Tag Archives: Sprinklers

How to Reverse Engineer a Sprinkler System

Sprinkler systems need flow and pressure to operate.  Sometimes you might need to know the flow and pressure requirements of an existing sprinkler system.   For example the flow and pressure are needed if adding on to the existing irrigation system or adding or replacing a pump.  This article contains instructions on how to determine those values.  This article uses the USA measurements GPM for flow and PSI for pressure, however conversion to metric is easy using standard conversion formulas.

How to Reverse Engineer the Flow (GPM)

This is going to take some time and a lot of crawling around on your hands and knees… sorry, that’s just how it is.

  1. Look to see the sprinkler brand and which nozzles are installed in the existing sprinklers on a single valve circuit.  Write them all down.  You may have to look very close to find the nozzle number, it is usually imprinted using tiny text on the nozzle itself.  It may be right next to where the water comes out, or it may be on the top of the nozzle.  It is often hard to see.  Each sprinkler may have a different nozzle, so you will need to look at every one of them and write them all down.  Rotor type sprinklers (streams of water that rotate) tend to have numbered nozzles, #1, #3, #9, etc..  For rotors you often need to pull the pop-up riser up from the sprinkler body to see the nozzle outlet and the number.  Spray type sprinklers (steady spray like a shower head) tend to have a number followed by a letter that indicates the arc, like 10F, 12H or 15Q. 
  2. Look up the flow requirement (GPM) for each sprinkler and nozzle using charts you should be able to find on the sprinkler manufacturer’s website.    Add all the GPM values together to determine the total GPM for the valve circuit. For older discontinued sprinkler models you may have to contact the manufacturer’s consumer help department and ask them to email you performance charts.
  3. The sprinkler manufacturer’s website will probably give you a  chart that shows different flow values for the nozzles depending on the “PSI”.  To determine the PSI to use measure the distance between adjacent sprinklers in feet.  Measure several and determine the average distance.  Now use that average distance between sprinklers as the “PSI” value– but do NOT use a value less than 30.   Example:  If the average distance between adjacent sprinklers is 45 feet, use 45 PSI to find the GPM in the chart.  If the average distance between sprinklers is 25 feet, use 30 PSI.  Do not use less than 30 PSI!
  4. Repeat for each valve circuit.
  5. Assuming you run one valve circuit at a time, your flow requirement for the pump will be the same as the single valve circuit with the highest flow value (GPM.)   If you run more than one circuit at a time, add together the GPM values for the ones you run together as they essentially become one big circuit when run together.
  6. To recap, calculate the total GPM of each group of sprinklers that run at the same time.  The flow (GPM) value to use when determining the pump size that of the group of sprinklers that has the highest total flow (GPM).

Determining the pressure requirements can be difficult.  First off, pump pressure in the USA is measured in either “Feet of Head” (Ft.Hd.) or “PSI”.  (The rest of the world uses “bars” but this article is USA based. )  We’ll talk more about this later, but for now you can use either “Ft.Hd.” or “PSI.”   You can switch back and forth between these two values using simple conversion formulas:

____ PSI x 2.31 = ____ Feet of Head (ft.hd.)
____ Feet of Head x 0.433 = ____ PSI

 

How to Reverse Engineer the Pressure
(3 different methods)

One quick rule of thumb- too much water pressure is much easier a problem to deal with than too little pressure.  If you are uncertain at all, always go with the higher value.  It is very easy to throttle down the pressure if you have too much, if you don’t have enough pressure it is very hard and expensive to increase the pressure.  So if you are looking at a sprinkler head and asking yourself: “should this sprinkler head use 30 PSI or 35 PSI, I’m just not sure?”, the answer is easy, use the higher pressure, 35 PSI.

Method #1:  Measure It with A Gauge.

If the irrigation system is still operational install a pressure gauge on the pipe as close as possible to where the water source, turn on the system, and the gauge will tell you the pressure the existing system uses.   You may need to cut the water supply pipe and install a tee for the gauge to connect to, or possibly you can drill a hole in the pipe, thread the hole with a 1/4″ NPT thread tap, and then screw the gauge into the hole (most gauges have 1/4″ male NPT thread connections on them, but you might want to make sure before you drill and tap!)

If the irrigation system uses a pump to run it you typically would measure the pressure within a foot or two of the pump outlet.  Remember that if you do have an existing older pump the pressure you measure may be lower than it should be due to the pump being tired, old, and worn out.  You might want to add another 10 PSI to the pressure you measure at the pump to compensate for age.

Method #2: Calculate the Pressure losses.

If you can’t take a pressure reading on the existing system, the next best method is to completely redo all the calculations for the sprinkler system.  Let’s be honest, this is too difficult and time consuming for most people, but it is the best way.  If you want to try it  you need to read through the Sprinkler System Design Tutorial to learn how pressure requirements for a sprinkler system are calculated. You should be able to then reverse engineer your existing sprinkler system by calculating the pressure loss in each section of pipe, each valve, each sprinkler head, etc.  to figure out the PSI it requires to operate.  You may have to dig up some pipes to determine what size they are.  It is a lot of work, you will have to basically learn how to design irrigation systems to do it.  Seriously, it is unlikely you are going to do this unless you are an engineer or just very anal-retentive… let’s move on.

Method #3: Guesstimate It.  

If you really can’t figure out the pressure needed you can use a guesstimated pressure value.  Most of you are likely to use this method.  Obviously this method is not optimal and there are no guarantees it will work but it’s a lot less effort that the first two methods above.  The idea here is to guesstimate high as previously mentioned in the introduction.  Not sure?  Add 5 PSI!  Really feeling uncertain?  Add 10 PSI.  You get the idea. Instead of measuring with a pressure gauge, the guesstimate method is going to require you to grab a tape measure (which most people have) and you won’t need to cut into any pipes or dig anything up.

FYI: This guesstimate method is based on some hydraulic principles that define the water pressure needed at a sprinkler head in order to shoot water a specific distance, along with some very rough assumptions of how much pressure is typically needed to move water through all the various pipes, valves, etc.

Guesstimate formula:
Sprinkler spacing in FEET + 30 =  guesstimated PSI required at water source.
If the resulting total is less than 50, use 50.
Do not use a guesstimated water pressure value less than 50 PSI !

To guesstimate the pressure needed take the largest distance in feet between adjacent sprinkler heads, and add 30 to it.  If the answer is less than 50, use 50.  Do not use a pressure lower than 50, very few sprinkler systems will function well at a pressure below 50 PSI.  Which sprinkler heads to measure?  Generally you should measure and write down the distance between all your sprinkler heads that are next to each other.  It’s not uncommon to have two heads that are way further apart than all the others.  If so you can choose to ignore that set of sprinklers.   The examples below will help this make more sense.

Example: let’s say you have 6 sprinklers and you measure the distances between the adjacent ones and you get 50′, 32′, 29′, 33′, 35′, and 29′.   In this case 50′ is way out of line with the other values so let’s ignore it and use the next greatest distance, which is 35′.   So then 35′ + 30 = 65 PSI.  So in this case 65 PSI is the guesstimated pressure required for the system.  Understand there may be a dry spot between those two heads that are 50′ apart (there probably already is a dry spot there!)  That 50′ distance is really a design error on the original sprinkler system and there should probably be another sprinkler head in the middle of that space.

More Guesstimate Method Examples:

Sprinklers 15 feet apart:  15 + 30 = 45 PSI.  This is less the 50, so use 50 PSI.
Sprinklers 35 feet apart:  35 + 30 = 65 PSI.  Use 65 PSI.
Sprinklers 45 feet apart:  45 + 30 = 75 PSI.  Use 75 PSI.
Remember, 50 PSI is the minimum!

Remember:  No guarantees, this method gives you a guesstimate!  You understand that you are taking a risk using this.  Buying a pump?  It is strongly recommended that if you guesstimate the pressure you buy your pump from someplace with a generous return/exchange policy.  You may need to return or exchange the pump.

Install Sprinklers on the Risers

Quick Summary:  Start by installing the sprinkler riser on the lateral pipe outlet.  Then the sprinkler is screwed onto the riser.  Adjust the sprinkler to be in the desired location and perpendicular to the ground surface.  Position sprinklers at the edges of the irrigated area about 4″ away from hard surfaces like sidewalks and driveways.  If growing a new lawn from seed make provisions to prevent the water spray from the sprinkler from washing the seed away.  Details follow!

Continue reading Install Sprinklers on the Risers

Drought & Shutting Off Sprinklers for Long Periods

Just turning off your sprinkler system to deal with drought could be an expensive mistake!  Before you unplug that sprinkler controller/timer or switch it to “rain mode” consider what precautions you should take if you don’t plan to run your sprinklers for an extended period of time.  To be brief, all kinds of expensive-to-fix things happen to sprinkler systems that are not operated for a period of a year or more.

Fortunately there are a few precautions you can take to reduce these problems:

  1. The best solution is don’t completely shut off the system.  Instead, run each of your sprinklers zones for 2 minutes once each month.  This will keep the system in “operating condition.”
  2. A less desirable solution is to “Winterize” your sprinkler system, just like people in cold climates do each year before shutting the system down for the winter.  Honestly this is probably not a practical option for most people.  See the article on “How to Winterize Your Sprinkler System.”
  3. When you do return to regularly watering again, give your sprinkler system a “tune-up.”  See the detailed step-by-step instructions at “How to Give Your Sprinkler System a Tune-Up.”  This will get your system back to “like new” operating condition.

For more details, in-depth suggestions, and answers to most common questions regarding extended shut down of sprinkler systems continue reading…

Continue reading Drought & Shutting Off Sprinklers for Long Periods

Sprinkler Head Risers

The short section of  tube that attaches a sprinkler to the underground lateral pipe is called a “riser”.  But the riser does much more than attach the sprinkler.  It must hold the sprinkler in the correct position, it must allow you to adjust the sprinkler location, and we can also use it to protect the sprinkler from damage.  The riser type you use is an important choice and deserves some attention.  A good riser choice can save you time and money over the years.  This article will take you through the many choices and the pros and cons of each.  (“Lateral pipe” is the name given to the pipes that go from the zone valve to the sprinkler heads.)

Continue reading Sprinkler Head Risers

Types of Sprinkler Risers

Definition: riser (irrigation).  A riser is a set of pipes that connect and/or support a piece of irrigation equipment on or to the irrigation system.  Typically the equipment is mounted at or above ground level and the riser connects it to pipes or tubes located below ground.   Thus the source of the name riser, as it “rises” up above ground to the equipment.  Risers are typically used to support sprinklers, drip emitters, valves, backflow preventers, air vents, and just about anything else.

This article is specifically about types, as well as the pros and cons, of risers used for sprinklers and drip emitters.

Risers for Drip Irrigation: On most drip irrigation systems the emitters plug directly into the drip tubing without using risers.  Some drip systems, where the emitters are attached to threaded outlets, also use risers to attach the emitters. These are often called “hard piped” drip systems.  The following article on sprinkler risers would also apply to a hard-piped drip system.  Just substitute the term “drip emitter” for sprinkler.

There are any number of ways you can attach a sprinkler head (or drip emitter) to the lateral pipe/tube. (Lateral pipe/tube is the term used for the piping/tubing that carries water from the zone control valve to the sprinkler heads.)

Sprinkler Placement:

Before we get into risers let’s quickly cover the related topic of sprinkler placement or positioning in relationship to adjacent objects or surfaces.

Sidewalks:  4 to 6 inches is the normal distance a sprinkler should be from the edge of a sidewalk. (Before you ask, no, a 6 inch distance does not cause a dry spot along the edge of the sidewalk.  Sprinklers are designed to be installed 4-6″ away and allow sufficient “back-spray” to water these areas.)  If closer than 4″ lawn edgers and string trimmers will tend to damage the sprinkler.

Fences and Walls:  Keep sprinklers at least 12″ away from fences or freestanding walls.    If the sprinklers are within 36″ (3 feet) of a fence you most likely will see water stains from the sprinkler spray on the fence or wall.  This can look pretty bad.  In areas with strong winds a wall or fence will be discolored with water stains even if it is as much as 5 feet away.

Building Foundations and Walls:  Keep sprinklers at least 18″ away from foundations and building walls.  No water should spray onto a building wall.  For this reason any sprinkler that sprays water should be at least 36″ away.  Bubblers or “flat” spray sprinklers may be closer if unavoidable and soils are suitable.  The water must not spray onto the wall or foundation and the soil must not be expansive (see next paragraph.)

Expansive Soils:  If you have expansive soils (wet soil cracks when it dries) there are special rules and precautions regarding sprinkler placement around buildings and structures.  If you get expansive soil near your foundation wet it can break your foundation!  Read the Sprinklers and Expansive Soils Tutorial.

How can I water grass next to a wall or fence if the sprinklers are 36″ away?!!  You can’t if you use sprinklers.  This is one  reason why professional landscapers put a foundation planting of low shrubs around the perimeter of buildings and along fences.  The shrubs are watered using drip irrigation or bubblers that minimize the water volume and do not spray water in the air where the wind can blow it around.  Another option is to use subsurface drip irrigation for the lawn watering.  Even then it is not a good idea to put the volume of water needed by a lawn right up against a foundation.  It is just asking for structural problems like moisture damage,  rot, and termites.  Plus it is not considered good esthetic landscape design to put lawn directly against a building, unless the building has a significant architectural feature at ground level that needs to be highly visible.  Nothing says “amateur design” like lawn planted up against the wall of the typical home.  OK, to be clear, if it is your house, do as you wish.  Maybe you think it looks great, that’s fine, I’m just letting you know that every pro who passes by is going to snicker!

But I WANT lawn against my house you landscape design snob!!!  OK, I am being a bit of a design snob.  Sorry.  If you do want lawn installed right up to a building foundation you should put a concrete apron (or other non-irrigated surface like rock or gravel) between the lawn and the foundation.  Typically an apron at least 18″ wide is needed to keep water away (if the sprinkler heads are 6″ out from the concrete edge that is a 24″ distance to help minimize water on the wall.)  I like a concrete apron because it gives a clean sharp edge to the grass that is easy to trim and goes well visually with the building’s hard edge.  Make sure the concrete surface is sloped away from the building so rain and any irrigation over-spray water flows away from the building.

OK, back to our discussion of risers.

Simple Pipe Risers (i.e.; Pipe Nipples):

One of the most common sprinkler risers used for residential systems is a simple short section of pipe called a “nipple”. Actually a nipple is the standard plumbing term used for any short section of pipe, usually with male threads on the ends, regardless of where it is used.  While a nipple is the least expensive riser type, it also has some very distinct disadvantages. If the nipple is made of metal the nipple won’t easily break. A rigid PVC plastic nipple (like the gray SCH 80 PVC nipple) is not easy to break either (although I have seen it happen.) Now this may seem like a good thing, as we don’t generally want things to break. However, when the sprinkler mounted on a rigid nipple is hit hard by a mower or car tire, something probably WILL break!  So what do you want to break?  The sprinkler head is expensive to replace if it breaks, but fortunately it doesn’t usually break.  If you use a hard plastic or metal nipple for the riser it won’t likely break either. Unfortunately, what usually does break is the fitting on the lateral pipe that the nipple is screwed into. While not expensive, this fitting is going to be a real pain in the behind to replace if it breaks.  You’ll have to dig up several feet of pipe, bail out several gallons of water that drain out of the broken pipe, cut the broken section out of the pipe, repair it, put the sprinkler back in place, then backfill the muddy hole.  You’re talking at least an hour of hard, dirty work.  The better solution is to use soft polyethylene (poly) nipples for your risers.

Poly Cut-Off Risers:

If you want to go the really cheap route and use a nipple for the riser I suggest that you use what is typically called a “poly cut-off riser” or some other similar name depending on the brand.  A poly cut-off riser is a short pipe section (typically 6″ long) with multiple sets of threads molded into it (see photo below.) You simply cut it off to the desired length with a knife or a pipe cutter. Because the poly material is very soft, the nipple will bend under stress and will break before either the sprinkler or the lateral fitting break.  While it is not fun to replace the broken poly nipple, it is a lot easier and faster than replacing the lateral pipe fitting below it and much cheaper than replacing a broken sprinkler head!

instal06c

 

Poly Cut-off Riser

The arrows show where to cut the riser to make it the correct length.

When cutting the poly cut-off riser always cut it at the top of one of the sections of thread, as shown by the arrows in the photo below. Cut-off nipples generally cost less than a dollar a piece, which is pretty inexpensive to replace. Keep in mind that sooner or later you are going to have to replace a few of them. After all, they’re designed to break! So buy a few extra when you install your system. You don’t need to use thread sealants like Teflon tape on poly risers, the soft plastic will seal itself. Amateurs should never use liquid or paste thread sealers on sprinkler systems, if some of it squeezes through the threads to the inside of the pipe the water will take it straight to the sprinkler nozzle where it will clog the nozzle.


Swing Joint Risers

A much better solution for risers than the simple nipple system described above is to use something designed to allow the sprinkler to absorb an impact without anything breaking. The riser most professionals use for this is a “swing joint” or “swing riser”. In addition to deflecting to prevent breakage, most swing risers also allow the sprinkler head location to be easily adjusted. With the swing riser types known as “flexible arm swing risers” and “quadruple swing risers” the sprinkler head doesn’t need to be directly over the lateral pipe fitting, so it is not nearly as critical that the pipe be installed in the right place. Thus the trenching and pipe installation is going to be much easier and faster. I don’t know about you, but I like methods that are easier and faster– especially when they also give better results!

Flexible Arm Swing Risers:

The flexible arm swing riser is cheap and easy to install but not as durable as a rigid arm swing riser (but it is still much more durable than the cut-off riser mentioned above). This is the method I recommend for a residential or even a light commercial application, and it is what I use on the majority of my fast-food restaurant irrigation systems. It provides a good balance between cost, ease, and durability. The flexible arm swing riser consists of a length of flexible pipe (sometimes referred to as “Funny Pipe ®” a trademarked name of the Toro Company) with a insert ell on both ends. One ell attaches to the sprinkler, the other to the lateral pipe fitting. You can buy these swing risers preassembled, or you can buy the flexible pipe and insert ells separately and assemble them yourself.

Rotors: Don’t use these flexible arm swing risers with rotors that have a 3/4″ or larger inlet. That means don’t use them with most rotors!  See the rigid riser below for 3/4″ and larger inlet size rotors.  The small flexible tubes used on these swing risers restrict the higher water flow that most rotors need for proper performance.

The preassembled swing risers often have 3 or even 4 ells which makes them much easier to install. You can duplicate this feature by adding street ells to the build-it yourself risers. A street ell is just an ell that has female threads on one end and male threads on the other (see photo below.) I suggest adding a street ell to one or both ends of your swing riser to make it easier to install. The street ells you use should be high density polyethylene, which is black in color and has a slightly oily feel. “Marlex” is a common brand name of high density poly that you may encounter. Do not waste your money on white PVC street ells, they are worthless for swing risers!  PVC threads seize up which defeats the whole idea of a flexible joint.

Do not use more than a 18″ length of flexible pipe for your riser! The flow through this pipe is very restricted. Longer lengths cause a high amount of pressure loss and this can mess up the performance of the sprinkler head. If the head is more than 18″ away you should run a branch pipe over to it using the same size and type of pipe as the lateral.

