Designing Your Own Sprinkler System - Part 2

In order to install a do-it-yourselfer sprinkler system, you need to check water pressure to know how much is available. This will tell you how many sprinkler heads you can run at one time and is essential for successful sprinkler system design. To do this, you will need a pressure gauge.
First, attach the water pressure gauge to an unregulated (without a pressure regulator) outdoor water faucet. Turn on the water (no water should be flowing out) and record the water pressure reading.
Next, you need to measure the diameter of your main irrigation line. Take a piece of string, wrap it around your main sprinkler line and mark the string where it wraps completely around the pipe.

Pipe Line Size
Length of string	2”	2 ¾”	3 ¼”	3 ½”	4 ¼”
Copper pipe	½”	¾”		1”
PVC/galvanized pipe		½”	¾”		1"

Once you have determined the size of your main sprinkler pipe, you need to determine the gallons per minute (GPM) capacity of your sprinkler system. With the information you gathered previously, you can quickly determine your new sprinkler system's capacity.

Water Pressure (PSI)
Main Line Size	35 lbs	40 lbs	45 lbs	50 lbs	55 lbs	60 lbs	65 lbs	70 lbs	75 lbs
½”	3.5	5.0	6.0	6.5	7.0	7.5	8.0	9.0	9.5
¾”	7.5	9.0	10.0	12.0	13.0	14.0	15.0	16.0	17.5
1”	10.0	11.5	13.5	15.0	16.0	17.5	18.5	20.0	21.0

If you do not have access to an unregulated outdoor faucet, contact your local water district/company to get an estimated PSI. If your water pressure exceeds 80 PSI, you will need to use a pressure regulator or pressure reducer so the high water pressure does not damage your sprinkler system.
Once you have determined your main line size, GPM capacity and water pressure, you can begin working on your sprinkler system layout.

Related:

• Installing a Sprinkler System - Part 1
• Installing a Sprinkler System - Part 3
• Installing a Sprinkler System - Part 4
• Installing a Sprinkler System - Part 5
• Installing a Sprinkler System - Part 6