Jess Stryker's Landscape Tutorial Series, Sprinklers & Irrigation.

Jess Stryker's
Irrigation Q&A

Sprinkler Heads & Spacings


I have a drainage ditch that runs through the whole neighborhood's front yard including mine.This area is owned by the city or county, though each homeowner takes care of it because it's part of the front yard. My question is EVERY irrigation system in the neighborhood does not have heads placed on the road side of the ditch. The closest are approx... 20' from the road (granted most of the systems put in are by the same contractor). Of course, this does not give head to head coverage. The water only goes one way, from the middle lawn to the road. It does not go from the road back to the middle lawn. Should I put heads by the road or do it like the other yards?
 

It seems your neighbor's solution is the worst of all possibilities. If you put a row of heads along the road the drainage ditch will get watered, which will keep it green but also require more maintenance to keep weeds down or you will need to plant something in the ditch. If you don't want to mess with maintaining plants or grass in the ditch you should put your row of heads along the edge of the ditch on the yard side with the arcs selected so that they go just a little beyond 1/2 circle. That way a little of the edge of the ditch behind the sprinklers gets watered. Putting the sprinklers 20' from the road gives you bad coverage on the ditch side, your neighbors probably have to overwater to keep things green.


Is there a way of calculating the GPM usage of a spray nozzle after the radius has been reduced by the radius adjustment screw? I have an 8 foot strip of grass and plan to use spray heads that have an 11 foot radius at 15 psi. I was planning on reducing the radius from 11 feet to 8 feet with the adjustment screw, and I need to know what the GPM water flow is to determine the number of heads to put on a zone.

It's extremely simple, but hard to explain! Essentially you use the same chart provided by the manufacturer that shows PSI, radius, and GPM of the nozzle. Just use the chart backwards. First, find the nozzle you plan to use on the chart. Now look under the listings for that nozzle and find the radius you plan to reduce down to. The chart will have a GPM and PSI associated with that radius. That's all there is to it!

Example chart:

Sample Spray Nozzles Performance

Pattern

Part No.

15 PSI

20 PSI

25 PSI

30 PSI

15H

11' - 1.30 GPM

12' - 1.50 GPM

14' - 1.65 GPM

15' - 1.85 GPM

Let's say you want to reduce the radius of this nozzle to 12'. You have 30 PSI pressure at the sprinkler. Look across the chart and find the entry where the radius is 12' (or the closest you can find to 12'). At a 12' radius the chart says the flow from the nozzle will be 1.5 GPM. You will also note that the operating pressure inside the nozzle will now be 20 PSI. This is because turning the radius adjustment screw on the nozzle closes a small valve inside the nozzle, which causes the pressure to drop. As the pressure drops, the radius becomes shorter. So now you know how the radius adjustment screw reduces the radius. It does it by reducing the water pressure in the nozzle! Remember, this is only for spray type sprinklers. Rotors do NOT work the same way. When you reduce the radius on a rotor you are simply deflecting the water so it doesn't go as far. The GPM does not change on a rotor unless you install a different size nozzle!



Does each sprinkler in an area with heightened ground cover like bushes need to be higher than the highest object in its radius? Some of these could be 3 or more feet high, so that's not always possible. Or do I need to treat it as an obstruction and space the sprinklers accordingly?

You treat it as an obstruction. Generally, unless the obstruction is very close to the sprinkler it does not create a large problem provided you design with head to head coverage as I recommend in the tutorial. for a god example of problem blockage consider items like hedges along the edge of a walk. These can be a problem if you need to irrigate other shrubs behind the hedge. You have to look at it from a logical point of view. If the spray from one sprinkler is blocked is the spray from at least one other head going to reach the blocked area? If not, there may be a problem. All in all, for most landscape and irrigation systems blockage is not a serious problem.


Is there any advantage to the stainless risers available on some rotors? They claim an advantage in durability especially in sandy soils, which I have.

