Irrigation 101


Sprinkler support (the connection between the pipe and sprinkler) can be of two types: swing joints and swing pipe assemblies. Swing joints are available in 1/2-inch and 3/4-inch sizes, but are more commonly seen on sprinklers with 1-inch or larger inlets. Swing pipe assemblies are preferred in the smaller sizes and consist of two threaded elbows, one to thread into the pipe fitting and the other to thread into the bottom of the sprinkler. In between the two elbows is a piece of small-diameter flexible pipe. The flexibility allows for the sprinkler to absorb weight going over it without breaking and makes the installation easier.

The length of pipe is measured and cut to the required length needed in the field. Some manufacturers prefabricate and sell swing pipe assemblies of specific lengths. Swing joints are made of PVC and have a minimum of three elbows for flexibility. The elbows have o-ring seals so they can remain loose and absorb movement without leaking water.

Turf and landscape systems are broken into zones to reduce flow requirements. A small zone may have four sprinklers, and a large zone may have 30 or more. An electric zone valve activates the zones. A zone valve can be plastic or brass, pressure rated for 150 or 200 psi. The zone valve is actuated with a 24 VAC signal, but opens and closes hydraulically. The valve opening and closing speed depends on the pressure and flow at the valve. Valves are as small as 1/2 inch and as large as 3 inches for turf and landscape systems. Most residential systems use 3/4- or 1-inch plastic valves. You should never have the valve completely open for valves equipped with flow control. Back off at least a half or whole turn from fully open. Install every electric valve in a valve box. The size of the valve box depends on the number and size of valves that you need to install in it. Also, install wire splices and shut-off valves in valve boxes.

Most irrigation systems use PVC or polyethylene pipe. The type of pipe you use will be dictated by the size of the system, your design requirements or geographical preferences. On smaller systems, depending on where the system is being installed, you might see all polyethylene pipe (New England), a combination of PVC mains and polyethylene laterals (Virginia) or all PVC pipe (Florida). Laterals are piping that is downstream of the control valve and not under continuous pressure. The type of pipe, the pipe size and the operating pressure of the system dictate the type of fittings you should use. Polyethylene pipe uses compression or insert-type fittings with clamps. Insert fittings are either PVC or Nylon. For small systems, use schedule 40 PVC glued fittings. Larger systems may use schedule 40, glued or gasketed, epoxy steel or ductile iron fittings.

The wire you use in an irrigation system should be made specifically for irrigation systems. Telephone or thermostat wire is a poor choice. The design should determine proper wire size. Waterproof connectors, such as the 3M DBY or Paige DBM connectors, are popular for irrigation systems. UL-listed connectors are available, but are expensive. They may need to be used depending on the area where the system is being installed. Color-coded wire helps in troubleshooting and repair.

Hundreds of controllers are available on the irrigation market. The number of stations and other features you desire will determine which is the best for a particular project application. Controller sizes start with as little as four stations and go up to 48 stations. Even larger controllers are available for golf applications. Look for features such as the number of stations, number of start times per schedule, number of schedules, water budgeting, self diagnostics, non-volatile memory or battery back-up, internal or external transformer, cabinet type and sensor overrides.

Rain shutoffs come in various types. Again, choose the one that best fits the application being irrigated. You can view irrigation products at most green-industry trade shows or on manufacturers' web sites. Equipment catalogs also are available from local distributors.

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