Landscape Architect Articles

LCN September 2006 Inside Irrigation09-25-06 | News

Low-volume Micro Sprinklers

By Stuart Spaulding, C.L.I.A.

Low-volume ?EUR??,,????'??spinners?EUR??,,????'?? and adjustable mini impacts have diameters up to 40-feet, so larger areas and slopes can be irrigated with fewer heads, and the drawbacks of excess tubing and can be avoided.

Like many products in the current commercial drip irrigation market place, low-volume micro sprinklers were first developed for use in the agricultural industry where wholesale growers, nurseries, and tree farmers have utilized them with much success for many years. Recently their use in the landscape field has accelerated for two primary reasons: these efficient emission devices share both the water saving benefits of drip irrigation systems and the reliability, durability, and ease of maintenance of conventional sprinkler systems.

What is a Micro Sprinkler?

They have been given many names like jet-sprayers, micro sprinklers, micro jets, micro sprayers, spray jets, but they are all, simply put, low-volume spray heads. It may help to think of them as hybrids, a cross between low volume drip-emitters and conventional high volume spray heads. They are similar to spray nozzles because both devices broadcast small droplets of water in spray form over a defined coverage area, but like drip emitters, they operate at low pressures (15 to 30psi) and discharge water at rates measured in gallons per hour (GPH), rather than gallons per minute (GPM). Today micro sprinklers are available in several different styles and spray patterns, a wide range of flow rates (2 to 42 GPH), and like other drip components, they can be easily configured to connect to a variety of water supply sources including PVC pipe, risers, polyethylene tubing, distribution tubing, and both high and low pressure plastic pop-ups.

Micro sprinklers have a variety of assemblies?EUR??,,????'??+this is a semi-rigid riser anchored by a stake. They are designed for areas where drippers are not practical, such as larger areas of ground cover or small flower beds and for oddly-shaped areas. Like all low-volume irrigation systems, they require a pressure regulator and filter, and are available in a variety of flow rates and diameters.

Where They Should Be Used

This diversity of types and inlet connections make micro sprinklers a very versatile group of products. In certain landscape situations, they should be the first and only choice for installation. However, in some areas they should be entirely avoided. For example, they should never be selected to irrigate turf areas, even if it is a small lawn and even if they are adapted to high-pressure pop-up spray heads. Turf?EUR??,,????'???s water requirements are better suited to high flow conventional sprinkler systems that have a much higher precipitation rate than micro-sprinklers. They should also not be used in areas where there is a strong, consistent prevailing wind, as there is a greater possibility of water loss due evaporation, and a good chance the smaller sized droplets will be blown away from the target zone.

But for some parts of the landscape, low-volume micro sprays of one type or another are the ideal choice. They should definitely be considered for use in any planters or flowerbeds where there are many low-profile plants close together (i.e. annuals or small areas of groundcover) where it would not be practical to install a single drip emitter near each plant, and using soaker tubing could create maintenance problems.

For a vandal proof, easy to maintain commercial-grade system, use below-grade PVC pipe laterals and in the front of these beds, or adjacent to turf areas and/or walkways, install half-circle micro sprayers on low-pressure pop-ups. Select a model with at least a nine-inch and a MNPT inlet, which simplifies the connection to a swing assembly. In the back of shrub beds next to buildings or walls, use low-volume-sprayers with FNPT bases on conventional schedule 80 risers. Various patterns including circle, full circle and strip (bow-tie) patterns are also available, offering flexibility for oddly-shaped areas.

Micro sprinklers are also excellent emission devices to utilize on sloped terrain where traditional high flow sprinklers my cause the water to run off before it has been able to penetrate down deep enough into the root zone. In addition, the low precipitation rate of micro sprinklers makes them ideal to irrigate plants in dense clay or compacted soils. Shrubs and trees in sandy, fast draining soil may also do better with micro-sprays. This type of soil does not hold water well and when irrigated with conventional high flow sprinklers, a large amount of water can be lost due to deep percolation. Using low-volume sprayers in these soils will foster a more developed root system while using less water.

To efficiently irrigate plants and trees in containers of any size, perhaps there is no better method than to use micro sprays, misters or so-called ?EUR??,,????'??spitters.?EUR??,,????'?? It is not uncommon for containers to be filled with fast-draining potting soils, and if single-point source drippers are used, the water may tend to not spread far out laterally below the soil surface. Over time a vertical path may form below the dripper eventually boring a vertical tunnel down through the soil before quickly draining out the bottom. Several different types of container sprayers are now available which connect to the distribution tubing, and most include a stake that holds the sprayer four to eight inches above the top of the soil. The water is then more evenly distributed over the entire soil surface, creating a more uniform wetted area below for the roots to grow.

Under-tree irrigation with low-volume micro sprinklers is probably the most efficient method to irrigate fruit, citrus, nut and ornamental specimen trees. In this case, the best choice may be a longer range full circle micro sprinkler; these are typically mounted on a stake with a feeder or on a riser.

This slender, low-volume pop-up emerges from the base during the watering period and sits retracted the rest of the time. With slower watering rates, low-volume systems typically run for longer periods, which can help water percolate deeper into the soil.

Technical Aspects

Micro sprinklers, like other low-volume emission devices, are designed to operate at lower than normal pressure levels, so a pressure regulator is usually a must. Both pre-set and adjustable models are available; the direct-acting, low-range adjustable version is preferable. Up-stream of the regulator, a minimum of 155-mesh screen or disc filter should be installed to prevent debris from clogging the small inlet orifices. Even though you are dealing with low-flow, low-pressure heads, it is still essential to know the total system flow rate and verify that the valve and lateral line run lengths (and sizes) are appropriate to achieve the desired operating pressure. Low-volume systems have a low-precipitation rate, so typical system run times are much longer than high-pressure systems. A well-designed and installed low-volume micro sprinkler system can be just as durable and easy to maintain as a conventional sprinkler system, and if the system is monitored on a regular basis, both water savings and improved plant growth can be achieved.

Stuart Spaulding is an Irrigation Association Certified Landscape Irrigation Auditor with DIG Corporation in Vista, Calif.

This semi-rigid riser stands in this position during watering times?EUR??,,????'??+and all the time. Low-volume sprinklers are good choices for the annual flowers seen here, but are not recommended for lawns because of turf?EUR??,,????'???s more demanding water needs.