When installing the flexible swing riser do not bend the flexible tube to help position the sprinkler.  Position the sprinkler by turning/twisting the ells to move it into position.  Poly tube has what we call “memory”- it tries to return to its previous shape when bent. Chances are the tube was coiled or curved slightly when you purchased it and that is the shape it will want to remain.   When it does try to return to the previous shape it will pull your sprinkler along with it and the end result will be a sprinkler that leans at a weird angle. If the pipe is curved when you buy it, work with the curve of the pipe. Twist the ells around on the end of the pipe until the sprinkler is in the position you want without bending the pipe. Cut the pipe length shorter if need be. (I recommend starting with a 12″ to 18″ length of flex pipe and then cutting it shorter as needed to position the sprinkler.) One more time; do not bend the flexible pipe. Believe me when I tell you that it will save you a lot of headaches later!

Clamps:  You do not need to use clamps on the special insert ells that are made for swing risers. These ells are made differently than the ones used for standard poly pipe. They have a self-locking ridge on the ell that seals it and locks the flexible tube on. Most of these swing riser insert ells also have spiral barbs, so you need to twist them into the pipe– just like screwing a light bulb into a socket. You do know how to install a light bulb, right? Finally, you should use Teflon tape on the male threads of the ells to seal them. You don’t have to use a lot of Teflon on these, a little leak here isn’t a huge problem.  While they shouldn’t, my experience is they tend to leak if not sealed with Teflon tape.  Again, unless you are a professional pipe fitter, I would recommend that you not use a liquid or paste type thread sealer. See my rant on that topic above in the Simple Pipe Riser section.

Inserting the ells into cold tubing:  OK, I confess it is often not as easy to get the insert ell into the tube as it is to install a light bulb. So if it’s cold, the flexible tube is stiff, and the insert ell just doesn’t want to go in, here’s a trick– use original KY Jelly (not the “warming” variety) on the insert ell barbs. Don’t use any other type of oil or soap, they can damage the plastic.  (Don’t know what KY Jelly is? It is a water-based lubricant. Don’t head for the hardware store like I did when I was first given this tip. Now that was an embarrassing incident!  Go to the drugstore or supermarket. It’s in the women’s hygiene section– ’nuff said guys?  Try not to have a silly grin on your face when you check out.)  You can also soften the tube by dipping it into hot water.  WARNING: Do not heat the tube with a heat gun, torch, etc. as the uneven heating that results from directional heat will severely weaken the tube.

Riser
Flexible Swing Riser

 

 

Photo of flexible riser pipe and insert ells
Photo of flexible riser tube and insert ells

 

A preassembled flexible pipe swing riser attached to a PVC fitting and a pop-up sprinkler.
A pre-assembled flexible pipe/tube swing riser attached to a PVC fitting and a pop-up sprinkler.

(The riser in the photo above is made by Hunter and features 4 ells for ease of installation and added flexibility.)

High Density Polyethylene (Marlex) Street Ell
High Density Polyethylene (Marlex) Street Ell

 


Rigid Arm Swing Risers:

The rigid arm swing riser is the standard riser type used for rotor heads, including the large ones found in parks and golf courses. For small rotors with 1/2″ inlets and spray heads I would recommend using the flexible swing joint described above, although there is no reason you can’t use a rigid arm swing joint if you want. But for most rotors a rigid arm swing joint is the way to go. The pipe and fittings used to make the rigid arm swing joint should be the same size as the inlet on the rotor.

There are various types of rigid arm swing risers depending on how many ells the swing riser has. The double swing riser has two ells at the bottom of the rigid arm and is pretty much worthless for most situations in my (not so humble) opinion. It allows the head angle to be adjusted, but does not allow the head to be moved up or down. Double swing risers are used primarily for shrub style sprinklers mounted on a pipe above ground.

The triple swing riser is much better and is the standard swing riser used by most professionals. The triple swing riser allows the head to move up and down and allows it to be angled in any direction (i.e.; you can install the head at an angle so that it is perpendicular to a slope.) But you still can’t move the sprinkler head from side to side with a triple swing riser. That’s why I use quadruple swing risers when I use a rigid arm swing riser.

The quadruple swing riser allows the sprinkler head to be moved in any direction. It can be adjusted up or down, angled in any direction, plus it can swing from side to side. For example, lets say you install your lateral pipe parallel to a sidewalk and for whatever reason, the pipe winds up being 10″ away from the edge of the sidewalk. With a triple swing riser your sprinkler is also going to be 10″ away from the sidewalk unless you install a small branch pipe over to the sidewalk from the lateral. With a quadruple swing riser you simply swing the sprinkler over so it is as close to the edge of the sidewalk as you want it to be. (Again, 4 to 6 inches is the normal distance a sprinkler should be from a sidewalk.) A quadruple swing riser costs about a dollar more than a triple swing riser, but gives you total flexibility– which is important if you want a really efficient sprinkler system! A typical rigid swing riser is constructed using a 12 inch long SCH 80 PVC nipple for the rigid arm (generally SCH 80 is gray colored) and high density polyethylene street ells (see photo of a street ell above.) High density polyethylene is typically referred to as “Marlex”. Marlex is black in color, softer than PVC, and works better for swing risers than PVC because it has a naturally oily surface. Do not use standard threaded white or gray PVC ells on swing risers! The threads on standard PVC ells tend to stick to each other and keep the swing riser arm from moving as it should. I recommend that you use a small amount of Teflon tape on the male threads, even when using Marlex street ells. By the way, the black plastic used for the swing pipe risers mentioned earlier are not Marlex! If you can’t scratch it with your fingernail, it is not Marlex.

Several manufacturers make preassembled rigid swing risers for sprinklers. Most of these preassembled swing risers are very high quality and use special PVC ells with o-ring sealed swivels built into them. Unlike standard threaded ell joints these swivels allow very free movement of the swing riser and are superior to swing risers made with standard threaded ells. They are often used with the large, expensive sprinklers used on golf course and park irrigation systems. The large, heavy tractor mowers used on parks and golf courses make it essential that the swing risers be able to move freely.

Drawing of a Rigid Quadruple Swing Riser
Drawing of a Rigid Quadruple Swing Riser

 


Flexible Risers:

What if you really need to bend the riser tube? There is a very flexible pipe riser product that is now sold at most irrigation supply stores and home improvement stores. It is durable and can be bent to pretty much any position you want. Tie it in a knot if you wish. I have been very pleased with this product so I feel I can recommend it for situations where you need a really flexible riser pipe. It is especially useful for sprinkler replacements. It looks like a flexible electrical conduit. (In fact that’s exactly what it is, a flexible plastic electrical cable protector with a length of vinyl tubing inside it!) Don’t use it for anything other than small spray head risers. It can’t withstand high pressures and will not work with high flow sprinklers.  I usually put a threaded street ell on one or both ends to make it easier to install.  The vinyl tube used in these risers is very small and creates high pressure loss.  Do not string multiple riser tubes together to make a longer riser.  The resulting high pressure loss will make your sprinkler not work very well.

Flexible Riser. This one is a Cobra Connector brand riser.
Flexible Riser. This one is a Cobra Connector brand riser.

 

Riser Pressure Loss

The amount of water pressure lost through the risers varies greatly.  Some manufacturer’s provide pressure loss data for their risers, most do not.  If you are using my Sprinkler Design Tutorial to design your system you don’t need to worry about pressure loss in the risers.  As long as you use one of the riser types as described above you are covered.  I have included compensation for the riser pressure loss in the lateral pipe sizing tables and spreadsheets.

 


This article is part of the Sprinkler Design Tutorial Series
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How to Find Your GPM & PSI – Gravity Flow

caution
STOP! If you’re using one of those design-it-yourself brochures or websites all bets are off! You need to either forget you ever read them or do not continue. You can NOT try to mix the “almost guessing” methods most of them use with the method in this tutorial. If you are going to use this tutorial (and you should!) you need to use ONLY this tutorial. If not you are going to be in big trouble. Gravity flow is tricky, this is not going to be an off-the-shelf irrigation system.  Use this tutorial exclusively and save yourself a lot of grief and get a professional quality sprinkler system. Please, please, please! Thank you. You are helping save my sanity. Now on with the tutorial.

Tip

There is a Design Data Form that you can print that will make things easier for you. If you would prefer a pdf version see PDF Design Data Form.

What in the World?

This is going to be interesting. The “Backwoods Water Method” is the catch-all category for everything that doesn’t fall into the other two categories (city water or systems that use pumps.) I’ve no idea what kind of water system you have, but it seems that most likely it will be some type of gravity flow system, so here’s some information about gravity flow systems. The principles here apply to just about any type of system, so you should be able to figure out at least a rough idea of your water supply using this information.

cautionDo not use the methods below if you have a pump or if your water comes from a water company pipe!

When dealing with gravity flow systems your water supply is effected by at least three different factors. They are water availability, pipe size, and the elevation of the water supply above your irrigated area (known as “pressure head”). These are really the same factors that determine water supply for all irrigation systems, however you will measure them using different methods.


Measure the flow.

If your system ever runs dry, or the flow appears to vary from time to time, you will need to take that into consideration when measuring your flow. You really should measure flow at a “worst case” time, that is, at a time when you are experiencing low water availability. This is probably not practical, so you may need to do a bit of guessing and adjust your test results accordingly.

The “Bucket Method”. We’ll start by assuming your water is already being piped to the location of the proposed irrigation system (or someplace close to it.) A typical situation would be a small dam created using sandbags in a stream and a pipe is stuck in under the sandbags. Water collects in the area behind the sandbags and some of it is diverted into the pipe. Normally a piece of nylon or galvanized steel window screen or mesh hardware cloth is placed over the pipe inlet to keep out small fish and twigs. The pipe transports the water to the area you want to irrigate. The Bucket Method of measuring flow is pretty easy, but you may get wet! Simply measure the time in seconds it takes to fill a 1 gallon container from the pipe! Measure the flow at the downhill end of the pipe. If there is a hose on the pipe end, take it off as the hose will restrict the flow. To assure a more accurate measurement turn on the water and allow it to flow freely for a few minutes before you take the measurement. Avoid measuring the flow from a small valve such as a hose bib, as the valve may substantially reduce the flow. Remove the valve and measure the full flow from the open pipe end if possible. Get a one gallon container, and time how long it takes to fill it with water. For the best accuracy measure the flow 3 or 4 times and average the times together. The formula to find GPM is 60 divided by the seconds it takes to fill a one gallon container (60 / seconds = GPM).

pencil

Enter the Maximum GPM (inflow) on your Design Data Form.

Example: The one gallon container fills in 5 seconds.
60 / 5 = 12 GPM.

(60 divided by 5 equals 12 gallons per minute.)

If you have a high flow you may need to use a larger container to get an accurate reading. To determine GPM using a larger container take the container capacity in gallons, divided it by the number of seconds needed to fill container, then multiply times 60. The result is the GPM.

Container size in gallons / Seconds to fill container X 60 = GPM

Example: Using a 5 gallon container it takes 14 seconds to fill the container.

5 / 14 X 60 = 21.4 GPM.

(5 divided by 14, then multiplied times 60, equals 21.4 GPM.)

 

If you have a Storage Tank.

If you do not have a water storage tank skip down to the section titled “Pressure Head”.

Hopefully the tank is on a hill, or a tower or some other elevated location. If not, the tank won’t help, so skip down to the next section.
If you have a storage tank you MUST measure the water inflow to the tank. Do NOT design your system based only on system outflow, which often exceeds inflow. You must measure both inflow and outflow, and design based on whichever is LESS! To start, drain the storage tank. Now shut off the flow out of the tank completely. Time how long it takes to fill the tank. If you don’t know the tank capacity in gallons you will need to find it. (The formula is at the bottom of this page). Divide the capacity of the full tank in gallons by the time it takes in minutes to fill the tank. The result is your “Tank Inflow GPM”.

Example: A 200 gallon tank fills in 10 minutes.
200 / 10 = 20 GPM

If you have a storage tank with a capacity over 1000 gallons you may be able to increase your Tank Inflow GPM by “buffering” it. Multiply the number of hours you will be irrigating per day by 60 (you will probably need to guess the number of hours you will be irrigating, so guess low to be safe). Keep in mind that the irrigation hours per day plus the hours it takes to fill the tank may not be greater than 24 hours! Divide the tank capacity by this number to get the buffer GPM. Add this buffer GPM to the old Tank Inflow GPM to get the new higher Tank Inflow GPM. Buffering simply takes into account the fact that as the water is flowing out to the irrigation system, water is also flowing into the tank helping to refill it. It will not empty out as quickly as it would if there were no water flowing in! I know that was confusing, so look at the example below which will help clarify. Let me worry about why it works (it does), you just do the math!

Example: 2500 gallon tank capacity. You plan to run the irrigation system for 8 hours per day. When totally empty the tank takes less than 12 hours to refill. 8 hours + 12 hours is less than 24 so we can buffer the Tank Inflow GPM. The buffer formula is:

2500 / (8 * 60) = 5 GPM.

If the original Tank Inflow GPM was 4 GPM, the new buffered Tank Inflow GPM will now be 9 GPM (4+5=9).

pencil

Enter the “Tank Inflow GPM” on your Design Data Form.

 

 

How to measure flow in gravity flow systems.
Simple Gravity Flow Water System using a Tank.

 


Pressure Head:

Now we need to measure the amount of “pressure head”. There are two methods, you can use either method.

Method #1. Pressure head is based on elevation or, in this case, the height of the tank above the highest area to be irrigated. If you don’t have a tank it is the height from the point where the water enters the pipe. This height is the elevation difference, not the distance away. In other words, if you imagine a level line extending from the tank over your yard, it is the height that line would be above your yard. Take a look at the drawing above. The water pressure in PSI can be determined by multiplying 0.433 times the height (feet) of the tank above the yard. It’s that simple, don’t try to make it harder! It doesn’t matter if the tank is on the top of a cliff adjacent to the yard, or if the tank is a mile away on a hill. As long as the elevation is the same, the pressure will be the same! It’s one of those abstract hydraulic principles I told you about that are hard to understand. (Okay, no doubt some hot shot out there wants to argue with me. So here’s an exception. If the tank was far enough away, much farther than would ever apply here, the pressure COULD vary due to changes in the gravitational pull of the earth and moon. Wow, isn’t that “cosmic”!)

Example #1: Tank is 100′ away on a hill behind the yard. Tank elevation is 70′ higher than the yard.

70 * 0.433 = 30 PSI.

Example #2: Tank is 1000′ away on the side of a mountain. Tank elevation is 70′ higher than the yard.

70 * 0.433 = 30 PSI. Pressure is STILL 30 PSI!

Method #2. An alternate method of measuring pressure is to install a pressure gauge (you can buy them at most plumbing stores) on the water pipe at the pipe outlet or the point you plan to tap into it for the irrigation system. This is probably the easiest method for most people. The water must not be running (turn off all faucets) when you take the measurement! (That’s why it’s called “static” pressure.) Read the PSI from the gauge. Warning: your water system may already have a pressure gauge installed on it. Inexpensive gauges (an expensive top-quality gauge will say something similar to “liquid filled” on the dial) tend to loose their accuracy after a year or two of use, so you may not want to rely on an old gauge.

pencil

Enter the pressure you calculated or measured in the space labeled “Design Pressure”on the Design Data Form.

cautionPossible bad news: If you have less than 25 PSI you just don’t have enough pressure for a standard automatic irrigation system to work well (the automatic valves need a higher pressure to work). You will need to use a manual control system, add a pump, or use a special type of valve used to heating systems.  See my article about automation of a rain barrel irrigation system for more information on these options.


Initial Design Flow:

If you don’t have a storage tank the Initial Design Flow will be the same as the Maximum GPM you measured using the “Bucket Method”. Pretty simple! If you Do have a storage tank the Initial Design Flow will be the lower of your “Maximum GPM” or your “Tank Inflow GPM”.  If your Maximum GPM was measured at 20 GPM, and your Tank Inflow GPM was 18 GPM, your Initial Design Flow will be 18 GPM because it is lower than 20 GPM. Use the lower number! Still pretty simple!

pencil

Enter the “Initial Design Flow” on your Design Data Form.

caution

This is really important! Later in step #3 of the tutorial you will determine the friction loss in your mainline. With a gravity flow system your mainline includes the pipe that brings the water to your yard from the water source! If you have a pipe that goes from the water source to a tank, you do not need to include the pipe that goes to the tank.  However, the pipe that goes from the tank to the yard is part of the mainline.  Therefore, when you calculate the mainline friction loss you will need to calculate it for both the pipe going from the water source (or tank) to where your sprinkler system taps in to the pipe, and also the pipe from the sprinkler system tap to the valves. You then add the friction loss for both pipes together to get the “mainline friction loss”. You might want to write this down on the Design Data Form so you don’t forget!

Example: Joe Backwoods has a pipe (pipe #1) that runs from the creek way up the canyon to a storage tank on the hill above his house. From the storage tank, a second pipe (pipe #2) takes water down the hill to his house. Next to the house Joe plans to tap a new pipe (pipe #3) into the house supply pipe to take water to his new sprinkler system valves. Pipes #2 and pipe #3 are considered part of the irrigation system mainline. Joe will need to calculate the friction loss in both those pipes and add it together to find out his “mainline friction loss”. Joe isn’t worried about how to calculate the friction loss because Joe knows that he will learn how to do it in Step #3 of the tutorial!


Do you have enough water available?

You are going to need about 20 GPM of water to irrigate 1 acre of grass with sprinklers. One acre is equal to 43,560 square feet (or 4047 square meters).  Therefore, if you have a 2 acre grass yard you will need to have 40 GPM of water available in order to water it. If you have shrubs, they typically only use 1/2 as much water as grass,  in that case 20 GPM would water 2 acres of shrubs.

If you don’t have enough water you will either need to find a larger water supply, or reduce the amount of area watered. Another option is to plant shrubs and use drip irrigation on them. With drip irrigation you only water the area the plant foliage actually covers. Therefore, if the plants only cover half the actual ground area, you only need half the water.

why

There are only so many hours in the day to water. The amount of water needed varies with the climate, these values are typical for hot summer areas where most sprinkler systems are installed (daily high temperatures over 90 degrees F., 32 degrees C.) These values assume you would water as much as 10 hours per day.  Water more time per day and you can have more area irrigated.


Related things…

Filtration:

You should probably consider installing a filter of some type on your system if the water is from a river, stream, pond, or lake. There’s a pretty good chance that all kinds of crud are in the water such as algae, sand, mineral deposits, fish, snails and clams. (No kidding!) All of these things can damage your irrigation system. For more information on filters see the irrigation filtration tutorial.

Storage Tank Capacity:

To find the capacity of an upright, round tank (measurements in inches):
radius * radius * depth * 0.01359 = gallons

example: 48 inch diameter X 48 inch high tank = 376 gallons
(24 * 24 * 48 * 0.01359 = 376)


This article is part of the Sprinkler Design Tutorial Series
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Selecting the Right Sprinkler Head

This article is intended to give you an introduction to the various sprinkler heads used for irrigation.  It will help you choose the best sprinkler for your situation.  At the same time it will warn you away from some common and costly errors often made in sprinkler head selection.  Similar information on bubblers is found in the last section of this page.

