For years, growers have asked irrigation manufactures “How can I tell if my pressure regulator is bad?” and for years the industry has responded with “Well, it’s not that easy.”
The benefits of incorporating pressure regulators in any pivot irrigation system are clear. Pressure regulators limit excessive and varying inlet (source) pressure to a constant outlet pressure. They keep sprinklers operating at design pressure and flow, and save water by preventing misting, runoff and other issues related to poor uniformity.
Most growers understand the importance of pressure regulation and its connection to water and energy savings. But for many it is difficult to determine exactly when it is time to replace their pressure regulators.
The most common signs of bad or faulty pressure regulators include leakage between the device’s housings, misting or overwatering in some areas, and increased water and energy consumption. These symptoms are easily spotted during a visual check of the system or due to unusual flow meter readings.
There are ways to test pressure regulators with precision. However, manufacturers have long preferred to train grower’s eyes and show them how to spot potential issues. This is not because testing pressure regulators and seeking precise measurement readings is impossible. Manufacturers made this choice because the time and effort time-strapped growers would have to dedicate to testing is normally unfeasible.
Pressure gauges accurately monitor system pressure. Senninger’s gauges are vibration and shock resistant. They are designed according to ANSI/ASME B40 standards and have a high accuracy class of +/- 1 to 2.5% of span.
The best way to know if the pressure regulator is working is to install a pressure gauge on each side of the regulator. Growers can measure inlet pressure with a pressure gauge above the regulator. Then they can measure the outlet pressure with the gauge below the regulator. Inlet pressure should be at least 5 psi (0.34 bar) above the pressure regulator rating for the regulator to function.
If a pressure regulator delivers an outlet pressure significantly above its rating it is considered faulty. However, pressure regulators are typically rated for an accuracy of +/- a certain percent and growers need to check with the manufacturers to determine how much variation is permissible and/or expected. For example, a 15 psi (1.03 bar) pressure regulator delivering an outlet pressure of 20 psi (1.38 bar) would be regarded as malfunctioning if the manufacturer establishes an accuracy of +/- 6 percent.
Pressure gauges can provide an accurate reading, but getting gauges installed on a number of test drops is a time consuming process. First, a grower needs to dismantle each hose drop to remove its components and install the gauges above and below the regulator. Then he or she must restart the pivot and read each individual gauge.
Depending on the size of the pivot, a grower could have anywhere between 5 and 15 drops to test in order to get an accurate picture of the system’s pressure regulation status. Growers can keep two gauges in place – one at the beginning and one at the end of the pivot. The grower will have to test one span and slowly move on to another with the two other gauges.
Many growers can also perform a test using a pitot tube inserted in the nozzle stream. This device can be a bit tricky to use as the reading may vary depending on where growers place the tube along the stream. They will also need to refer to a nozzle flow chart to compare the measurement to the nozzle and pressure needed for that hose drop.
You can measure water with a simple bucket test at the point where sprinklers apply water to the field. You can record water flow from your water meter and compare with results from the bucket collection results.
The operating pressure of an irrigation system always affects the flow rate. Higher-pressure increases flow along any pipe and as that flow increases, water velocity increases as well. This means that growers can also test the functionality of their regulators by measuring the flow that comes out of each sprinkler head.
The first thing growers need to do is check to see if the drops along their pivot are mounted in the correct place. A sprinkler package checklist can help them determine if higher or lower flow nozzles have been installed correctly.
Growers can also measure their flow with a bucket-type collector to catch water from sprinklers. This catchment must be timed to be able to calculate the flow rate (GPM or L/hr) from an individual sprinkler head and compare it to the flow that nozzle should produce. If the amount of water caught is not between +/- 3% of the design flow rate, this implies there may be a problem with the pressure regulators.
Why Visually Inspect
After testing system pressure, growers who encounter issues must then ask themselves how many pressure regulators need to be replaced. Should the grower assume they all need to be replaced if only a certain number are malfunctioning at key points along the pivot? Should the regulators along the entire system be replaced? It’s a judgement call on the part of the grower.
This is why most manufactures recommend growers study their system’s application pattern and consider replacing pressure regulators after approximately 3 to 5 years of use.
Investing in new pressure regulators may not seem worth the investment. However, if an irrigation system is not performing up to standard, the time and money lost in wasted input costs and yield loss is a high price to pay. Growers can test their regulators with precision if they choose. It is an excellent idea for anyone who wants to know exactly what is happening in their system. But the time it takes to perform these tests is simply not feasible for many others.
Eyeballing a field and looking for trouble spots may not be the most scientific or data driven way to check pressure regulators, but it rarely fails at identifying issues and it fits right into an grower’s schedule.