Planning Your Lawn Irrigation System

Even if you can’t draw a straight line, you have to make a map of your property to plan your irrigation system. Draw your map to scale (such as 1 inch equals 10 feet) on graph paper as accurately as possible (most irrigation system instructions include graph paper for a map). Note all measurements, trees, shrubs, sidewalks, driveways, the house, tool sheds, gazebos, and any other obstacles that you need to consider. Be sure to note where you plan to hook up to the main source of water. You’ll use this map to either get help from a professional irrigation designer or to plan the system yourself.

Contact your county clerk’s office or local utility company to find out whether you need to be aware of any regulations concerning irrigation systems. This is also the time to determine where the electrical, gas, cable, phone, and sewer lines run through your property.

To run an irrigation system, your house needs water pressure of 40 to 50 pounds per square inch (psi). The easiest way to measure water pressure is to call your water company and ask whether they have that information for you. If not, borrow a water-pressure gauge from your irrigation equipment supplier or friendly plumber. Measure psi with the gauge by turning off all the faucets inside the house. Then hook up the gauge to an outside spigot, turn the spigot wide open, and read the pressure. Water pressure can vary, so measure your psi several different times during the day and average the readings.

You also need to know how much water flows through your pipes, measured in gallons per minute (gpm). Ask your irrigation specialist for help or do it the old-fashioned way by placing a one-gallon container under an outdoor spigot and timing how long it takes to fill up with the water running at full blast. Divide this time into 60 to determine your gpm. For example, if it takes 20 seconds to draw 1 gallon of water, 60 divided by 20 equals 3. In other words, your system flow rate is 3 gallons per minute.

Often, your irrigation equipment supplier can take the map you’ve drawn and give you a sample design to work with.

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The map also can tell you how large an area each sprinkler covers. If possible, you want the underground lines and the sprinkler heads to run around the outside edge of your lawn so that few or no sprinkler heads are in the middle of the lawn where they can get damaged by lawn mowers. Perimeter placement isn’t always possible, but that’s what you’re shooting for. Remember to overlap your sprinkler spraying pattern diameters by 50 percent so that you get good, even watering.

Here are some tips for designing your system:

  • Draw the spraying circles and the sprinkler head locations on your map so that the whole lawn gets watered: Remember to overlap the diameters of the spray patterns by 50 percent to ensure good coverage.

  • Break up your sprinkler heads into clusters of different circuits, each regulated by a control valve: Otherwise, you won’t have enough pressure to operate all the sprinklers at once. Your manufacturer’s workbook, which comes with all sprinklers, can help you with the details of choosing different sprinkler types and patterns. Putting different brands of sprinklers on the same circuit isn’t a good idea because the variation may upset the constant, steady flow you’re trying to achieve.

  • If you have a large system, group some of your control valves into a manifold that you then attach to the controller:

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    This takes a disorganized army of pipes, fittings, sprinklers, and valves, and organizes them into a smoothly functioning system.

    Having a manifold in the front yard and another one in the back is common. In areas where the ground freezes in winter, each circuit needs an automatic drain valve at its lowest point. Otherwise, the pipes freeze and can possibly break. Sometimes the drain valves are already designed into a special sprinkler that gets placed at the lowest point of the circuit.

  • Sketch in the piping and make sure that you have exact measurements for distances between valves, manifolds, controllers, hook ups, and more.

  • Make a list of all the piping, fittings, control valves, risers, sprinklers, manifolds, controllers, and all the equipment you need to assemble your irrigation system: Otherwise, you’re liable to forget something. Have the equipment retailer review your list and make sure that you’re getting all that you need.

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