Types of Sprinklers:

Traditionally sprinkler heads are grouped into two broad types based on the method they use to distribute the water, spray type sprinklers and rotor type sprinklers.  However new technologies are blurring the traditional boundaries between the types.

sprinkler12a

Spray Heads:

More properly called “fixed spray heads” these are the small heads that spray a fan-shaped pattern of water. Think of a shower nozzle. Most use interchangeable nozzles installed on the sprinkler which determine the pattern (1/2 circle, full circle, etc.) and the radius of the water throw. Some specialty patterns are available for long, narrow areas. Spray heads are spaced up to 18 feet apart.  The basic physics of water spray limit the distance between heads.  They need between 20 and 30 PSI of water pressure to operate properly.

Rotors:

Rotor is the term used to describe the various sprinklers which operate by rotating streams of water back and forth or in circles over the landscape.  The example which most people are familiar with is the “impact” rotor sprinkler (often improperly called a “rainbird*”) which moves back and forth firing bursts of water.  You probably know this sprinkler best for the distinct sound it makes when operating– tooka, tooka, tooka, tic, tic, tic, tic, tic, tooka, tooka, tooka, etc… The impact rotors are rapidly being replaced now by gear driven rotors which are very quiet, lower maintenance, and much smaller in size.  It won’t be long before the average person has no clue what I am describing!  These new turbine and gear driven rotors have one or more streams of water which move silently across the landscape. The prettiest of these are the “multi-stream rotors” where multiple streams of water rotate over the landscape one after the other. Multi-stream rotors are fascinating to watch. Rotors can be spaced from 8 feet to 65 feet apart. There are rotors available that can be spaced farther apart than 65 feet but I don’t advise using them in most situations, even golf courses are moving away from using them due to problems. The traditional rotors with spacings over 20 feet require a lot more water pressure to operate than spray heads. Here’s a rule of thumb, “The water pressure at the rotor head in (PSI) must exceed the distance (feet) between the heads.” (Known as Stryker’s Rule, admittedly that’s a little ego stroking on my part, but I did create the rule!) Thus if you want to space rotors 35 feet apart you will need 35 PSI of pressure at the sprinkler head.  That means you will probably need around 45 PSI minimum to operate the system since pressure will be lost in the pipes and valves as the water flows to the sprinklers.   More on that later.  The small 3/4″ inlet rotors sold for residential use work best at 25 to 35 foot spacings.

(* Rain Bird is the name of a sprinkler company and is a registered trademark. The Rain Bird company makes many different types of sprinkler heads, including impact rotors. They also manufacture or distribute many other irrigation products.)

Rotary Nozzles & Rotators:

A new type of miniature rotors has been introduced in recent years and have become extremely popular. These are often called rotary nozzles or rotator nozzles.  The first brand on the market was called the “MP Rotator”, and several other similar products quickly became available from other companies. Most manufacturers classify these as “spray heads” in their catalogs.  They are called rotary nozzles because they are a very small rotor that is the same size as the standard nozzle on a spray-type sprinkler. Thus they fit onto the smaller, and less expensive, spray head pop-up bodies. Rotary/rotator nozzles are more efficient than traditional spray heads because they produce less “mist” that evaporates before it reaches the ground.  Thus they are often promoted for use in place of standard spray heads by water conservation agencies.

These rotary nozzles have a radius generally between 15 and 35 feet*. The exact distance depends on the model. They all use multiple streams of water that rotate around the nozzle and look like rotating spider legs.

*New models are being introduced each year as the technology advances and I expect to see shorter radius rotators available.  Already there are add on devices like the Little Valve brand devices that will reduce the radius of a rotator.

A few words of caution on rotary/rotator water savings claims:

Keep in mind that the water savings are primarily found when comparing rotators to spray heads.  For spacings over 20′ it is typical to use rotors rather than spray heads.  I haven’t seen any independent lab data that suggests that using a rotator nozzle in place of a rotor head will save water. (As of 2013.)

Like all other claims you must compare apples with apples.  I once had a city official, who obviously had just been visited by a rotary nozzle salesman, order me to replace all the sprinklers on a shopping center irrigation system with “rotators”.  The planters I was watering were 6 feet wide, and at that time the smallest rotator on the market had a minimum radius of 15 feet.  Thus if I had done as he suggested I would have been watering 9 feet of the parking lot!  Not a good move if you want to save water…  The moral of the story is that you need to use your head and select the right product for your situation.  Replacing a 6′ radius spray head with a 12′ radius rotator is NOT going to save any water!  Yet I hear that same blanket statement “switch to rotators and save water” over and over.

Guide to Selecting the Right Sprinkler Type:

Which to use, sprays, rotary nozzles, or rotors? Here are some questions to guide your selection.

  1. Is your water pressure less than 40 PSI static? If so you should consider using sprays or rotary nozzles.
  2. Is the area long and narrow, between 12-28′ wide? Then you should look into rotary nozzles.  They may also be appropriate for narrower areas, at the time I am writing this Hunter has introduced a “side-strip” rotator for 4 to 5 foot wide strips that are at least 12′ long.  More combinations of widths will likely be introduced in coming years.
  3. Is the area you want to water greater than 30′ x 30′ in dimensions? If so, rotors may be the best solution.
  4. Is the edge of the area to be watered curved? If the edge has sharp curves (less than 20′ radius) then rotors with longer radii will have difficulty watering the edges without over-spraying them. This may not be an issue depending on what is beyond the edge. If the area beyond the edge should not get water on it you might want to consider a smaller rotary nozzle or spray-type sprinkler.

Installation Issues related to Sprinkler Selection:

Rotors and rotary nozzles are spaced farther apart than sprays.  Therefore installation of them requires less pipe and trenching, but they also cost more per sprinkler.  For most normal-size city residential yards spray heads or rotary nozzles are usually the better choice.

Cost Issues in Selecting Type of Sprinkler:

Surprisingly, regardless of the type of sprinkler you use, the cost per square foot of area irrigated comes out about the same, assuming correct design of course.  When using rotors or rotary nozzles there is less pipe and trenches, but the rotors themselves cost more. Spray heads are less expensive to buy, but they require more pipe, trenches and valves to install. In the end, the price really comes out pretty close either way.

caution  Note: If your static water pressure (“design pressure” on your Design Data Form)  is less than 40 PSI rotors will not work properly, DO NOT USE THEM.  See the previous pages of the Sprinkler System Design Tutorial if you don’t know what static water pressure or design pressure means.  If you have a well and pump you must have your pump-on setting adjusted to no less than 40 PSI if you plan to use rotors. A “40-60” setting is typical. Contact your pump company for assistance.

Tip
If you are unsure, try using rotors in your design. If they don’t work out well, then erase them from your plan and try rotary nozzles. In many situations the best option maybe to use rotors in large areas, and spray heads or rotary nozzles in smaller or more narrow spaces. So you may have a mixture. This is OK, but there are some things you need to be careful of when mixing different types of sprinklers. The first is that each type must be separated and connected to a separate control valve. You can’t mix the types together on a single valve circuit or valve zone.  More on this later in the tutorial. The second is determining how to space the heads where the different types meet each other. For example, if you have a 30′ radius rotor next to a 15′ radius spray head, how far apart should they be from each other? There are many different schools of thought on this, but my general recommendation is to split the difference. In this example put them 22′ apart. Yes, the rotor would overspray the spray head by a considerable distance. But if you put them 30′ apart you will get a distinct dry spot between them.


Basic Body Styles:

Pop-Up Style Sprinklers:

Pop-up style sprinklers are installed below ground.  A piston that contains the nozzle lifts up from the sprinkler body when the sprinkler is operating and then retracts back below ground when not in use.  Consider using pop-up style heads even in shrub areas. Pop-up sprinklers often don’t cost any more than shrub sprinklers when you include the cost of the riser (the upright pipe the sprinkler is mounted on).  Two major advantages of pop-up sprinklers are safety and appearance.

What Pop-up Height Should You Use?

Pop-up style sprinklers are available in a variety of heights, generally 2″, 3″ , 4″ 6″ and 12″ are the common heights.  Most of my commercial clients ask me to use at least a 6″ height, even for lawns.  The extra height avoids problems.  I wouldn’t use anything less than 4″ on fescue, rye, St. Augustine, or bluegrass lawns.  For close mowed Bermuda grass 3″ will work.  My experience is that the spray from 2″ pop-up heads is often blocked by even recently mowed grass!  For that reason I do not recommend any model of 2″ pop-up, you will get dry spots in the lawn.  For groundcover and shrubs use 6″ and 12″ heads.

Groundcover Design Trick:

Here’s a tip for watering a groundcover area next to a lawn.  Place the sprinklers for the groundcover about 12″ away from the groundcover, in the lawn area, and aim them back at the groundcover.  That way the groundcover does not block the spray as easily.

Shrub Style Sprinklers:

Shrub style sprinklers were a type of sprinkler head designed to be installed above ground on top of a pipe.  In the old days they were used for shrub areas, thus the name.  For liability reasons, most irrigation professionals no longer use shrub sprinklers, except in very limited situations where nothing else will work.  You should take a hint from the pros and also avoid using them!  Read the warning below!  (For shrubs you really should look into using drip irrigation, it is a better choice than sprinklers for most situations.)

caution Many people are injured each year when they trip over, or fall on, shrub style sprinklers.  Think Safety.  Do not use shrub style sprinklers unless a very tall riser is needed to raise the sprinkler spray over the tops of tall shrubs. When needed, shrub style sprinklers should only be used in areas well away from sidewalks, patios, and areas where children play.  They should be clearly visible.  A good idea is to strap them to a large post, like a 4″x4″ wood or plastic fence post, to hold them stable and make them easy to see.

sprinkler12b


Metal or Plastic?

At the grocery store it’s “paper or plastic?” but with sprinklers the question becomes “metal or plastic?”. The conventional wisdom is that metal is more durable than plastic, and therefore is better. Up until the late 1970’s metal (usually brass, sometimes zinc) was the standard material from which almost all sprinklers were made. However, times have changed and now plastic is the most common material for sprinklers. Very few manufacturers even bother to make an all-metal sprinkler anymore. The primary reason for this change in materials is cost; machined metal parts are enormously expensive in comparison to injection molded plastic. Fortunately, most of today’s plastic sprinkler heads are very well engineered and will perform as well as, if not better than, the old metal sprinklers.

Hybrids: A few companies manufacture plastic sprinkler bodies which accept brass nozzles, which they claim results in a better water pattern. Other manufacturers claim that plastic nozzles perform as well as brass. The research tends to indicate that a really well-machined brass nozzle has better water distribution. But that’s laboratory tests, and in the real world a lot of other factors come into play. I personally haven’t noticed any significant difference in performance between most brass and plastic nozzles in well-designed, sprinkler systems, although brass nozzles will no doubt last longer. More importantly, there are a few nozzles, both brass and plastic, which don’t seem to perform as well as others. Fortunately, they are easily identified by comparing prices (as in “you get what you pay for.”) Typically these bad nozzles come pre-installed on sprinklers that don’t have the features I list below, so if you stick to sprinklers with my recommended features you will get acceptable quality nozzles.


Features to Look For:

The following features are common to all good-quality sprinkler heads (for both rotors and spray type heads.) Choosing a sprinkler without these features is asking for trouble.

sprinkler12c

  • Spring Retraction: Make sure a spring is used to pull the pop-up piston down into the case when the sprinkler isn’t on. As a general rule the stronger the spring, the less likely the piston will “stick up” and get mowed off.  Stay away from sprinklers that rely only on gravity to retract the pop-up piston.
  • Wiper Seal: This is a soft plastic seal around the pop-up riser stem that seals the riser so it won’t leak . The wiper seal also is responsible for keeping dirt out of the sprinkler body, and is the most important part in determining how long the sprinkler will last. Make sure the sprinkler model you select has a wiper seal. Note: on some sprinklers you must remove the sprinkler’s cap and look inside the bottom of it to see the seal. Be careful when removing the cap, on some models the spring will shoot out!
  • 3 Inch Pop-Up Height (or higher): Unless you just like to trim grass around sprinkler heads, make sure the pop-up height is 3″ or more. This way the spray nozzle will clear the top of the grass. Most professionals use 4″ pop-up sprinklers in lawn areas, and 6″ or 12″ pop-ups in shrub areas.
  • Rat Traps.  This is a design type to avoid if you can.  A “rat trap” is a derogatory name used in the sprinkler business to describe any sprinkler with a design that allows debris to fall into the sprinkler body when the riser is raised.  The more proper name is a “bucket” style body, but I like the visual image of the problem that rat trap provides.  The debris collects in the bucket area and eventually there is enough garbage in there to prevent the mechanism from dropping back down.  The stuff that falls in there can get pretty ripe smelling as it decomposes, too!  Do rats really get trapped in them?  I’ve never seen one.  The “trap” only opens when the sprinkler is operating and rats tend to stay away from a sprinkler that is operating!  Mostly grass clippings and dirt get trapped.

Sprinkler Make and Model Recommendations:

Mix and Match.  One common question I get from users of this tutorial is “who makes the best sprinkler heads” or “which model should I use?”  This probably won’t help you much but most of my designs have a mixture of brands and models as I feel different products are best for different situations.  But what you should get out of that is that it is OK to mix and match– within limits. On any single valve circuit you should use one brand and model of sprinklers only.  This is because precipitation rates vary between makes and models and if you mix a high precipitation sprinkler on the same valve zone as a low one you will get mud in one area and dry spots in another.  But you can create two different valve zones and use different sprinklers in each.  So one valve might turn on a group of brand X rotors to water a large lawn area.  Another valve might turn on a group of brand Y spray heads to water a small lawn in a parking strip.  And a 3rd valve might turn on a drip system using brand Z emitters that waters some shrubs.

Brands and Models. While I don’t recommend specific brands of equipment, I do have a few irrigation product reviews you might want to look at.  I try to be as objective as possible and I do present hard facts when I have them (like results from tests on my sprinkler test stand,) but my tests aren’t statistically relevant (I can’t afford to buy and test sprinklers from 30 random stores and random times in order to get a statistically solid sampling.)  So the reviews are mostly my personal opinions.  If you get 4 industry pros together you will get 4 different opinions of products, each a heartfelt honest opinion.  I try to focus on products sold to retail customers at hardware and home stores.  I figure other pros aren’t looking for my opinions!

More on selecting your sprinklers is coming later on in the tutorial.  At this point in the design process what you need to know is an approximate sprinkler operating pressure. You may have noticed I used the term “operating pressure” here rather than “pressure loss” as previously used for other irrigation equipment like valves and backflow preventers. While pressure loss is a perfectly accurate term for the pressure used by sprinkler heads and emitters, operating pressure is more commonly used. Operating pressure is simply the pressure that needs to be present at the sprinkler or emitter inlet for it to perform as intended.

Manufacturers of sprinklers and emitters provide specifications for each of their products.  These specifications typically have a table that lists the operating pressure, the flow the sprinkler will use, and how far the water will spray at that pressure.  You will need to obtain these specifications for each of the sprinklers you intend to use. This information may be printed on a label attached to the sprinkler, or on the sprinkler packaging.  Most manufacturers also make these specifications available on their web sites. Typically for a sprinkler this specification will list an inlet pressure as pounds per square inch (PSI) and then give a watering radius (feet) and flow rate in gallons per minute (GPM) that will occur at that pressure. A typical table might look like this:

Pressure PSI Radius Ft Flow GPM
20 10 2.10
30 12 2.60

The table above is a sample only, please do not assume these values shown are “typical”.  In this sample we can see that at 20 PSI this sprinkler will have a radius of 10 feet and it will consume 2.10 GPM or water flow.   Or at 30 PSI this sprinkler will have a radius of 12 feet and it will consume 2.60 GPM or water flow.  As you can see a higher water pressure results in a larger radius and higher flow requirement, this relationship between pressure, radius and flow is true of most sprinklers.  This is why it is so important to calculate what the water pressure will be when designing.  If you design your sprinkler system with the sprinklers 12′ apart you, you would need 30 PSI of pressure at the sprinkler head so that it would spray the required 12′.  You would be in big trouble if the pressure lost in pipes and valves resulted in the pressure at the sprinkler only being 20 PSI.  You would get a dry area between the sprinklers.  This is why it is so important for you to actually go through this whole tutorial and do the design right.  (No that spacing is not an error, if the sprinkler radius is 12 feet, then you space the sprinklers 12 feet apart, not 24 feet.  More on this later in the tutorial when we discuss sprinkler spacings and placement.)  Don’t try to guess or assume “it will work.”  I hear from tons of people wanting to know how to fix a system that they just threw together, and now it installed and there are dry spots all over the place.  Unfortunately it almost always is very expensive to fix at that point, costing them far more than it would have if they had taken the time to learn how to do it right the first time.

For an emitter the product specification tables would include only operating pressures (PSI) and a flow rate in gallons per hour (GPH) for each of those pressures. (Radius of throw isn’t applicable to drip emitters.)

Can’t find a performance chart or specification for the sprinkler or emitter?  Then I would suggest you find another brand and model. Not providing this vital information is an sign of lack of professionalism on the part of the manufacturer.  My experience is that most products sold retail without specifications are poor quality “knock off” products, often made by a “copy cat” production plant that makes knock offs of anything they can find with expired patents that will fit into their molding machines.  This week they make sprinklers, next week it will be cd cases.  They often cut corners like using poor quality raw materials, reducing the amount of plastic in the body and using low quality molds.  They are then sold in bulk cheap with no support or guarantee.

Pressure Requirements for Sprinklers

Spray Type Sprinklers, Rotary Nozzles, and Rotators:

For spray type sprinklers, rotary nozzles, and rotators most designers use an operating pressure of 30 PSI, unless a lack of available pressure forces a lower level. The vast majority of spray type heads and rotary nozzles/rotators are designed to operate most efficiently at 30 PSI.  Remember that if you use a lower pressure the sprinklers will need to be spaced closer together, because the water won’t spray as far. Check the manufacturer’s performance chart for the sprinkler. Additionally, almost all spray type heads have a radius adjustment screw that allows you to reduce the watering radius for using the sprinkler in smaller areas.  (When you adjust the radius using the adjustment screw on a spray head, you are actually reducing the pressure at the nozzle by means of a small valve inside the nozzle.  As the pressure is reduced the water doesn’t throw as far, it’s exactly the same as shown on that performance chart, a lower pressure gives less radius.)  At pressures above 45 PSI most spray heads start to create lots of mist, which results in poor sprinkler performance. This can also be controlled by using the radius adjustment feature to reduce the pressure.  If all the heads are misting a better solution is to throttle the sprinkler zone control valve (cheapest solution) which will reduce the pressure at all the sprinklers on the valve circuit.  A better solution is to install a pressure regulator on the mainline to reduce the pressure in the whole sprinkler system, or use special pressure regulating sprinkler heads or nozzles made by some sprinkler manufacturers.  Use of these pressure regulators gives more accurate pressures than adjusting a nozzle or throttling a valve, thus they increase the sprinkler system’s efficiency.  But they cost a lot more than throttling a valve.  If you have a water source with reasonably steady pressure, like most municipal water systems, throttling a valve or adjusting a nozzle will be “good enough” for most people.

