Understanding PR and Zone Area


#1

So I figured the hardest part of my irrigation system would be all the digging, but here I am, lost and confused with setting up my zones!

I want to make sure I’m doing this right with my first zone before working through the other 7. I have all Rain Bird heads in my setup, combination of rotors and fixed spray. The front yard is the most basic setup, 6 rotors total. Each head has a different nozzle from .75 GPM to 1.5 GMP. If you average them out, it is 1 GPM per head, 6 GPM total for the zone. I understand that the PR formula uses Number of heads, GPM flow per head, and the zone square footage in its equation. To create a custom nozzle for the front yard I have figured PR = 6 heads * 1 GPM (average) divided by 744sqft area to give me .776 inches per hour.

Now, when you configure the zone, I give it the area again, and also tell it which nozzle I am using. My confusion comes from having to enter the area twice, then also having an Efficiency value in the zone setup. Is my math correct? Will calculating the PR for each zone individually give me good results with using the Flexible Daily schedule?

Otherwise having a great time with this project, yard work and IT work are a fun combination for me!


#2

Create a custom sprinkler and call it Rain Bird 5000s. At 40 psi they apply about .4 inch per hour, and I have never measured an application rate of .76 for RB 5000 rotors. That is very high.
Your nozzle description means you have matched precipitation. That is the correct way to nozzle a zone.
Yes you can go through the calculations if you know square footage, but I would just go with the precipitation in the Rain Bird calculation. Keep it simple. I would look at the manufacturer specifications.


#3

I get .76 PR with 6 heads watering 744 sqft, according to the calculation Rachio provided for PR. Going off of the published performance specs Rain Bird has for the 32SA, I actually might be too low still, as my dynamic pressure is closer to 100psi.


#4

Have you reduced the flow with radius adjustment? If you look at the chart for 25 PSI, you will see that the flow is significantly lower at smaller radius. You might be only using 4.5 GPM, not 6.

I haven’t done this myself, but many in the community here use catch cups to measure the actual PR, and create a custom nozzle with the measured PR.


#5

I have the cups, but it’s currently pouring outside and all my valve boxes are underwater… Waiting for that sun now…

On the bright side however, Rachio delayed my watering because rain was predicted for this afternoon :smile:


#6

If you are operating at 100 psi, then you must install a brass pressure reducing valve after the backflow to lower the pressure. Residential gear drive rotors are not intended to operate at such a high pressure. Another option is to install Rain Bird 5000 Series with 45 psi pressure regulation. At 100 psi the water blows away with the mist. This is wild.

https://www.google.com/url?sa=t&source=web&rct=j&url=http://rainbird.com/prs/calculators.htm&ved=0ahUKEwirxf2s-tzVAhVprVQKHWsZDnIQFghOMAM&usg=AFQjCNHK05ZsDj3cRiynx_RbACxGKwEnng

Did you or a contractor install the system? Was a permit pulled for a licensed plumber to install a backflow preventer. If you have no backflow your homes drinking water is not safe from contamination - e coli, pesticides, etc.


#7

32SA is a home depot version of 5000 Series. Maximum operating pressure is 65 psi. I encourage people to shop where the contractors shop. Distributors will have the pressure regulated 5000 prs rotors.