Center pivot irrigation

related topics
{@card@, make, design}
{island, water, area}
{math, energy, light}
{system, computer, user}
{car, race, vehicle}
{line, north, south}
{ship, engine, design}
{build, building, house}

Center-pivot irrigation (sometimes called central pivot irrigation), also called circle irrigation, is a method of crop irrigation in which equipment rotates around a pivot.[1] A circular area centered on the pivot is irrigated, often creating a circular pattern in crops when viewed from above.

Contents

How it works

Central pivot irrigation is a form of overhead (sprinkler) irrigation consisting of several segments of pipe (usually galvanized steel or aluminium) joined together and supported by trusses, mounted on wheeled towers with sprinklers positioned along its length. The machine moves in a circular pattern and is fed with water from the pivot point at the center of the circle. The outside set of wheels sets the master pace for the rotation (typically once every three days). The inner sets of wheels are mounted at hubs between two segments and use angle sensors to detect when the bend at the joint exceeds a certain threshold, and thus, the wheels should be rotated to keep the segments aligned. Center pivots are typically less than 500m in length (circle radius) with the most common size being the standard 1/4 mile machine (400 m). To achieve uniform application, center pivots require a continuously variable emitter flow rate across the radius of the machine. Nozzle sizes are smallest at the inner spans to achieve low flow rates and increase with distance from the pivot point.

Most center pivot systems now have drops hanging from a u-shaped pipe called a gooseneck attached at the top of the pipe with sprinkler heads that are positioned a few feet (at most) above the crop, thus limiting evaporative losses and wind drift. There are many different nozzle configurations available including static plate, moving plate and part circle. Pressure regulators are typically installed upstream of each nozzle to ensure each is operating at the correct design pressure. Drops can also be used with drag hoses or bubblers that deposit the water directly on the ground between crops. This type of system is known as LEPA (Low Energy Precision Application) and is often associated with the construction of small dams along the furrow length (termed furrow diking/dyking). Crops may be planted in straight rows or are sometimes planted in circles to conform to the travel of the center pivot.

Originally, most center pivots were water-powered. These were replaced by hydraulic systems and electric motor-driven systems. Most systems today are driven by an electric motor mounted at each tower.

For center pivot to be used, the terrain needs to be reasonably flat; but one major advantage of center pivots over alternative systems is the ability to function in undulating country. This advantage has resulted in increased irrigated acreage and water use in some areas. The system is in use, for example, in parts of the United States, Australia, New Zealand, Brazil and also in desert areas such as the Sahara and the Middle East.

Full article ▸

related documents
Bouldering
Bubble Wrap
Amphora
Cyan
Figure-of-eight loop
Post and lintel
Tachi
Preform
Sampler (needlework)
Argent
Backscratcher
Blu-Tack
Kickflip
Belgian euro coins
Greek euro coins
Knapping
War hammer
Gouache
Tangram
Hairpin
Bifocals
Penrose triangle
Carat (mass)
German euro coins
Fisting
Clove hitch
Blackwork Embroidery
Mahogany
Mergenthaler Linotype Company
Indy grab