Rotor Type Sprinklers:

For rotor type sprinklers the higher the operating pressure the better, within reasonable limits. We don’t want to blow the sprinkler apart with high pressure– and rotors can cause mist too under extreme pressures.  As a general rule, most rotor type sprinklers do not work well with less than 30 PSI operating pressure. The optimal pressure is easy to determine for rotors using the following rule, keep reading!

Tip
“Stryker’s Rotor Spacing Rule” states that the spacing in feet between rotor-type sprinklers can’t exceed the pressure in PSI at the rotor. So what that means is that if you want to put the rotors 35 feet apart, your rotor will need to operate at 35 PSI or higher, pressure.  I like to aim for at least 5 PSI higher than the minimum, so for that 35′ spacing I would aim for 40 PSI.

Important!  There is a lot of competition in the sprinkler business to see who can get the greatest radius from a rotor-type sprinkler. Manufacturer’s literature and packaging tends to wildly exaggerate the maximum spacing of rotors. They get those distances by testing the rotors inside a big building with no wind. Even the most gentle breeze will shorten the real-world watering radius (water droplets are very light). If the package says the rotor has a radius of 35 feet at 30 PSI– that all wonderful, but don’t try to install those rotors 35′ apart! In the real world you will not get that distance (unless you are watering inside a building.)  If you have 30 PSI do not space the rotors more than 30 feet apart. If you ignore this rule, 9 chances out of 10, you will have dry spots in your lawn! (Yep, over-size ego alert, the rule is named after me.  I came up with this rule many, many years ago.  So it got my name.  That’s how it works!)

Rotor Spacing Example: If you want to space the rotors 30 feet apart then you will need to use a pressure of at least 30 PSI for the rotor. If you want to space rotors 40′ apart you will need 40 PSI for the sprinkler head pressure.

Maximum Rotor Spacing: I don’t recommend spacing sprinklers farther than 55 feet apart unless you have an experienced professional design the sprinkler system. Many tricky problems occur with sprinklers when they are spaced greater than 55 feet apart.  Remember that cost is consistent regardless of spacing so it will not save you money.  Bigger sprinklers cost a lot more money as well as the larger pipe, plus you almost always need a booster pump to get enough water pressure, so you have pumping costs (pumps are expensive to buy, maintain, and operate.)

Drip Emitters:

Most emitters operate best at around 20 PSI. Some emitters are “pressure compensating” which means they should put out approximately the same amount of water over a wide range of inlet pressures. (I’ve found that many pressure compensating emitters are not a whole lot more “pressure compensating” than standard emitters are. Keep in mind that at pressures over 45 PSI emitters may blow apart. Barbed emitters installed in poly tubing may pop out of the tubing at pressures over 30 PSI.

Mix and Match:

Sometimes you need to use sprinklers that require high pressure such as rotors, with sprinklers that use low pressure on the same irrigation system. To do this the system is designed using the pressure requirements of the high pressure sprinklers. The low pressure sprinklers (or emitters) are installed so that a separate valve turns them on and off, and a special pressure reducing valve is used. These valves have a built-in pressure regulation device that reduces the pressure down to the correct amount for the lower pressure sprinklers or drip emitters. Almost all irrigation manufacturers now make pressure reducing valves, although you may have to go to a specialty irrigation store to buy them.

 


pencil If you are working through the Sprinkler Design Tutorial, enter the sprinkler head operating pressure (or the drip emitter pressure if no sprinklers) on the “Sprinkler Heads” line of the Pressure Loss Table.

caution  Remember– the pressure you enter in your table is the pressure for a single sprinkler head. So if you will have 10 sprinklers and they each require 30 PSI you still only write “30 PSI” on your pressure loss table. Also the value you enter should be the highest sprinkler head pressure requirement. So if you plan to use a spray head that will need 20 PSI and also a rotor that will need 35 PSI, you will enter the higher value– which in this case would be 35 PSI. Finally, remember why pencils have erasers. You can always come back and change this value later if you want to! So don’t agonize over it.

why  A lot of people ask me why you only write down the pressure for a single sprinkler. This is a bit difficult to understand but I will try to explain. I think the easiest way to understand is with a mental image. Think of the water moving through your sprinkler system as millions of water droplets, rather than a single mass of water. On it’s journey through your sprinkler system a single drop of water will loose pressure along the way. Each place where it will lose pressure is one of the items that is listed on your pressure loss table.

Let’s follow a drop of water through a typical sprinkler system!  First our water droplet will travel through a pipe from the water company to your water meter. Then it will proceed through the meter into the house supply pipe and on to the irrigation system connection. From there our drop goes into the irrigation system and may pass through a backflow preventer. Onward it travels to the sprinkler zone control valve and through that valve into the lateral pipes leading to the sprinkler heads. Finally the drop goes into one of the sprinkler heads and is propelled out onto the lawn. Note that our droplet only passes through one sprinkler head on the way to the lawn. I’ll bet you’ve never seen water on the lawn jumping back into the sprinkler head so it can go back and try going out through another sprinkler! So it only passes through one sprinkler head.  Awwwwwww!!!  Starting to make sense, right?  Thus we only consider the pressure needed for a single sprinkler head. (O.K. wise guy, yes I have seen water sucked back into a sprinkler head. But that’s not supposed to happen, it means something is wrong with the sprinkler system.) At any rate, even if you still don’t understand why you use the pressure loss for only a single sprinkler, please trust me, it’s correct!  I’ve been doing this sprinkler design stuff for over 35 years and have designed thousands of systems.  Plus this tutorial has been around since 1997 and successfully used by thousands of people.  Plus it is used by dozens of colleges as an irrigation design text.


Still have some questions about sprinklers?  Much more information on sprinkler selection is coming later in the tutorial, such as detailed information on the spacing to use between sprinklers and nozzle selection. If you want to jump ahead and check it out, click here. Just don’t forget to use your “back” button to return here!


Bubblers

Bubblers are generally used to flood small areas of the landscape with water.  In most cases they are not suitable for lawn irrigation and are used for watering shrubs or sometimes groundcovers.   They are most often used to water smaller areas where sprinklers would overspray water out of the area, although there are other specialty uses for them.  For example, I often use near floor to ceiling windows where I don’t want water spray to drift onto the windows.  Bubblers generally need to be in level areas, since they flood water over the ground surface.

Some sprinkler manufacturers make “bubbler nozzles” that fit onto their standard spray-type shrub style or pop-up sprinkler bodies.  The classic bubbler is simply screwed directly onto the end of a 1/2″ pipe.

Bubblers and drip emitters:  The difference between a bubbler and a drip emitter is flow rate.  Drip emitters flow at very low rates, most often 4 gallons per hour (16 liters/hour*) or less.  The intent of a drip emitter is that the water would soak into the ground at the emitter location with a minimum amount of water puddling around the emitter.  Bubblers flow at higher rates, often measured in gallons per minute rather than hour, and the intent of a bubbler is to flood the ground surface with water.

(*A little optional puzzle for you.  Q. If you do the math 4 gallons rounds to 15 liters, so why did I say 16?  A.  Emitters aren’t designed in English units, they are actually metric.  They are designed using liters, so in reality it is a 16 l/h emitter, not a 4 gph emitter.  16 liters rounds to 4 gallons, while 4 gallons rounds to 15 liters.  It’s a rounding error issue caused by the unit values rather than bad math.  OK, enough fun for the geeks.)

Combining bubblers with sprinklers:  Normally bubblers are separated onto a valve circuit of their own so that the watering time can be fine-tuned for exactly how long it takes to flood the desired areas with water.  However, a small number of bubblers with adjustable flows can usually be installed on the same valve zone with spray-type sprinklers that are watering adjacent shrubs or groundcovers.  Installing bubblers on the same zone wtih spray -type sprinklers is not the most efficient way to go, but as long as it is only 2 or 3 bubblers and they are watering a very small area (not more than 3′ square per bubbler) you can generally play with the bubbler’s flow adjustments and get a reasonably workable watering balance.  When watering a larger area using many bubblers or when using non-adjustable flow bubblers you should place the bubblers on a separate valve zone/circuit consisting only of bubblers.  Placing bubblers on the same valve zone with rotors or drip irrigation seldom works out well.  Do not combine bubblers on the same zone with lawn sprinklers.

There are a number of different types of bubblers available, so let’s start by attempting to group them into some loose categories.

Flood Bubblers

Flood bubblers do just what the name implies, they flood the area around them with water.  They further divide into two types, adjustable and non-adjustable.

The adjustable flood bubblers are by far the most common type found, and are what most people think of if they are familiar with bubblers.  An adjustable flood bubbler is essentially just a small water valve.  It typically has a screw or knob that is used to adjust how much water flows out of it.  Most bubblers are designed so that the water gently “bubbles” out of them, the reason being to avoid erosion caused by a strong stream of water.  The amount of area they will water is very hard to predict, it depends on how far open the valve is (how much water is coming out), how long it is left on, and the soil type.  For purposes of planning your irrigation system, I have found that in most situations flood bubblers will water an area about 3 feet in radius, at a flow of 2 GPM.  Understand that this would be a circular 3′ radius area, so if you put them 6′ feet apart that would give you 6′ diameter wet circles that just barely touch each other!  In practice if I am watering a long planter strip 3′ wide with shrubs in it I will install flood bubblers 3′ to 4′ apart down the length of the planter.  If the area is wider than 3′ I will install a second row of bubblers.  Again, bubblers tend to be very hard to predict, you may find you can water a much wider area with a single row, or if you have sandy soil you may have difficulty getting the area flooded with them 3′ apart!

Non-adjustable flood bubblers are just that, non-adjustable.  Water flows out of them at a fixed rate.  The flow rate depends on the manufacturer, common flows are 1/4 GPM, 1/2 GPM, 1 GPM, and 2 GPM.  They are a bit harder to determine spacing for, but that is solved by the intended use.  Typically you install one fixed flow bubbler at each shrub or if they are very small shrubs (not more than 18″ – 24″ diameter full grown) you might install 1 non-adjustable bubbler between two shrubs to water both of them.  Once again the area watered is very variable depending on which flow rate you choose, how long you run the bubbler, and the soil type.  Other than having a non-adjustable flow they are very similar to the adjustable flood bubbler.

Tip
A trick you can use is to go to the store and purchase a flood bubbler to use as a test.  Also purchase the adapters needed to attach it to the end of a garden hose, it will probably be an odd “Rube Goldbergian” type assortment of adapters and nipples.  Install the bubbler on the end of a garden hose, turn it on, adjust the flow, and see how large an area it will flood with water in your yard.  To determine the flow you are using for your design, you can measure the flow by using a 1 gallon bucket and seeing how long it takes the bubbler to fill it.  15 seconds to fill is 4 GPM, 22 seconds is 3 GPM, 30 seconds is 2 GPM, 60 seconds is 1 GPM, etc.

 Stream Bubblers

Stream bubblers spray a narrow stream of water, most often the stream shoots out 2 to 5 feet from the bubbler.  The purpose of stream bubblers is to get the water out away from the bubbler and thus allow watering a larger area with it.  In actual practice my experience is that they don’t do a good job of actually flooding a large area.  However they are great for watering a group of plants provided the plants are located in the immediate vicinity of where the stream lands.  So study the spray pattern of the streams and examine whether the streams will reach the plants you want to water.   For example, for large hedges I often will use a stream bubbler that has two opposing streams, one in one direction and a second in the other (called a “center strip” pattern.)  I can center one of these between two plants that are 3 to 6′ apart and water both plants with a single bubbler.  This is great for large hedges and limited budgets.  Keep in mind that foliage will block the spray from a stream bubbler so you may need to trim the plants to keep them out of the bubbler’s spray trajectory.  As with other bubblers the area watered by stream bubblers needs to be reasonably level so the water puddles up and doesn’t run off.

TipI have used lots of stream bubblers on commercial projects where drip irrigating shrubs is impractical due to the high maintenance of most drip systems.  These are typically new landscapes where I am designing both the landscape planting and the irrigation system.  In this situation I lay out the irrigation system with stream bubblers 36″ apart with the streams adjusted to spray 12 inches.  Then I plant the plants at the end of the streams around the bubblers.  A full circle stream bubbler typically has 6 streams of water allowing it to water 6 small plants, like daylilies, that are grouped around it.  Note that my experience is that this idea doesn’t work as well with larger plants and/or plants placed further than 24″ away from the stream bubbler.  If I need additional rows of bubblers I put the rows 24″ apart forming a triangle pattern with the bubblers.  Because these are commercial projects where I typically use this stream bubbler layout, I usually use stream bubbler nozzles and install them on 6″ pop-up bodies so they drop to ground level when not running.  It looks nicer and it is much safer.

Micro Bubblers

Micro-bubblers are lower flow bubblers often sold as adjustable flow drip emitters.  They often have barbs so that they may be installed on poly drip tubing.  They are called bubblers because they typically have flows over 4 gallons per hour, which is a higher flow than most soils can absorb without the water pooling on the surface.  Although they are adjustable flow, micro-bubbler flows are too low to be compatible with spray or rotor type sprinklers, so don’t put them on the same valve circuit. For more on micro-bubblers see the drip irrigation guidelines tutorial, where they are called adjustable flow emitters.


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How to Remove a Valve Zone from Sprinkler system

Q.  I have 3 zones for my sprinkler system.  I need to remove the valve/pipe/heads from one of the 3 zones in my backyard.

A. You may not even need to turn off the irrigation system water for this project.  But it is a good idea to know how to turn it off.  You never know when you may need to.

Definition:Zone valve” when used in irrigation, is the valve that turns on and off a group of sprinkler heads.  In most cases the zone valve is an electric activated valve and has a solenoid with wires leading into it on top of the valve.  The wires connect the zone valve to the irrigation controller (sometimes called the “timer” or “control box.”)  The power to the valve is typically 24 volts AC.  It usually will not harm most people if they touch a live wire, but it will give you enough of a shock that you will never want to do it again!  Obviously if you have a pacemaker or sensitivity to electrical current you will want to be extra careful around the wires.  If you touch your cell phone to a bare wire it may become an expensive paperweight.

Shut off the water. (Optional, if you are not going to remove the zone valve you don’t need to do this.)  Turn off the water to the entire sprinkler system.  Many sprinkler systems have a main shut off valve that turns off all the water to the sprinkler system.  Look around for the shut off valve.  It may be in a box underground.  Often it it near the location where the pipes enter the house.  Often it it in a basement if other water pipes are located in the basement.  Once you found a possible shut off valve, turn on one of your sprinkler zone valves so you can see that the system is running.  Now try turning off the possible shut-off valve.  It the sprinklers stop running you know the valve shuts off water to the sprinkler system.  Now check and see if it also turned off the water to the house.  If it did, you just found the house main water shut off valve.  You may not find a valve that turns off only the sprinkler water.  A lot of homeowner installed sprinkler systems don’t have them.  You may just have to turn off all the water to the house in order to work on the sprinkler system.

The easiest way is to leave the zone valve installed and not remove it.  Just plug it.  I’ll tell you how to do that first.

Identify the valve.  Now you need to figure out which of the sprinkler zone valves is the one you want to remove.  Hopefully you know where the valves are.  If not, see the article on how to find missing valves.   To determine which valve you want to remove, you manually turn on the zone valves (without using the control box) and see which one turns on the sprinkler you want to remove.  On top of your zone valves is a solenoid, written on it you will see ON/OFF arrows.  Turn the solenoid in the “ON” direction about 1/4 turn or so.  This should open the valve and the sprinklers should come on.  Note: Some valves have a lever that turns them on and off, some have a bleed screw you partially turn to make them manually open.  Each valve make and model is a little different, so you may have to use some deductive skills to figure out how to manually open your valve.  By turning them on one at a time you should be able to determine which valve operates the sprinklers you want to remove.  When finished, turn off the valve by by reversing the procedure you used to turn it on.  If your valve uses a bleed screw to open it, DO NOT completely remove the bleed screw.  Just unscrew it slowly until the valve turns on.

Typical sprinkler zone valves.
Typical sprinkler zone valves.

3. Now that you know which valve you want to remove, carefully dig the dirt away from the valve and expose the pipe on the downstream side of the zone valve. If you clear the dirt off the top of the zone valve it should have a flow direction arrow someplace on the valve body that points toward the outlet side.  (It may be on the side of the valve, using a small mirror makes it easier to find it.)

Once you know which direction the water flows through the valve, cut out a short section of the pipe right after the valve. Water may squirt out when you make the first cut into the pipe, so be prepared to get some muddy water sprayed at you!   A lot of water may drain out when you cut the pipe, depending on how much water was in the pipes and the slope of your yard.   You may have to bail water out of the hole with a bucket to remove it.  With the pipe section removed you can now use a wrench to unscrew the remaining pipe from the valve outlet.  Take the pipe section you removed from the valve (with the threads on it) to a hardware store and buy a threaded plug of the same size and a roll of Teflon tape.  Wrap several layers of the Teflon tape sealant onto the threads of the plug and then put the plug into the valve outlet opening.  Hand tighten the plug, then use the wrench to tighten it another half turn.  Do not overtighten it, if you overtighten the plug the valve body may split open.  Now that valve zone is plugged off.  You can remove the wires for that valve from the controller if you wish.  Now remove any of the pipe or sprinklers you want from that valve zone.

You can remove the entire valve if you want to.  I didn’t have you remove the valve because that does not require you to turn off the water to the entire sprinkler system, which is easier for most homeowners to do themselves.

To remove the entire valve:  Turn off the water to the entire sprinkler system.  Then manually turn ON the valve you want to remove, the sprinklers will come on for a few seconds then slowly shut off as the water discharges from the pipes and the pressure is released.  If the sprinklers keep running the water is not shut off!  Now follow the directions above.   Once the outlet pipe section is cut and removed, cut the wires off the valve, then unscrew and remove the entire valve.  Seal the ends of the wires with PVC glue or silicon caulk/sealer if you think you may ever want to use them again.   Put a threaded cap on the pipe that formerly connected to the valve.

Removing sprinklers.  To remove a sprinkler you can sometimes just grab the top of it and turn it counter-clockwise.  It will unscrew from the pipe below it and then you can lift it out of the ground.  Often you will need to dig away grass from it so you can twist it out.  In most cases you don’t need to dig a big hole around the sprinkler head, just dig away enough dirt and grass to allow you to grip the sprinkler.  Fill in the hole with dirt after you remove it.  Assuming you are abandoning the pipes, there is no need to cap the pipe off below the sprinkler, just leave it there.  If you don’t plan to ever use it, it doesn’t matter if it gets dirt in it.

Removing Pipes.  Most of the time we just leave the pipes in the ground.  They are a lot of work to remove and most of the time they don’t bother anyone if left buried.  If the pipes are not very deep you can often pull them up using “brute force”.  Dig down to expose the end of the pipe, grab the end and pull it up out of the ground.  If there is thick lawn you may need to cut a slit in the lawn surface to allow the pipe to be pulled up easier.  Use a edger to cut the turf directly above the pipe.  A string trimmer with heavy string in it may be able to cut the turf.  It may use up a lot of string!

