When it is time to pressurize for the season, it is important to ensure the machine is running like it was designed to do. The pivot chart, the schematic by which the system was designed to work, gives you information about every drop on the system and the total system output. If you cannot find the pivot chart, you can always request it from the dealer you purchased it from. They should have a record of it. The pivot chart will show the drops by number and distance, starting from the center and working outwards. If this is a lateral or linear move, the numbers should start at the cart end.
Check Nozzles, Pressures, and System Performance
The first and easiest way to check the system is by just walking along the system, confirming that what is on the pivot chart matches the color and number on the nozzles. Also, look for obvious clogging, leaks, and damage, and fix them accordingly. If capable, you may check the flow rate. However, you do not need to take a measure from every sprinkler drop – focus on the center, the end, and the highest point of the machine. You may look back at your yield records and find a correlation in sprinklers not working at the right pressure. However, narrow issues (i.e., one sprinkler in each span) may be hidden by the size of the combine header. Looking at summer aerial imagery is often used in these cases to identify issues during the off-season, when you have more time to fix them. The regulators are working properly when the pressure in the mainline or right before the regulator is at least 5 PSI over the rated pressure.
If the pressure is too high compared to the pivot chart, check for plugged nozzles, clogged drops, or any other restrictions across the mainline or pipeline.
If the pressure is lower compared to the pivot chart, then there is likely an outlet releasing too much water or a pump output concern. In many cases, flow meters can be a helpful tool to determine if you have more or less water flowing through the system than the original design called for. It is easy to assume the flow meter is wrong when the values shown differ from the pivot chart. Some differences between the two can be normal due to equipment age or friction losses throughout the system, especially during linear moves and hose dragging. However, a flow meter can be removed and tested by manufacturers to ensure proper readings.
Confirm Travel Speed and Application Depth
In addition to verifying pressure and total system flow, it is important to confirm that the machine travel speed matches the pivot chart design. The application depth delivered during a pass depends not only on sprinkler flow but also on how long the machine takes to move across an area. A simple check is to time the machine over a known distance (e.g., one full revolution) and confirm that the travel time aligns with the sprinkler chart for the selected percent timer or speed setting associated with the intended application depth. Changes made to a system over time, such as different tire sizes or drive components, can alter travel speed. If the sprinkler chart is not updated accordingly, the system may appear to operate normally while unknowingly over- or under-applying water with each pass.
Assess Water Distribution and Replace Worn Components
In a properly functioning system, the water distribution should gradually increase the water volume from the center to the outer end. Worn-out pressure regulators and sprinklers can be hard to spot, making it important to check pressure against a chart. A timelier option would be to do a catch-can test early in the season, before the crop gets tall. However, every piece of equipment has a lifespan, including sprinklers and regulators. Replacing them every 8 to 10 years is a good investment. When replacing, it is good practice to take the sprinkler, the place on the pivot (i.e., sprinkler number), and the pivot chart to the irrigation dealer to ensure the correct match.
Tina Sullivan, Northeast Area Agronomist
tsullivan@ksu.edu
Daran Rudnick, Professor and Director of Sustainable Irrigation
drudnick@ksu.edu
Jonathan Aguilar, Professor and Irrigation Specialist
jaguilar@ksu.edu
Tags: irrigation equipment