The stainless sleeves do lessen the scratching of the risers in very sandy soil, which helps prevent the risers from sticking in the up position. They are what is called a "specifier item" in the industry, that is, a feature provided primarily for the high end market. Mostly used by Cities and on projects where cost is not a big concern. The key to whether you really need them is how sandy the soil is and how "sharp" the sand. Rub some wet sand between your fingers. If it feels gritty, (you can feel the individual sand grains) consider using the stainless risers. My personal experience is that I have had few problems with wear on rotor risers. Spray heads have been much more of a problem in this regard, I'm not sure why. Maybe smaller diameter risers make the wear more significant? But spray heads are so cheap you just get a new one when the riser gets worn.



My sprinkler heads aren't working right. I have dry spots, but I've checked the spacing between heads and it is correct.

Some suggestions for sprinklers that don't perform. These suggestions assume the sprinkler system design is correct, that is the spacing between sprinklers is head-to-head, the pipes are the right size, valve is the right size, etc.

  1. Make sure the radius adjustment screw in the top of each nozzle is turned to the full open position.
  2. Remove one of the nozzles. Most sprinklers have a screen installed under the nozzle. Remove the screen. Is it dirty?
  3. Look at the bottom of the nozzle. Is the small round inlet hole blocked by anything?
  4. If you found dirt in the screen or nozzle you should flush out the pipes again. 90% of the time this problem has been caused by dirt left in the pipes that then clogged the heads. See the next question for how to flush out the pipes.
  5. Check for anything that could be blocking the flow through the sprinklers. Maybe they had a manufacturing problem. I've experienced this from time to time with almost every company's products. A plastic mold gets out of adjustment at the factory and leaves a glob of plastic in the wrong place. Yes, they should catch it at the factory!
  6. If all else fails, brainstorm and check out everything and send me every little detail you can think of. Maybe something that seems unimportant to you will mean something to me!



My pop-up sprinkler heads keep sticking in the up position. What can I do?

First, if you are using the little sprinklers that don't have a retraction spring, this is normal. They pretty much stick up no matter what. You should replace them with a spring loaded pop-up with a pop-up height of at least 3", I recommend you use a 4" pop-up if possible. Now if you do have spring loaded pop-ups the problem is most likely caused by a small grain of sand, a stick, or something similar in the wiper seal. Here are a few things to try:


The water isn't coming out of the sprinkler nozzles in an even pattern causing dry spots. How do I fix this?

The nozzle has something stuck in it or it is scratched. I recommend that you replace the nozzle with a new one rather than trying to clean it. You can try to remove whatever is in the nozzle with a small screwdriver or a piece of wire, but this usually scratches the nozzle which will also cause the pattern to be bad, especially with plastic nozzles. Nozzles are cheap, you're better off just biting the bullet and replacing them. But you need to do more than replace the nozzle--

Now you need to find out why there was something stuck in there. Sometimes bugs crawl into the nozzles when the sprinklers are off. See if you can figure out what is tuck in the old nozzle. Usually it is dirt or some other foreign item that was in the pipes. That means you need to flush out the pipes (which you really should do yearly anyway). Here's how:


In my town the building permit folks say I cannot put sprinklers next to the curb or the side walk in my parkway (an 8 foot strip between my sidewalk and the street). They say I can only put sprinklers down the center of the parkway. Are there sprinkler heads or placement patterns that will cover a 130' x 8' long strip without dry spots?

Nothing that I know of will spray 8' wide from the center without making a BIG mess (water in street, water on sidewalk). You could put a row of full circle heads down the center, but its going to spray all over the sidewalk and street. I think your City people have gotten a bum steer from someone. Point them at my tutorial and tell them to feel free to email me if they want some free advice. Make sure they identify themselves as City planners so I know who they are, I'll do my best to help them out. I do it all the time for lots of Cities. My guess is they think you have a 3 or 4 foot wide park strip rather than an 8'. There are nozzles that would work in those cases but they still aren't the best solution unless you want water in the street or on the sidewalk. A nozzle called a "side strip" is the best nozzle for those narrow planters. It still may overspray either the sidewalk of the street, but unlike the center strips at least they don't overspray BOTH. Sidestrip nozzles also seem to have a better water pattern in my opinion. I do not like center strip sprinklers at all.


