why matched precipitation is important for your sprinkler system

In order to talk about nozzle selection, we need to quickly cover the concept of matched precipitation. Let’s say you have one rotor that goes 360 degrees, another rotor going 180 degrees, and another rotor only covering 90 degrees and they’re all in the same zone. They may even all have the same nozzle installed.

The 180-degree rotor will cover the same patch of grass twice for each time the 360-degree rotor goes around once. That means that the patch of grass serviced by the 180-degree rotor gets twice as much water as the patch watered by the 360-degree rotor. The rotor that goes 90 degrees will cover the same patch of lawn 4 times for every one time the 360-degree rotor will turn.

Understanding The Flow Rate Of A Sprinkler

It’s important to pick and install nozzles in such a way as to balance your irrigation system out. Now, what does that have to do with flow rate you may ask? Well, your full circle rotors should have a nozzle installed that has twice the flow rate of your half circles.

Your half-circle rotors should have a nozzle with twice the flow of your quarter circle rotors. Let’s look at a nozzle chart and nozzle tree (chart shown in the video). Nozzle charts are often included with the purchase of your rotor. If you didn’t get one, you can find the chart for your particular rotor on SprinklerWarehouse.com.

Matching Your Water Pressure To The Right Nozzle

Most residential rotor manufacturers assume an ideal water pressure of 45 PSI. You probably don’t know your exact water pressure and that’s fine, let’s just assume it’s 45 PSI. If we use a number 8 nozzle for the full circle you can see that at 45 PSI, it has a flow rate of about 8 gallons per minute. We choose a nozzle with half that flow rate for the half-circle.

The number 4 nozzle has a flow rate of roughly 4 gallons per minute, and the number 2 nozzle has a flow rate of roughly 2 gallons per minute. We’ll choose that one for the quarter circle. Here’s another chart laid out differently but with similar information. The number 8 nozzle at 45 PSI has a flow rate of 8 gallons per minute (GPM). The number 4 has 4 GPM, and the 2 has 2 GPM.

Problems You May Face When Choosing A Nozzle For Your Irrigation System

Here’s another issue that may arise: will your sprinkler system have enough water pressure for these nozzles? Most residential irrigation systems have a water pressure of 16 to 18 gallons per minute. Let’s look at an example, say we have 1 full circle rotor and it gets 8 gallons per minute. Then we have 3 half-circle rotors at 4 gallons per minute and 2 quarter circle rotors at 2 gallons per minute. Add all that together and we have 24 gallons per minute. Our system cannot support that. Oh no!

Let’s slide over to the chart. We’ll use a 6 GPM nozzle for the full circle. Three 3 GPM nozzles for our half-circles and half of 3 gallons per minute is 1 and a half. One and a half gallons per minute nozzles for our 2 quarter circle rotors. Our grand total of gallons per minute for the zone is 18 GPM.

Testing The Flow Rate Of Your Nozzles

You probably don’t know the exact gallons per minute that your system can support and that’s also okay. Here’s an example of what you can do. Install the nozzles based on the formula of making sure that your half circles get twice the flow rate of the quarter circles, and your full circles get twice the flow rate of your half circles. Then, turn on the system and see if the nozzles are putting out a decent stream of water.

If it doesn’t look right, go to a smaller flow rate for your nozzles. Now the tendency is to get frustrated that your quarter circle nozzles look like they’re not putting out enough water. They don’t have quite the pretty spray that the half or full circles do, but that’s the point. In a properly nozzled system, the quarter circles are going to look a little sad by comparison. That’s a good indicator you’re doing things right.

Head To Head Coverage To Keep Your Lawn Green All Year Round

As long as your spray is reaching the next rotor over (which it should) that’s called head-to-head coverage. The rotor sprays need to overlap each other for even coverage. A few manufacturers have also come up with easy-to-use nozzle selection solutions. I’m not going to cover all of them here but here are a few examples. One example is the Rain Bird MPR Nozzles. Choose which set you want to use by choosing the radius, which is your watering distance. Then, pick the nozzle based on whether it will be used in a full circle, half, third or quarter-circle pattern.

Another example is Hydro-Rain’s HRX rotor with its easy-to-match precipitation nozzle system. For instance, nozzle #1 is for your quarter circle, #2 for your half-circle, #3 for your three-quarter circle, and #4 for your full circle.

And one more consideration in choosing nozzles. Do you live in a particularly windy area? You should use low-angle nozzles. These nozzles have a lower trajectory. Otherwise, the wind is going to blow away much of the water you paid for. Many manufacturers include low-angle nozzles with their rotors. Often indicated by LA or an L by the nozzle number. If they aren’t included with the rotor, most rotors do have additional nozzles that can be purchased separately including low angle nozzles. That’s the quick and easy basics on how to choose a nozzle for your rotors.

The More You Learn, The More You Grow At Sprinkler Warehouse

Order your rotors and extra nozzles on SprinklerWarehouse.com. Subscribe to our YouTube channel for more how-to videos and irrigation tips. Sprinkler Warehouse has everything you need for your irrigation needs so that your trees, lawns, gardens, and flowerbeds are lush and beautiful. If you have any questions, chat with one of our customer service experts at SprinklerWarehouse.com. They really know their stuff and they’ll be able to get you squared away.