Wednesday, August 27, 2008

Center pivot irrigation

Center-pivot Irrigation, is a method of crop irrigation in which equipment rotates around a pivot. A circular area centered on the pivot is irrigated, often creating a circular pattern in crops when viewed from above. The system is fed with water from the pivot point at the center of the circle.
Central pivot irrigation is a form of sprinkler irrigation consisting of several segments of pipe galvanized steel or aluminium, joined together and supported by trusses, mounted on wheeled towers with sprinklers positioned along its length. 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.
Centre pivots are typically less than 500m in length (circle radius) with the most common size being the standard 1/4 mile machine (400 m). 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. 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 Low Energy Precision Application. Crops may be planted in straight rows or are sometimes planted in circles to conform to the travel of the center pivot.
Most systems today are driven by an electric motor mounted at each tower. The equipment can also be configured to move in a straight line, where the water is pulled from a central ditch. In this scenario, the system is called a linear move irrigation system. Te
rrain needs to be reasonably flat, but one major advantage of centre pivots over alternative systems is the ability to function in undulating country.

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