The Pressure's On: Irrigation Pressure

Unlike horseshoes and hand grenades, close isn’t good enough when it comes to proper pressurization in irrigation systems. Since irrigation systems are designed to operate within exact specifications, even slightly incorrect pressurization can throw everything off, according to David Zoldoske, director, Center for Irrigation Technology, Fresno, Calif. “Irrigation equipment is designed to operate within certain parameters,” he said. “If the pressure is too high or low, the system won’t work right.”

While improper pressurization presents a problem for contractors and their customers, it also wastes a tremendous amount of water, which is an especially serious offense in drier climates, said Don Thompson, director of sales, Buckner By Storm, Fresno, Calif.

Unfortunately, improper pressurization is a fairly frequent occurrence. “Pressure problems are more common than people would admit,” Zoldoske said. Thompson agreed: “People just don’t pay as much attention to pressure as they should.”

ROOT OF THE PROBLEM. A range of factors can cause improper pressurization. The water source is one common variable. Depending on whether the irrigation system draws water from a well or a municipal water supply, there can be fluctuations that will seriously affect pressure, according to Steven Silverberg, president, Ecosystems, Old Bridge, N.J. Because of often heavy residential water consumption through such uses as laundering, showering, car washing or dishwashing, there are many areas where municipal water systems are simply overloaded and, this, in turn, will detrimentally affect pressure, said Jeff Carowitz, vice president of marketing, Hunter Industries, San Marcos, Calif.

Geography also plays a role in proper pressurization. In Rick Pate’s case, the relatively flat terrain of central Alabama works in his favor. Without a lot of elevation change, pressurization is not usually a problem in the irrigation systems he works on, said Pate, president, Pate Landscape Co., Montgomery, Ala. This is not usually the situation, however, and elevation change often has a direct effect on pressure if it is not accounted for in the system’s design.

An irrigation system’s components and their arrangement can also obviously influence pressure. Too many sprinkler heads in a zone, for example, can lead to uneven distribution, and, in turn, a pressure problem. “You may have enough water flow to run three sprinklers but try to run four sprinklers and there may be a problem,” Thompson pointed out. Taking standard water pressure calculations into account can alleviate these issues (see “Water Pressure Calculations” on page 144), but these aren’t always followed.

Overall, the better the system design, “the less these variables will matter in terms of an irrigation system’s effectiveness,” Pate said. Still, design problems are rampant.

OFF TO A BAD START. One of the most frustrating causes of improper pressurization is a poorly designed irrigation system. If a system is flawed to begin with, addressing a pressurization problem can be a real headache, according to Thompson. “Fixing a bad system is very difficult, while fixing a good system is very easy,” he observed.

One of the most common design problems is simply not tailoring a system to a customer’s specific needs, Silverberg said. Designers need to be careful not to generalize and overlook the specific requirements of a system, such as elevation or water source issues, Pate added. “What works in one scenario will not work somewhere else,” he pointed out. “That’s where we see people getting in trouble. Design rules of thumb are good 95 percent of the time – it’s the other 5 percent you need to worry about.”

When he can avoid working on poorly designed systems, Pate said he tries to do so. Otherwise, contractors inherit a host of problems, including improper pressurization. Thompson agreed, noting that contrary to an increasingly popular notion, irrigation design isn’t a skill learned at the local Home Depot. “If this is the case, the chances of a lousy system are pretty good,” he said.

Thompson strongly advised consulting manufacturer catalogs to make sure a system is running to its proper specifications. That alone could take care of a pressurization problem in many cases, he emphasized.

Unfortunately, there is no easy resolution when contractors are dealing with a flawed system. “Once the system is installed, repairs can be very costly,” said Silverberg. “Sometimes, the only change is to redo the system.” This is a worst-case scenario, however. Usually, minor design flaws, such as an incorrect nozzle size, can be corrected without “too much fanfare,” he said.

RECOGNIZING THE PROBLEM. Improper pressurization is a relatively straightforward problem to identify (see “Telltale Signs” on page 140). Most obviously, with both high and low pressure, a system isn’t going to work effectively. In particular, a low-pressure system will often have large droplets of water “gurgling out of its heads,” Silverberg said. Also, the heads won’t pop up all the way or at all. Low pressure can also result in brown spots as well as soil compaction throughout the irrigated area.

In the case of high pressure, the water will have a tendency to mist and “blow away in the wind,” Thompson said. This takes place because the nozzle will put out very tiny droplets of water, producing a poor pattern of coverage likely to evaporate.

When this happens, the radius of effective coverage is greatly reduced. “The water doesn’t go as far as you want it to go,” Zoldoske said. Needless to say, this ineffective irrigation results in a colossal waste of water in addition to poor irrigation results.

FIXING THE PROBLEM. Unless a system is hopelessly flawed, most pressure problems can be resolved after a bit of troubleshooting. Before taking any drastic measures, however, check the system’s specifications. “When a technician goes out, he needs to make sure the system is to plan,” Thompson advised. Test pressure at both the water source and at the sprinkler. “If the system is set for 35 psi, but you’re getting 20 psi, then there’s a problem,” said Thompson, who advised looking at the more obvious potential problems first. Sometimes, correcting pressure is as simple as cleaning dirt out of valves. If you can, “find the easy way out first,” Thompson said.

Changing system components, such as the nozzles, for a different screen size is also a common solution to pressure problems.

Generally speaking, in high-pressure situations, pressure-reducing valves should be installed, while in low pressure scenarios, reducing nozzle size is a likely solution.

With a serious pressure problem, a booster pump might be required to correct the problem. Since a booster pump can be expensive and labor intensive, Zoldoske recommended only using one as a last resort measure.

The author is Associate Editor of Lawn & Landscape magazine.