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How to Select the Best Spray-type Sprinkler

 

In order to make good decisions about which products will work best for you it is necessary to have some basic knowledge of how sprinklers work and what the various options available to you are. Therefore the following few paragraphs are intended to give you the background necessary to understand the terminology used in my reviews. The background information below is much more in-depth than that in the tutorials, so even if you have read the tutorials you should still look through this page.

Fixed Spray-Type Sprinkler Basics

Sprinklers fall into one of two types based on the method they use to apply water to the ground; fixed spray-type (sprays) or rotor-type (rotors.) Spray-type sprinklers are the type of sprinkler that spray a fixed water pattern similar to how a old-fashioned shower head works. Rotor-type sprinklers use a rotating stream (or multiple streams) of water to apply the water to the ground. Spray-type sprinklers are also called “fixed spray heads”, “spray heads” and often just plain “sprays”. Most of the professionals I know call them "spray heads", and you will note that is the term I use also. They are typically used for smaller size areas. Rotor-type sprinklers are used for larger areas (generally more than 18' in width.)

Where should spray heads be used?

Spray heads work best for smaller areas and areas with tight, curving edges. I like to use them for anything less than 25 feet wide. Although rotors are available for areas as narrow as 18 feet, spray heads tend to be more economical in these smaller areas than rotors. Another advantage of spray heads is their relative simplicity. There is not a whole lot to go wrong with one. By far the most common problems result from clogged nozzles, a problem that can be almost totally eliminated by flushing the pipes thoroughly prior to installing the spray heads and installing a filter on your sprinkler system. (Install the filter upstream of the automatic sprinkler system valves so the valves benefit from filtered water too!) Although most spray heads come with a small filter screen that installs under the nozzle, in my opinion these filters are not sufficient. I recommend installing a 100 mesh filter at the water source for ALL sprinkler systems.

How a Typical Spray-Type Sprinkler Works

Water enters the base of the sprinkler and passes up through the body to the nozzle. On the way to the nozzle the water passes through a filter screen. As previously mentioned I do not suggest that you rely on this screen for filtration, consider it a backup to your sprinkler system filter. Do not remove the filter screen, some spray type sprinklers will not work properly without the screens! After passing through the screen the water enters the nozzle and passes through a small valve. This valve is operated by a screw on top of the nozzle, which is known as the “radius adjustment screw”. As you turn the screw the valve closes slightly. This causes the water to speed up as it tries to force it's way through, resulting in an increase in turbulence and friction. This turbulence and friction causes a drop in the water pressure. The pressure drop in turn causes the radius of the sprinkler to be reduced. From the radius adjustment valve the water continues up into the nozzle and is sprayed up against a plate or through a small slit(s), which causes the water to fan out as it leaves the nozzle. This is what creates the fan-like spray pattern typical of a spray head. The shape and size of the plate or slit is what determines the nozzle pattern and angle. Some spray nozzles have adjustable plates or slits that allow the spray arc to be adjusted.

A typical spray head consists of two separate parts, a body and a nozzle. Often these are sold separately, but sometimes retail stores package them together. Typically various different nozzles are available, anywhere from just a few different patterns and radii combinations, up to hundreds of variations. In most cases all of a manufacturer's nozzles will fit on all of their spray head bodies.

Pop-Up vs. Shrub Spray Heads

The bodies come in two basic styles, “pop-up” and “shrub” style. Pop-ups do just what the name implies, the sprinkler nozzle is attached to a riser which lifts the nozzle up into the air when the sprinkler is operating. After the irrigation is complete, the riser and nozzle drop back down into the sprinkler body. Since the body is typically installed below ground, the sprinkler becomes more or less invisible when it is in the “down” position. This has two advantages. The first is that the sprinkler does not detract as much from the appearance of the landscape. The second advantage is that the sprinkler is not as likely to trip someone, or be damaged by yard care equipment such as lawn mowers.

Recommended Pop-Up Heights

The 6 inch height bodies are the primary height I use for my projects in both lawn, shrub, and most ground cover areas (I use a lot of low growing ground covers with 4-6 inch mature height.) The 12 inch bodies work good for taller ground covers and low shrubs. Keep in mind that with shrubs you don't always need to throw the water over the top of the shrub. When the shrubs are first planted they are small and a 6" height will spray over them. As the shrubs grow they begin to block the spray, but by this time the shrub has developed a good root system and will seek out the water. Generally in a landscape design shorter shrubs are used at the edges of planters and larger, taller shrubs are used farther back in the area. So 6 or 12 inch pop-ups spaced 10 to 12 feet apart at the perimeter will usually provide adequate coverage.

