Impact sprinklers are typically made of brass or plastic. They are so named because they use the force of the water exiting the nozzle to swing an arm around to make “impact” with the sprinkler frame. This impact causes the sprinkler to rotate slightly. This motion happens repeatedly so that the sprinkler rotates providing coverage of a large area and results in the common “cha-cha-cha” sound as it rotates.

Because of the inconvenience of mowing around the impact sprinklers mounted on pipes, the pop-up impact sprinkler was invented. The same type of sprinkler was enclosed in a cast iron or plastic case 4-6 inches in diameter with a lid on top of the sprinkler head. The enclosed sprinkler case could then be placed in the ground. When water pressure was applied to the sprinkler, it would rise out of the case about 4 inches above the soil surface and spray the surrounding area. When the water was turned off, a spring inside the case would force the sprinkler head and lid back down into the case so it no longer extended above the ground.

These pop-up impact sprinklers had issues as well. A particular brand of high-vacuum mowers would occasionally suck the sprinkler head up out of its casing enough to chop it off. In certain landscapes, sand and dirt would also get into the casing, preventing the sprinkler from retracting leaving it in an extended position. This led to more improvements.

Rotor and Gear Driven Sprinklers

To overcome the problems experienced with pop-up impact sprinklers, manufacturers tried to find a solution that eliminated the need for the large cavity inside the pop-up impact sprinklers. The new design to fix this used an internal drive mechanism.

Rotor and gear driven sprinklers look and work very much the same. While they both have different internal drive mechanisms, they both depend on a flow of water moving past some internal part of the sprinkler. When water pressure is applied, a 1-inch or so diameter shaft extends about 4 inches above the ground. As water flows past the internal drive mechanism, it causes part of the extended shaft to rotate. The shaft is sealed to prevent sand and dirt from entering the sprinkler which helps to eliminate many of the problems with the previous generation of pop-up impact sprinklers. This also made the tops of the sprinklers virtually impossible to see when retracted.