I see this all too often. I go out to a client’s house to work on their sprinkler system and there it is staring me in the face! My old evil adversary…. THE MIXED ZONE!
What is a mixed zone? A mixed zone is a sprinkler zone that has two types of sprinkler heads that put out different rates of water.
For example: You may have a zone primarily consisting of rotors and on that zone someone has added a spray. Rotors are heads that rotate and usually throw water thirty feet or more. Sprays are heads that have a short spray pattern, generally fifteen feet or less.
“Why is this a problem?” you may ask. “After all, we just need to get stuff wet right?” WRONG and here’s why.
The typical installation here in town, running off of a residential water meter, is going to give you a few rotors that put out approx two gallons of water per minute each. If your rotor is throwing thirty feet, the area you are watering is approx 2800 sq ft. If someone adds in a spray just to wet a corner or something, it will be much different. Let’s say they add an 8H. That is a spray nozzle that throws eight feet in a half circle pattern. Now that nozzle only puts out .4 gallons per minute and covers an area of 100 sq ft. Remember the rotor puts out two gallons per minute.
Which type of head do you think puts down more water? The big rotor at 2 gpm or the little spray at only .4 gpm? If you said the big rotor, you guessed WRONG!
This typical scenario is full of major issues and creates a huge imbalance in the zone. If we break it down to how much water is hitting the ground per sq ft, per half hour it works out like this. The rotors are putting down 0.02 gallons of water per sq ft, each half hr. The spray is putting down 0.1 gallons of water per sq ft, per half hr. THAT’S FIVE TIMES MORE THAN THE ROTOR!!!
If you run that zone long enough to have the rotors cover the rest yard, you drown the area covered by the spray. If you only run the zone enough for the spray to water correctly, the rest of the yard will burn up.
The bad thing is, I see this problem almost daily!
Remember this the next time you have your sprinkler system worked on and DON’T LET THEM DO THIS!