount of water iliffcrcnt sizes of straight iron pipe toill carry with- 

 out excessi re friction for spray irrigation. 



Diameter of pipe. 



1 inch . . . 



2 inch. . . 



1 inch . . . 

 1 ; inches 

 1} inches 



2 inches . 

 24 inches 



Quantity 

 per minute. 



Gallon*. 



1 to 2 



3 to 4 



5 to 8 



9 to 10 



17 to 25 



25 to 45 



45 to 75 



Diameter of pipe. 



3 inches . 



V. inches 



4 inches. 



5 inches. 

 f> inches . 



7 inches . 



8 inches . 



Quantity 

 per minute. 



Gallons. 



75 to 125 

 125 to 176 

 175 to 250 

 250 to 400 

 400 to 600 

 fiOO to 908 

 900 to 1,200 



