Irrigation headaches

Of the problems that can occur in an irrigation system, those associated with sprinkler heads are the most noticeable to clients and the public. These problems are visually noticeable and manifest themselves in non-uniform green areas of the turf (donut patterns and dry spots), ponding water and misting and drifting that cause wet sidewalks and streets.

If these conditions exist on a landscape that you manage, the first thing you should do is evaluate your sprinkler heads. To do this, you need to figure out what type of sprinkler head your irrigation system uses. Most modern sprinkler systems include two types of heads: spray and rotary. The type of head used by your irrigation system depends on the dimensions of the area it is irrigating, water pressure available for operation and a variety of other factors.

Spray heads

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Spray heads are what people commonly think of when they think of irrigation heads. These types of heads are uniformly spaced within an area and are used to irrigate lawns, shrubs and groundcover beds. The main difference between spray heads and other types of heads is their spacing. Although the spacing of spray heads can vary depending upon the specific nozzle the designer selected to use in the head, they are usually not spaced more than 15 feet apart. The majority of spray heads are “pop-ups,” which are designed with the nozzle on the tip of a riser that can pop up 2 to 12 inches out of its housing during operation. When irrigation is complete, water pressure drops and the riser retracts to the soil line so that it is out of sight and does not interfere with mowing or normal use of the lawn. The 6- and 12-inch pop-ups are called “high pop-ups” and are used in shrub and groundcover beds as well as flowerbeds. You can also install spray heads in planting beds on fixed risers that do not pop up. You should base riser height on the projected height of the shrubs and plants to provide uniform application of water.

Rotary heads

Rotary heads are larger than spray heads and are usually used to irrigate larger areas including commercial property, parks, large lawns and sports fields. They can project water a distance of 20 to 50 feet or more. Like spray heads, rotary heads are available as pop-ups or fixed versions on risers. There are two types of rotary sprinklers: gear-driven and impact. The difference between them lies in the mechanism that causes them to rotate.

  • Impact rotors. Impact heads were originally developed for watering agricultural crops in the 1930s and have been used in landscape irrigation since the 1940s. A spring-loaded arm causes impact heads to rotate. As water flows from the outlet in the head, it triggers the arm to pivot away from the water stream until it hits a stopper attached to the head assembly. The spring causes tension in the arm, which then returns the arm to its original position, and the process starts again. The impact against the stopper causes the entire assembly, including the stream of water, to rotate slowly. The slow, continuous rotation of the assembly will slowly irrigate its designated area.

    You can set up impact heads to irrigate in a full or part circle, depending on your needs. Just switch the lip or spring to reverse the rotation and cause the assembly to move backwards before it completes a full circle of revolution. This back-and-forth rotation allows you to get better use of a sprinkler in areas such as corners and along curbs and walks.

    The coverage provided by impact-type rotors can be highly uniform. However, they also can be high maintenance. When you activate an impact sprinkler, it rises out of the head casing, exposing the open housing of the head. This open cavity is prone to catching mud, grass clippings and other debris. Therefore, it requires frequent maintenance to keep the housing and mechanisms clean, which is especially important in preventing damage to the assembly. Impact rotors also have many exposed, moving parts. The springs can be especially troublesome because clippings and twigs can become entangled in them. They are also easily bent, can fall off the assembly and are prone to rust. Another negative characteristic is their clatter during operation, which can be annoying to some people.

  • Gear-driven rotors: Gear-driven rotary sprinklers are used in most modern systems and are the most popular type of rotary head. Water turns a small turbine in the base of the unit, which drives a series of gears that cause the head to rotate. Unlike impact sprinklers, the drive mechanism is sealed from dirt and debris, quiet during operation and easy to adjust. However, because of their long throw of water, it's easy for inexperienced designers to misuse and misapply them. Although gear rotors cost more than spray heads, their wider spacing capability means that you'll need fewer heads to cover a given area. Consequently, landscapers frequently use them in spaces too small for efficient rotor operation in an attempt to reduce the number of heads, connections, trenching and labor costs. If you force a rotary sprinkler to cover an area too small for its intended design, you will get increased misting and inefficient coverage, especially if you have to adjust it below the manufacturer's specification.

    Sprinkler nozzles

    Nozzles are the devices that disperse water onto the landscape as it passes through the head assembly. They control the amount of water being applied and the distance of throw. The amount of water distributed over an area can vary greatly depending on the nozzle selected.

    Assessing spray-head and rotor performance

    Problems with spray heads and rotors can be caused by major system flaws resulting from poor overall design including improper zone layout, lack of proper overlap and disregard for available pressure and flow. It is more than likely, however, that the problems are non-system related. Fortunately, non-system-related problems are easier and less expensive to correct.

    Non-system related problems that affect head performance include:

    • Heads that are too close to walks and pavements

    • Displaced heads that are sunken, offset or unstable in the soil

    • Improper installation and repairs (including keeping dirt and debris out of the system)

    • Normal head wear and tear

    • Incorrect arc adjustment

    • Obstructions such as turf and branches

    • Water quality including secondary water, well water and surface water from a pond or stream

    • Broken heads as a result of lawn mowing, edging or snowplowing, or from the roots of a growing and maturing tree or shrub.

