Can't Stand the Pressure?
Strategies for solving water-wasting irrigation pressure problems
When it comes to spray head nozzles, most are designed to operate at 30 PSI.
PHOTO COURTESY OF HUNTER.
If you live in an area with high water pressure, you've seen it. Spray sprinklers supplying the neighborhood with a fine, misty fog. The sound is similar to what you hear when you pull a nail out of your tire - hissing, but at a much higher decibel level. You've seen it so often that you think it's normal, and since the landscape is getting wet, all must be good.
In all likelihood however, that cloud of mist is the ghost of money and resource wasted. Sprays that look and sound like that are using a lot more water than they need to each time they run, and depending on how they are scheduled, the waste can be enormous for just one property. Multiply that by an entire neighborhood, and it becomes a monumental waste of water.
Too much pressure
We hear it all the time from irrigation professionals that call into our technical service line: "the spray zones at the Jones house have a lot of dry spots." The technician then asks for a pressure reading and generally gets a response something like this: "Oh, we have plenty of pressure." Pressure is the number one culprit when it comes to wasting irrigation water in your landscape, whether the operating pressure is too high or it's too low. Either one wastes water, but usually the pressure is too high. It leads to misting, evaporation, wind drift and poor uniformity, which usually leads someone to increase the run time to battle the dry areas. This wastes even more water.
When it comes to spray head nozzles, most are designed to operate at 30 PSI. Almost all manufacturers show this on their performance charts as the recommended operating pressure, with a 10 PSI window in either direction as the limits of the chart and thus the operating range. Rotating stream nozzles are designed to operate most efficiently at 40 PSI, with a little bit larger operating range, generally about 15 PSI in either direction.
When you start using either of these products outside the upper boundaries shown on their performance charts, you begin to start seeing the poor performance mentioned earlier, poor results in your landscape, and on the water bill. It also means that each head on the zone is putting out more water. For example, a 15-foot, half-circle nozzle running at 50 PSI, compared to the optimal 30 PSI, will flow over .5 gallon per minute more. Multiply that by a run time of 10 minutes, and that one sprinkler flows 5 gallons more than it needs to. If the zone runs twice a day, three days a week, that's 25 gallons of water per week for that one sprinkler. Since it is applying the water much less uniformly as well, most of that extra water is not doing what is intended. Now take that waste, and multiply it by the number of heads on the zone, then the number of zones on the system, and you can see that big numbers happen quickly.
So if you are in an area with high pressures, what are you supposed to do? You have some options, but the first thing you'll want to find out is what pressure you have for your system. There are devices to attach to a hose bib, and others that allow you to remove a nozzle on a head and put a tee with a pressure gauge in its place to check the pressure right at an operating sprinkler.
You can always call the water utility if you are on the municipal service, but they can only give you the pressure at the street. It's much handier to know what the sprinkler actually has for an operating pressure. Once you've determined the pressure, you'll need to decide if you want to regulate the entire system upstream from the valves using an inline pressure regulator, regulate at selected valves with a regulator attached to the valve, or replace spray head bodies with pressure regulating style bodies. There are also some manufacturers that have pressure-compensating devices that attach below the nozzle, but these do not regulate the pressure, and may not give you the desired results.
Installing a whole-system regulator can be expensive, and it may be that you don't want the entire system to have the reduced pressure. Regulating at the valve can be a simple alternative if the valves you have in your system have a means to install a device in the field. Using spray head bodies with built-in regulation is often a simple, cost-effective solution especially if the heads you have in the ground have a pressure-regulating counterpart so you only have to replace the internal portion of the sprinkler.
Regulating at the head offers the advantage of ensuring that all your sprinklers are operating at the same pressure, which is particularly important in sprays because of the narrow desired operating range for the nozzles. Of course on new installations, adding pressure-regulating sprays makes a lot of sense in areas with high static pressure. For the small additional cost, you get a better system overall, and the payback in water savings can happen quickly, depending on your cost of water.
You may be thinking, "Why don't manufacturers make all sprays with pressure regulation?"
There are some areas that don't need the feature, and don't want to pay for it, and may actually have poor performance if they tried to use them when they don't need them. Sometimes designers may want to regulate at the valve and ensure through their design that the heads are all operating within a desired pressure range. So, pressure regulated sprays aren't for everyone, and manufacturers need to provide products that will meet the needs of almost every project.
We know that if water pressure is too high it can have an adverse effect on sprinkler performance, and operating sprinklers at the correct pressure gives you a better chance for an efficient irrigation system. You must know what the pressure is on a system to help you troubleshoot problem areas, and determine what to do about various system issues. It's also a good idea to check older systems to see if perhaps the pressure has changed. Sometimes water utilities will boost the pressure to help in one area, and it can have an effect on a different area they service. Pressure regulated spray bodies can be a great solution in areas where they are needed and can help to save a huge amount of water. They should be considered on all new installations, and looked at as an upgrade to older systems when it's time to replace sprinklers.
Phil Robisch, CID, CLWM, CLIA, is a 24-year veteran of Hunter Industries and product technical manager at Hunter Industries, San Marcos, Calif.