On a typical zone of rotors you should have 4 halves, 4 quarters, and a full spinner in the middle. If installed properly, all heads should spray from head to head, so each section of grass is getting double coverage, but this is usually not the case. In order for these heads to put down the same amount of water to each part of the grass, the halves are going to have to put out double the amount of water than the quarters. This is because it takes double as long for the half to make a full pass as the quarter. It takes the full spinner even longer than the half. I'm not a mathematician, but there is an equation that tells you exactly how long it takes for each head to complete a full pass. You have to have a small nozzle in the quarters a medium nozzle in the halves and a big nozzle in the full. For example: 1 gpm in the quarter, 2 gpm in the half, and 4 gpm in the full. This can also be helpful in areas in the lawn that require more water than others. An area along the sidewalk in full sun, will need more water than the grass in the shade under a tree. You can put a bigger nozzle in the rotor by the sidewalk, to help it get more water on the dry area, without over watering the shady spot, and still run the sprinklers the same length of time.
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