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PLANNING YOUR SPRINKLER SYSTEM
09/10/10
* 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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