I don’t recommend using a vehicle to pull the pipe out, but I know some will try it.  If you do this and get yourself injured or killed, you will be featured in those “knuckleheads in the news” columns!  If you try attaching a rope to the pipe and the other end to a garden tractor or truck to pull the pipe out of the ground – be very careful.  Wear protective clothing, gloves, eye protection and a hard hat.  Keep everyone else far away.  Have someone there watching from a distance who can call 911 if you get hurt!  Here’s why I say you shouldn’t do this:  Plastic pipe breaks suddenly and violently when pulled hard.  If the pipe or rope breaks while pulling on the pipe both the rope and the pipe can whip around violently and cause injury or damage, ie; break a window.  The white hard PVC plastic pipe can shatter and release small, very sharp pieces of plastic that act like shrapnel and cut like dozens of little knives.  If the pipe does not come out easily and you see the rope stretching, STOP, it’s going to break!  Don’t be an idiot, use common sense and extreme care.

If you can’t pull the pipe up and you absolutely can’t just abandon it in place, the only way I know of to get it out is to dig it out.  Ugghh.  Lots of work.

 

 

Watering a very narrow 30″ wide lawn strip

Q. I need to water a 2.5′ wide by 21′ long grass strip in the middle of my driveway. What is a good method for this narrow an area? My home is located in Southern California.

A. Irrigating lawn in areas less than 4′ wide is very hard and results in a lot of wasted water. It is illegal to install a grass area less than 4 to 6 feet wide in many cities, especially in California and other western States, including ALL of Arizona and most of Nevada (the minimum width varies from town to town.) Enforcement is typically limited to new development, but if you get a permit from the city for the work you may get nailed on this issue.

Using Sprinklers

If you do use sprinklers there is going to be a lot of water waste from over-spray onto the concrete. It will likely run down your driveway and when (not if) the next big drought cycle hits and they start with the “water police” thing you will likely have to stop watering your strip or risk a “fix it” ticket.

If you do use sprinklers you will reduce the radius of each sprinkler to your 30″ width and then you reduce the distance between sprinklers by a similar %. I recommend using side-strip sprays rather than the center-strip type as you will have a lot less over-spray on to the concrete with them. The side strip side are installed down both sides of the strip. Center spray types are installed down the center of the strip. Using center strips type will require half as many sprinklers, but the cost of this initial savings is lousy performance, poor efficiency, and lots of wasted water (it is common when using center strips that 50% or more of the water applied will be wasted.) So let’s say you decide to use 4′ x 12′ pattern side-strip spray nozzles in 4″ pop-up bodies. Since your area is only 30″ wide you would need to reduce the spray width from 48″ to 30″. That would be 62% of 48″ ( 30″ / 48″ = 0.625). So you would also need to reduce the 12′ distance down to 62% also, which is 7.5′ (12′ x 0.62 = 7.44′). So in your 30″ x 21′ area you would space the heads 7′ apart on both sides. After installing the system you would reduce the radius of each head as best you can using the radius reduction screw. It is unlikely you will be able to avoid some over-spray onto the walk as noted earlier. If you decide to use center strip nozzles the procedure and spacing would be the same, there would only be one row of heads, however, installed right down the center of the strip. With center strips you will have to allow more water to overspray onto the cement driveway, if you don’t you will get dry yellow edges. If you want a better explanation of why see this page on sprinkler spacing.

Using Subsurface Drip

Your other option is to use subsurface drip. This is what I would do. In this case I would use three drip tubes running the length of the grass strip. Place one down the middle and the other two should be 4″ in from the edge of the driveway concrete on each side. Use dripperline with 1 gph emitters spaced 12″ apart. Netafim, Rainbird, and Toro all make subsurface dripperline. Make sure the dripperline is a model that the manufacturer claims in their literature is for subsurface installation. Subsurface dripperline uses a different type of emitter designed to keep out dirt and roots. Read my drip guidelines for info on filters and pressure regulators you will need. The salesperson at the irrigation store may tell you that you only need two tubes, which normally would be correct, they typically are spaced 18″ apart, not 12″. There are a couple of reasons I am suggesting 3 tubes rather than 2. First is to get the total flow up because the area is so small and most automatic solenoid valves don’t work very good at really low flows. Another reason is that the concrete on both sides absorbs and radiates a lot of heat, and this is going to make your little lawn strip dry out fast. That’s also why I suggest the dripperlines at the edges of the area be 4″ from the concrete, otherwise the lawn edges right up against the concrete tend to dry up and turn yellow. You are going to need to be careful in selecting your valve, the dripperlines in your 21′ long area are so short that the total flow using 1gph emitters is only going to be 1 GPM; (3 tubes, 20′ long with 1gph emitters every foot. So 20′ x 3 tubes = 60′ of tube. 60′ of tube x 1gph/ft = 60 gph. 1 gpm = 60 gph.) A lot of automatic valves will not work at flows that low. Make sure the rated flow range in the literature for the valve goes that low.

To install your drip system remove the top 5″ of soil from your planter. Now till the soil another 4″ deep. Tamp down the soil to lightly compact it and get rid of air voids. A 8″x8″ hand tamper tool is good for this, you can buy one at any decent garden shop or home improvement store. Now place your dripperline tubes down on top of the soil and use steel erosion control staples to hold the tubes in place. Put a stake every 36″. You can buy the stakes at the irrigation store, they all carry them. The metal stakes work much better than the plastic ones made for drip tube. The stakes are very important, they will rust into the soil and hold the tubes in place. Without them the empty tubes will float to the surface during the winter when the soil becomes saturated during rain storms.

Now put down the final 3″ of soil over the top of the tubes, tamp it down and install your sod (which should be about 1″ thick and should bring the sod surface up even with the top of the concrete.) You will need to lightly hand water the sod for a week or two to keep it cool and moist. It needs time to grow roots down to where the subsurface water from the dripperline is. Slowly back off the hand watering after a couple of weeks. Watch the sod’s color to see how well it is rooting in. If the sod is still in need of top-watering by hand it will turn a dull “flat green” color. When you first install it, the sod will be that dull flat green color because it is stressed from the cutting,shipping and installation. It’s easier to see the color if you stand back and look at it from a distance. Right after you install the sod take a minute to look carefully at it and notice the stressed dull color. Then also note the brighter green color it changes to after you water it the first time it. Now you know what stressed sod looks like and what to look for over the next few weeks. If it is hot or the warm winds are blowing when you install the sod you may need to hand water it more often. Usually watering a couple of times a day is sufficient until the sod is established.

Pump Cycles On Briefly When Irrigation is Off

Q.  My irrigation pump runs fine when the system is operating, but after it turns off it cycles on for 5 seconds every 10 minutes or so.

A.  If you are using a pressure switch and pressure tank to turn the pump on and off my first guess would be that you have a water leak in your irrigation system.  The water leaks out, which cause the water pressure to drop, then the pump kicks on and recharges the pressure.  Then the pump shuts off again.  That would cause exactly this symptom.

Knowing the problem is the easy part.  Finding the leak, that could be harder to do.  It could be a zone valve that isn’t turning off all the way or it could be a leaky pipe.  You can narrow the search area a little,  the leak will be someplace in the pressurized part of the system, that is, between the pump and the zone control valves.  Start by looking for obvious dripping, then look for someplace that seems wetter than it should.  If it is a leaky zone valve then the water will be leaking through the valve into the sprinkler zone pipes and will dribble out at the lowest sprinkler head.  So look at the sprinkler heads.  There will be a small “swampy” area around the lowest sprinkler head that is controlled by that valve.

Pressure Loss in Sprinkler Risers

Q.  How do I calculate sprinkler risers losses in a sprinkler zone where the risers are extra long, 3 ft or more above ground?  I have 10 risers in a zone for my proposed sprinkler irrigation system.

A.  If you are using my Sprinkler System Design Tutorial and a standard riser of the recommended size, then you don’t need to worry about pressure lose in the riser, the tutorial has friction loss for the risers built-in to the formulas it uses.  So you can ignore the riser pressure loss.  Some standard risers are shown on the page on Sprinkler Risers in the Irrigation Installation Tutorial.  The recommended size for a riser?  In most cases it should be the same size as the threaded inlet on the sprinkler.  But please actually read that page on risers, as there are some exceptions to that rule for certain types of standard risers!

Non-Standard Risers:

OK, I realize that didn’t answer your question, you are asking about a non-standard riser that uses a long pipe to hold the sprinkler high above the ground.  In that case you must calculate what the friction loss will be in the longer-than-normal riser pipe. (In this case that would be the 3 ft long pipe you described in your question above.)  To do that you simply use the same friction loss spreadsheets that you use to calculate the friction loss in any other pipe.  Just use this link to get the proper spreadsheet from my website for the type of pipe you are using.  Then open the spreadsheet and on the first line enter the pipe size, GPM of the sprinkler you will install on the riser, and the length of the riser.  Enter an error factor of 1.4 rather than the default 1.1.  This is because even your “longer” riser is shorter than the typical pipe length that the default error factor is based on.  Now read the friction loss.  That’s it, you have the friction loss for your non-standard riser!  Don’t worry about the fittings like ells and couplings that are part of the riser, that is part of what the error factor is compensating for.

When adding the riser friction loss into the total friction loss calculations for your whole sprinkler system, just add in the loss for a single riser.  Use the friction loss value for the riser that has the highest friction loss.  (This is most likely the one with the highest GPM sprinkler, or it may be the longest riser if you have different riser lengths.  You may have to calculate the friction loss for several different risers to figure out which of them has the highest loss.)  Why do you add in the friction loss for only one sprinkler, rather than the combined loss for all of them?  Because as a single drop of  water goes through the sprinkler system it only goes through one sprinkler, not all of the sprinklers.  You have to think about the water as a collection of millions of drops, not as one solid body.  So the pressure loss is what a single drop would experience as it travels through the system.  As a drop of water enters the sprinkler system it travels through a water meter, lots of pipe, a valve or two, then it finally blows out through a single sprinkler onto  the landscape.  The pressure loss  calculation for the whole sprinkler system is determined by what the worst case pressure loss values would be for a single drop of water traveling through the sprinkler system.

OK, so you calculated the friction loss, but what if it is a really high value, or maybe the calculator complained about the velocity being to high.  In this case you need to use a larger size pipe for your riser.  For the velocity in a riser you can go all the way up to the 7 ft/sec maximum without too much risk.  Velocities in the marginal “use caution” zone are generally OK for risers.  High velocity in a riser will seldom cause a water hammer problem, unless you are using a special type of sprinkler that has a solenoid valve built in to it.  Those sprinklers are called “valve-in-head sprinklers”, they are very expensive, and are mostly used for golf course greens.

 

Sprinkler Buddy Sprinkler Head Indicator Review

Sprinkler Buddy retail packaging.

The Sprinkler Buddy is a cone shaped plastic collar that fits around a sprinkler head to prevent grass from growing up next to it.  It serves two purposes, the first purpose is to keep grass from growing over the sprinkler head, thus make the sprinkler location obvious in the lawn.  When using heavy power mowers this allows you to mow over it while avoiding hitting and breaking the sprinkler heads.   The old standard method of keeping sprinklers visible is to trim around them each week with a line trimmer to remove the grass around them.  Obviously this is a lot of work that is not needed when the Sprinkler Buddy is installed around the sprinkler.   A second use for the Sprinkler Buddy is as a sprinkler head stabilization device.  According to the manufacturer, the wide cone shape helps keep sprinklers in an upright position.  Another advantage of the Sprinkler Buddy that isn’t heavily promoted by the company is that it keeps tall grass away from sprinklers with low pop-up heights, again reducing the need for frequent grass trimming around the sprinkler head.  The Sprinkler Buddy is made to fit on all pop-up sprinklers, both the smaller body spray types and the larger residential rotors (up to 2.5″ diameter, and maybe a bit larger.)  It is a product of RyRo, Inc. of Florida, USA.

 

Newly installed sprinkler buddy around a sprinkler head.

Installation:

The Sprinkler Buddy is made of a semi-rigid, UV protected, plastic material that is soft enough to cut with a pair of scissors, but rigid enough to maintain it’s shape.  To install you start by cutting away the grass from around the sprinkler in an area just large enough to fit the Sprinkler Buddy into.  Next, the sprinkler head is unscrewed from the pipe (the proper name for this pipe is a “riser”) to remove it.  Using scissors, simply cut slits in the Sprinkler Buddy base that are large enough to allow your sprinkler to slide into the bottom of the Sprinkler Buddy.  In a few situations you may also need to trim the edges of the Sprinkler Buddy to custom fit it to unique situations, for example if the sprinkler is very close to a sidewalk or wall.   Finally the Sprinkler Buddy is pushed onto the sprinkler head, and the head is screwed back onto the pipe.  A set of complete installation instructions are on the Sprinkler Buddy Website.

Test Results:

I installed two Sprinkler Buddies into a professionally maintained  condominium complex in Portland, Oregon during the summer of 2011.  The Sprinkler Buddies were installed per instructions over existing brass sprinklers, one was a flush mounted no-pop-up spray head, the other was a low pop-up with gravity piston retraction.  (I need to insert a disclaimer and warning here.  Both these sprinklers are older types, they were state of the art in the ’50s and ’60s, but are still found on a lot of older sprinkler systems.  While still available for sale in stores, these heads are an antiquated design that are high maintenance and water wasters.  As a professional my first recommendation for these sprinklers would have to be that they be replaced with new plastic-body pop-up type sprinklers with at least a 4″ rise height.  See my recommendations and reviews of sprinkler heads.)

The Sprinkler Buddies immediately performed as expected, they held back the grass that had previously interfered with the sprinkler’s spray patterns, allowing for better water coverage.  The maintenance caretaker  also reported that he no longer had need to trim the grass  back around those heads as he does with all the other heads on the property.  He did note that periodically some bermuda grass would grow up between the sprinkler body and the sprinkler buddy.  This appeared to be an infrequent issue that might require a check of the sprinkler once or twice a year in order to remove any grass growing inside the Sprinkler Buddy.

Sprinkler Buddy after sitting through winter, before removing collected debris and mowing lawn.

The Sprinkler Buddies were left in place for the winter and rechecked in the spring and again in the summer of 2012.  Upon examination in spring we found that the Sprinkler Buddies had each filled with leaves and pine needles over the winter.  The leaves and needles were easily swept out using an old broom, and an examination showed no damage from frost or snow to the Sprinkler Buddies.  Further, no grass was growing inside either of them and no grass trimming was needed around them before restarting the sprinklers.  By way of contrast, we could not even locate the other sprinklers in the lawn that did not have the Sprinkler Buddies.  Despite having the grass trimmed well away from them in the fall, these sprinklers were now completely covered with grass that had grown during late fall and early spring while the sprinklers were shut down for the rainy season.  We had to turn on the sprinkler system to locate the other sprinklers and then mark their locations so the grass could be trimmed away from them.

Conclusion:

The Sprinkler Buddy worked as promised.  It clearly marked the sprinkler locations making them very visible, and it looked attractive if you are into that edged sprinkler look.  While not my thing, I have met a lot of people who love the look of a clean cut edge around their sprinkler heads, and for them the Sprinkler Buddy will be something they love.  It will create a near perfect edge of uniform size around each sprinkler head.   In my tests the Sprinkler Buddy was also very effective at reducing maintenance at the sprinklers where we installed it, saving about a minute a week in grass trimming effort for each sprinkler.  It was also a huge labor saver at the spring season sprinkler system start-up, saving about 10 minutes of time per sprinkler (for sprinklers without the Sprinkler Buddies the caretaker had to turn on each valve circuit, located and flag the sprinklers, then return later with the string trimmer to trim away grass from them.)  The caretaker was able to mow over the Sprinkler Buddies with his rotary mower without damaging them.

On the minus side the Sprinkler Buddies were a bit harder to install than I expected, mostly because I needed to remove the sprinkler heads and they were rusted in place.  Some people have stated that they successfully have installed the Sprinkler Buddies without removing the sprinklers.  I did try this and I was not successful at installing the Sprinkler Buddy to my rather high quality standards (ie; I was able to get it on but I didn’t like the way it looked when finished and it wasn’t nearly as stable.)

Sprinkler Buddy post winter, after removing debris and mowing lawn.

 Caveat:

The Sprinkler Buddy is made to cure a problem that you really shouldn’t have.  (Unless you are one of those people I mentioned who like the look of a neat cut-out area around each sprinkler head, or you just want to be able to see all your sprinklers all the time.)  A properly designed sprinkler system should be able to take a direct strike on a sprinkler head by a heavy mower without any damage.  Properly selected sprinkler heads should also utilize pop-up risers that allow the nozzle to rise well above the grass level so that grass does not interfere with the water spray pattern.  Almost all sprinkler bodies now are constructed of high-impact plastic, engineered in a way that, when properly installed, can take the shock of being hit by a large rider mower wheel without damage.  However for this to occur the sprinkler must be installed on the proper type of riser that allows them to both absorb the shock and stay in an upright position.   This website has suggestions for identifying both quality sprinkler heads and the proper risers to use.  Unfortunately switching over a older sprinkler system to utilize new sprinkler heads and risers can be time consuming and expensive.  The Sprinkler Buddy is a good temporary fix for these older systems that will reduce maintenance time and costs until such time as a proper repair may be made.  A wise approach would be to use the maintenance cost savings created by the Sprinkler Buddy,  and save back that money to fund a future replacement of the sprinkler heads and risers.

Link to the Sprinkler Buddy Website

Irrigation Sprinkler Head Selection

Types of Sprinklers:

There are a lot of sprinkler head brands and types out there.  So how do you decide which one(s) to use?  This page will break down the types of heads available and what each type is best suited for. We’ll look at the advantages and disadvantages of each type as well as issues such as brass vs. plastic construction.

To start, sprinklers heads are divided into two types based on the method they use to distribute the water, called spray heads and rotor heads.

Spray Heads:

More properly called “fixed spray heads” these are the small heads that spray a fan-shaped pattern of water. Think of a shower nozzle. Most use interchangeable nozzles installed on the sprinkler which determine the pattern (1/2 circle, full circle, etc.) and the radius of the water throw. Some specialty patterns are available for long, narrow areas. Spray heads are spaced up to 18 feet apart.  There are some brands that promote radii up to 20 feet, but I’ve had really poor experiences with those.  Spray heads need between 20 and 30 PSI of water pressure to operate properly so they are the best choice if you have low water pressure.

