# Figuring Out Sprinkler GPM

• posted on November 2, 2006, 9:14 pm

I'm trying to figure out the maximum Flow GPM for my sprinkler system. On the sprinkler (Rainbird 1800 series) it shows a chart listing the PSI, the radius of the coverage area and the Flow GPM. For example, the bottom entry on a quarter circle sprinkler is listed at 30 PSI, 14' radius, and 1 GPM. Is this the maximum GPM the sprinkler will emit? If my PSI is 60, twice the PSI listed on the sprinkler, will it double the Flow GPM to 2?
My water line's PSI tested between 50 and 60, and the flow is 11.5 GPM. It seems like I'd have to install a lot of valves to keep the GPM within limits, and all for a very small lawn. :/
-Fleemo
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• posted on November 2, 2006, 9:23 pm

No,m it won't double. Does the chart have a way to plot waht you need?

Why a lot of valves? All you need is a pressure reducing valve if you don't like hte pattern the sprinkler head is giving you. . Don't confuse volume and pressure. While they have some dependency on each other, you use different methods to control each.
If the lawn is that small, jut use a plain old hose and sprinkler for \$5.99
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• posted on November 2, 2006, 11:11 pm
snipped-for-privacy@comcast.net wrote:

It's been 5 or 6 years since I did my sprinklers, let's see what I remember. I think the pressure number on the sprinkler represents the minimum pressure that the sprinkler needs to operate reliably. The flow rate represents the maximum flow for that sprinkler head with the screw cranked wide open to achieve the 14' radius. I think once you're past the minimum pressure required to operate the sprinkler, the flow rate is relatively constant.
The sprinkler manufacturers (Toro, Rainbird, etc) usually produce a brochure to assist you in planning - you can probably find one in the sprinkler section of your local BORG. In there, you'll find a chart that summarizes the flow rates that can be supported with a given supply pressure and a given supply pipe size (1/2, 3/4, etc). Use that chart to determine your supply pipe flow rate in GPM, and add up the GPMs of all your sprinkler heads. If your total demand is less than the supply GPM, everything can go on one circuit. Otherwise, split it up into separate circuits.
Hope this helps, Jerry
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• posted on November 2, 2006, 11:54 pm

1 gpm @ 30psi roughly gives a Cv of _.179_.
60 psi gives you something like 1.5 gpm.
Try calling Rainbirds help line.
-zero
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• posted on November 3, 2006, 3:47 pm
-zero wrote:

The chart means that at 30PSI, set to a 14' radius, it will put out 1GPM of water. Many of these have nozzles that can be changed, so they have tables showing the flow for the various nozzles and supply pressures.

No, it will be higher, but not double. There should be chart entries for enough pressures so you can either determine it, or approximate it. However, I've found that actual measured can vary quite a bit from the rated values.

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• posted on November 6, 2006, 9:04 pm
Thanks for all the input here, folks. :)
-F