  • Donut patterns and other dry spots could be the result of a number of problems associated with heads, including non-compatible heads in the same zone, lack of proper overlap, basic nozzle or arc adjustment and obstructions caused by turf, plants or structures.

  • Misting and drift is caused by high pressure at the sprinkler nozzle that results in the breakup of spray into a fine, atomized mist that sometimes looks like fog. The presence of misting is an indication that you should make adjustments to increase the size of droplets by either regulating pressure or changing the type of head or nozzle.

  • Spitting, lack of discharge and general poor head performance is probably an indication of clogged nozzles or partially closed valves resulting from low pressure. Debris in the nozzle can misdirect the spray and result in partial spray patterns or even a complete plugging. You should carefully remove debris in nozzles. Digging or gouging could permanently change the spray pattern. Clean nozzles with air, water or a soft-bristled brush, such as a pipe cleaner. Using a wire or a screwdriver can permanently scratch the nozzle and misshape the orifices.

  • Rotation flaws are likely an indication of:

    • Debris in the sprinkler head

    • Pressure that is too low or high

    • Flow that is too low

    • A damaged head

    • Normal wear and tear

    • Oversized nozzles

    • Improperly adjusted flow-control valve

    • Vegetation obstructions

    • A bypass in need of adjustment

    • Foreign lubricants.

  • Excessively rapid rotation of rotary heads is likely an indication that the pressure is too high and you need to regulate it.

  • Damaged heads could be the result of vandalism, poor head location, pressure problems, normal wear and tear or poor maintenance procedures.

  • Runoff, ponding and soggy turf could be signs of major problems unrelated to the system or heads. There are a number of reasons these conditions exist including grading problems, compacted soils, an improper watering schedule, system drainage to a low head or valve problems. However, if the problem is associated with spray heads and rotors, these could be the causes:

    • Improper head layout and location

    • Head rotation problems

    • Leaking or stuck sprinkler

    • Improperly adjusted arc

    • Cracked housing

    • Non-compatible heads in the same zone.

    Common irrigation mistakes that affect sprinkler heads

    The following is a list of the most common irrigation mistakes that pertain to using and maintaining spray heads and rotors. Correcting them is generally simple and inexpensive and could reduce your operating costs.

  • Adjusting or reducing the throwing distance of nozzles more than 25 percent of the manufacturer's specifications. Besides violating the manufacturer's specifications and warranty, this adjustment will produce an uneven precipitation, wasting water and increasing operation costs.

  • Disregarding significant overspray. Overspray wastes water, is irritating and leaves a negative impression with the public. Liability is also an issue with overspray because it can be potentially hazardous to pedestrians and motorists and can deteriorate pavements, curbs and other structures.

  • Exceeding the manufacturer's specified head-to-head spacing. Space heads at a distance equal to the selected nozzle's throwing distance at working pressure as listed in the manufacturer's catalog. In the end, using a greater distance between heads will cost clients more in operating costs than can be saved during installation.

  • Installing different types of irrigation heads on the same zone. The precipitation rate for different types of components varies greatly. If you install heads with a lower precipitation rate in a zone with heads that have a higher rate, they will not apply water uniformly and dry spots will occur. Also, you will have to run sprinklers in these zones longer in order to apply enough water to irrigate the dry spots. This will result in wasted water, higher water and energy bills for the client and increased wear on the system — all without necessarily correcting the non-uniform appearance of the lawn.

  • Installing heads on risers next to pedestrian areas. Heads on fixed risers next to sidewalks, plazas and play areas can be a danger. A person or pet could fall on one of these hazards, causing injury or death. If you routinely incorporate these in your systems, you should notify your insurance agent to make sure you have sufficient liability coverage to protect yourself and business should an accident occur.

  • Using incorrect nozzle patterns for the area you are watering. Irrigation manufacturers make their spray nozzles in several part-circle patterns that throw water a maximum distance ranging from 8 to 15 feet. A professional irrigation designer will only use nozzles that have the correct pattern and distance required for an area. Using the incorrect pattern and throwing distance will, over time, waste a considerable amount of water and significantly increase operating costs.

  • Using nozzles within zones that have mismatched precipitation rates. Many landscapers assume that, in order to water an area evenly with rotor heads, they need to use the same GPM nozzles in every head. However, manufacturers make different GPM nozzles resulting in more flexibility for you. Save water used in a zone by proportionally matching the precipitation rate of the nozzles.

    Make sure you've got it covered

    As professionals, you know that maintaining a system for uniform coverage in the most efficient and cost-effective manner requires a broader knowledge of system pieces and parts than just the heads. It also requires skilled knowledge in the art, science, engineering and management of irrigation components in general. You cannot assess major system or zonal problems without looking at the system as a whole. You can quickly tell if a system is professionally designed, installed and maintained or if the work is a result of inexperience or indifference. The performance of a system depends on the integrity of its design, installation and maintenance. When any of these three components is compromised, so is the performance of the system and overall system durability.

Phil Jeselnik is a senior staff designer and project manager for Jeffrey L. Bruce & Company, L.L.C. (Kansas City, Mo.), which specializes in landscape architecture and irrigation system design. You can e-mail him at pjeselnik@jlbruce.com.

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