Shrub-Style Spray Sprinklers

Shrub-style sprinkler bodies are mounted above ground level on a vertical pipe. This allows the sprinkler to be elevated above the level of the plants, where it can spray water over them. Shrub type sprinklers are most often used in areas with tall, dense shrubs. Shrub type bodies should not be used next to sidewalks, paths, driveways, lawn edges, or anywhere near places people walk or play. This is because the shrub sprinklers may trip people, or worse, someone may fall on one and be impaled (more likely just badly bruised, but the injury is still significant). Not a pretty thought. For this reason I recommend, as do almost all professionals, that shrub type spray heads only be used when there is no other option. If you have tall shrubs adjacent to a sidewalk you should consider replacing them with ground cover or lower growing shrubs. I use shrub style sprinklers mostly on inaccessible hillsides where I am trying to grow plants for erosion control. I usually install them 36" above ground to avoid problems with people tripping over them or falling onto them. One of the arguments often given for using shrub style sprinklers is cost savings. Cost wise, I have found that shrub style sprinklers are no less expensive than pop-up style bodies once you include the cost of the riser pipe and a stake to keep the sprinkler from wobbling. In order to make a shrub style sprinkler cost less than a pop-up you must install it within 6" of ground level. That is the height that makes it most dangerous. Your homeowner's insurance rates will likely go through the roof if someone trips on a sprinkler and files a claim for injuries. This will be far more expensive than the cost would have been to use pop-up sprinklers!

Spray-Type Sprinkler Radius

The radius of a spray-type sprinkler is determined by the nozzle used. The sprinkler manufacturer will list the radius for each sprinkler nozzle on the packaging, a separate reference chart, or their website. The radius will vary based on the water pressure, more pressure will result in a larger radius. So for a typical nozzle you will see a table that gives the various radius, pressure and flow combinations for the nozzle (see example below.) Most spray head nozzles have a radius between 4-15 feet, some are claimed to have a radius as great as 21 feet, but I would urge caution using a radius over 15 feet. It's a physics problem, water simply doesn't spray further than 15 feet very well or evenly. When selecting a nozzle, look for one with a radius as close to your desired radius as possible. If you can't find the desired radius, get the nozzle with the next size larger radius than you need. The radius can then be reduced by means of a radius adjustment screw on the top of the sprinkler nozzle. As the adjustment screw is closed, the water pressure at the nozzle is decreased, this results in the radius and flow of the sprinkler being reduced. For example, if you wanted to water a 14 foot wide area you would install a 15 foot radius spray head and use the radius reduction screw to reduce the radius to the desired 14 feet. With most nozzles the radius can be adjusted down to almost nothing, however I don't recommend reducing it by more than about 40% when using the radius adjustment screw. Further reduction can cause coverage and operation problems. Often times a nozzle with a severely reduced radius will stop working on warm days. This is because the heat causes the radius reduction screw to expand, which causes the flow to be completely shut off. One last thing to watch for when selecting a nozzle is the angle of spray. Some nozzles are designed to spray the water at a very low or even flat angle. Be careful of these nozzles, if you have mounds or hillsides they may spray the water into the ground. It is best only to use low angle nozzles in flat areas.

Spray-Type Sprinkler Spacing

As a general rule I advise against spacing spray-type sprinklers more than 18 feet apart. Spacing them farther than that often gives unsatisfactory results. Spray heads require what is know in the industry as ";head-to-head spacing". This means that the water from one sprinkler must spray all the way to the next sprinkler in all directions- to the right, left and also to the head across from it. This is very important, spacing the sprinkler heads too far apart is one of the most common design errors, and it is almost impossible to go back and correct the problem later without spending tons of money. The sprinkler design tutorial gives a more in-depth description of the importance of head-to-head spacing. Head-to-head spacing is critical in lawn areas for avoiding dry spots and disease problems. In shrub and ground cover planting there is more room for fudging, you can generally space the heads at up to 60% of their diameter of water throw. Examples: Using a 15' radius head for lawn areas you should not exceed 15' between sprinklers. Using 15' radius spray heads for shrub areas you should not exceed 18' (30' diameter x 0.6) between sprinklers.

Sample Spray Nozzle Performance Table (this sample is for a Toro nozzle)
Pattern Part No. 20 PSI 30 PSI 40 PSI 50 PSI
12Q 11' - 0.40 GPM 12' - 0.50 GPM 13' - 0.60 GPM 13' - 0.63 GPM

 

Example: From the chart above you can see that this nozzle at 30 PSI will have a radius of 12 feet and a flow of 0.50 GPM (gallons per minute). If you wanted to operate this nozzle at 25 PSI you would need to extrapolate the data from the chart. For example for this nozzle 25 PSI would give 11.5' radius and 0.45 GPM flow.

 

Reducing the radius of a nozzle.

As previously noted you can reduce the radius of most nozzles using the radius reduction screw. This allows you to use the nozzle in a smaller area. A common question I am asked is what happens to the flow of the nozzle when you decrease the radius? The answer is that the flow (GPM) is reduced, but not by much. In most cases you can just ignore it and use the full radius flow. If you really want to find out how much the flow would be reduced, simply refer back to the manufacturer's performance chart for that nozzle. As previously mentioned, the radius reduction screw works by reducing the water pressure in the nozzle. If you look at a performance chart it will give you the radius at various pressures. Make sure you are using the right chart for the nozzle you plan to use. Find the radius on the chart that you plan to create using the radius reduction screw. The chart will show you the flow the nozzle uses at that radius.