I did not see the subject of bubblers addressed in your tutorials. Are bubblers a good alternative? I'm worried about shrubs blocking the sprinkler water.

First of all, shrubs blocking water from sprinklers is not as big a problem as many people imagine it will be. Sprinkler spray is pretty good at getting past the foliage of most plants. In smaller planters less than 8 feet wide it is almost never a problem. Keep in mind that the water can soak under ground 3 feet from where it lands. In general, I try to use a maximum spacing of 12' between sprinklers in shrub areas.

Bubblers are a very inefficient watering method, however they have their good uses. Bubblers are a form of what is termed "flood irrigation", which is the least efficient method of watering. About 40-50% of the water will be wasted, that is, the water will not be available for use by the plants. (By comparison, sprinklers waste 25-30% of the water, drip systems 5-10%.)

Bubblers do have some good qualities. They are most often used in areas that are too small for sprinklers, or in areas where water spraying on windows or walls would cause problems. We often use them in commercial landscapes around low signs where sprinkler water will sometimes find it's way into the sign and cause problems.

Bubblers only work well in areas that are flat- really flat! The water won't run uphill, not even an inch, so keep that in mind. If you want to use bubblers in an area that has even a very minimal slope you will need to build terraces for each bubbler. Also remember that the buildup of mulch from leaf drop will block the flow of water under thick shrubs with time. Just as "thatch" in lawns can prevent water from reaching the grass roots, leaf mulch can dam up the water around the bubblers. When this happens the word most likely to come to mind is also pronounced "dam", but it's spelled different!

There are two types of bubblers, Flood Bubblers and Stream Bubblers.

Flood bubblers are basically a small faucet that releases water onto the surrounding soil. Most have adjustable flows, you can control how much water they release. Flood bubblers are generally spaced about 5 feet apart or less.

Stream bubblers shoot short streams of water out of them. They are available in various patterns, just as spray sprinklers are. The streams usually shoot 3 feet or so out from the bubbler. The streams can cause minor erosion problems where they hit the soil. Like flood bubblers, many stream bubblers can be adjusted for varying flow rates. The theory behind stream bubblers is that they can be spaced farther apart than flood bubblers because the water shoots out farther from the head. In practice, I have found little support for this theory. I use them a lot, but I still keep the spacing at 5 feet apart or less. I find them more useful for directing the water in the way I want it to flow by selecting a stream pattern that fits well with the shape of the area being watered.

You can purchase bubbler nozzles for pop-up spray head bodies. Most of these are the stream bubbler type. These are an excellent choice for areas where the bubblers might be tripped over. The bubbler nozzle screws into the pop-up body just like a normal spray nozzle.

All bubblers need periodic maintenance so don't place them where they will be buried in foliage and inaccessible. They should not be within a foot of a plant stem as the constant water can cause rot and disease problems. I prefer to install bubbler near the edges of the planter rather than in the middle, so that they are easy to reach for servicing.




.) How do I make sure a Zone has the expected sprinkler head pressure (letís say 30 psi.). What do you do to compensate for some heads maybe needing
20 psi for the desired radius/GPM and others needing say, 30 psi in the same zone? What do I do for another rotor zone that I have calculated out to need 45 psi?

Spray type sprinklers have a screw in the nozzle that allows you to adjust the radius of throw. The screw actual operates a small valve in the nozzle which reduces the pressure when you turn the screw. This in turn causes the radius to decrease. Another question on this page explains more on the subject of adjusting radius of spray sprinklers. For rotor type sprinklers you need to use a smaller nozzle size to reduce the radius. Remember that spray sprinklers and rotors must not be installed on the same valve circuit. The Sprinkler Design Tutorial will give you much more information on this topic.