Rotor Heads:

Rotor sprinkler heads, often just called “rotors”, is the term used to describe the various sprinklers which operate by rotating streams of water back and forth over the landscape. The example which most people are familiar with is the “impact” rotor sprinkler (often improperly called a “rainbird*”) which moves back and forth firing bursts of water. You probably know this sprinkler best for the distinct sound it makes when operating– tooka, tooka, tooka, tic, tic, tic, tic, tic, tooka, tooka, tooka, etc… The impact rotors are rapidly being replaced now by gear driven rotors which are much quieter, lower maintenance, and much smaller in size. These gear-drive rotors have one or more fingers of water which move silently across the landscape. The prettiest of these are the “multi-stream rotors” where multiple streams of water rotate over the landscape one after the other like rotating spider legs.  Rotors can be spaced from 15 feet to 65 feet apart. There are rotors available that can be spaced farther apart than 65 feet but I don’t advise using them in most situations, even golf courses are moving away from using them due to problems. Most rotors require a lot more water pressure to operate than spray heads. Here’s a rule of thumb, “The water pressure at the rotor head in (PSI) must exceed the distance (feet) between the heads.” (Known as Stryker’s Rule, admittedly that’s a little ego stroking on my part, but I really did write the rule!) Thus if you want to space rotors 35 feet apart you will need 35 PSI of pressure at the rotor. More on this later. The small rotors most often used for residences work best at 25 to 35 foot spacings.

Note: If you have chosen to use the Prescriptive Standard the maximum spacing you can have between rotors will be 30 feet.  This is due to the 30 PSI sprinkler pressure used by the Prescriptive Standard.

* Rain Bird® is the name of a sprinkler company and is a registered trademark. The Rain Bird company makes many different types of sprinkler heads, including impact rotors. They also make a full line of other irrigation products.

Rotary Nozzles: A new type of miniature rotor has been introduced in recent years. These are often called rotary nozzles.  The first brand on the market was called the “MP Rotator”, and several other similar products quickly became available from other companies.  Rotary nozzles are a very small turbine-driven rotor mechanism that is the same size as the standard nozzle on a spray-type sprinkler. Thus they can be installed onto the smaller, and less expensive, spray head pop-up bodies. These rotary nozzles have a radius generally between 15 and 30 feet. The exact distance depends on the model. They all use multiple streams of water that rotate around the nozzle and look like rotating spider legs. Some research indicates these rotary nozzles are more efficient than standard spray heads and result in lower water use. So far they have performed well overall, but beware of recently introduced models as this is tricky technology and new products may have a lot of “bugs”.

Guide to Selecting the Right Sprinkler Type:

Which to use, sprays, rotary nozzles, or rotors? Here are some questions to guide your selection.

  1. Is your water pressure less than 45 PSI static? If so you should consider using sprays or rotary nozzles.
  2. Is the area less than 16 feet wide? Then you should consider sprays or short radius rotary nozzles.
  3. Areas between 16′ and 25′ wide are good candidates for using rotary nozzles.
  4. If the area you want to water is greater than 25′ x 30′ in dimension standard rotors are likely the best solution.
  5. Is the edge of the area to be watered curved? If the edge has sharp curves (less than 20′ radius) then rotors will have difficulty watering the edges without over spraying them. This may not be an issue depending on what is beyond the edge. If the area beyond the edge should not get water on it (like a sidewalk, patio, driveway, road, or structure) you might want to consider a smaller rotary nozzle or spray-type sprinkler.

Installation Issues related to Head Selection:

Rotors are spaced farther apart and require less pipe and trenches, but they also cost much more per sprinkler.  Systems that use rotors, and to a lesser extent rotary nozzles, are easier to install due to less trenches to dig and back fill.

Cost Issues in Selecting Type of Sprinkler:

Surprisingly, regardless of the type of sprinkler you use, the cost per square foot of area irrigated comes out about the same (assuming proper design.) When using rotors there is less pipe and trenches, but the rotors themselves cost more. Spray heads are less expensive to buy, but they require more pipe, more trenches (labor cost), and more valves. In the end, the price really comes out pretty close either way.

 Note: If your “design pressure” is less than 40 PSI standard rotors will not work properly, DO NOT USE THEM.  (That’s Design Pressure, not the pressure at the sprinkler head.)  See the section “Measure Your Water Supply“. If you have a well and pump you must have your pump-on setting adjusted to no less than 40 PSI if you plan to use rotors. A “40-60” setting is typical. Contact your pump company for assistance.

 If you are unsure, try using rotors in your design. If they don’t work out well, then erase them from your plan and try rotary nozzles. In may situations the best option may be to use rotors in the large areas, and spray heads or rotary nozzles in smaller or more narrow spaces. So you may have a mixture. This is OK, but there are some things you need to be careful of when mixing different types of sprinklers. The first is that each type must be on a separate valve circuit. More on this later in the tutorial. The second is determining how to space the heads where they meet each other. For example, if you have a 30′ radius rotor next to a 15′ radius spray head, how far apart should they be from each other? There are many different schools of thought on this, but my general recommendation is to split the difference. In this example put them 22′ apart. Yes, the rotor would over-shoot the spray head by a considerable distance. But if you put them 30′ apart you will get a distinct dry spot between them.


Basic Body Styles:

Pop-Up Style Sprinklers:

Pop-up style sprinklers are installed with the sprinkler body below ground. A portion of the sprinkler, appropriately called the “riser”,  rises up out of the ground when the sprinkler is operating and then retracts back below ground when not in use.

Shrub Style Sprinklers:

Shrub style sprinklers are installed above ground on top of a section of pipe. Read the warning below!

Which style to choose?  In most cases you will want to use pop-up style heads, even in shrub areas. Pop-up sprinklers are more expensive to buy, but with shrub sprinklers you also need to include the cost of the extra section of pipe needed to hold the shrub sprinkler above ground.  In fact, in recent years mass production of popup style sprinklers has lowered their price, while increases in pipe costs have made shrub style sprinklers overall more expensive.

Many people are injured each year when they trip over, or fall onto, shrub style sprinklers. For shrub and ground cover areas pop-up sprinklers are available with pop-up heights of 3″, 4″, 6″ and 12″ above ground. A few brands are available with lower pop-up heights, but be warned that lower heights often cause problems. I recommend that you not use any sprinkler that pops up less than 3″. As a general rule it is best to also avoid shrub style sprinklers unless a very tall riser is needed to raise the sprinkler spray over the tops of tall shrubs. When needed, shrub style sprinklers should only be used in areas well away from sidewalks, patios, and areas where children play.


Metal or Plastic?

The conventional wisdom is that metal is more durable than plastic, and therefore is better. Up until the late 1970’s metal (usually brass, sometimes zinc) was the standard material from which almost all sprinklers were made. However, times have changed and now plastic is the most common material for sprinklers. Very few manufacturers even bother to make an all-metal sprinkler anymore. The primary reason for this change in materials is cost; machined metal parts are enormously expensive in comparison to injection molded plastic. Fortunately, most of today’s plastic sprinkler heads are very well engineered and perform better than the old metal sprinklers.

Hybrids: A few companies manufacture plastic sprinkler bodies which accept brass nozzles, which they claim results in a better water pattern. Other manufacturers claim that plastic nozzles perform as well as brass. The research tends to indicate that a really well-machined brass nozzle has better water distribution. But that’s laboratory tests, and in the real world a lot of other factors come into play. I personally haven’t noticed any significant difference in performance between most brass and plastic nozzles in well-designed, sprinkler systems, although brass nozzles will no doubt last longer. More importantly, there are a few nozzles, both brass and plastic, which don’t seem to perform as well as others. Fortunately, they are easily identified by comparing prices (as in “you get what you pay for.”)  Typically these bad nozzles come pre-installed on sprinklers that don’t have the features I list below, so if you stick to sprinklers with my recommended features you will get acceptable quality nozzles.


Features to Look For:

The following features are common to all good-quality sprinkler heads (for both rotors and spray type heads). Choosing a sprinkler without these features is asking for trouble.

  • Spring Retraction: Make sure a spring is used to pull the pop-up riser (sometimes called a “piston”) down into the case when the sprinkler isn’t on. As a general rule the stronger the spring, the less likely the riser is to “stick up”. Don’t worry about the spring being too strong, or creating too much “resistance” that might hurt the sprinkler performance.  The sprinkler is designed to compensate for that.  Stay away from sprinklers that rely only on gravity to retract the pop-up riser.
  • Wiper Seal: This is a soft plastic seal around the pop-up riser stem that seals the riser so it won’t leak . The wiper seal also is responsible for keeping dirt out of the sprinkler body, and is the most important part in determining how long the sprinkler will last. Make sure the sprinkler model you select has a wiper seal. Note: on some sprinklers you must remove the sprinkler’s cap and look inside the bottom of it to see the seal. Be careful when removing the cap, hold both the cap and body tightly! On some models the spring will shoot out!
  • Screens:  A screen inside the sprinkler helps protect it from getting messed up by junk in the water.  Consider this screen to be a back up filter to catch stuff that might have gotten into pipes when making repairs.  These in-sprinkler filters quickly become clogged if the water is even remotely dirty.  You should still have a good quality water filter at the water source upstream of the valves.
  • 3 Inch Pop-Up Height (or higher): Unless you just like to trim grass around sprinkler heads, make sure the pop-up height is 3″ or more. This way the spray nozzle will clear the top of the grass. Most professionals use 4″ pop-up sprinklers in lawn areas, and 6″ or 12″ pop-ups in shrub areas.
  • Check valve:  This feature is optional, but I highly recommend it.  Sometimes these are called “anti-drain valves”.  The built-in check valve keeps the water from draining out of the pipes through the sprinkler head each time the valve circuit is turned off.  Check valves save water, obviously, since they keep the water trapped inside the pipes.  But there are other advantages as well.  They reduce muddy areas around the heads that are caused by the water slowly draining out.  Since the water stays in the pipes the sprinklers come on faster and work more efficiently.  If the water has drained out of the pipes, then each time you turn on the sprinklers the sprinklers will spit and spew air as the pipes refill.  As the water quickly fills the pipes it slams into the fittings  (bends and turns in the pipe) and then into the bottom of the sprinkler heads.  This causes a lot of stress on the pipe and sprinklers and can result in premature failure.  So there are a lot of good reasons for getting sprinklers with built in check valves.  These check valves are nothing more than a rubber washer on the bottom of the sprinkler riser stem.   You can easily remove them if needed.  They are so cheap for manufacturer’s to make that I really think they should be standard equipment on all sprinklers!  One final note on check valves.  In cold season areas where it is necessary to drain the water from the system to prevent freeze damage the check valves will prevent the water fro draining out.  You must either remove the check valves in the cold season, or use compressed air to blow the water out of the pipes.  Most people blow out the pipes.

Other Sprinkler Features:

  • Pressure regulators: Generally this feature is not necessary with a well-designed system.  Pressure regulation can be done at the valve or water source and will provide more benefits when done at those locations as opposed to regulating it at the sprinkler.  These built-in pressure regulators provide a constant pressure at the sprinkler nozzle, which creates more uniform water coverage.  There is a catch however, a pressure regulator can only decrease the water pressure, it can’t increase it.  So it is only useful if your water pressure is already too high.  In the industry this feature is known as a “spec item”.  It is a gold-plate option that is sold primarily to landscape architects and municipalities for projects with high budgets.  My opinion is that pressure regulators in sprinklers are a device that 90% of the time is used to correct for poor design practices.  I have often seen systems that use these pressure regulators and then add a booster pump to create enough pressure for them to work.  That is like buying a economy car and then towing it around with a truck so that it will get better mileage!  Another legitimate use for the pressure regulators is that if the nozzle breaks off of the sprinkler the pressure regulator will limit the size of the geyser produced, and thereby save water.  While true, I question the expense to benefit ratio of this solution.  Plus it only saves water if the nozzle comes off.  If the whole sprinkler breaks off (just as common a problem) then it saves no water at all.  Warning: if you have low water pressure, a built-in pressure regulator will seriously harm performance of the sprinkler.  They should only be used with systems that have excess water pressure.  When using a built-in pressure regulator increase the pressure requirement of the sprinkler by 2 PSI.  This is because pressure is lost as the water goes through the pressure regulating device.  So if the sprinkler performance chart says 30 PSI you should increase that by 2 PSI to 32 PSI.
  • Pressure Compensating Screens and Nozzle Inserts:  In high pressure situations these will reduce sprinkler misting and improve efficiency.  These are different from the pressure regulators built into the sprinkler bodies, these are not as accurate as the regulators.  They work different and, while not perfect, they actually work pretty well.  The pressure compensators are small rubber discs with a hole in them, color coded for specific flow rates. Like the pressure regulators they will not increase the water pressure, so if you don’t have enough pressure they are not going to help you at all.  However, unlike the pressure regulators built into the bodies they do not require you to add 2 PI to the sprinkler pressure required.  This is because each one is made for a specific flow.  But one of the best uses for these is to reduce the radius of spray type sprinklers, using them in place of using the radius adjustment  screw on the nozzle.  To figure out which pressure compensating insert to use for the radius you want you will need to consult a reference chart supplied by the manufacturer.  The advantage to using these pressure compensating screens/nozzle inserts is that they hold the radius adjustment constant, regardless of temperature.  The radius adjustment screws that are built into spray head nozzles are notoriously fickle, when you use them to reduce the radius, as the water and air temperature change so will the radius.  This is because the screw acts as a valve, to reduce the radius you turn the screw and this reduces the flow through the nozzle.  So if you want to reduce the radius you would turn the screw, which then reduces the size of the opening the water flows through.  The problem is that as the temperature gets warmer this screw expands and as it expands it throttles the flow even more.   This causes the radius to be reduced.  Often in hot weather the radius adjustment screw will expand so much that it will completely shut off the flow of water!  That will not happen when you use these pressure compensating screens to reduce the radius.
  • Ratcheting Risers:  Almost all pop-up sprinklers now have ratcheting risers as a standard feature.  The ratcheting riser allows the riser stem to be twisted to align the direction of the water spray.
  • Side Inlets:  Side inlets allow the pipe to be attached to the side of the sprinkler.  This allows for shallower installation of the pipe and can save labor during installation.  The problem with side inlets is that when you use the side inlet on most sprinklers the built-in check valves do not work.  Also if you plan to “winterize” your sprinkler system by blowing it out with air the use of side inlets can make it very difficult, sometimes impossible,  to get all the water out of the sprinklers.  Most sprinklers that have side inlets have both a bottom and side inlet.  They come with a plug installed in the side inlet, to use the side inlet you remove the plug and place it in the bottom inlet.  The problems listed above only occur if you use the side inlet.
  • Shut-Off Devices:  These devices generally fit under the sprinkler nozzle and shut off  the flow if the nozzle is removed or comes off.  Another “spec item.”  For most people these will offer little or no value.  They save water if the nozzle comes off, but that seldom occurs.  Depending on the design of the shut-off device they might also stop flow if a riser sticks up and is mowed off.  Some are located near the top of the riser, so it is likely they would be mowed off along with the riser, thus providing no benefit.

Sprinkler Make and Model Recommendations:

The most common question I get from users of this tutorial is “what do you think of the ABC model sprinkler made by XYZ sprinkler company”. Would I risk making the major sprinkler manufacturer’s mad by publishing that kind of information? Of course!  See my irrigation product reviews.

More on selecting your sprinklers is coming later on in the tutorial. For now lets just get an operating pressure. The first thing you may have noticed is that I used the term “operating pressure” here rather than “pressure loss” as previously. While pressure loss is a perfectly accurate term for the pressure used by sprinkler heads and emitters, operating pressure is more commonly used. Operating pressure is simply the pressure that needs to be present at the sprinkler or emitter inlet for it to perform as intended.

Manufacturers of sprinklers and emitters provide specifications for each of their products that list the various acceptable operating pressures for the units and how they will perform at that pressure. You will need to obtain the specifications for the products you intend to use. You may find this information printed on the sprinkler box or you may need to request it from your supplier. Most manufacturers also make specifications available on their web sites. Typically for a sprinkler this specification will list an inlet pressure as pounds per square inch (PSI) and then give a watering radius (feet) and flow rate in gallons per minute (GPM) that will occur at that pressure.

For an emitter the information would include only operating pressures (PSI) and a flow rate in gallons per hour (GPH) for each of those pressures. (Radius of throw isn’t applicable to drip emitters.)

Pressure Requirements for Sprinklers

Spray Type Sprinklers:

For spray type sprinklers most designers use an operating pressure of 30 PSI, unless a lack of available pressure forces a lower level. Remember that if you use a lower pressure the sprinklers will need to be spaced closer together, because the water won’t spray as far. Sprinkler manufacturers provide charts that tell you how much pressure is required for the sprinkler and how far it will spray with that pressure. Look on the package for the chart. Additionally, almost all spray type heads have a radius adjustment screw that allows you to adjust the watering radius down for smaller areas.  (When you adjust the radius using the adjustment screw on a spray head, you are actually reducing the pressure at the nozzle by means of a small valve under the nozzle.  The reduced pressure results in a decreased radius of throw.)  At pressures above 45 PSI most spray heads start to create lots of mist, which results in poor irrigation. This can be controlled by using the radius adjustment feature to reduce the pressure, partially closing the valve to reduce the pressure, installing a pressure regulator on the mainline to reduce the pressure, or by using special pressure regulating nozzles made by some sprinkler manufacturers (which, you guessed it, reduce the pressure!

Rotor Type Sprinklers:

For rotor type sprinklers the higher the operating pressure the better. (O.K., within reason. We don’t want to blow the sprinkler apart with high pressure– and rotors can cause mist too under extreme pressures.) But as a general rule, most rotor type sprinklers do not work well with less than 30 PSI operating pressure. Keep reading!

“Stryker’s Rotor Spacing Rule” states that the spacing in feet between rotor-type sprinklers can’t exceed the pressure in PSI at the rotor. There is a lot of competition in the sprinkler business to see who can get the most radius from a rotor-type sprinkler. Manufacturer’s literature and packaging tends to wildly exaggerate the maximum spacing of rotors. They get those distances by testing the rotors inside a big building with no wind. Even the most gentle breeze will shorten the real-world watering radius (water droplets are very light). If the package says the rotor has a radius of 35 feet at 30 PSI– DO NOT BELIEVE IT! In the real world you will not get that distance. If you have 30 PSI do not space the rotors more than 30 feet apart. If you ignore this rule, 9 chances out of 10, you will have dry spots in your lawn! (Yep, over-size ego alert, it’s my rule, thus the name.)

Rotor Spacing Example: If you want to space the rotors 30 feet apart then you will need to use a pressure of at least 30 PSI for the rotor. If you want to space rotors 40′ apart you will need 40 PSI for the sprinkler head pressure. I don’t recommend spacing sprinklers farther than 55 feet apart unless you have an experienced professional design the sprinkler system. Many tricky problems occur with sprinklers when they are spaced greater than 55 feet apart.

Drip Emitters:

Most emitters operate best at around 20 PSI. Some emitters are “pressure compensating” which means they should put out approximately the same amount of water over a wide range of inlet pressures. (I’ve found that many pressure compensating emitters are not a whole lot more “pressure compensating” than standard emitters are. Keep in mind that at pressures over 45 PSI emitters may blow apart. Barbed emitters in poly tubing may pop out of the tubing at 30 PSI.

Mix and Match:

Sometimes you need to use sprinklers that require high pressure such as rotors, with sprinklers that use low pressure on the same irrigation system. To do this the system is designed using the pressure requirements of the high pressure sprinklers. The low pressure sprinklers (or emitters) are installed so that a separate valve turns them on and off, and a special pressure reducing valve is used. This valve reduces the pressure down to the correct amount for the low pressure sprinklers. Almost all irrigation manufacturer’s now make pressure reducing valves, although you may have to go to a specialty irrigation store to get them.