Example: Let's say you install the nozzle shown in the table above in a situation with 30 PSI, but you only want it to throw 11 feet. You would use the radius reduction screw to reduce the radius to 11'. According to the chart at an 11 foot radius the nozzle would use a flow of 0.40 GPM.

Matched Precipitation Rates

Most spray heads now have what are called "matched precipitation rates". Matched precipitation (ppt) rate nozzles mean that the nozzles can be mixed and matched on the same sprinkler zone without concern that one might apply more water than another. Back in the bad old days, only nozzles with the same radius were matched. So you had to use all the same radius nozzles on each valve circuit. But now with matched ppt rate nozzle sets, you can use the radius that works best. So you can use 8 foot, 12 foot, 15 foot, and strip nozzles on the same valve circuit and you will still get nice uniform coverage (provided you don't exceed head-to-head spacing, that is!) You don't even begin to know how much easier this makes designing a sprinkler system! There are two exceptions you need to keep in mind however. First, only those nozzles in a manufacturer's set that are labeled "matched precipitation" are matched. Most manufacturer's also make nozzles that are not matched to the others. So make sure they are labeled “matched precipitation”. Second is that all the nozzles must be made by the same manufacturer. Each manufacturer uses a different precipitation rate as the default one for the nozzles to match. So don't mix manufacturer A's nozzles together with manufacturer B's nozzles on the same valve zone, even though they both may be labeled “matched ppt”.

Misting and Fine Tuning:

All spray-type sprinklers will mist and waste water if the water pressure exceeds the levels listed in the performance data tables. Some misting is normal. To determine if the misting is excessive adjust one sprinkler as follows:

The sprinkler is now operating efficiently, and you will be able to observe the normal level of mist. If all the heads are misting too much, you should use the flow control on the valve rather than the radius reduction screws to reduce the misting. Simply follow the steps above, but close and open the valve flow control rather than the radius reduction screw. If only a few are misting, use the radius reduction screw on the sprinkler.

 

Special Situations

Most spray-type sprinklers are available with a number of optional features. Here are some situations where you should consider using a spray-type sprinkler with one of these optional features.

Optional Features

Check Valves (CV). The most popular option for spray heads are built-in check valves. If your sprinkler system is being installed in an area where the elevation change exceeds the depth you are burying the pipe you should probably use sprinklers with this feature. Example; if the elevation change is 10 inches and you are burying the pipes 6 inches deep, you should use check valves. But in this same situation if you were burying the pipes 12 inches deep you would not need them.

The check valve prevents water from draining out of the pipes through the sprinkler head after the valve closes. When the water drains out of the pipes it is replaced with air. The next time you turn on the sprinklers this air must be expelled from the pipes, so for the first couple of minutes the sprinklers spit and spew air. This puts a lot of stress on the pipe and the sprinklers. As the water rushes into the pipes it slams into the ells and tees where the pipe changes direction. The air also messes up your uniformity as some sprinklers are watering the lawn while others are just blowing air out! The last problem is that the water that drains out of the sprinkler heads after the valve closes has to go somewhere. So it either runs across a sidewalk or driveway and grows moss and mold, or it makes a big mud puddle around the sprinkler head.

There is one large misunderstanding in the industry about check valves that you should be aware of. Many people, even professionals, erroneously believe that check valves will prevent water from running out of the heads if the valve leaks. This is absolutely not true. If the valve is leaking when it is closed, water will still run out of the lowest head, even if you have check valves installed in the head. This is because the water leaking from the valve is pressurized, and the pressurized water has sufficient energy to force open the check valves. The bottom line is that if you have a leaky valve, the water is going to come out of one of the sprinkler heads and check valves will not stop that. Now this is such a prominent “urban sprinkler legend” that I know a few people out there are going to want to argue with me about it. So before you fire off an angry email to me please test it out yourself. Install a valve zone with check valves on all the heads. Then open the valve just a tiny bit, just as if it were leaking. Now check out the water leaking out of the heads!

Pressure Control Discs. These small disks fit into the bottom of the nozzle or are built into the screen. They are essentially a rubber disk with a small hole in it that restricts the water flow. They control the water pressure and flow into the nozzle. As the water pressure presses against the soft rubber of the disc, the disc deforms and the hole gets smaller, thus reducing the flow through it. They are very handy for reducing the radius of a spray-type sprinkler as they work much better than the radius reduction screws on the nozzles. The sprinkler manufacturer will have a chart showing which disc to use with each nozzle to give the exact radius you need. You will probably need to go to an irrigation specialty stores to purchase these. The Pressure Control Discs can be easily retrofitted into existing sprinklers.

Other available features and options for spray-type sprinklers are described on the spray sprinkler listing page.


 

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