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Heads Up on Sprinkler Head Spacing

KEITH ROBERTS | Sprinklers

No two snowflakes are alike, everybody has their own unique fingerprint, and no set head spacing fits all lawns. Depending on the sprinkler head, type, water pressure, gallons per minute (gpm) rating, and location, proper head spacing varies and could mean the difference between consistent green lawns, or brown turf.

The time and money that will have to be spent if sprinklers are installed wrong is considerable to say the least. For one thing, it won’t help your reputation, your client won’t hire you again nor will he recommend you.

Unless you’re an out and out crook, no contractor goes out to do a poor job. The problem is that many have never bothered to learn the proper skills. It is just as easy to do the job properly and not. So for the sanity of your client, the health of the lawn, and the soundness of your business and your reputation, it pays-like most things- to install sprinklers right the first time.

To do it right, let’s first understand the goal. This shouldn’t come as rocket science, but the point is to keep turf uniformly green and healthy, without stress areas. Proper distribution of water achieves this. So what the contractor needs to do is make sure that the whole lawn is getting the proper irrigation to grow properly. Uniform coverage is a necessity.

There are two types of heads that are most commonly used: spray heads and rotors. As expected, these heads apply water in different ways and therefore a few separate considerations apply to each. However, there is one very important and consistent concept to remember.

The number one rule is to overlap the spray from sprinkler head to sprinkler head, known as “head to head coverage.” This applies to fixed spray sprinklers and rotors. “The actual distance between sprinkler heads is determined by the gpm nozzle and the water pressure in the system,” says a spokesperson of Rain Bird. “If stand alone spacing is used, your lawn will likely develop brown areas where insufficient water is being applied. This can be partially overcome by increasing watering time, but this approach will increase cost of watering and waste considerably more water.”

The projected length of spray that manufactures label their sprinklers with should be read with caution. The odds are that the sprinklers were tested inside a building, sans real world interference like wind. Therefore, be sure to compensate for expected or periodic wind conditions by placing sprinkler heads closer than recommended. “Along the coast, we compensate for winds by bringing them even closer to head and head,” says Greg Parker, marketing and product manager for the Toro irrigation line of residential, commercial controls and valves products.

Parker, a former landscape contractor and architect for a number of years, knows first hand the trouble that improper head spacing can create. “While coming in for the landing at an airport, maybe you’ve seen brown rings in the lawn of parks or on the turf of a ball field,” relates Parker. “When you see those brown “doughnuts” it is because of improper head spacing.”

On that note, there is a reason why golf courses most always look so evenly green and lush. When planning the irrigation system, the irrigation designer will ensure good coverage from the sprinklers. The radius of coverage from the sprinklers has an error margin of only three to five inches. Needless to say, sometimes it pays to be precise.

Pardon the clich?but it’s better to be safe than sorry. A contractor will not be doing his client any favors by installing a system that requires him to water the brown spots by hand. Choosing a sprinkler that is rated to have a slightly higher radius than the amount of turf is recommended. “If I am irrigating an area that is 13 feet across, would I use a nozzle with a 12 foot radius? I sure wouldn’t. I would use one that sprays 15 feet,” Parker said.

The concept of overlapping the sprays of water to head to head coverage is universal. “It doesn’t mater if they’re rotors, fixed sprays, interchangeable valve heads, etc: it all involves basic physics. For water to be uniformly distributed, the sprays must extend to head to head coverage,” says Parker.

With the importance of head to head spacing in mind, there are different styles, rather methodologies that help with placing sprinkler heads onto a property. The two most popular and recommended styles are the “equilateral triangle” method and the “square/rectangle” method. Considerations for picking the method that suits your needs involves taking a look at the size, shape, and climate of the area where you’re installing.

The square/rectangular layout method is best for defined geometric spaces, such as rectangle shaped yards and square lawns that may or may not be divided by sidewalks and other paved areas. Overthrow is kept at a minimum, as the sprinklers are placed in the corners and along the perimeters. Toro recommends increasing or decreasing the spacing of spray heads ? 1 foot and rotary sprinklers ? 3 feet. However, if the sprinkler spacing is increased, do not increase the row spacing; nor should you increase sprinkler spacing if row spacing is increased.
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Line drawing courtesy: Hunter Industries

Line drawing courtesy: Hunter Industries

For example, if a sprinkler is rated to have a radius of 25 feet (remember, its best to assume that is the maximum distance of spray and adjust according to “reality factors,” just to be safe); the recommended spacing from one sprinkler to another would be 25 feet. The row spacing would also be 25 feet. The spacing distance, plant type and wind conditions should go into adjusting spacing between sprinklers and rows to fit the site, which gives the system a rectangular shape in the layout.

For areas that are irregular in shape and where overthrow won’t be a big issue, triangle layout is a good choice. This method tends to provide better overall coverage as compared to square spacing, but there will most likely be an oddly shaped sprinkler that is throwing water beyond the edge of the site.

For the mathematically disinclined, the following shouldn’t make you cringe. Using triangle spacing, designers usually like to place the sprinklers 50% to 55% of the sprinkler diameter. The row distance is determined by multiplying the actual distance between sprinklers by .866. As with the square spacing, this will give you a general distance to go by, while you may adjust the sprinkler location to the idiosyncrasies unique to an individual project.


Line drawing courtesy: Hunter Industries

Line drawing courtesy: The Turf Irrigation Manual

 

Here is another formula recommended by Jess Stryker, a landscape architect and irrigation contractor who owns architect and irrigation designing/consulting firm Jess Stryker and Associates, based in Ventura, California. “The spacing in feet between rotors can never exceed the operating pressure in PSI at the sprinkler inlet,” says Stryker. “For example, if the rating is 30 PSI operating pressure, that would equate to a 30 foot maximum spacing. Ignore this rule and you will be very sorry,” he warns.

In most cases, if it turns out you did place sprinklers a bit too close together and have too much overlap, as what would more likely be the case with rotor sprinklers, that isn’t necessarily a bad thing. “If the sprinkler sprays too far, most rotors have a radius reduction screw that will allow you to easily fix the problem,” Stryker says. “But if the rotor does not spray far enough, there is nothing you can do about it without a major expense. It’s best to play it safe.”

Sometimes, spacing based on geometrical spacing won’t work as well on certain projects. An instance where a contractor could run into some difficulty using one of these styles would be on circular patches of turf, or those that are heavily conformed with curves. Jeff Carowitz, marketing manager for Hunter Industries in San Marcos, California, suggests using the ‘edge method.’ “This method is so named because you begin by placing sprinklers at the edges of the area, and then move inward toward its center,” advises Carowitz.

Just like the rectangular method, start by placing sprinklers around the perimeter. It will be easier to determine these locations by converting the curved edge to a series of straight lines; the length of which is determine by the sprinkler radius. Carowitz then recommends placing part-circle heads at each intersection of two lines.

“After this is completed, place full circle spray heads inside the area, from the perimeter toward the center of the area. Instead of using grid lines to place these interior heads, draw the circular spray pattern using the spacing criteria of the manufacturer. Continue this process while moving toward the center of the area,” Carowitz says.

If there is still not uniform coverage, additional heads may have to be installed.

A properly designed and installed irrigation system is vital to a beautiful landscape. Leaving the client high and dry (pun intended) when it comes to irrigation will leave him assisting a useless system by having to water himself. If sprinklers are properly spaced right the first time, that system will work for many years to come, and will provide years of green. Which, of course, is what you’re all about.

JUNE 04

 
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