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# How to figure out the maximum number of sprayheads on a zone?

#1
04-23-12, 02:01 PM
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How to figure out the maximum number of sprayheads on a zone?

I'm landscaping my backyard and working on the sprinkler system. I need to reposition the existing spray heads and add additional heads for the lawn I'm getting ready to put in. So that leads me to my question...How do I figure out the maximum number of spray heads that I can put in?

I know that it all depends on how my system is set up and here is what I have:
1" meter
1" steel supply pipe into the house
65 psi at the hose bib
3/4" lateral lines after the valves

Based of what I've read, a 1" steel pipe can deliver up to 18 gpm. Also, if my hose bib psi is 65, how do I know the psi in my lateral pipes? 20, 25, 30, or some other amount?

From Rainbird's website, the nozzles deliver different gpm based on the psi. For example, a 360 degree nozzle with 25 psi puts out 3.3 gpm, compared with the same nozzle with 30 psi putting out 3.7 gpm.

And finally, once I figure out the gpm for each spray head, do I simply them all up and make sure they don't total more than 18 gpm?

#2
04-23-12, 02:10 PM
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The Rain Bird website tells you how to do everything. Best is to test your water flow at the point where your irrigation system will connect. If you can't do that you can test it at a nearby spigot. The 18 gpm is the maximum for that size pipe. You will have something less. And with a pressure gauge hooked in you will probably see your pressure drop dramatically when you are flowing water at high volume. So, you may end up only having 30 or 40 psi at 10 gpm and have so size your zone accordingly.

#3
04-23-12, 02:27 PM
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Thanks Pilot Dane. I tested the gpm at the hose bib near the main line feeding the irrigation. A 5 gallon bucket filled in 34 seconds and that adds up to 8.82 gpm. But doesn't the hose bib have a lot of flow restriction? If so, than I've narrowed my available gpm to between 8.82 and 18. So without digging up the main line and putting a pressure gauge on it, how do I get a more accurate reading?

#4
04-23-12, 02:40 PM
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I assume you will be tying your irrigation system into the plumbing somewhere near the spigot where you tested? If so, the flow from the hose bib is probably not a bad number to work from since you will also have restrictions in your plumbing to get to the valve box. And, you don't want to push the gpm number to the limit with your zone design or you may have trouble with heads occasionally not popping up since raising the heads can require a higher flow volume until they get fully up and seal. When in transit the rising tube has a loose fit with the body and can leak a lot of water. Not a problem if they all pop right up but if you're flow volume & pressure is marginal they rise more slowly which can leak a lot of water, making the situation even worse.

#5
04-23-12, 03:34 PM
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Yes, the hose bib is next to the main line. But 9 gpm isn't very much water to work with, in fact, that would only allow for two 360 heads and one 180 head in the zone, at 30 psi. I know that the zone had 9 heads before it was ripped up during construction and it worked well. But I don't know what the total gpm was for those 9 heads.

So something doesn't seem right with my calcs. Would I get an accurate reading if I checked the psi directly on the 3/4" lateral pipe?

#6
04-23-12, 03:47 PM
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Just to reiterate,

It seems you already have a irrigation system?

If so that's not really a good idea. The easiest way at this point to figure what you have currently is to post back how many zones you have now.

Then on each zone count the # of heads. post back that info.

Then post back what heads are on each zone. Sprays, rotors...?

Then each head has a nozzle. If you get the make and # off the nozzle you can cross reference them. Each zones nozzles gpm should add up to the total gpm for each zone. Which is the gpm and psi your system was designed at.

Ex: 5 heads. Each head has a rotor. The nozzles are #5's which are 2 gpm. Thats 10 gpm. And say on the chart that is @ 50 psi because you should have a gauge on the system that shows your running pressure. If no gauge get a gauge that attaches to the hose bb attached to the irrigation system and check your running pressure.

Since each zone is designed for the gpm of your system adding heads will reduce the gpm and the other heads will not function correctly.

Possibly you can add one or two heads with a low flow and not see a reduction but its best to run an additional zone for a larger area.

It may be possible to add a additional head from each zone for your new area, but running a new complete zone is probably the same labor.

We will get into pipe size lather.

Hope this helps.

Mike NJ

#7
04-23-12, 03:58 PM
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Oh and I used this link to design my system on a 5 gpm well. 11 zones, one 4 gpm head per zone..LOL.

Irrigation Tutorials Homepage and Main Index

Except the sprays I have 6 sprays at .60 gpm. All designed at 55psi.

Yes I turn them on manually...LOL..again.

Total cost of material \$200. My labor all hand dug. ( Hey, a company wanted \$4000 to do it with a booster pump. I threw them off my property)

Funny but true.

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#8
04-23-12, 04:11 PM
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Thanks for the info Mike.

I currently have three zones, sprays only. I'm just working with one of my three zones and it only has four heads intact (there was 9 just two weeks ago from the original design). All the other five heads were removed and capped since they're underneath where pavers are now. So I can do one of a couple things: I can put in 5 more heads (getting back to nine), but I'd be hoping that the total gpm wouldn't increase, exceeding total supply. The yard area is generally the same, but it has a different design, so I can't just plug heads back in where there were.

Or I could look at the nozzles from another zone (that was untouched), get the # off those nozzles, cross-reference them to come up with that zone's gpm and use that number as my benchmark.

Do either of these plans sound okay?

#9
04-23-12, 04:43 PM
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Do either of these plans sound okay?
yes.

And are the sprays the same? Like all 180 degree adjustable arc or something?

For me to figure it I would need to know what spray pattern, make and model of nozzle at each head.

I,m sure you can figure it out now, right?

Mike NJ

#10
04-23-12, 09:16 PM
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I stopped at my local landscaping store on the way home and picked up a tool to measure the psi at the head. It's a little plastic adapter that I screw into the top of the head (remove the nozzle first) and screw the nozzle onto the top of the adapter. My pressure gauge screws into the middle of the adapter. Only \$2.69.

With the work I've done on my end and the help from the guys on this forum, I think I'm all set. I didn't know squat about sprinklers before this project. There's a lot more involved than most people think and it was fun doing to calcs to do this job right.

Thanks to Mike and Pilot Dane.

#11
04-27-12, 10:32 PM
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Here's an update. I checked the psi at the spray heads (the last head on the lateral) and it was 55 psi. Everything I've read says 30-40 is best. Should I just leave things the way they are and lay down pipe and the heads as I planned. Or should I do something to lower the pressure in the line.

#12
04-28-12, 08:57 AM
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Leave it. As long as the spray heads are not misting you should be fine.

Mike NJ

#13
04-28-12, 01:03 PM
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If you do have trouble it's easy enough to add a pressure reducer for the entire zone or use pressure reducing heads.

#14
05-07-12, 11:56 AM
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I found some pressure regulating spray bodies on Rainbirds website. They're the "PRS" series and they control the head pressure to 30psi. I bought a bunch of these since they cost just a little more than standard sprays. I went with their "MPR" nozzles too since the lower GPM gives me more flexibility to place some extra sprays. (You have to water for longer periods with the MPR nozzles).

Here's a follow up question, does it make a performance difference to use 1" laterals that branch off of the main to the sprays (approx 10' from the main)? Or are 1/2" laterals just fine? I don't mind spending an extra \$20 bucks in material today if it means less headaches in the future.

Last edited by kevinf.; 05-07-12 at 01:44 PM.
#15
05-07-12, 01:29 PM
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1/2" laterals is fine for spray heads & MPR nozzles especially since you are only going about 10 feet.

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