Irrigation System Heads Introduction

Irrigation heads, also known as sprinkler heads, are an integral part of many residential and commercial irrigation systems designed to distribute water to the landscape.  While sprinkler heads come in myriad sizes, shapes, brands, and styles, there are four basic types of sprinkler heads[1]:

  • Pop-up spray and rotor heads
  • Impact rotors
  • Gear-driven rotors
  • Large turf rotors

Pop-up Spray and Rotor Heads

pop up spray headsProbably the most widely used sprinkler head, pop-ups are typically used for residential and small commercial applications. Pop-up spray heads are designed to supply a continuous stream of water – nozzles are used to distribute water in a variety of patterns to fit the contours of the landscape.  Typically, fixed spray heads are stationary and have no moving parts other than the “pop-up” stem in the center of the sprinkler head making them inexpensive and simple to operate. 

The body of pop-up heads range in height from 2 inch to 20 inches (5.1 cm to 50.8 cm). Two-inch pop-ups are usually used in situations where hard soil makes digging difficult.  Four-inch pop-ups are commonly used in turf areas; the current standard for mowing height in lawn areas is typically three inches – a four-inch pop-up provides sufficient clearance for a growing lawn and the fact that over time heads tend to “sink” as soil and thatch build-up around the sprinkler head.  Six to twelve-inch (15.2 cm to 30.5 cm) pop-ups can be used to irrigate groundcover, garden areas and shrub borders; heads can be installed on risers as the landscape grows and greater clearance is needed.

pop up rotator headsPop-up spray heads are designed to be installed on a zone with plant material of similar watering needs. Each zone is operated by an individual valve that is activated by a solenoid.  Pop-up spray heads are designed to cover relatively small areas with spray radius between 3 feet to 15 feet (.9 m to 4.6 m) with an operating pressure between 15 and 30 psi. The precipitation rate of fixed spray heads varies from 1.0 to 2.5 inches per hour (2.54 cm to 6.35 cm) and is dependent on the system pressure, spacing of the spray heads, manufacturer specifications, and nozzle size.

Manufacturers are continually improving pop-ups: features such as matched precipitation rates, adjustable and low trajectory nozzles, nozzles with square spacing and strips, contribute to improved efficiency of the irrigation system.  Several manufacturers have even developed nozzles that convert a pop-up sprayhead to a rotor capable of covering distances ranging from 8 feet to 30 feet (2.4 m to 9.1 m).  The advantage of these nozzles is that they reduce the precipitation rate, which improves infiltration and reduces run-off.

Impact Rotors

Orbit impact headImpact rotors can be recognized by the telltale tooka, tooka, tic, tic sound made by the swinging arm striking the body of the rotor.  Impact rotors provide single or multiple streams of water to the landscape and distribute water in an arc pattern typically ranging from 40 ° to 360 °. They are designed to cover larger areas than pop-up sprayheads; the spray radius for most rotors is 20 feet to 150 feet (6.1 m to 45.7 m) with a precipitation rate between 0.1 to 1.5 inches per hour (.25 cm to 3.81 cm).

There has been very little change in the design of impact rotors over the years; its uncomplicated design makes it suitable for irrigation with well water or where other types of heads might become fouled.  The radius and arc are easily adjusted, however they often require regular maintenance and the spring mechanism is often too noisy for residential sites. Because impact rotors are often made of bronze or brass they can last for many years although initially they may cost twice that of plastic, gear-driven rotors. 

Gear-driven rotors

gear driven rotor headsOlder impact heads are being replaced by gear-driven rotors in many situations making them the most widely used sprinkler types for medium- to large-scale areas[1].  Their low cost, quiet operation, and versatility provide a few of the advantages that gear-driven rotors have over impact rotors.  They typically require less maintenance because the enclosed body design prevents clogging of the drive mechanism from dirt and other debris.  \

Gear-driven rotors are best suited to small commercial sites or large residential areas.  They work better than pop-up sprayheads in areas with slopes or clay because their lower precipitation rate increases infiltration into the soil.

Some manufacturers provide a nozzle tree with each of their rotors making it easy to select the appropriate size nozzle for the desired radius and precipitation rate.  Typically, gear-driven rotors have a radius that ranges from 18 to 55 feet (5.5 m to 16.8 m) and an arc rotation from 40 to 360 degrees.  Operating pressures range from 25 to 75 psi and precipitation rates range from 0.2 to 0.8 inches per hour (.51 cm to 2 cm) depending on the pressure, nozzle size, and the layout of the zone.

Large turf rotors

Impact rotor headGolf course, parks, and some commercial properties require large turf rotors.  These rotors require operating pressures from 50 to 100 psi.  Their large size allows them to cover a radius up to 100 ft. (30.5 m) with flows as high as 80 gallons per minute (302.7 LPM).  Older model golf course heads were made of brass; some of these heads are still operating in the field 40 years after they were originally installed.   Because of the high cost of brass heads the current trend is towards using plastic gear-driven rotors. 

Knowing the conditions and requirements of the site to be irrigated is an important step in finding the right sprinkler head for the job.  Soil type, water pressure, water source and weather conditions are just a few of the many factors that influence the type of sprinkler head needed to deliver water to the landscape.  Homeowners, landscapers, and irrigation professionals benefit from a highly competitive irrigation market.  Continued improvements to materials increase the durability of sprinkler heads while decreasing their costs.  Advances in nozzle design can decrease overspray and runoff and reduce susceptibility to losses from wind.    Although there are only four basic types of sprinkler heads, ranging from small pop-up sprayheads to large, electronically-activated, golf course rotors, they are sufficient to meet irrigation requirements of everything from a small residential landscape to a PGA golf course.


 

[1] http://www.grounds-mag.com/mag/grounds_maintenance_irrigation_heads/. Grounds Maintenance for Golf & Green Industry Professionals. Irrigation heads. Gary S. Kay