Installing Water-Efficient Rotor Zones

By Robert Burrous, Rain Bird Corporation

Rotors set to standard throw distances like 25, 30 and 35 feet require different flow rates to put down water at similar volumes. Add arc patterns and Matched Precipitation Rates (MPRs) and you can see that irrigation requires basic-to-moderate math skills.

As water efficiency becomes more important, so does the ability to quickly and easily install more efficient sprinkler systems. This is especially true with the installation of rotor zones. Fortunately for contractors, the new rotor nozzle options that are available make it easy for installers to achieve greater water efficiency. Using these new nozzles is likely no more work than what contractors already do and it might just set them apart from other contractors while saving homeowners money on their water bills.

Flow Rates and Arc Patterns

Many installers today already try to match the flow rate of a nozzle with the size of the area (arc pattern) to be covered. The goal is to provide the same precipitation rate over the entire zone. For example, a 1.5 Gallon Per Minute (GPM) nozzle on a quarter-circle pattern and a 3.0 GPM nozzle on a half-circle pattern are common choices. In this example however, the maximum distance of throw increases with flow-rate, resulting in the larger nozzle throwing five feet further (see ???Standard Nozzle Options???? table). When the radius reduction screw is used on the 3.0 GPM nozzle to decrease the distance of throw from 40 feet to 35 feet to match the distance of throw for the 1.5 GPM nozzle, the distribution pattern of the stream changes and this introduces inefficiency. Furthermore, if the size or shape of a residential lot demands closer rotor spacing, then additional radius reduction will have an even worse effect on water efficiency.

A set of nozzles that takes into account the distance of throw and flow rates optimized for the most common arc-patterns offers an attractive solution. This eliminates the need to reduce the radius just to reach a similar distance of throw between nozzle types and provides a Matched Precipitation Rate (MPR) solution for greater efficiency. Additionally, these nozzle sets are optimized for a wide range of rotor spacings: 25 feet, 30 feet, and 35 feet (see tables below).

An irrigation rotor (center) and a collection of nozzle trees, which are color-coded for 25 (red), 30 (green) and 35 (beige)-foot throw distances. A 30-foot nozzle can be seen installed near the top of this rotor.

A Guide to Quick Installation

To achieve better irrigation efficiency with MPR nozzles, follow these installation steps:

This three step process is fast and simple and results in a more water efficient system, that provides water savings for homeowners. This is possible because the nozzles have been designed for the most common real world applications. This allows the installer to match the nozzle to the application and avoids the need for calculations in the field.

A color-coded nozzle tree includes 90, 120, 180 and 360-degree nozzles. This is a Rain Bird product; other brands use color-coding too to speed in-field maintenance.

Irrigation Insights

1/3: Amount of water saved by using Rotors instead of spray heads. Rotors and spray heads should not be installed on the same zone.

Source: Colorado State University Extension Service