Center Pivot Package Replacement

Center Pivot Package Replacement by Gene Ross, Nelson Irrigation

High production efficiency is essential for producers to maintain their economic return in an increasingly competitive global market. Irrigation scheduling, efficiency, and uniformity maximize production. Center pivot and linear move sprinkler systems are capable of attaining efficiencies of 90-95 percent with uniformity values of 85 percent generally considered the minimum acceptable level before a system needs maintenance or updating. There are a few simple checks an operator can perform to ensure they are getting the most out of their existing system. Growers also must stay aware of new technologies that may improve their mechanized irrigation performance.

HOW’S YOUR EXISTING SPRINKLER PACKAGE?

The primary objective in the maintenance of your sprinkler system is to maintain the design flow rate from each sprinkler, which requires that the design pressure and nozzle size at each sprinkler remain unchanged. Common problems are worn or plugged sprinkler nozzles, plugged or malfunctioning pressure regulators, and improper installation. Malfunctioning pressure regulators can be difficult to identify visually; however, some emit water through the sides of the regulator when they fail structurally. A malfunctioning regulator can result in a sprinkler pressure that will be too high. A sprinkler emitting a finer spray or faster rotation speed relative to adjacent sprinklers may indicate a regulator that is operating above its nominal rating. If operating below its nominal rating, sprinklers will produce larger droplets and slower rotation speed, as well as reduced wetted diameter. During the irrigation season, the operator should intermittently observe sprinkler performance. This is best done either early or late in the day when the sun is low as differences between sprinklers are easier to identify in this light.

Flow rate measurements from randomly selected sprinklers can be used to judge the condition of the sprinkler package. These can be made using a large graduated container and a stopwatch. Sprinkler flow rate can then be calculated and compared to the sprinkler chart. Flow differences greater than ±10 percent indicate a problem. The cause should be identified and corrected. Plugging in the nozzle or plugging upstream of the regulator, a “stuck” regulator, or low system operating pressure are common causes of lowered flow. High flows indicate a malfunctioning pressure regulator or worn nozzle.

Pipeline pressure on the machine should be monitored throughout the year. Pressure gauges at the pivot point and at the distal end of the system should match the computer generated sprinkler chart.

A flowmeter can also be a valuable tool and can ensure that the flow output of sprinklers, regulators, and end guns matches the sprinkler chart. Pressures and flowrates that change during the irrigation season could indicate problems with a sprinkler package.

Yield maps and overhead pictures can also be utilized to identify poor sprinkler performance.

A good strategy against wear is to replace the sprinkler package every 5–10 years depending on water quality and hours of use. An accepted industry rule of thumb is to consider replacing sprinkler packages at least every 10,000 hours.

REASONS TO CONSIDER UPGRADES

Runoff and deep wheel tracks are common problems associated with center pivots. A modern, properly designed sprinkler package will match application rates and droplet size to the intake properties of the field to minimize runoff. Part-circle devices at the wheel tracks are becoming more common to further keep the wheel track dry and prevent tracking.

Part-circle sprinkler devices give a 180 degree pattern.

Part circle sprinklers installed on boombacks keep tracks dry ahead of pivot.

Old sprinkler technology was oftentimes inefficient and required high operating pressures. Over the years, the industry has introduced new sprinkler options that provide low operating pressures in the 6–20 psi (0.4-1.4 bar) range that achieve high levels of uniformity and efficiency.

Sometimes older sprinkler packages don’t match the current field and crop requirements. The height of the sprinkler above the crop canopy, along with the spacing and wetted radius of the sprinkler nozzles, can significantly affect irrigation uniformity. In general, sprinkler height should be approximately 3 feet (1 m) above the plant canopy to ensure good irrigation uniformity. In most cases, excellent uniformity can be expected when sprinkler spacing does not exceed 50–65 percent of the wetted radius. At times this is not possible with taller crops such as corn. Extra attention is needed to ensure proper overlap and runoff control in these cases.

Consider dual nozzle clips to:

• Adjust flowrate to meet changing ET requirements during the growing season.

• Reduce flowrate and subsequent droplet size when germinating to maintain integrity of bare soil.

• Reduce flowrate when applying chemicals.