












30 BULLETIN 495, U. S. DEPARTMENT 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 crops 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 
carried in different sizes of iron pipe. 
TABLE 2.—Amount of water different sizes of straight iron pipe will carry with- 
out excessive friction for spray irrigation. 

g jantit B 
Diameter of pipe. ae ee A Diameter of pipe. Ropaeet 
Gallons. Gallons. _ 
NAY GLUT enes Saat Se a a ua B SN NON US ean L GO. Dey PS imelest sie se eee I ee a pe a 75 to 125 
SALTO CHS) is Se iy ee ee) Seca ia aay ee: 3100 .47)) 34ameches 72254 yo3 aes Seo eee tp LO mesic 
TV Nea ee Efi ARES CN A a sy Goa SMA iO en Sali AMC Mes ss 14 es oceans Stee a 175 to 250 
if ESET TOS eee es cS et ga eg Ort omiGu| lh Guin Ces ae so ae sO a aie anaes '250.to 400. 
AEM CLES ees esl ne lL fear erg De AT VOI251 Ov Gln OS eee eae aie ee ee ee ~ 400 to 600 
DATICH ES May seta am ease a Roe MOE PAN KOC) Wh OWNS wal san ke uae ewe tue eaca so kcoe 600 to | 900 
24 inches. =!:.-’. SIAR a OUR AChE Met 45to7oi || SmChes! 82 aavhe oe Oe Sem vero eee 900 to 1,200 













