Category Archives: FAQS

How to Use Pressure and Flow Switches with Irrigation Controls

Almost any major maintenance problem in an irrigation system will cause a unusual pressure level or flow level in your irrigation system.  Therefore pressure and/or flow monitoring is a good way to detect problems.  Most of the time the response to a abnormal pressure or flow level would be to shut down the system, or possibly to shut down the current valve zone  and try another one.  Irrigation systems are typically shut down using what is called a master valve.  A master valve is a single valve located at the water source that can shut off all the flow of water into the irrigation system.  For more details see my article on master valves. On systems with a pump you will probably want to shut off the pump.  Sometimes, as with booster pumps, you will need to both shut down the pump and close a master valve.

So what problems might an abnormal pressure or flow indicate? A very low pressure may indicate that perhaps the pump is broken (if you have a pump), an intake screen is clogged, a filter is dirty, a valve failed to open, or a pipe has broken.  Abnormally high pressure could be the result of  a valve not opening when it should, a dirty filter (if the pressure is measured upstream of the filter rather than downstream) or some obstruction in the pipes.  Low flow could indicate a valve failed to open, a filter is dirty, or that a pump isn’t working as it should.  High flow could indicate a broken pipe, a broken sprinkler, or a valve that is stuck open.   In most cases monitoring either flow or pressure is sufficient as opposed to monitoring both.


How to Monitor Your Irrigation System

There are a number of different ways to detect and respond to abnormal pressure or flows.  Following are a few or these.  If you would like to suggest other methods, please contact me.  I realize this is not an exhaustive list.

The image below shows the Hunter Pro-C Modular 4 Station Indoor Controller which makes automating your irrigation easy and user-friendly.

An image of the Hunter Pro-C Modular 4 Station Indoor Controller

If you need to irrigate a larger property, or require more specialty zones, check out the Hunter PCC 12 Station Indoor Controller.

Use a Smart Irrigation Controller that has a Sensor Input and Response Feature:
This is probably the easiest way to add pressure detection and response.   It is also what I consider to be the preferred method, as it is reliable and gives you the most control.  Some high-end irrigation controllers can use an electronic sensor hooked up to the mainline pipe to monitor the water in the irrigation system. Some of these controllers use flow sensors, some use pressure sensors, some can use both types.   These controllers with advanced features are typically sold as Smart Controllers and are expensive compared to ones typically found on a residential irrigation system.  Prices for these controllers typically start around $300.00 and go up into the thousands for ones that handle dozens of stations.  Some controllers can increase the number of zones with an irrigation controller expansion module. But then you get a lot more with them too.  They are sold through professional irrigation supply stores, both online and locally.

WARNING: Be sure the controller will do exactly what you want BEFORE you purchase it!  Not all controllers marketed as “Smart Controllers” have these sensor input features, many only work with specific types or even models of sensors, and some controllers may not provide the response options you want or need.  You need to research the controller carefully.  Don’t rely on a simple check list of features!  “Sensor input” can mean almost anything, you need details!  I have seen controller feature lists where the unit sounded fantastic and ultra flexible, only to discover after closer examination that the actual response features don’t do what I need or want.   Read the actual owner’s manual (most controller manufacturer’s have them available on their websites) to see what the true capability of the controller is.  Read the sections of the manual on how to hook up the sensor, then there will also be a separate section on how to program the sensor you should look through.  Some controllers allow for time delayed responses, some don’t.  If you have a pump you will almost always need a time delay feature to bypass the sensor when the pump is starting up.  Even those controllers that do allow you to add delay times may not allow as much or little time as you need.  It is critical that you do as much research as possible before you go to the expense and effort of purchasing, installing and programming the controller.

