Irrigation heads

Sprinklers vary as much as the landscape industry itself. Whether your project is a backyard landscape, municipal complex or golf course, you have a variety of sprinkler types and sizes from which to choose. The word sprinkler is not an all-inclusive term referring to irrigation. Many water-distribution devices are available that are not sprinklers, including the entire realm of drip emitters, bubblers and sub-surface irrigation.

Before embarking on the design and installation of the irrigation system, have a thorough understanding of how big your project is and what kind of irrigation it requires. A well-thought-out plan does not try to irrigate shrubs and trees with turf sprinklers. Various-size turf areas require different nozzles or, perhaps even, several different types of sprinklers. Most projects require two to five different sprinkler/nozzle combinations, which will water nearly everything. But first you must make the basic decision of what type of sprinkler to choose. In simple terms, we'll classify sprinklers into four basic categories: spray pop-ups, impact heads, medium gear-driven rotors and large turf rotors, describing smallest to largest.

Spray pop-ups Spray pop-ups are the common sprinkler type used in most residential- and small commercial-landscape projects. Spray pop-ups provide a continuous spray of water over the entire distribution pattern of the spray head. Many different sizes and nozzles are available in this category, most with a maximum throw of about 17 to 18 feet. These sprinklers are true to their name: A valve opens and several sprinklers pop up to deliver water in a stationary fashion. This type of actuation-where multiple sprinklers come on when a separate valve opens-also is referred to as "block-style" irrigation. Pop-up heads have no other moving parts besides the piece that pops up or down. Therefore, these sprinklers are the simplest and least-expensive type. Nozzle research and development for these sprinklers is always improving, and manufacturers now offer effective adjustable nozzles, square patterns, center strip, end strip, close-in watering and low-angle nozzles for windy locations. In tight or small, oddly shaped areas pop-ups are the best choice.

For turf areas, most people use the 3- and 4-inch pop-ups, the main difference being the 1 inch of additional body length. A 4-inch pop-up will clear the top of the turf and irrigate properly even when its surrounding grass needs mowing. Landscapers also use 4-inch pop-ups to combat the sinking of sprinklers over time. Actually, the sprinklers don't sink, but the level of turf rises after years of thatch build-up.

Some 2-inch and 2.5-inch pop-up spray heads are available, but you should only use these if the digging is extremely hard and you simply cannot get down to the minimum 7 or 8 inches of trench depth.

For shrubs, groundcovers and flower beds, longer pop-ups are available that rise 6 to 12 inches to clear the vegetation. You can mount these heads aboveground on a threaded riser and increase their maximum pop-up height to nearly 3 feet. If you are going to use this aboveground method, make sure that the riser is a solid Schedule-80 type (not a cut-off) and that the vegetation is thick enough to hide the body itself. Most manufacturers' nozzles are universal for both their turf and shrub pop-ups.

Impact heads Impact heads are sprinklers that have a spring-loaded swinging arm that breaks up the stream of water flowing from the head as the sprinkler turns, making the tell-tale impact-sprinkler sound as it rotates. Grounds managers have been using impact heads for many decades and still specify them today because of their simple, rugged and dependable design. The radius of throw for impact heads ranges from about 20 feet to more than 100 feet in some golf applications. Traditionally, these sprinklers were manufactured entirely in bronze and brass-and many 50- or 60-year-old sprinklers are still out in the field working today. The design of the bronze/brass impact head is basically the same as it was decades ago, although the outside cases, cap and a few internal parts are now made of plastic. One of the other advantages of this time-proven sprinkler design is that it can be used in dirty water applications without much trouble. With impact heads, the water simply blows right through the entire assembly with no small gears or intricate seals to get fouled by debris or build-up.

Adjustments to these sprinklers are also easy. Most impacts have a clip-type tripping lever on the body that instantly changes a part circle to a full circle and vice versa. Need to adjust the arc from a half circle to three-quarters? Spread the clips apart a little. Is the spray too strong, too long or not enough on the inside? Turn the diffuser screw near the nozzle. That is the nature of impact heads: simplicity. If the landscape situation requires an especially rugged, simple sprinkler, brass/bronze impacts are a good choice.

The main disadvantage of metal impact heads is their cost, which is roughly twice that of a comparable plastic gear-driven rotor. The large electric, brass, valve-in-head impacts for golf-course applications can run into the hundreds of dollars each. When considering the plastic impact head, you will find that they are much less expensive, but they are also much less rugged. Because gear-driven rotors generally water more efficiently and their cost is basically the same, most contractors today don't opt for the plastic impact head. While the ease of adjustment, radius, flows and precipitation rate of plastic vs. all-metal impact heads is usually the same, the all-important durability factor simply disappears when you use plastic.

