Hunter Industries - The Irrigation Innovators

Matched Precipitation

PRODUCT: Hunter Nozzles
SUBJECT: Matched Precipitation

Expressed in inches per hour, precipitation rate is the rate at which sprinklers apply water. The term "matched precipitation" means that all of the sprinklers on a particular zone are placing about the same amount of water on a given area.

To ensure proper application of water, different types of sprinklers should not be installed on the same zone. Large area rotors and small area sprays may use the same GPM, but because the size of the areas they cover are not the same, the inches per hour of water being applied is very different.

When designing an irrigation system, it is very important to be sure that the precipitation will be even over each zone of coverage. Matched precipitation in a landscaped area is best achieved by zoning like arcs together (e.g., quarter heads with only quarter heads, half with only half, full with only full) and then matching the precipitation rate by adjusting the controller run times.

Matched precipitation can be accomplished by selecting the appropriate nozzles. When zoning together sprinklers that will have different arcs, the two criteria to consider are a sprinkler's flow and area of coverage. Although you cannot achieve exact matched precipitation when mixing arcs, you can get very close by choosing nozzles according to the GPM, and then spacing all the heads on a system the same distance apart (i.e., reducing the radius on the half and full heads to the approximate radius of the quarter).

The illustration shown at the right depicts three different sprinkler heads with matched precipitation. In each case, one gallon per minute is applied to each quarter circle, and each quarter circle is the same size, therefore, precipitation is matched.

So, the rule of thumb to remember is: for heads with the same radius of throw, as the arc is increased, the flow rate of the nozzle should increase proportionally.

Referring to the performance data chart below, here are two examples of nozzles that could be selected to achieve matched precipitation at 50 PSI:

Square Spacing 90° GPM 90° Use Nozzle # 180° GPM 180° Use Nozzle # 360° GPM 360° Use Nozzle #
30' 1.0 1.2 2.0 2.0 4.0 4.2
35' 1.5 1.6 3.0 2.7 6.0 5.5

I-10/I-20 Ultra Standard
Nozzle Performance Data

Pressure Radius Flow Precip in/hr
Nozzle PSI ft. GPM
1.0 30
40
50
60
 30'
31'
31'
32'
 0.9
1.0
1.2
1.3
 0.19
0.20
0.24
0.24
 0.22
0.23
0.28
0.28
1.5 30
40
50
60
 32'
33'
34'
34'
 1.2
1.4
1.6
1.8
 0.23
0.25
0.27
0.30
 0.26
0.29
0.31
0.35
2.0 30
40
50
60
 32'
34'
36'
36'
 1.6
1.8
2.0
2.2
 0.30
0.30
0.30
0.33
 0.35
0.35
0.34
0.38
3.0 30
40
50
60
 34'
36'
38'
38'
 2.0
2.4
2.7
2.9
 0.33
0.36
0.36
0.39
 0.38
0.41
0.42
0.45
3.5 30
40
50
60
 34'
38'
40'
40'
 2.6
3.0
3.4
3.7
 0.43
0.40
0.41
0.45
 0.52
0.46
0.47
0.51
4.0 30
40
50
60
 37'
39'
41'
42'
 3.2
3.7
4.2
4.6
 0.45
0.47
0.48
0.50
 0.52
0.54
0.56
0.58
6.0 30
40
50
60
 35'
40'
43'
44'
 4.2
4.9
5.5
6.0
 0.66
0.59
0.57
0.60
 0.76
0.68
0.66
0.69
8.0 40
50
60
70
 41'
44'
45'
47'
 6.0
6.8
7.6
8.2
 0.69
0.68
0.72
0.71
 0.79
0.78
0.83
0.83