For example, I have a Rainmaster Eagle Smart Controller on my own irrigation system, as well as using it on the majority of the commercial systems I design.  This particular Smart Controller has flow sensing capabilities, but it does not have built-in pressure sensing capability.  It does have a delayed response allowing delays of 1-6 minutes, but only in one minute intervals.  It will also allow the use of one additional simple on/off type sensor (most controllers have a circuit for this type of very simple sensors.  A simple rain switch is an example of this type of sensor.)    It has an audible “chirp” alarm that alerts you that a sensor response has been activated.  While this particular controller meets my needs, it certainly will not meet everyone’s.  Almost every major irrigation company makes a Smart Controller, and each has different features and capabilities.  Be sure you are using up-to-date resources when checking out models.  Smart Controller models are introduced each year, and often the capabilities of existing models change from year to year, so it is hard to keep up with them.

When using a controller with a pressure and/or flow sensor you start by installing the actual sensor on  the mainline pipe.  The method varies with the brand and model of sensor, most are pretty easily installed.  The sensor is wired to a special terminal on the irrigation controller.  Typically the wire used must be a special shielded communications cable, rather than standard irrigation valve wire.  Consider installing communications cable in PVC conduit to protect it, as it is very sensitive to even the smallest nicks from shovels, animals digging it up, or rodents chewing on it.  Most pressure sensors work by sending a reading of the current pressure to the controller every few seconds.  A typical flow sensor has a small paddle that turns as the water flows through the pipe.  Flow sensors normally send a signal based on the amount of flow, for example they might send a signal each time 5 gallons of water has flowed past the sensor.  The controller then interprets that data from the sensor and responds.   In most cases you will pre-decide what the response will be when you set up the controller.  For example; if you have a system with a pump, you could program the controller to shut down the irrigation system if the pressure was below 10 PSI for more then 2 minutes during the set irrigation period.  The 2 minute qualifier (delay) for shut down would allow the pump time to pressurize the system during start up and also avoid “false alarms” caused by brief dips in pressure.

Using a Simple Pressure Switch with a Pump Operated System:
This method is for those with pumps.  What I am describing here is for emergency shut off only.  I’m assuming you already have something set up to turn on or off the pump during normal irrigation operation.  That might be a standard pressure tank with a pressure switch to control it.  Or you may be using the pump start feature on the irrigation controller to actually start and stop the pump using a 120v relay.  The new pressure switch we are talking installing in this case is used only to detect pressures that indicate a problem and turn off the pump.  So if all is hooked up properly, in the event of blockage or no water going into the irrigation system the pressure will drop and the new pressure switch will shut the pump off.

This method requires that your irrigation system is leak free and can hold pressure for days between irrigations.  If the system is not leak free see #4 below.

1. Make sure you have a really good quality spring-loaded check valve on the irrigation mainline pipe.  The check valve goes someplace after the pump, but before the pressure switch.  A good quality check valve is needed to keep the water from leaking backwards out of the system through the pump.  Typically the self-priming feature of the pump is not good enough by itself to do this, you need a separate check valve.

2. You will need to use a pressure switch that works backwards from normal ones used for household water systems, since you want the switch to shut off the pump at low pressure (standard switches used on household water systems turn on the pump at low pressure.)  Some switches can be wired to work either way, others can’t.  Keep in mind that the low end on many common pressure switches in around 25-30 PSI.  That might be a bit higher than you want for a low end shut off, especially if your system will be operating at less than 45 PSI.  You don’t want accidental “false” shut offs since the only way to get the system back on will be to manually start the pump and hold it on until the pressure is back above the shut-off level.

3. There a problem to be dealt with.  The problem is that valves close slowly, taking as much as a minute or two to close after the controller tells them to.  At the end of the last irrigation cycle a typical controller closes the last valve and immediately shuts off the pump.  But it takes the valve several seconds up to a minute or two to actually close.  During this closing period the system will depressurize.  With no pressure in the system the pump will not restart for the next irrigation cycle, because the low pressure shut-off switch is detecting low pressure and shutting off the power to the pump.  There are two ways to deal with this.