Quick “Prescriptive Standard” Set Up:

For the Prescriptive Standard use 30 PSI for the sprinkler pressure.   Do not space rotor heads more than 30 feet apart when using the Prescriptive Standard!


Enter the sprinkler head operating pressure (or the drip emitter pressure if no sprinklers) on the “Sprinkler Heads” line of the Pressure Loss Table.

 

Remember- the pressure you enter in your table is the pressure for a single sprinkler head. So if you will have 10 sprinklers and they each require 30 PSI you still only write”30 PSI” on your pressure loss table. Also the value you enter should be the highest sprinkler head pressure requirement. So if you plan to use a spray head that will need 20 PSI and also a rotor that will need 35 PSI, you will enter the higher value- which in this case would be 35 PSI. Finally, remember why pencils have erasers. You can always come back and change this value later if you want to! So don’t agonize over it.

 A lot of people ask why we only write down the pressure for a single sprinkler. This is a bit difficult to understand but I will try to explain. I think the easiest way to understand is with a mental image. Think of the water moving through your sprinkler system as millions of water droplets, rather than a single mass of water. On it’s journey through your sprinkler system a single drop of water will loose pressure along the way. Each place where it will lose pressure is one of the items on your pressure loss table. Let’s go along for the ride. First our water droplet will travel through a pipe from the water company to your water meter. Then it will proceed through the meter into the house supply pipe and on to the irrigation system connection. From there our drop goes into the irrigation system and may pass through a backflow preventer. Onward it travels to the valve and through the valve into the lateral pipes leading to the sprinkler heads. Finally the drop goes into one of the sprinkler heads and is propelled out onto the lawn. Note that our droplet only passes through one sprinkler head on the way to the lawn. I’ll bet you’ve never seen water on the lawn jumping back into the sprinkler head so it can go back and try going out through another sprinkler! So it can only pass through one sprinkler head. Thus we only consider the pressure needed for a single sprinkler head. (O.K. smart guy, yes I have seen water sucked back into a sprinkler head. But that’s not supposed to happen, it means something is wrong with the sprinkler system.) At any rate, even if you still don’t understand why you use the pressure loss for only a single sprinkler, please trust me, it’s correct!


Much more information on sprinkler selection is coming later in the tutorial, such as spacing and nozzle selection. If you want to jump ahead and check it out, click here. Just don’t forget to use your “back” button to return here!



Sprinkler Coverage, Nozzle Selection, & Sprinkler Spacings

This is important, read it carefully!

Sprinkler Coverage:

The area watered by each sprinkler must overlap substantially the area watered by the adjacent sprinkler. This overlap may seem like a waste at first, but it is a very important necessity. Without this overlap it would be impossible to design sprinkler systems that provided uniform water coverage.

Have Doubts?  See for yourself, it only takes a couple of minutes to prove! Grab a piece of paper and draw circles on it so that all areas of the paper are inside a circle, but no circles overlap. You can’t do it, can you?

Important!
Sprinklers are intentionally designed to require 100% overlap of watered areas. That means each sprinkler throws water ALL the way to the next sprinkler in each direction. READ THAT AGAIN!

That’s right, 100% overlap of watered areas is REQUIRED or you will get dry spots! This is known in the industry as “head-to-head coverage or head-to-head spacing”.  A lot of those free design guides you find in stores and on the Internet get this wrong.  They don’t show enough overlap!  The writers of those brochures think you are going to look at the overlap and buy the brand of sprinkler that shows the least sprinkler heads.  So they try to make it look like you can use less sprinklers with their brand.  After you’ve bought the sprinklers if you have dry spots, well hey, it’s YOUR problem now!  You’ll probably just buy a few more of their sprinklers to get rid of the dry spots. In fact, it will probably take more sprinklers to fix the dry spots than it would have to do it right the first time. $$$ Ching, ching!

Diagram of head-to-head irrigation sprinkler coverage
Lawn sprinklers spaced head-to-head

Rule: Sprinkler Radius = distance between sprinklers

 

One more time: The water from any single sprinkler should actually get the sprinklers on each side of it wet!

Now that I’ve told you that you SHOULD use head to head spacing I’m going to backtrack a bit and tell you that you can space a few of the sprinklers slightly farther apart as needed to work around odd shaped areas. I still recommend that you keep at least 80% of the sprinklers at head-to-head spacing! Take the sprinkler head watering DIAMETER and multiply it by 0.6 to get the absolute maximum distance that should ever occur between any two adjacent sprinklers. (Remember most manufacturer’s give you the radius of the sprinkler, you need to multiply by 2 to get the diameter.) For example, 15′ radius spray heads should never be more than 18′ apart (30′ diameter x 0.6 = 18′). Note that we rounded to the nearest foot. If the sprinkler system is in a windy area I suggest the majority of the sprinklers be spaced at 45% of the diameter (that’s closer than head to head!), as winds over 10 mph really mess up the sprinkler patterns.

(Optional reading for those who need explanations.) Back when I designed my first sprinkler system in High School I wondered why they wanted so much overlap of the sprinklers. It seemed to me to be nothing more than a ploy to sell more sprinkler heads! I was smarter than that, so I stretched them out to save my folks some money! The result was big dry spots, and my parents wound up replacing the sprinkler system a few years later. (They never said anything about it to me, I just noticed the new sprinklers a few years later on a visit home from college.) Ouch! Not a good start for a future irrigation expert! Now that I’m a bit wiser and more knowledgeable I realize there is a good reason behind the head-to-head coverage. Unfortunately, it’s rather hard to explain. The perfect sprinkler would put out a pattern of water that is heaviest right next to the sprinkler, then uniformly declines out to the radius. So the farther you move away from the sprinkler, the less water falls on any given patch of ground. When we test sprinklers for water coverage we set up a series of cups between the sprinklers to collect the water that falls. That way we can see how much water falls at various distances from the sprinkler. In the diagram below you can see what happens when there are various distances between the sprinklers.

Sprinkler coverage at various spacings
Close to 100% sprinkler overlap is important for good water application uniformity

In example “A” the sprinklers are just barely overlapping and much more water is falling in the cups next to the sprinkler heads. But the middle 3 cups are only getting ½ the water of the cups next to the sprinkler. If you watered long enough to keep the middle green, the areas around the sprinklers would turn to mud! In example “B” we see that moving the sprinklers closer together has evened up the amount of water a bit more. However the areas near the heads are still getting 25% more water than the other areas. Not enough to cause mud, but you would definitely see rings of greener grass around the sprinklers! Example “C” shows almost head-to-head spacing. The cups are almost all uniformly full! So don’t stretch the distance between sprinklers.

What if you need a smaller radius than the sprinklers available?

Almost all sprinklers have a radius adjustment device on them so that you can reduce the radius of the water throw. This is one way you can adjust for narrower areas. Keep in mind that for most sprinklers you can’t reduce the radius by more than 50% without causing problems. The other solution for smaller areas is to use nozzles made to spray less far, or that spray a special pattern. An example of a special pattern would be the nozzles that spray a 4′ x 30′ rectangular pattern. These are commonly used in long, narrow areas.

 Remember if you reduce the radius of the sprinkler you must reduce the distance between sprinklers by the same distance! Keep the coverage head-to-head!
Calculating the GPM for sprinklers when you reduce the radius is easy:

For spray heads you just use the manufacturer’s chart.  When you use the radius adjustment on a spray you are simply reducing the water pressure by closing a small valve in the nozzle.  As the pressure drops, so does the radius.  Just look at the manufacturer’s chart for the radius you plan to reduce the sprinkler down to.  Then read the GPM for that radius!  For example, you’re designing for 30 PSI.  The radius at 30 PSI of the sprinkler you selected is 15 feet with 1.85 GPM according to the manufacturer’s chart.  But you want the radius to be 14 feet.  Looking at the manufacturer’s chart you see that the radius of the same sprinkler is 14′ at 25 PSI with 1.65 GPM.  So the GPM of that sprinkler if you reduce the radius to 14′ will be 1.65 GPM.  That’s because when turn the radius adjustment screw to reduce the radius to 14′ what you REALLY did was reduce the pressure to 25 PSI!

For rotor heads the GPM stays the same no matter how much you reduce the radius!  That’s because reducing the radius on a rotor doesn’t change the amount of water coming out of the nozzle.  To change the radius a small screw extends into the stream of water coming out of the nozzle.  The tip of the screw deflects the water which “screws it up” (pun intended) so it doesn’t go as far.  This creates another problem, however, which is that it really messes up the uniformity of the water.  So when you use the radius adjustment on rotors, you tend to get dry spots.  This is one reason I strongly suggest that you use a smaller nozzle if possible rather than using the radius adjustment screw on the sprinkler.  The other reason is that when you reduce the radius you really should also reduce the GPM of the sprinkler.  Otherwise there will be a lot more water under the sprinkler with the reduced radius. Bottom line- use the radius adjustment screw on rotors only when nothing else will work.

 Warning for rotors only:
When designing systems with rotors do NOT rely on the manufacturer’s stated radius for design. They get those distances by testing the rotors inside a building with no wind. The real world is harsher! If the gallonage of the rotor is less than 6 GPM the maximum spacing should never be more than 35′ between rotor type sprinklers.

Stryker’s Rule: the spacing in feet between rotors can never exceed the operating pressure in PSI at the sprinkler inlet (So a rotor with a 30 PSI operating pressure = 30 foot maximum spacing between rotors.  Yes, I know the package says you can space them farther apart.)

Ignore the rule above and you will be very sorry!

 


Sprinkler Precipitation Rate and GPM

The precipitation rate is the amount of water the sprinkler throws onto the area it waters, measured in inches per hour. (Inches per hour is how deep, in inches, the water would be after one hour if it didn’t soak into the ground or run-off.) Precipitation rate must be considered when selecting your sprinkler heads to eliminate water application uniformity problems (dry spots).

Spray Heads: Almost all sprinkler manufacturers make their spray heads so that you can mix and match nozzle patterns and the precipitation rates will still match for all the heads. This is referred to as “matched precipitation rates”. Look for this feature when selecting your sprinklers. Important: do not mix different brands of spray heads and nozzles together on the same valve circuit without checking to see that they have the same performance specifications. Just because the nozzle will screw into the sprinkler body doesn’t mean it’s designed to work with that sprinkler!

Rotors: Rotor-type heads aren’t quite as easy. You must select the appropriate nozzle size for each rotor in order to match the precipitation rates. A simple illustration will help explain. Rotor heads move back and forth across the area to be watered. The rotation speed is the same regardless of whether the rotor is adjusted to water a 1/4 circle or a full circle. So the stream from a 1/4 circle head will pass over the same area 4 times in the same amount of time that it takes for a full circle head to make one pass over the area it waters. With the same size nozzle in both, a 1/4 circle rotor will put down 4 times as much water on the area under the pattern as a full circle rotor will. (Remember that after every quarter turn the 1/4 circle rotor reverses direction and covers the same area again!) To match the precipitation rates between these sprinklers, the quarter circle rotor must have a nozzle that puts out 1/4 the amount of water that the full circle nozzle puts out! A half circle rotor must have a nozzle that puts out 1/2 the water of a full circle. This is why when you buy a rotor-type sprinkler head they often include a handful of different size nozzles with it. Wait, there’s more (don’t panic yet, there is a simple solution forthcoming)!

If you have rotors that are adjusted for different radii you will need to adjust the nozzle size to compensate for the radius change also! For example if most of the rotors are set for a 30 foot radius, but one is adjusted down to 20 ft., the 20 ft. one will need a nozzle 1/2 the size. (Remember: when you reduce the RADIUS by 1/3 you reduce the AREA by a little more than half.)

 Avoid using rotors with nozzle flows that are less than 2.5 GPM, except in corners (quarter circle patterns). Flows under 2.5 GPM give very poor coverage due to the tiny water stream. Even a slight breeze will distort the watering pattern and give you dry spots. I strongly suggest that you stick to using nozzles as close as possible to the GPM of those in the cheat chart below.

O.K. Now that you understand the principles, let’s simplify this a bit by using a cheat chart…


Unless you really know what you’re doing (in which case you wouldn’t be reading this tutorial), you should stick with the nozzles on this chart:

Jess Stryker’s

Quick & Dirty Guide for Rotor Nozzle Selection

1. Find the section of the chart with your desired spacing.
2. Find the pattern (1/2, full circle,etc.) of the sprinkler.
3. The chart tells you the GPM the nozzle must have.
4. Use a nozzle size that comes close to matching both the PSI – GPM combination.
5. Ignore the radius given by the manufacturer.
6. Be sure to read the notes below the chart!


For 20-29′ spacing between sprinklers-
1/4 circle . . . 30 PSI – 0.8 GPM
1/2 circle . . . 30 PSI – 1.6 GPM
3/4 circle . . . 30 PSI – 2.4 GPM
full circle . . 30 PSI – 3.2 GPM
Important: see notes below!

For 30-39′ spacing between sprinklers-
1/4 circle . . . 40 PSI – 1.5 GPM
1/2 circle . . . 40 PSI – 3.0 GPM
3/4 circle . . . 40 PSI – 4.5 GPM
full circle . . 40 PSI – 6.0 GPM

For 40-55′ spacing between sprinklers-
1/4 circle . . .55 PSI – 3.0 GPM
1/2 circle . . . 55 PSI – 5.5 GPM
3/4 circle . . . 55 PSI – 8.0 GPM
full circle . . 55 PSI – 11.0 GPM

Important Notes:

It is critical that the water pressure (PSI) at the sprinkler be as high, or higher, than the distance between the sprinklers in feet (per Stryker’s Rule). For example, if you space the sprinklers 45′ apart, you must have at least 45 PSI of pressure at the sprinkler inlet. That’s the pressure at the sprinkler inlet, not the total pressure available. Remember, you will lose pressure in the pipes and valves, so the pressure at the sprinkler inlet will be lower than your available pressure! Go back to the tutorial pressure loss pages to figure out how much pressure will be lost in your sprinkler system.

Select the nozzle size closest to these GPMs without regard to the radius the manufacturer gives. For example, if you are looking at a 25′ radius, the chart above says to use a 1.6 GPM nozzle for a half-circle rotor. But you happen to notice that the rotor manufacturer’s literature says that at 25 PSI, a 1.6 GPM nozzle has a radius of 32 feet. So why am I telling you to space it at 25′? When the manufacturer tested the rotor on their test range (inside a large building with no wind) they measured a few drops of water 32′ from the rotor. When you install it out in your yard it will not perform as well. You may still get a few drops of water 30′ or even 32′ from the head, but not enough to grow anything. You need to trust me on this one! Remember, if the sprinkler sprays too far, most rotors have a radius reduction screw that will allow you to very easily reduce the radius. But, if the rotor does not spray far enough there is nothing you can do about it without a major expense! Best to play it safe.

You may want to make additional adjustments to nozzle sizes after installation to compensate for your specific conditions. Most rotors now come with a “nozzle tree” that contains most of the different nozzles for the rotor, so you can change the nozzle sizes if you need to. Some manufacturer’s don’t offer nozzles sizes larger than 3.0 GPM for their economy-priced heads (providing those extra nozzles would probably cost them at least another nickel in costs!). You may need to upgrade to the next better model line if you have a large yard! The larger size nozzles for 40′ spacing are not available with most of the “mini-rotor” models sold for residential use. You will need to upgrade to the next model. Also, sometimes other nozzle sizes are available separately from the manufacturer, for example low angle nozzles. You will probably need to get these from a store that specializes in irrigation sales, rather than a hardware or home store. Look in the yellow pages under “Irrigation” or “Sprinklers”, or try one of the online stores listed in the tutorial links pages.

There is a conflict between the nozzles recommended for the 20-29′ spacing range of the chart and my previous advice to “avoid using rotors with nozzle flows that are less than 2.5 GPM”. This is because the Nozzle Selection Guide assumes you will be mixing 20-29′ radius rotors together on the same valve with 30′ plus radius rotors. To keep from having enormous nozzles on the larger radius rotors I am recommending that you use smaller nozzles than I would otherwise consider for the smaller radius rotors. This is essentially a compromise. Sometimes it is not practical to obtain perfection! If all or a majority of your rotors will be spaced at 20-29′ apart, then you should probably use larger nozzles than I recommend in the chart. In other words, use those listed in the chart for 30-39′ spacing for the 20-29′ spacing. This will help avoid problems caused by the wind blowing the spray out of the irrigated area. However, if your sprinkler system will be located in an area with little or no wind you can go ahead and use the smaller nozzles in the chart. What is little or no wind? Go outside in the evening or early morning when you will likely be irrigating. If you can feel the wind blowing even gently against your face, I would consider that enough wind to need the larger nozzles.

If you calculate the precipitation rates you will notice that the shorter spacings result in a higher precipitation rate than the larger spacings. This is because the smaller heads with lower GPM rates are more susceptible to wind and evaporation, and thus it is assumed less of the water is actually reaching the ground. The higher precipitation rate compensates for this.

 


Windy Locations

If you are designing a sprinkler system for an area where the wind blows a lot you should look at the Irrigation and Wind FAQ.


Select Your Sprinklers

If you haven’t started shopping for sprinklers yet, now’s the time to start checking out what’s available.  Check out which sprinklers are available and look them over.  Write down a list of the heads you think will work well for your irrigation system on your Design Data Form. Be sure to list the PSI and GPM for each head as given in the manufacturer’s literature, along with the maximum spacing between heads.

 

 One last warning!!!

Do not blow off my advice on sprinkler spacing in order to save a few bucks on sprinkler heads! Right now you may be feeling pretty smug about how much money you saved by stretching the sprinkler spacing. But next summer you’re going to look pretty stupid to the neighbors, standing out there with a hose watering the yellow spots your new sprinklers don’t cover!  I have a collection of “wish I’d listened to you” letters from people who didn’t take this advice. I get a few more of these every year, and these are just the brave folks willing to confess they messed up. They all say you should listen to me on this!

Later on you will need to know the flow rate for each sprinkler you use, so it might be helpful to make some notes on the back of your Design Data Form showing the nozzle size and GPM you will need for each different sprinkler you plan to use. Otherwise you’ll wind up having to look the information up over, and over, and over…

 


 

Draw the Sprinkler Heads on Your Plan

You’re now ready to pencil in the sprinkler head locations on your drawing. Hallelujah! I know it seems like it took a long time to get here, but to do a good job we needed to cover a lot of background information! Use a pencil to draw in the sprinkler heads so you can easily make adjustments to the locations later. Many people find it helpful to use a compass to draw a light pencil line showing the radius of water throw for each head.

