1.3 Overhead Sprinklers

Sprinklers have water distribution profiles that are important in establishing their performance in an irrigation system. A design consideration is how to place the sprinklers on a spacing that will achieve a uniform (as possible) water distribution.

A single sprinkler head typically will not provide a uniform distribution. The sprinkler discharge may be about the same at each point on the radius of throw, but the area on which the water lands increases as one moves farther from the nozzle. One can imagine the rings on a target. There is less depth of water on the area farthest from the sprinkler.

Sprinklers are typically placed in a square or rectangular pattern so that they overlap each other by 40% to 60%. Head-to-head coverage on a 50% spacing means that the discharge from each sprinkler will just reach the other sprinkler. The individual sprinkler patterns overlap each other.

Figures 1.3a shows a typical metal agricultural full circle impact sprinkler. These are spaced as described above to give coverage on large areas. The overlap determines the application pattern and uniformity. Figure 1.3b shows a typical plastic impact sprinkler with guide on it so that the degree of rotation can be set to target the crop. Rotation of less than 360 degrees causes more frequent application on less than a full circle. This must be taken into account and will be discussed under matched precipitation nozzles.


Figure 1.3a Agricultural metal impact sprinkler (Rain Bird 20B-ADJ) with single nozzle.

(Photo courtesy of Rain Bird Corporation)

Figure 1.3b Agricultural plastic impact sprinkler (Rain Bird 2045-PJ Maxi Bird) with single nozzle.The degrees of rotation are adjustable at the base so it can be part circle in coverage.

(Photo courtesy of Rain Bird Corporation)