A. You can fool the controller into keeping the pump running after the last valve circuit has finished watering.  Your controller needs to have the capacity for one extra valve on it to do this, so if you have 10 valves you will need a controller with 11 stations.  The last station on your controller needs to not have a valve attached to it.  Program 1 minute of time on that last station.  Now the controller thinks it is operating one last valve, so it keeps the pump running.   That will keep the system pressurized while the final valve closes.  If one minute is not enough time for the final valve to close then add another minute of run time to that last empty station.

B. Some controllers have a built in delay feature that keeps the pump running after the last valve closes.  This feature keeps the pump start circuit energized, which keeps the pump running for a minute or two after the last valve is signaled to close.  This gives the valve time to close before the pump is shut off.   Some less expensive controllers have this feature.  But typically only high-end controllers have this feature, so this method isn’t very practical.  If you are going to buy an expensive controller you might as well forget about using a pressure switch and use a Smart Controller and a sensor to shut the system down, as described in the first section of this article.

4. Often a small leak will cause the system to depressurize between irrigation runs.  This can be a major problem.  The pump will not start if the pressure is low, the low pressure switch is going to shut off the power to it.

If the leak is very small you can install a pressure tank, just like on a typical house water system.  Assuming a small leak, the tank keeps the system pressurized.  But that only works with a very small leak and it can take a huge pressure tank to supply enough water to keep the system pressurized.   If your system has a larger leak you will need to find and repair the leak.  If you can’t get the system leak free, you will need to take a different approach, as described below.

You can use a timer to over-ride the low pressure switch, and allow the system to start even with no pressure.  You will need a “Time Delay Relay”.  The time delay relay needs to be the type that allows the power to flow when energized, then shuts it off after a minute or two of delay.  It needs to have an automatic reset.  You then install the relay on a bypass wire around the low pressure switch.  That way the pump can start even when the pressure switch is “off” due to low pressure.  You will need to work with someone knowledgeable when ordering the time delay relay to be sure you get the correct relay, as they make many different kinds.

Using a Pump Controller with a Sensor:
This is essentially the same method as the Smart Controller method I described earlier.  Only the “smarts” are in the pump controller rather than in the irrigation controller.  Some of the newer digital pump controllers (don’t get confused here, we’re talking about a separate pump controller, not the sprinkler controller) are programmable, they are simply a small computer that operates a relay that starts and stops the pump.  You hook them up to a pressure sensor, also to the irrigation controller, and to any other sensor you want (wind, rain, temperature, light, flow, you name it.)  Then you can program them to do just about anything using that information input.  They can turn off the pump if a low pressure occurs for more than x number of seconds, turn off the pump if a high pressure occurs for x number of seconds, turn on the pump at a given time of day, etc.  Pretty much any input you want can cause the pump to turn on or off.  The capability depends on the brand and model of the pump controller. The downside is it takes electronics know-how to set the thing up and someone tech savvy to program it.  Typically you hook up a laptop to the pump controller to program in the logic, then once it is programmed it runs by itself.  The laptop just gives you an interface that is easier to work with.  I really can’t give you much more details beyond that, this type of pump control is beyond my expertise, I just have seen pump system experts use them to do amazing things.

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 courtesy of the Rainmaster irrigation controller company, which makes very good “Smart” irrigation controllers.   I use one of their Eagle model controllers in my own home.  (Rainmaster gets 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.

A WiFi-ready controller can help automate watering your lawn. The Rain Bird ESP-Me 4 Station WiFi Ready Indoor Controller is pictured below:

This is a picture of the Rain Bird ESP-Me WiFi ready sprinkler controller.

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 .  Enter your zip code or a nearby zip code, 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 the 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 efficient sprinklers can have efficiencies of 80% (use 0.80).  Drip irrigation systems typically have efficiencies of 90% (use 0.90).

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 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!

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

Anti-Siphon Valve Controls

Here are a few common anti-siphon valve models with the valve control features labeled.  Most other solenoid valves are very similar in design and use similar controls.  The Anti-Siphon Vent is a feature found only on anti-siphon valves.

