PLANNING YOUR SPRINKLER SYSTEM

02/07/12

* The first step in planning your system is to check with your local building department and get any permits you may need. Then make a sketch of your property, showing the locations of all structures, walkways and driveways and trees and shrubs (Fig. 2). Call your local utility companies and have them come out and mark the location of buried gas, electrical and telephone lines. Note those locations on your sketch.

* Next, determine your water pressure and flow rate. Borrow or rent a water pressure gauge and attach it to a hose bibb. Turn the water on full (with all other water in the house off) to find the pressure. Systems vary, but you'll probably need a minimum of 20 pounds per square inch (psi) pressure to install sprinklers.

* Check the flow rate by placing a 1 gallon bucket under a hose bibb, turning the water on full (with all other water in the house off) and time how long it takes to fill the bucket. Divide the number of seconds by 60 to find the gallons per minute (gpm) capacity of your line. The result of this test will determine the size of each sprinkler circuit.

* Then plot the locations of sprinkler heads on your sketch. Multiply the throw distance of the heads (usually 15') by 1.4 to find the spacing between sprinkler heads so the areas covered by each head overlap. In windy areas, space the sprinkler heads the same as the throw rating.

* Finally, divide the system into circuits. The manufacturer's instructions will include an output chart that gives you a gpm rating for each sprinkler head. Divide the gpm capacity of your water line by the rating of each head to find the number of sprinkler heads that you can put on each circuit. Never combine different types of sprinkler heads (e.g., lawn sprinklers with low-shrub sprinklers) on the same circuit.

* As a rule, you'll use 3/4" PVC pipe to lay a system with circuits that are less than 100' long, or 1" pipe for circuits over 100'. In any case, your system pipe will be no larger than the supply line you tap into.

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