Under Pressure

The rising cost of water encourages water conservation among irrigation contractors, elevating a common irrigation concern - pressure regulation - to a top priority. Pressure regulators, when installed correctly, cut down on water usage by ensuring uniform pressure and, thus, wasting less water.

Rapid changes throughout a system, based on the terrain, water usage in the area over time or even the time of day, cause pressure discrepancies. In addition, initial design plays a part in the correct pressure, said Robert Reaves, landscape water conservation specialist, Lower Colorado River Authority, Austin, Texas. "Probably one of the biggest problems is not taking into account all the design factors," he explained. "There really shouldn't be a problem with pressure, but unfortunately, it's the No. 1 problem in waterways in the United States."

THE REGULATOR. As a solution to fluctuating pressure, pressure regulators sense pressure changes in a system and adjust accordingly. Ron Wolfarth, marketing manager, Rain Bird Corp., Commercial Division, Tucson, Ariz., said pressure regulators work by sensing the water pressure downstream and generating pressure losses within the device, thus creating a constant downstream pressure.

Although pressure can be controlled at many points within a system, Wolfarth recommended using a sprinkler that has a pressure regulator built into the head. "Different heads have different pressure requirements and within a single zone there are differences in pressure at the head due to elevation changes and the different lengths of pipe going to the sprinkler head," he said. "Having the pressure regulator at the head results in uniform pressure and more uniform application of water at the site."

Since installing the regulator at the head is the most expensive option, Wolfarth suggested positioning the device in the remote control valve as an alternative. "It's potentially a very good solution - you always want to have all heads on a single valve to have the same operating pressure requirement, and putting the pressure regulator device in the valve is a good balance between economy and performance," he said. "This limits the difference in operating pressure at the head to those caused by elevation change and friction loss in that zone instead of the entire system."

To identify pressure problems, Reaves suggested looking at the water output. Low pressure results in large droplets of water and a reduced flow radius, generating circled green areas and brown spots where the water cannot reach, while high pressure usually creates misting. Further, Reaves pointed out that sometimes, low pressure symptoms occur due to a potential blockage or restriction in the system.

In addition, Brian Vinchesi, irrigation consultant, Irrigation Consulting, Pepperell, Mass., described the importance of a pressure differential when using a regulator. "It will not regulate unless you have a pressure differential, and you basically need to have 10 pounds of differential across the regulator to regulate the system," he clarified. Although currently used primarily in commercial jobs, Vinchesi foresees eventual widespread use of regulators in residential properties, based on their ability to clear up common pressure complications.

ALTERNATE METHODS. If pressure regulators pose a financial obstacle, pressure can be regulated through other methods, Wolfarth said. "Assuming you want to reduce pressure in the system, use some sort of valve on the mainline or the manual flow control device in the valve," he explained. "Some people inappropriately use the valves on the backflow preventer to reduce pressure. This can cause wear that makes them useless during the annual testing of the device. This manual approach is a last resort method of reducing pressure since there is only a constant pressure drop and no response to changes to water pressure from the source.

"Also, water pressure can only be increased by adding energy to the system with a pump," Wolfarth continued. "Some incorrectly believe that reducing the diameter of pipe increases pressure. This only increases the velocity of water in the pipe and actually causes more friction loss resulting in lower pressure."

Reaves explained that often, pressure changes result from irrigation contractors who feel rushed for time and may not examine the hydraulics thoroughly. Yet, Wolfarth highlighted several causes of pressure problems not necessarily related to inattentive contractors.

"Water pressure does vary throughout the day," he pointed out. "The system operates automatically during the night when not many people are using water, and the pressure goes up. The water from the city mainline is not constant. Also, over time, as more homes, businesses, schools, etc., are built on that water supply, the pressure will drop as well." He added that multiple zones operating at the same time on one system also pose regulation difficulties best solved with a pressure regulator at the valve or head.

However, Vinchesi identified current economics as playing a part in increasing pressure regulator use. "If you run the sprinkler at the right pressure and use less water you'll be a lot more efficient, and the cost of water will also force it that way," he said.

Even though pressure regulators may cost more than some of the more old-fashioned, manual methods, Wolfarth maintained the benefits outweigh the costs. "You have longer operating life of the system, and lower operating costs in terms of better uniformity," he said. "Better uniformity means you can irrigate less and apply the optimum amount of water to the driest part of the system. Over time and over the life cycle [of your system], your operating costs are lower."