SPRINKLER TALK FORUM - You Got Questions, We've Got Answers

You have to count up the gallon per minute (gpm) for each head based on the nozzle you are using. Total the gpm's for the number of heads you want on a single zone. Determine the pipe size of the main line water supply to the sprinkler system and the main line going through the valve.

The totaled gpm's tells you how much water the zone will want to use.
The main line pipe size will tell you how much water the pipe will be able to deliver. As long as the pipe will deliver the total gpm's required by the sprinkler heads, you can have sprinkler heads on one zone. If the total gpm's required by the sprinkler heads exceeds the amount of water the pipe can deliver, you can not have that many heads on a zone.

To determine how much water a pipe of given size will deliver, by looking at the friction loss charts found on the following link:
http://www.sprinklerwarehouse.com/LawnCare/frctn_ls.pdf
or this link on Rain Bird's website:
http://www.rainbird.com/rbturf/technical/reference/pvc.htm
To use the either chart, you find the chart for the type of pipe you are using and you find the size pipe you think you need and then see what the water velocity through the pipe will be when you try to supply water to the zone in your sprinkler system that will use the most water (most gpm). To calculate the gpm for a zone, you add up the number of sprinkler heads on each zone and how much water each head uses based on the nozzle you will be using with the various sprinkler heads. Once you total the number of gpm's your largest zone will have (should be under 18 gpm's since your water meter will not handle any more gpm's), you look at the chart.
Using the chart determine what the velocity in the pipe will be for the number of gpm's you want to put through the size pipe you have chosen. *** Important*** If the velocity exceeds 5 feet per second, you must use the next size bigger pipe until the velocity is lees than 5 feet per second. This will tell you the pipe size you need as the mainline.
After you begin to branch off the mainline and supply sprinkler heads you can use smaller pipe since the water through the branched pipe is much less than the mainline pipe.

*** To get a good understanding of how to design and pipe your sprinkler system please use the following link to go through a step by step tutorial or summary (includes great pictures) of how to design and install a sprinkler system:
http://www.sprinklerwarehouse.com/LawnCare/NewSprinklers.asp

You can also use our charts and technical info sheets found in our Technical Data section of our website to assist you in the design and installation of your sprinkler system:
http://www.sprinklerwarehouse.com/LawnCare/technicaldata.asp
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