# GPM or inches/hr?



## SpiveyJr (Jun 7, 2018)

I just purchased 7 Rainbird 5000 rotors and I'm trying to determine which nozzles to use. Does it matter if you look at the precipitation rate or gpm?

My lawn is rectangular 60x30 so 3 heads go across the front and back with 1 in the middle going 360. The 4 corners running at 90 degree arcs are going to be spitting out twice the amount as the two in the middle doing 180s. So the nozzles I choose for the corners should put out half the amount of water, correct?


----------



## g-man (Jun 15, 2017)

And the one in the middle is double from the 180 (4x from the 90).

But check irrigation tutorial or the rotor documentation. It's been a while since I've done this. The match precipitation takes away with these calculations.


----------



## SpiveyJr (Jun 7, 2018)

The thing is, one nozzle does 4.01gpm and .44 inches per hour while another does 1.05gpm and .23 inches, at different radius. I'm starting to lean towards using gpm unless the precipitation rate already takes into account the radius. These heads are all PRS so I'm not looking at or taking into account water pressure since they all should be at 45 psi.


----------



## Ballistic (Mar 19, 2018)

Id just keep it simple and do GPM.

Just make sure your middle one is the bigger GPM out of all of them.

Also did you run 3/4" or 1" and 1 or 2 zones just making sure you got the right flow to all the heads?


----------



## SpiveyJr (Jun 7, 2018)

They are two zones. 4 heads on one and 3 on another. I'm not sure if the pipe is 3/4" or 1". The system was installed in the early '90s when the house was built, so whatever was popular back then is probably in the ground.

I really wanted to go with rotary heads but that would have required digging and adding more heads. I also couldn't come up with a placement pattern for the heads that would give me head to head coverage.


----------



## Green (Dec 24, 2017)

You go by the rules first when setting up the initial nozzle set...

And then after catch can audits, you tweak your levels by swapping nozzles that put out too much or too little, to try to get even coverage.

So, both...gpm and inches per hour matter.


----------



## SpiveyJr (Jun 7, 2018)

I agree. Ultimately it comes down to getting 1" of deep watering a week, right? Whether it's 1" an hour or two hours as long as I get to that point. I supposed I will have to do a best guess to start and adjust accordingly.

I thought draining and filling my 14,000 gallon pool was bad but after looking at the gpm of some of these heads and how long they need to run to put down an inch a week makes me cringe.


----------



## g-man (Jun 15, 2017)

Draw your layout and do the calculations. The idea is to get 1in * evenly*. Otherwise you get 1in in the middle and 1/8 in the corners.


----------



## Green (Dec 24, 2017)

SpiveyJr said:


> I agree. Ultimately it comes down to getting 1" of deep watering a week, right? Whether it's 1" an hour or two hours as long as I get to that point.


Yeah, that's a good starting point and works in many lawns during 70-80 degree temps.


----------



## Darkshadow (Oct 25, 2017)

To the OP: Do you know what your maximum available flow is? I see that you said you have two zones (on your controller) that control the seven heads. Based on your maximum available flow, you may have to use smaller nozzles than the recommended ones in the tutorial. You still want to aim for matched precipitation rate based on the rotation of the head as has been mentioned here already. For example, I am working with 11 GPM and have four heads on one zone as follows (180 degrees, 360, 360, 180 degrees). I had to use smaller nozzles to not exceed my GPM, but to make up for it, I just run that zone longer relative to zones with different rotations.

Depending on the nozzles you end up using, you can adjust your run times accordingly to get the even coverage you're looking for. It may mean having to run one of your zones longer if you don't have the available GPM to use the larger nozzles. I suggest getting some catch cups with the detailed measurement markings on them initially to get a sense of how long each zone needs to run to get the output you're looking for. Once you get it dialed in initially, then you can just do periodic audits with catch cups to make sure you're still getting the coverage you think you are.


----------



## SpiveyJr (Jun 7, 2018)

I'm not sure what my max flow is. I am on city water and I purchased the pressure regulated nozzles because the ones now seem to mist a bit. I plan on going with Rainbird 1.5 nozzles in the corners, 3.0 for the two middles and a 6.0 for the center 360 spinner. I have catch cups to put down to measure how much water is going down and that will be the deciding factor in how long I run these for. I have 6 rotors in the backyard all on one zone and they seem to be doing fine even when I had a hole in the line due to roots.


----------



## Darkshadow (Oct 25, 2017)

The link below will give you some background on safe available flow for your system in GPM. I suggest reading it because if you choose to exceed the safe max GPM on one or more zones, you should at least know the risks. If the Rainbird nozzles are numbered similar to the Hunter PGP blue nozzles, you're pushing at least 15 GPM through that one zone (1.5, 1.5, 3, 3, 6).

https://www.irrigationtutorials.com/gpm-psi-municipal-water-source/


----------



## SpiveyJr (Jun 7, 2018)

Darkshadow said:


> The link below will give you some background on safe available flow for your system in GPM. I suggest reading it because if you choose to exceed the safe max GPM on one or more zones, you should at least know the risks. If the Rainbird nozzles are numbered similar to the Hunter PGP blue nozzles, you're pushing at least 15 GPM through that one zone (1.5, 1.5, 3, 3, 6).
> 
> https://www.irrigationtutorials.com/gpm-psi-municipal-water-source/


Thanks! With my planned nozzle setup I would be just over 12gpm. I am leaning towards using a Rainbird rotary head for the middle sprinkler now since the distance it needs to spray is under 24 feet. The precipitation rate is nearly identical and the gpm is half of what the Rainbird 6.0 nozzle puts out, so this would make my total flow at 9 instead of 12.

For now this is all irrelevant because it turns out I received PGP nozzles for my Rainbird heads...


----------



## unclebucks06 (Apr 25, 2018)

Gpm x 96.3÷sq footage will also give you your precipitation rate.


----------

