Irrigation 101

Elevation changes

The last item to consider that will affect pressure in an irrigation system is elevation change. Significant elevation changes can drastically affect pressures. For every foot of elevation change, the pressure will change 0.433 psi. Going downhill increases the pressure by that amount, going up hill decreases the pressure by the amount. Remember, excess pressure is as bad, if not worse, than insufficient pressure. Failing to recognize the pressure difference caused by elevation leads many systems to irrigate improperly.

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Setting up controllers

Two wires-the power wire and the common wire-are installed between the controller and the electric valve. These wires are sized based on the draw through the wire, the available voltage at the controller, the voltage needed by the zone valve and the number of zone valves being operated per controller station. Wire sizing also depends on the operating pressure of the system. For small residential systems, multi-strand #18 AWG wire is commonly used by contractors where valves are being manifolded together. Where valves are installed remotely, the multi-strand wire is too expensive, and a larger single wire is used. Commercial irrigation systems use individual wires for each zone valve, usually #14 AWG.

Automatic controller selection is based on the number of zones and the features required to manage the irrigation system. Small residential controllers handle a limited number of stations and have few features. Commercial controllers can handle many stations and have sophisticated features that may not be needed on all projects.

Lawns, flowers and landscape plants should have different schedules. Established plantings may require watering only twice a week while turf areas may require watering daily or every other day. Schedule drip zones separately from conventional irrigation equipment. The drip zones may need to operate for hours, while the conventional zones may require only several minutes. The irrigation design will dictate the number of schedules. Determine which features are required for your design and select the appropriate controller. Remember to design a rain shutoff, moisture sensors or both into all irrigation systems so that the system will not operate in the rain, and the plant material will not be over-watered.

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