Impact sprinkler



An impact sprinkler (sometimes called an  impulse sprinkler) is a type of irrigation sprinkler in which the sprinkler head, driven in a circular motion by the force of the outgoing water, pivots on a bearing on top of its threaded attachment nut. Invented in 1933 by Orton Englehart, it quickly found widespread use. Though it has in many situations been replaced by gear-driven "rotor heads", many varieties of impact sprinkler remain in use.

Development
The original horizontal action impact drive sprinkler was invented in 1933 and patented in 1935 by Glendora, California citrus grower Orton Englehart. He later sold it to Clem and Mary La Fetra who manufactured and marketed it under the brand name Rain Bird.

Design and operation
The basic design operates as follows: The sprinkler base is fixed to the water pipe with a threaded attachment nut. The head can pivot on a bearing above the base. The force of the outgoing water flings the sprinkler arm on a circular motion. The arm, which is weighted for a particular speed of operation, is pushed back in to the stream of water by a return-spring. At the end of its travel it impacts a part of the sprinkler-head structure. The angular momentum of the arm is thereby transferred onto the head, so that the whole assembly turns slightly.

Uniform coverage of the watered area was a key point of the design: Already in the original invention, the actuator plate onto which the stream of water pushes, is shaped so that the jet of water is temporarily broken up, in order to irrigate the portion of the field near the sprinkler. In the later "part-circle heads", which intentionally only cover a chosen sector of a circle, the close range watering coverage role is provided by the rapid "return cycle", while some modern "full-circle heads" feature an additional, opposing, short range "spreader" nozzle (see image) for that purpose.

On a part-circle head, two limiting collars can easily be adjusted with the fingers, to achieve the area of coverage desired.

The uninterrupted flow path of impact heads makes them less vulnerable to damage and clogging by dirt and sand in the water. Thus, they are suitable for systems fed by well water. One defining feature of impact heads is they almost always have male pipe threads, as opposed to the female threads found on virtually all other sprinkler types.

The sprinkler head has traditionally been manufactured from cast metal. Since the 1970s some smaller models also use thermoplastics for improved corrosion resistance.

Usage
The impact sprinkler's long spray radius and uniform water distribution re-creates the effect of natural rainfall. The device provides an above-ground alternative to furrow irrigation, in which trenches are dug between rows of crops and flooded.

Variations
An underground pop-up version of the impact sprinkler was introduced as a way to avoid the problem of having to carefully and time consumingly mow around overground sprinkler heads. When not in operation, these sprinklers disappear out of sight below turf level. Although these variants provide regular convenience, malfunctioning sprinkler heads that fail to recede may become damaged by an inattentive landscaper mowing over them.

Although largely replaced by gear-driven "rotor heads" by the 1990s, impact sprinklers still have many advantages, including uniformity of coverage, sand and grit resistance, and operation at lower water pressures.