Additional articles on this website related to anti-siphon valves:

How to Install a Anti-Siphon Valve  gives a general overview of anti-siphon valves including situations where they won’t work or will leak, as well as step-by-step installation instructions and troubleshooting problems related to installation.

How to Repair a Anti-Siphon Valve

Rainbird Anti-Siphon Valve Leaks, Won’t Fully Close

Installing Valves Downstream from Anti-siphon Valve

How to Fix a Automatic Irrigation Valve that Won’t Open

Backflow Preventers will guide you in deciding if an anti-siphon valve is the best choice for your irrigation system.

Lawn Genie Anti-Siphon Valve with controls labeled
Lawn Genie Anti-Siphon Valve with parts & controls labeled


Orbit Anti-Siphon Valve with controls labeled
Orbit Anti-Siphon Valve with parts & controls labeled


Rainbird Anti-Siphon Valve with controls labeled
Rainbird Anti-Siphon Valve with parts & controls labeled


Water-Master Anti-Siphon Valve with controls labeled
Water-Master Anti-Siphon Valve with parts & controls labeled


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.



How to Remove PVC Cement From Your Hands

There are several hand cleaner products made for removing PVC cement/glue from your hands.  Most combine a solvent with an abrasive grit and a hand moistening lotion into a single product.  The ones I have used work very well.  They are typically sold at irrigation supply stores.  For some reason I have never seen them sold at the home improvement stores where homeowners tend to buy irrigation supplies.

For the “weekend warrior” who just needs to get the cement/glue off infrequently, acetone will remove it quickly.  Be sure to immediately wash any skin you apply acetone to thoroughly with soap and water after getting the glue off.  Do not leave acetone on your skin!

caution  Repeated skin exposure to acetone may cause serious health issues, so it should not be used by pros who need to remove glue from their hands often.  Be sure to read and follow all precautions on the acetone can.

How to Remove Paint from PVC Pipe

PVC pipe that is exposed to sunlight should be painted to prevent sunlight from destroying the plastic.  But what if you need to repair the PVC pipe later?  You can’t glue pipe that has paint on it.  In fact, you need to remove all of that paint from the area to be glued, even a small amount may cause leaks in the glued joint.

Using a small brush “paint” acetone onto the area of pipe where you want to remove the paint.  (PVC primer will also work as a replacement for acetone, but the purple color makes it hard to make sure all the paint is off.)  Allow the acetone to soak in for a few seconds then scrape off the paint with a knife blade or other metal edged tool like a putty knife.  If some of the paint doesn’t easily come off re-coat the paint with more acetone.  Once most of the paint is off, apply another coat of acetone.  This time use a paper towel to wipe off the remaining paint.  You may need to wipe down the PVC pipe 2-3 times with fresh paper towels to get a nice clean white surface.  Now you can glue your joint using the normal method for gluing PVC pipe as described on the cement/glue can.  The acetone will leave the pipe surface feeling sticky, that’s OK, you don’t need to wait for it to dry before you glue the joint.  The primary ingredient in the purple PVC primer that is used to clean and prepare PVC pipe for gluing is acetone.

caution  Use caution when working with acetone.  Read and follow the warnings on the can.  Repeated skin exposure to acetone may be harmful to your health.


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.

Creating Water-Proof Irrigation Wire Connections

Water-proofing your irrigation system’s wire splices is one of the most critical tasks in any installation or repair that involves wire splices.  The splices need to be completely water-proof.  Taping them up with electrical tape will NOT work for this!  The electrical tape will allow water into the splice as it becomes old, brittle, and the adhesive on it dries out.  If you don’t water-proof your splices it WILL cause your valve to fail!  Don’t save a buck on a wire splice and ruin a $20 valve! I’ll explain in detail why waterproofing is so important later, first let’s get down to the details on how to make a good waterproof wire splice.

General Things That you Need to Know about all splices!

