Sprinkler Heads (Emitters) Overview
- Heads & Emitters: Types and Resources
- Head Spacing
- Sprinkler Precipitation Rate and Matched Precipitation
- Sprinkler Head Optional Features
- Additional Resources
We highly recommend creating a conceptual layout of your system using our Schematic Irrigation tool before placing your heads (emitters). The Schematic zones you place in your drawing will give you a good idea of the flow requirements in various areas of your site. You can then place your heads with the confidence that you've created a viable basic layout.
Heads & Emitters: Types and Resources
- Rotors: Rotors are gear-drive movements best used for 18- to 55-foot spacing (5.5 m to 16.8 m), with options for larger diameters that are mainly used for golf courses or special circumstances. They usually come with a number of nozzle sizes and offer some flexibility in upsizing or downsizing nozzles in case you find a deficiency in coverage.
- Pop-up spray heads: The term "spray heads" essentially refers to fixed-arc and adjustable-arc spray heads that are intended for smaller areas serviced by heads up to about 15 feet (4.6 m) in radius.
- Rotary heads (aka Rotator, Rotating, and Stream Rotor Heads): Rotary heads are spray head type bodies with a small mini-rotor as the nozzle type.
- Using heads with our software:
Head Spacing
Head-to-head coverage, where each head is spaced the distance of the radius, is best. In windy areas, use a spacing less than head to head, such as 90% of the radius, rather than 100%. For spray systems, some designers like the edge heads (quarter and half heads) to be tighter than head to head. To achieve this goal, they will often loosen up a bit on the full-circle heads.
Rotors
For rotors, head-to-head coverage may be inadequate. Different designers will have different ideas of the overspray, but consider a spacing of 90% or 85% of the radius for the head-to-head spacing.
Turf & Shrub Areas
Turf areas need tighter spacing – certainly head-to-head coverage – and shrub areas can be more lax in spacing.
Manufacturer-Listed Radius
The manufacturer-listed radius of heads is often not reflective of the real world. The best way to test a radius is to see the heads in operation. Spray heads may be close but still off by 10% or more. Rotor heads are worse than spray heads when comparing the actual radius to the manufacturer-listed radius. The actual radius may be up to 20% less than the manufacturer listing, so test them in the field. Remember: Irrigation F/X offers a radius reduction feature you can use when adding a head to a project. This tool allows you to reduce, by a percentage amount, the radius the manufacturer lists for that head.
The pressure dialog box, pictured to the right, opens when you add a head to your project. Here, you can reduce the head's radius using the Radius % slider.
Sprinkler Precipitation Rate and Matched Precipitation
Precipitation Rate
Precipitation rate, measured in inches per hour, is the amount of water applied over a general planted area. The precipitation rate becomes quite useful when you need to know how much watering time each valve requires in order to apply the proper amount of water to a planted area for a given time period.
Precipitation rate is determined by how all the heads interact with one another in order to apply, ideally, an even distribution of water over the planted area. Matched precipitation defines how different heads match one another for an even distribution of water.
Matched Precipitation
Spray heads are matched precipitation, so you can mix different radius heads and the rate will remain uniform (if all are at head-to-head coverage). Rotator (or rotary) heads also apply a matched precipitation.
Rotors are somewhat different with matched precipitation. You generally select the appropriate nozzle size for each rotor in relation to its arc. For example: Rotor heads with an arc of less than 360 degrees move back and forth across the area to be watered, while a full-circle, or 360, head moves in just one direction. The speed of the rotation is the same, so if you look at two rotors, one with a ¼ arc pattern, 45 degrees, and one with a full, or 360 degree, arc patter, by the time the full circle head makes one pass over the wetted area, the ¼ arc head will go back and forth four times over its wetted area, so with the same nozzle the ¼ circle arc head would have a precipitation rate four times as much as the full circle.
To match the precipitation rate where the ¼ arc head and the full-circle arc head share the same valve, you would have to ensure that the flow of the full circle head is four times that of the ¼ arc head. This is usually not a good solution with most rotors as the low flow head used in the case of the ¼ arc is also a much lower radius, so they won’t line up very well. Some rotors are touted as matched precipitation, but these are extremely limited in type and availability.
The solution is to simply have separate valves for a certain type of arc, such as a valve for just full circles, just half circles, and even a valve for just quarter circles. Even if you do this, however, variations will occur. For instance, the ½-circle heads will occasionally have some patterns that are larger or smaller than 180 degrees, so you may need to somewhat upsize or downsize the nozzles in this case in order to accommodate the different areas of coverage for a similar precipitation rate.
Remember: When you start to determining your watering window, or how much time you are allowed to put down the water you need, you need to think about the precipitation rates of the heads. Heads with low precipitation rates will take longer to apply the water, and may not be functional for certain situations. Also, certain sloped conditions, such as a steep slope with clay soil, require heads with lower precipitation rates that will put down smaller amounts of water over time. These heads give the water a chance to percolate into the soil with minimal runoff.
Sprinkler Head Optional Features
Check Valves
Built into the body of the head, these valves prevent low head drainage when the valves closes, for at least a 10-foot elevation change. Check valves are a good option – especially if your project has level changes. They save water and help prevent an issue known as "water hammer," where a system's water is drained out and replaced with air. When water hammer occurs, the water rushing in will be hard on the entire system the next time the valve is turned on.
We recommend using check valves if you want to be “green.” They save water by preventing it from flowing out of the low heads.
Pressure Compensating Devices
These devices, also built into the body of the head, control the amount of pressure affecting the nozzle. If you have high-pressure conditions, pressure-compensating devices prevent high-pressure misting.
Again, use pressure-compensating devices if you want to be “green.” They also save water by preventing misting that blows away in the wind.
Additional Resources
PDF Downloads
- Irrigation Getting Started Guide
- Irrigation Design Rules of Thumb – Imperial Units
- Irrigation Design Rules of Thumb – Metric Units
Video Resources
Contact
- Land F/X
Our software tailors AutoCAD® to the needs of landscape architects, irrigation designers, and other professionals. We automate your most tedious tasks and ensure accuracy, giving you more time to design.