Remember these tips:

  • Keep the distance as uniform as possible between heads. To the extent possible a sprinkler should be equal distance from the adjacent sprinkler in each direction (forming a triangle if possible). Changes in spacing between adjacent sprinklers should be made as a gradual transition when possible.
  • Try to position heads so that if you were to draw a straight line between adjacent heads they would form an equilateral triangle (each side of triangle is same length). This is called “triangular spacing” and creates more even water coverage than “square spacing” (ie; lines between 4 heads form a square). That said, you will often be unable to form a triangle so don’t panic if you can’t.
  • Don’t stretch the spacings, use “head to head” spacing. Using too many sprinkler heads is seldom a problem, using too few sprinklers heads is ALWAYS a disaster!
  • Start by drawing a sprinkler in each corner. Next, draw sprinklers around the perimeter of the irrigated area, watching that they are not too far apart (one more time, better too many than too few!). Adjust the locations to make the spacing between sprinklers as even as possible. After the perimeters are done, then draw the sprinklers in the interior area.
  • If the sprinklers need to overlap so that the spray from one head goes over and beyond the next that’s OK. While you don’t want to over-water, it is always easier to correct an over watered area than a under watered one. For example, you can use the radius adjustments on the sprinklers to cut down the water in the over-irrigated areas. If need be you can even remove or relocate a sprinkler later. It’s much easier to remove one than to add one!
  • Sprinklers that are placed closer than 6 feet apart need some special consideration. Standard spray-type sprinklers don’t work well if the radius is adjusted below 6 feet. (The opening the water goes through is so tiny that the normal expansion of the plastic or metal on a warm evening can close off the water flow!) If the area is long and narrow (4′ wide or less), use the strip pattern nozzles. I prefer the so called “side-strip” type that you place along the edge of the area, they have better patterns than the center strip nozzles. End-strip nozzles have notoriously bad patterns, they shouldn’t be more than 10′ from the next head! When using standard spray sprinklers (like quarter, half, and full circles) in areas where the radius must be adjusted to less than 6 feet use a “pressure compensating device” to reduce the radius. The pressure compensating device is normally installed under the nozzle where it reduces the flow and pressure through the nozzle. The good news is that by using an under sized pressure compensating device you can also reduce the nozzle radius! Unlike the adjustment screw on the nozzle these devices work well regardless of the temperature. However, you will need to select the proper size pressure compensating device for each nozzle. It is possible that every nozzle will need a different size! To select the right device you use a special chart provided by the pressure compensating device’s manufacturer. The chart will tell you exactly which device you must use with each different nozzle in order to get the radius you want. Most major sprinkler manufacturer’s make pressure compensating devices for their spray sprinklers, and the charts you need can be found in their catalogs. You may need to go to a commercial sprinkler supplier to find them.

Study the example drawing below.

Sprinkler spacings -Draw the sprinkler head locations on your plan
Sprinkler spacing for optimal head-to-head water coverage

Again, notice that the radius of each sprinkler’s spray goes all the way to the next sprinkler! This is critical.

Note that in the example above only the lawn area outlined with a green curving edge is being watered. The area between the lawn (green line) and the edge of the property (brown line) would most likely be planted with shrubs and irrigated separately from the lawn. In most cases a drip system would be considered for watering the shrubs as it is less expensive and more efficient. See the separate guidelines for designing drip irrigation systems.

Bonus landscape design tip: Creating a border of shrubs around the perimeter of your yard is, in most cases, a good landscape design practice. A shrub border helps to reduce the visual impact of the fence (assuming that like most residential properties you have a fence.) Shrubs also typically use less than half the water of lawn areas of the same size, saving money spent for water. Once a month you need to weed and trim shrub areas, as opposed to the lawn that needs to be mowed every other week at the least in summer. A border using shrubs of various sizes, textures and colors can add greatly to the attractiveness of your yard. Place smaller shrubs near the lawn, with larger growing varieties behind them next to the fence.

 


 

Sprinkler Layout for Narrow Planters:

Sample sprinkler head layout for narrow planters
Sample sprinkler head layout for narrow planters using strip nozzles

This example shows the typical placement for sprinkler heads in a narrow planter. In this example, special spray sprinkler nozzles called “end-strips” and “side-strips” are used. These nozzles spray a long, but narrow, pattern. A typical pattern is 4′ x 30′ (4′ out and 15′ in either direction from the head). There are also spray nozzles called “center-strips” which don’t work as well. Be careful when using end-strips. They tend to have a weak coverage area on either side of the nozzle (the yellow area in the drawing above). Avoid using 2 end-strips facing each other in a lawn area. If possible always install a side-strip in the middle between 2 end-strips. The sprinkler layout above is for lawn. In a shrub area you can eliminate the sprinklers on one side as long as the width of the planter is 4 feet or less- so you can install the sprinklers on one side only. Shrubs don’t need as even a watering pattern. Lawns require heads on both sides. Note the triangular arrangement of the sprinklers, which gives more even coverage. Yes, it takes an extra head to create the triangle pattern, and you need to space the heads a little closer together than the normal maximum on one side to create the “triangle pattern”, but it’s worth the cost.

For narrow strips wider than 5′ you would use regular half circle heads on both sides. The distance between the sprinkler heads should not be more than 1 foot greater than the width of the planter. In other words, if the planter is 8 feet wide you would install half circle heads on both sides of the planter, not more than 9 feet apart from each other. As with the example above, it is best if you arrange the sprinklers in a triangular pattern.

 


Sprinkler GPM

As we saw previously, the flow rate in gallons per minute (GPM) of each sprinkler head is determined by the nozzle installed in the head. It is necessary to know the GPM for each head in order to determine which heads will be connected to each valve and in order to determine the size of each pipe in the sprinkler system.

You will probably need to dig up the sprinkler manufacturer’s literature again. In the literature the manufacturer shows different GPM and radius information for each sprinkler nozzle based on the operating pressure (PSI). Now we can use that information to find the GPM for each sprinkler head. First, determine what the SPACING is between each head and the others around it. Next, look for the radius closest to that spacing and use the corresponding GPM as the flow for the head.

Write down on your plan the GPM for each sprinkler next to the sprinkler symbol.

Hint: You will find the GPM and radius data for many of the popular sprinklers in the product reviews .

Example: You note that a spray type head on your plan is a 1/2 circle pattern and the distance to the 3 closest adjacent heads are 13 feet, 12 ft., and 14 ft.. So the spacing for this head is 14 ft. (the highest of the 3). Looking at the manufacturer’s literature you note that a radius of 14 ft. for the 1/2 circle nozzle in this sprinkler requires a pressure of 25 PSI and a flow of 1.65 GPM. Write down the flow of 1.65 GPM next to the sprinkler head on your drawing. You then repeat this procedure for each sprinkler head on your drawing.

Add sprinkler GPMs on your plan.

Note sprinkler GPM on your plan
Write the GPM of each sprinkler on the plan next to the sprinkler

 


This article is part of the Sprinkler Irrigation Design Tutorial
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How Far from a Fence Should Sprinklers be Installed?

Q. How far should the sprinkler line be from a wooden fence? Im gonna run lines next to a wooden fence all around the perimeter of my backyard. Fence is about 8 feet tall.

A. There are several issues here that come to mind.  Most of this applies to walls as well as fences.

Installation:
If your are using a trencher or [plow to install pipe the machine will likely not get closer than 18 inches to the fence.  I would stay even further away, maybe as much as 3 feet.  Both of these machines have a tendency to slip from side-to-side or get out of alignment when operated, especially by a inexperienced non-pro.  You don’t want the machine to go through the fence.

Future maintenance:
One issue here is future maintenance should you need to dig up the pipe for a repair.  You want enough room that you aren’t whacking the shovel handle (or your shoulders) against the fence if you need to dig.  That would mean at least a foot of distance from the fence.  Maintenance of the fence is another issue.  If you spray water on the fence it will shorten the life of the fence, not to mention leaving ugly water stains on it.  It is near impossible to remove water stains from a fence.

Sprinkler Heads and Water Stains on the Fence:
The sprinkler heads should probably be about a foot minimum from the fence.  The closer they are, the more water they will get onto the fence.  The water will
stain the fence and also shorten the fence life.  To keep the water off the fence completely means the sprinklers have to be very far from the fence, typically at a minimum 24″ away for spray type, 36″ for the larger radius rotors.  There are variables that impact that distance they need to be away from the fence.  Different sprinklers have different amounts of accuracy as to the edge of the water pattern.  Impact type rotors often spray a lot of water to the side, outside the normal watered area, thus they need to be very far away.  In fact, with impacts I would say that you are not going to keep the fence from getting wet, period (unless you keep the head farther away than the radius of the impact sprinkler!)  Also wind plays a huge factor in blowing water onto the fence.

Don’t Plant Lawn Next to a Fence!
When I want to keep a fence dry I plant a minimum 3 foot wide strip along the fence with shrubs and water them with drip irrigation (or use shrubs that don’t require irrigation).  That way I can keep sprinkler watered lawn at least 3 feet from the fence so the sprinklers are at least 3 feet away.  If the area is windy I go with 5 feet distance.

Generally it is considered bad landscape design to put a lawn next to a fence, unless it is an extremely attractive fence that you want to be a focal point of the landscape!  Standard practice is to “buffer” the appearance of the fence with a shrub planter along the base of the fence.

All Valves Come on and Stay On Continuously

Q.  I just restarted my sprinkler system after it had been winterized. When I turned on the water to the system, all the valves stations came on at once, as if by-passing the timer unit.  Even when I turn the timer unit Off, the sprinklers keep running.

A.   This is a common problem when restarting after your sprinkler system has been winterized, or after the system has been turned off for an extended period of time.  It also often occurs with brand new solenoid valves that have just been installed.  There are a  couple of possible problems that can cause this, so we’ll look at a couple of solutions.  One of the tricks below should get your irrigation valves opening and closing properly again.

Air Trapped in the Valve:

The valves may have air trapped in them.   A small bubble of air becomes trapped in the tiny water ports of the valve, this stops the water from flowing through the port.  Since the water flowing through the port is what holds the valve diaphragm closed, the valve stays open.

1. Turn on the main water supply.

2. Now go to the individual valves and using the manual open & close control on the valve.  The manual open & close control is either a lever on the valve (most often it is under the valve’s solenoid), or it may be a screw on the top of the valve bonnet.  If it is a screw don’t fully remove it, just open it until water starts squirting out.  Set it to open, wait a few seconds, then set back to closed.  If the valve doesn’t close within a minute, try it again.  It may take several tries to get the air bubble to “burp” itself out.  Try tapping the valve to dislodge the air while the valve is open if needed.  Note: old plastic valves may become brittle and crack when tapped, so if the valve is plastic and old don’t tap on it except as a last resort if the air doesn’t come out.

3. If that doesn’t fix the problem, you can almost always force the air out using the manual flow control on the valves.  Unfortunately, some inexpensive valves do not have a flow control.  The flow control is a handle, similar to what a manual valve has, that is on the top of the valve.  It works just like a regular faucet, turn clockwise to close.  Most flow controls have a hand operated flow control, others have a cross handle that is turned using a tool (pliers will work if you don’t have the special valve opening tool.)  A few valves have a screw for the flow control that requires a screwdriver to turn.  Try completely closing and then reopening the manual flow control on each valve.  That should force the air out and fix the problem.

Valve Needs to be Throttled:

If air in the valve doesn’t seem to be the problem it is possible that your valves don’t have enough pressure differential and they need to be throttled in order for them to close by themselves.

Here’s how to throttle them using the flow control adjustment:

Note: some inexpensive valves do not have a flow control adjustment feature on them.  If that is the case you are not going to be able to do this.  You will need to replace the valve with a better quality valve that has a flow control.

1. Use the manual flow control on each valve to close all of the valves.  Now the main water supply should be on, but none of the valves should be allowing water through.  So no sprinklers are running.
2. Start with just one valve at a time.  Rotate the manual on/off lever to the on position.  Open the manual flow control knob all the way (turn as far as it will go counterclockwise). The valve should come on and sprinklers run.
3.  Next rotate the manual on/off lever under the solenoid to the closed position.  The valve should close (it may take it a minute or two to close) but probably won’t, because that is the problem, they won’t close!   If the sprinklers turn off the valve is working correctly, go to the next valve and start again with step #2.  If the valve does not close by itself, you need to throttle the valve.  Continue to step #4.
4. To throttle the valve you partially close the flow control knob.  Start by turning it one full turn clockwise.  Wait a minute for the valve to close.  If it doesn’t close, turn the handle another half turn clockwise.  Wait again.  If the valve still doesn’t close turn it another half turn.  Keep doing this, at some point the valve should suddenly make a whooshing noise and close.  If the valve is broken it will never close by itself and eventually as you close the flow control more and more the sprinkler radius will start becoming noticeably reduced.  If that happens you need to repair or replace the valve.  But in most cases the valve will close by itself after you have partially closed the flow control.  It might take 4-5 complete turns before this happens.

You shouldn’t see any significant change in the sprinkler performance with the valve flow control in the partially closed position, except that the sprinklers may mist a little less (which is a good thing.)  This is called “throttling the valve” and some valves won’t close by themselves unless they are throttled.  The way a solenoid valve works is that the pressure differential as the water goes through the valve is what the valve uses to power itself into the closed position.  If there isn’t enough pressure differential the valve will not close by itself.   Often there is not enough pressure differential when there aren’t very many sprinklers on the valve circuit. When you throttle the flow control you are simply increasing the pressure diferential.

You can leave the flow control in a partially closed position permanently, it will not hurt the valve.  The valve is designed to allow you to do this.  The sprinklers should still operate well as the amount of water throttled when you partially close the valve is not significant.

For valve repair instructions see  how to fix a solenoid irrigation valve.

Why not use those huge sprinklers?

Q.   I don’t understand why I can’t apply the same guidelines from your tutorial and choose 2 or 3 heads with 70 foot spacing?  That would mean a lot less sprinkler heads on my large acreage lawn.  Other than not being able to aim them as selectively, I’m missing the reasons I shouldn’t go this route.  But you caution against it, so I’m sure I’m missing something.

A.  Someplace around 55 foot spacing things start to get all screwy.  They do make sprinklers that will shoot that large radius.  They are pricey, the cost works out about the same per square foot irrigated regardless of the spacing (funny how that happens!)   The problem is there’s just too much wind drift, evaporation, etc. at those wide spacings.  Plus to get water to fly those long distances you need big, heavy water drops with lots of momentum.  Those big drops just beat the crud out of the lawn, and cause compaction of the soil.  Think of what it would be like if a really hard rain storm occurred each time you watered.  Where the huge droplets don’t compact the soil they may erode it.  Golf courses and parks have fought this problem for years.  Most city parks have now settled for 55′ spacing rather than deal with the grief of citizen complaints about dead grass.

The bigger radius heads work better with pasture grasses, where long unmowed grass blades soften the droplet impact and a few dry spots and general “ugliness” aren’t as important.

It also takes lots of water pressure and volume to get that water out there.  70 feet radius means you need 70 PSI and 30 GPM at each sprinkler head.  That means probably 85 PSI or more coming out of the pump.  Most systems with big sprinklers like that run at over 100 PSI of pressure, which means lots more wear and tear on the system, and a shorter life-span.   With those high pressures, design becomes critical, mis-design a single thing and it is unforgiving; water hammer can rip the whole system apart in a big hurry.

Then there is the safety issue.  You ever been hit by a 30 GPM stream of water flying from a nozzle at 70 PSI?   I have, it knocks you on your butt and hurts like hell!  Keep in mind that the really big impact guns used on farms reverse with enough force to kill you if you are struck in the head by the sprinkler arm.   Liability is the biggest reason that parks and golf courses are ditching the big water guns for smaller sprinklers.

Bottom line is that using big radius sprinklers just gets really tricky and the results are ho-hum at best.  It’s not a good solution in the vast majority of situations.  If you do want to mess with it, get professional help with the design.  Most of the sprinklers over 70′ radius are only sold by agricultural irrigation dealers.

Large Radius Sprinklers
Big Irrigation Guns in Florida

How to Estimate Water Useage Required for an Irrigation System

The amount of water needed for irrigation depends on many different factors.  A reasonably accurate estimate of the amount of irrigation water needed can be made using Eto data for your actual zip code.  “Eto” is the amount of water needed for irrigation, based on scientific research.  You can find the historic Eto for any zip code in the USA at the website http://www.rainmaster.com/historicET.aspx courtesy of the Rainmaster irrigation controller company, who makes very good “Smart” irrigation controllers.   I use one of their Eagle model controllers on my own home.  (Rainmaster get a plug from me as well as a big “thank you” for providing the ETo look up service online.)  Unfortunately the Eto value only tells you how many inches per day are needed, which for most folks is a meaningless value. It makes more sense if you think about rainfall which is often also measured in inches.  If you find you need 0.20 inches of irrigation, then 0.20 inches of rainfall would provide the required water.  But most people in the USA want a value in gallons, which requires you to provide a little more information about your yard.  Then you plug the values into a simple formula, and do a little multiplication and division on any calculator.

Formula to calculate the gallons of irrigation water needed per day:
(Eto x PF x SF x 0.62 ) / IE  =  Gallons of Water per day

Values for the formula:
Eto: Get this from http://www.rainmaster.com/historicET.aspx .  Enter your zip code, or a nearby zipcode, and the website will give you the average daily ET value for each month of the year.  Use the highest value or the “suggested reference value”.  Usually they are the same thing.

PF: This is the plant factor.  Different plants need different amounts of water.  Use a value of 1.0 for lawn.  For water loving shrubs use .80, for average water use shrubs use 0.5, for low water use shrubs use 0.3.

SF: This is the area to be irrigated in square feet.  So for a 30 foot x 50 foot lawn you would use 1500.

0.62: A constant value used for conversion.

IE: Irrigation efficiency.  Some irrigation water never gets used by the plant, this value compensates for that.  I suggest using 0.75 as the value for this.  Very well designed sprinkler systems with little run-off that using efficent sprinklers can have efficiencies of 80% (use 0.80).  Drip irrigation systems typically have efficiencies of 90% (use 0.90).

Example:
A 1500 square foot grass lawn in zip code 85232 (Central Arizona)
Start by looking up the Eto for zip code 85232 at the Rainmaster website, which displays a suggested reference value of 0.3 inches per day using June, the driest month of the year in that area.

Now rewrite the formula inserting your values into it:

0.3 (Eto value)  x  1.0 (grass value)  x 1500 (sq ft)  x 0.62 ÷ 0.75 (efficency factor) = gallons of water per day

Now do the math, just punch the values into a calculator and get your answer:
0.3   x   1.0   x   1500   x   0.62   ÷   0.75   =   372 gallons per day



We could figure out the average daily water use for other months of the year also.  Just use the same formula but insert the Eto value from the Rainmaster website for the month you want to get a valve for.

Remember this calculation just gives you an estimated value.  There are many other factors that could make this value higher or lower.  When planning for how much water a system that has not yet been designed or installed will use, it would be very wise to allow for  error by adding 10% or more to the daily water use needed.  It is generally better to have too much water, than to have too little!  Play it safe!

A common related question is “how much water pressure will my irrigation system need?”  The answer depends on a lot of factors, but as a rule of thumb, I would suggest 50 PSI of water pressure as a good starting point for sprinklers, 45 PSI for drip systems.  If you have a large yard and want to put the sprinklers farther than 30 feet apart you will need more pressure.  For example, if you want your sprinklers 45 feet apart you will probably need 65 PSI of water pressure.  To get a real value you will need to create an actual sprinkler system design. See the Landscape Sprinkler Irrigation System Design Tutorial .

Never buy a pump, sprinklers, or any other materials before your sprinkler design is completed!