Center pivot irrigation systems efficiently water large, circular fields using a long, self-propelled pipeline supported by wheeled towers. The pipeline rotates around a fixed central point, delivering water to crops in a uniform, controlled manner. This method helps conserve water and optimize crop yield across vast tracts of land. The machines are a common sight in farming regions globally. The mechanism moves slowly and continuously, ensuring even distribution as it rotates like a giant clock hand.
Key Structural Components for Motion
The physical structure of a center pivot system facilitates rotational movement. The fixed pivot point is anchored to a concrete pad, serving as the central water supply and control hub, allowing the entire pipeline to rotate 360 degrees.
Extending outward from the pivot are multiple pipe segments, known as spans, which are joined together and supported by trusses. These spans rest on A-frame drive towers, which are wheeled supports that bear the system’s weight and provide locomotion. Each drive tower is equipped with a pair of large wheels that provide the necessary traction to move the heavy structure across the field.
The connections between the spans at the drive towers are flexible, allowing the pipeline to flex and articulate over uneven terrain. This flexibility prevents structural components from twisting or breaking during movement. The towers translate power from the motors into the slow, circular travel of the entire system.
Powering the Rotation: Drive Mechanisms
The motive force for a center pivot system is supplied by individual motors located at each drive tower. Electric drive mechanisms are commonly used, offering reliability and energy efficiency. These systems route electrical power from the central pivot point, often using a collector ring assembly that allows for continuous current flow during rotation.
Each drive tower contains a small electric motor that powers the two wheels on that tower. The motor’s rotational speed is reduced significantly by a gearbox, which increases the torque delivered to the wheels. These gearboxes often utilize worm gear configurations to achieve the necessary speed reduction and power transmission.
The electric drive system operates using an intermittent, start-stop motion for each individual tower. When set to a specific speed, the motor runs for a short period and then stops, awaiting alignment with the next segment. This stop-start pattern contrasts with hydraulic systems, which are powered by a central pump supplying high-pressure fluid to motors at each tower, offering continuous, smoother movement.
How Alignment and Speed are Controlled
Maintaining a straight line is complex because the outermost tower must travel the farthest distance and sets the pace for the entire machine. The overall system speed and water application rate are determined by the movement of this final tower. A percentage timer in the main control panel dictates the running time of the outermost tower, controlling the rotation speed.
The alignment between the spans is maintained by mechanical or electronic sensors at each tower. A physical arm and microswitch mechanism monitors the angle between two adjacent pipe segments. If the angle exceeds a set threshold, indicating a bend, the mechanism activates the drive motor for the lagging tower.
The inner towers operate under a “catch-up” principle, moving only when the span ahead pulls too far away, correcting the angle and keeping the pipe straight. This stop-start movement continues down the line, with each tower adjusting its movement to maintain proper alignment with its neighbor. The outermost wheels travel at the fastest rate, while the innermost wheels move much slower to complete the circle simultaneously.