Rotor Nozzles: Your Key to Correct Coverage

by Erik Skindrud, irrigation editor

LSMP publisher George Schmok (left) spent an afternoon with editor Erik Skindrud (right) and photographer Guy Nelson (who took this photo) to compare the performance and spray patterns of a range of rotor nozzles. In place here is a Hunter red size 8.

Plastic nozzles are interchangeable and offer openings that vary in shape and size. The Hunter nozzle type was introduced in the early 1980s. The three blue nozzles seen here are part of the manufacturer?EUR??,,????'???s recently-introduced line. The company claims blue replacement nozzles offer better coverage and easier installation. Both styles include slots (seen at top here) where set screws extend to adjust spray volume. Photo by Guy Nelson

Irrigation rotors use two pieces of hardware to set spray volume and application pattern. The first are small plastic nozzles. Invented in the early 1980s, these interchangeable wonders fit in rotors, which rise from the ground and send their stream over a predetermined arc.

Tightening the set screw with the blue size 8 in takes a far-throwing stream and shortens the throw to deliver a high volume of water to a compact area. Photo by Guy Nelson

A rotor?EUR??,,????'???s set screw has a big impact on the spray pattern. The screw on this blue size 8 is set back from the stream, maximizing flow and sending an even, jet-like stream of water over the residential turf. Photo by Erik Skindrud

Inserting the set screw extends the screw into the water stream, reducing volume and application radius. Such a setting might work in a small area that requires a higher application rate than adjacent ones. Photo by Erik Skindrud

The second part is a stainless steel screw that adjusts volume by extending over the nozzle?EUR??,,????'???s opening. The screw is critical for raising water pressure and limiting throw when bigger nozzle openings are used.

In a pinch, a nozzle with a bigger opening can be used on a rotor, but manufacturer charts should be used to select the correct rotor size.

A blue 2.5 was selected for this spot near the corner of a hilltop lawn in Orange County, Calif. Years of testing have created a spray pattern that gives even coverage from the rotor out to a distance of about 15 feet. Photo by Guy Nelson

The size 12 is seen here with the set screw extended to limit water flow and increase system pressure. The combination works like a thumb set over the end of an open hose. This configuration puts down a large amount of water close in to the rotation point. Photo by Guy Nelson

For our test, we used Hunter PGP rotors in a residential setting. The same principles apply, however, for bigger rotors and rotors from different manufacturers. Hunter?EUR??,,????'???s big I-90 rotors, which can send water almost 100 feet from the rotor, use similar plastic nozzles?EUR??,,????'??+but with much bigger flow rates.

Where a PGP may use from 1 to 10 gallons per minute (gpm), I-90s send out from 30 to 70 gpm.

The red size 12 nozzle had the largest opening of any nozzle tested. Set wide open, its circular opening sent this thick stream shooting like the stream from a hose or squirt gun. This might work with a higher-pressure system, but in this residential setting the size 12 caused the overall system pressure to fall and put down little water close in. Photo by Guy Nelson

Hunter rotors of various sizes include a rubber cap that protects the unit from mowers and other wear but complicates the adjustment process. Workers need to peel the cap back to access the set screw. Photo by Erik Skindrud

Gotcha! Hardware designers have spent considerable time calculating the optimal angle for water flow. Designed for residential use, these PGP rotors have a maximum radius of about 50 feet, making them suitable for some public areas too. Photo by Erik Skindrud

One basic rule remains the same with different nozzles and manufacturers.

The size of openings is the best way to control flow rates. If an area is dry, try a bigger nozzle. If an area turns into a mud puddle, a smaller nozzle may be in order.