What I wanted to know is a formula to figure out infiltration rate. Example was 2/10 of hour (how do I figure how long to get 1 inch of
infiltration?)

How's your class coming along? Hope your learning lots of new stuff! (Only irrigation class students ask questions like this one!)

2/10 of an inch is 0.20 (2 divided by 10 = 0.20). 1 inch divided by 0.20 inch per hour = 5 hours. So it would take 5 hours to get one inch.

The amount of water a sprinkler system applies is a function of the precipitation rate of the sprinklers. To find out the precipitation rate you have to design the sprinkler system. Once you know the GPM of the sprinkler you are using and the sprinkler spacing you can calculate the precipitation rate, the formula is on the formulas page of my web site. http://www.JessStryker.com/formulas.htm

The infiltration rate is a function of the soil type. Different soils have different infiltration rates. You need to know what type soil you have to determine the infiltration rate. Infiltration rate has nothing to do with the sprinklers. Some people try to select sprinklers based on the soil infiltration rate. This is very common in college irrigation classes. While theoretically possible it is not practical in the real world. There just aren't any decent sprinklers with precipitation rates as low as most soils. Those with low precipitation rates are rotor type sprinklers with very small water streams. These small streams are blown all over the place so the sprinkler efficiency tanks, and very little water reaches the area it is supposed to. Thus matching sprinkler precipitation to soil infiltration rates is worthless. Good in theory perhaps, and a good learning exercise for students, but a Crappie* idea in actual practice. So what's the solution? (Dozens of professors just read this and removed my tutorials from their "recommended reading" lists!)

In the real world we use irrigation scheduling to match the precipitation rate to the soil infiltration rate. For example, the infiltration rate of the soil might be 0.20 in/hr as per your example. That's the rate (speed) at which the soil can absorb the water. However most spray sprinklers apply about 2.0 in/hr. So there is no way the soil will absorb all the water applied to it. The solution is to run the sprinklers for a short interval, then allow some time for the water to soak in, then apply another short irrigation. This procedure is repeated until the soil has enough water and is known in the industry as "cycling" the sprinklers. So by using the soil infiltration rate and the sprinkler precipitation rate you can calculate how long the sprinkler should run for each cycle, and how long you need to wait for the water to soak in between cycles. I'll let you figure out how to do that. It is your assignment after all!

*Crappie is a type of fish, as in "Dam it*, I caught another Crappie". What did you think I meant?

*Dam it, as in "Oh hell*, if we don't move away from the dam, it will be a full day of catching nothing but Crappie".

*Hell -- you've heard of it-- where those dam crappie people are going!



I'm offended by your dam crappie comments above.

I'm sorry. I'll try to behave better. :(



We have high water pressure. Normally not a problem, the advantages far outweigh the disadvantages. My sprinkler system for my front lawn uses impact heads and I have never had a problem with it. However, I have just finished installing a smaller system in a portion of the back yard where I used regular pop-up sprinklers. The water pressure has been blowing these guys into the next zip code!! Is a pressure regulator the answer? If so, what kind of regulator and where on the system should it be installed? If not, then how do I deal with this problem?

A pressure regulator is indeed the answer. Look for a brass model with a pressure adjustment screw. Make sure to get the proper size based on your flow, pressure regulators are very flow sensitive, you can't just use a 3/4" size because you have a 3/4" pipe. Install the pressure regulator on the pipe upstream of the valves. Until you get the regulator installed, only partially open the valve rather than fully opening it. Open it just enough that the sprinklers work right. That will help reduce the pressure and prevent further damage.



Is there a good rule on how low I should keep the head of the sprinkler below the sidewalk?

The sprinkler heads should be lower than the walk and even with the soil level, or not more than 1/2" above the soil level.


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