What is a two-wire system? Conventional wiring from the irrigation controller to the valves in the field requires one common wire plus a hot wire from every valve in the system back to the controller. In other words, however many valves there are in that system is equal to the number of hot wires there are, and there may be more than one common wire if valves are spread throughout the landscape. A two-wire system is only comprised of two wires. Every valve in the system is connected to that same pair of wires. A decoder connects the two wires to the valve, and communicates with the controller for that valve. A two-wire system saves copper wire, simplifies troubleshooting, allows the easy, quick addition of new stations, minimizes trenching, and with some products, permits remote sensor operation over the two-wire path.

My familiarity with two-wire systems was that the two-wire idea was great, but I had never been impressed with the controllers that were set up to work with the two-wire approach. After doing my research, I found out that two-wire systems are now available with many of the industry’s best controllers. There are even two wire systems with modules that connect to almost any conventional controller. So, I decided to suggest a two-wire controller for both of the projects that were to be installed in phases.

The first project is a new residential property with substantial landscaping planned. Because the landscape will be completed in phases, a two-wire approach will be ideal. With one wire path, a decoder can be added anywhere along the path at any time. The decoder is then programmed as a particular station and wired to the new valve. When that decoder activates, the valve opens.

On this site, the point of connection to the water source is several hundred feet from the controller. The system includes a flow sensor that is installed in the main line prior to any valves. In a conventional system, two separate wires would be run from the flow sensor to the controller. With the two-wire system, we can install a sensor decoder along the wire path in close proximity to the flow sensor – no extra wires to run.

The best part of this is that we can use the two-wire system in conjunction with a state-of-the-art smart controller. I chose a Hunter ACC Decoder Controller with a Hunter Solar Sync weather sensor, but several manufacturers offer two-wire options with some of their best controllers. Review the choices and choose the best fit for your project. There are links to manufacturers below.

The second project where we are currently using two-wire technology is a 15 acre existing hospital and medical office campus. When I was beginning the irrigation master plan for the campus, I realized the need for a flexible, intuitive control system that was easily expanded. Two-wire was a perfect fit! There are two water meters servicing the campus, thus two points of connection. We are again specifying a Hunter ACC Decoder Controller with a Hunter Solar Sync for each point of connection. The landscape is to be renovated in phases over a long period of time. A two-wire system will provide the flexibility and expandability that this site needs. And just think how much copper wire will be saved!

Functional, modern two-wire systems are now a judicious choice. Several manufacturers offer choices for both large and small projects. Check out these links for more information: www.hunterindustries.com, www.rainbird.com, www.underhill.us, and www.igin.com/article-658-is-two-wire-too-good-to-be-true.html.

Approaches to Spacing
Triangular, square, and rectangular sprinkle r spacing are the traditional approaches to sprinkler head layout. With square spacing, sprinklers are arranged so that the distance between the sprinklers in a row and the distance between rows is the same, i.e., four sprinklers form a square.
Square spacing is ideal for square and some rectangular areas. The drawback of this type spacing is that the diagonal distance between sprinklers in adjacent rows is about 40 percent larger than the sprinkler spacing. Therefore, less water falls in the center of the square and distribution uniformity is lower.
Triangular spacing eliminates this problem. In a triangular arrangement, three sprinklers form an equilateral triangle (each side is the same length) and the diagonal distance equals the radius of throw. The row spacing is less than the sprinkler spacing (row spacing = sprinkler spacing x .866); however, edge control is difficult with triangular spacing. Large parks and golf courses can often use this pattern successfully.
In rectangular spacing, the diagonal distance is shorter than in the square pattern, but not as short as the diagonal of the triangular pattern. This reduces the weak spots created by the square pattern, and provides better edge control than the triangular. For large areas, a rectangular or square spacing pattern can often be used at the edges, converting to a triangular pattern as you move toward the center.
Most landscape situations don’t conform to our perfect geometrical shapes. At sites with curved shapes, another spacing method is used. It is called the edge method. This method specifies that you place sprinklers at the edges of the area, and then move in toward the center. To demonstrate the edge method, we’ll use a real-world example.

Learning Through Examples
Figure 1 shows a residential backyard landscape. The turf area is large, with irregular edges. We want to design a sprinkler system with a high distribution uniformity. Where do we start?
This area is a minimum of 24 feet wide. The operating pressure range is between 30 and 60 psi. The area is flat and wind is not a factor. A rotor head with a radius of 20 to 30 feet is an appropriate choice.
We want to first place heads at the critical points (corners) of the area. Next, we need to position the sprinklers at equal distances around the perimeter. The outside perimeter (point A to point B) is 198 feet. Our narrowest width across the turf area is 24 feet, so we want our sprinkler spacing to be close to 24 feet.
To determine the spacing, we need to know how many 24 feet spaces are in 198 feet. If we divide 198 by 24, we get 8.25, or eight spaces. Equally dividing the perimeter into eight spaces gives a sprinkler spacing of 24.75 feet (figure I). We finish up the inside perimeter with the same spacing. To place the needed interior heads, we draw the spray pattern of each perimeter head.
We continue this process, moving to the center of the area. We’ll place two full-circle heads in the center, as shown in figure 2. We will want to select nozzles for the various arc patterns, which will create matched precipitation rates within each circuit.
By making informed choices in a sprinkler layout, we are taking basic steps toward creating an efficient and uniform irrigation system. Part 2 will cover, in more detail, how to choose the correct sprinkler and some tips on scheduling your irrigation for optimum water use.

Project: Lathrop High School, the first secondary school in the Manteca Unified School District located in Lathrop, opened in August 2008.

Size of Project: 49 acres

Scope of Work: Irrigation plan includes recycled water system for playing fields, and potable water system for landscape surrounding the school buildings. There are two pumping stations, and the entire site is designed to be controlled with a Rainbird Maxicom Central Control System.

Client: Paul Niemuth & Associates
Landscape Architects and Planners
6366 Paseo Santa Maria
Pleasanton, CA 94566

Project: Olive Grove is a 128 unit affordable apartment project on a rectangular site located between an existing school and shopping center in Santa Rosa.

Size of Project: 4.33 acres

Scope of Work: Irrigation plan designed for optimum water efficiency. Includes in-line drip irrigation in parkway turf strips.

Client: Earth Design Group
Landscape Architect
486 Parquet Street
Sebastopol, CA 95472

Project: Kaiser Permanente’s Modesto Medical Center has earned national recognition as one of the “greenest” health care facilities in North America. The 670,000-square-foot hospital features energy-reducing materials and advanced green hospital furnishings and fixtures that use fewer toxic chemicals.

Size of Project: 40 acres

Scope of Work: Irrigation plan for the entire site, featuring point source drip irrigation, in-line drip irrigation, development of irrigation specifications and guidelines, installation details, and a central control system. The system is capable of switching between two different water sources including irrigation district canal water.

Client: pollock + partners, inc.
Site Planning and Landscape Architecture
5350 Dunlay #3115
Sacramento, CA 95835