Center Pivot Irrigation
Listening to the news about a potential drought facing Alberta, I was reminded of driving home to Ontario last summer and seeing these large sprinkler systems alongside the highway. They appeared to rotate about a wellhead and I imagined used up great quantities of water. Digging a little further in Wikipedia, they are called center pivot irrigation systems and it was interesting to read how they maintain a straight line and adjust water flow for consistency across the radius of the circle.
The outside set of wheels sets the pace for the rotation. The inner sets of wheels are mounted at hubs between two segments and use angle sensors (microswitches) to detect when the bend at the joint exceeds a certain threshold. When the angle is too large, the wheels rotate to keep the segments aligned. Typical periods for a full rotation include three days; while other sources have the outer edge of the structure moving at 2 to 3 m (6.6 to 9.8 ft) per minute, which would equate to 14 to 21 hours for one full rotation of a 400-meter-radius (1⁄4 mi) system.
To achieve uniform application, center pivots require a variable emitter flow rate across the radius of the machine. Since the outer-most spans (or towers) travel farther in a given time period than the innermost spans, nozzle sizes are smallest at the inner spans and increase with distance from the pivot point. Aerial views show fields of circles created by tracings of quarter-mile or half-mile (400 or 800 m) radial irrigation pipes, which consume up to several thousands of gallons per minute.
If you're still with me after reading all that, the image itself was captured in harsh sunlight, which I tried to use to my advantage to better see the spray of water.
Center Pivot Irrigation
Listening to the news about a potential drought facing Alberta, I was reminded of driving home to Ontario last summer and seeing these large sprinkler systems alongside the highway. They appeared to rotate about a wellhead and I imagined used up great quantities of water. Digging a little further in Wikipedia, they are called center pivot irrigation systems and it was interesting to read how they maintain a straight line and adjust water flow for consistency across the radius of the circle.
The outside set of wheels sets the pace for the rotation. The inner sets of wheels are mounted at hubs between two segments and use angle sensors (microswitches) to detect when the bend at the joint exceeds a certain threshold. When the angle is too large, the wheels rotate to keep the segments aligned. Typical periods for a full rotation include three days; while other sources have the outer edge of the structure moving at 2 to 3 m (6.6 to 9.8 ft) per minute, which would equate to 14 to 21 hours for one full rotation of a 400-meter-radius (1⁄4 mi) system.
To achieve uniform application, center pivots require a variable emitter flow rate across the radius of the machine. Since the outer-most spans (or towers) travel farther in a given time period than the innermost spans, nozzle sizes are smallest at the inner spans and increase with distance from the pivot point. Aerial views show fields of circles created by tracings of quarter-mile or half-mile (400 or 800 m) radial irrigation pipes, which consume up to several thousands of gallons per minute.
If you're still with me after reading all that, the image itself was captured in harsh sunlight, which I tried to use to my advantage to better see the spray of water.