Medium-sized gear-driven rotors Gear-driven rotors are now the most widely used sprinkler type for medium- to large-scale areas, replacing older impact heads in many situations. Their radius can vary from 15 to more than 70 feet with flows from less than 1 to nearly 30 gallons per minute. An important fact to consider for landscape applications is their precipitation rate: medium-sized gear-driven rotors apply water at a much slower rate than spray pop-ups. If the site has a dense, clay-like soil, you can use gear-driven rotors instead of spray pop-ups to prevent puddles and runoff. The gear-driven rotors are generally larger and more expensive than sprays, and this means that you will be using 1.5-, 1- and 0.75-inch pipe and fittings instead of 0.75- and 0.5-inch, which is common for pop-ups. You'll also dig deeper trenches to accommodate the longer sprinkler bodies and larger pipe. When confronted with a job that could go either way, do a simple design on paper both ways and find out what the rough costs will be.

Two of the best reasons to use medium-size gear-driven rotors are variety and versatility. With small- and medium-size gear drives, several manufacturers provide a nozzle tree (with every rotor you buy) that has a dozen (or more) individual nozzles that slip into place easily. This provides a choice of many different precipitation rates and distances for each sprinkler. Some medium-size heads are available with a "multi-nozzle" that allows for easy adjustment of radius, flow and vertical arc by turning screws on top of the sprinkler instead of switching nozzles. Whichever type you choose, this group of medium-size sprinklers can effectively water everything from large residential projects to golf-course tee boxes.

The big guns: Large turf rotors Large projects such as public parks or golf courses require the use of either brass impact heads or large gear-driven rotors. Both types can throw anywhere from 50 to more than 100 feet. Flows range from 15 to more than 80 gallons per minute per head. The operating pressure for this category is between 50 and 100 psi, but most irrigation contractors base designs on 65 to 85 psi as a medium value. Sprinkler heads of this size generally rely on electric valve-in-head (EVIH) actuation. An EVIH sprinkler has its own solenoid valve connected to a control wire and common ground that goes back to the controller.

Hydraulically actuated heads offer an alternative to EVIH sprinklers. In this case, a small control tube filled with water actuates the heads. The hydraulic control tube serves as the signal wires that connect with an electric controller equipped with a hydraulic converter. Hydraulic systems develop problems associated with the tubing and are much less common than EVIH, but they do have one distinct advantage: They are much less prone to lightning damage than the wire-intensive EVIH system.

When you hear the term "check-o-matic" used with large turf rotors, it means it uses a "block-style" head, which-like its smaller spray pop-up cousins-actuates when an electric valve opens. Because the flows are so great with the larger heads, it is impractical to use check-o-matic heads for large irrigation systems because the size of the electric valves, pipe and fittings becomes large and cost prohibitive. Cost is also the reason why irrigation designers don't use brass impact heads much for large irrigation systems, where the overall price of the system often exceeds $1 million. The common sprinkler choice for a large modern irrigation system is usually EVIH gear-driven rotors, which are versatile, cost-effective and give excellent watering performance. The major manufacturers have concentrated primarily on this type of sprinkler for the last decade, investing most of their research and development on ways to improve and perfect their performance. Throughout a variety of radius and flows, you can expect uniform distribution, easy access/serviceability and a "good" rating for durability. Competition is intense in the large-turf-rotor market, and all of the major manufacturers seem to be working on advancements on a continual basis.

Tips for choosing sprinklers When starting the irrigation-planning process, a good first step is to visit your local distributors. From them, you can obtain the latest product catalogs of the various manufacturers. These catalogs offer you detailed specifications on all of the sprinkler types discussed here, as well as information on valves, bubblers, drip emitters, controllers and accessories. Most catalogs have a technical section that provides design data on spacing, calculating flows, friction losses, measurement-conversion tables and lots of other handy design tools.

Choose sprinkler heads based on medium values for pressure, flow and radius. Try not to pick sprinkler and nozzle combinations that are at the lowest or highest extreme values on the manufacturers' tables. Remember that the manufacturers base their information largely on ideal conditions that often do not take into account wind, soil, excessive heat or other natural conditions specific to your site. When in doubt, turn to local irrigation professionals with no manufacturer affiliations to analyze the various types of systems and ensure that you engineer your irrigation system correctly and at the right cost.

Gary S. Kaye, CID, is vice president of irrigation with Golf Engineering Associates Inc., Irrigation & Drainage Consultants (Phoenix, Ariz.).

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