Caution:  The methods described below are intended for low-voltage wires of 24VAC or less, such as those used in typical irrigation system controls.  They should not be used for higher voltages.

DO NOT BURY SPLICES directly in the ground.  Put a box around them to protect them and to help you find the later.  A small plastic utility box works fine.  Glue a large steel washer to the bottom of the box lid using epoxy.  This will allow you to find the box with a metal detector if grass grows over it.  Splices are the most likely place a wire will short out in the future, so a box makes the splices easier to find and repair.

2-wire irrigation systems:  These are a newer type of system that uses only 2-wires to control all the valves.  The irrigation controller sends a signal through the valves to a decoder at each valve.  The decoder then allows power to the valve solenoid only when told to by the controller.  These types of systems depend on electrical “signals” sent from the controller through the wire to the decoder.  Any voltage leak at a splice can severely impact the signal and cause the system to malfunction.  For this reason splices for 2-wire systems need to be made much more carefully.  Many of the 2-wire manufacturers have specific splice methods they require be used in order to protect your warranty.  Be sure to use these if required!

Not sure if your system is 2-wire?  As i write this in 2013, 2-wire systems are seldom used on residential systems, but they are also gaining popularity and will probably start showing up soon, first on larger systems.  The controller case normally will be clearly labeled as “2-wire”.  A 2-wire system will also have a “decoder unit” installed on the wires at each valve.  Standard irrigation control systems have two wires going to each valve.  But in a standard system one of the wires goes to a single valve and only that valve.  So if you have 4 valves there will be 5 wires (1 common shared by all the valves, + 1 individual wire to each of 4 valves = 5 wires.)  On a 2-wire system with 54 valves there would be only 2 wires and each valve would have a decoder unit installed on it.  The presence of a decoder to be installed at each valve is the best way to tell if it is 2-wire.

The best way to make the splice is to use special water-proof splice connectors that you can buy at any hardware store.  These are made for sealing outdoor wire connections and work very well.  There are many different styles and types available.

Water-Proof Twist On Connectors – “Nut” Style or “Wing” Style

Most of the connectors currently used by pros consist of an twist on type wire connector that is filled with a water sealing grease.  Sometimes these are called water-proof “nut” or “wing type” connectors.   These are inexpensive and very simple to use. Here are general instructions for use since a lot of these inexpensive connectors are sold without instructions.  If instructions came with the connectors please use those instructions, as they are intended for the actual connectors you bought!

  1. For every 3 connections you need buy 5 connectors.  Why?   Because you will probably make several bad splices, and you will have to remove those connectors and toss them in the trash.  They can’t be reused because when you remove them a lot of the sealer comes out with the wire.   (If you look close most connectors actually say “do not reuse” or similar language on them.)
  2. Start by stripping the insulation off the end of the wires to expose the bare metal wire.  Do not strip off too much insulation, the exposed  bare wire should be about 1/2 the length of the connector body.   You can splice 3 wires together easily using a single connector.  It’s OK to put 4 or 5 wires in a connector, but be warned that it gets a lot more difficult getting the wires to stay in the connector when you use more than 3 wires.
  3. Place the bare ends in one hand and using your other hand, align the wires side-by-side, so the ends of the bare sections are lined up together.  Those ends need to all go into the connector together at the same time, so hold the wires tight and don’t let them slip out of position.  Do not try to insert an additional wire into a wire connector that already has wires spliced together in it.  You need to remove all the wires and redo the splice to add more wires.
  4. Push the connector down over the bare ends of the wire.  Twist the connector clockwise to screw it on.  Hold the wires firmly in position as you twist the connector over them.  The connector has threads, a spring, or barbs inside it that will grab the wires and cinch them together tightly as you twist it on.  Stop twisting when you feel substantial resistance.
  5. Hold the connector in one hand and tug on each of the wires with the other to make sure the wires are secure and will not pull out.  If a wire feels loose or pulls out, disassemble the entire splice and try again.   Use a new connector as some of the sealer will probably be lost when you remove the connector, and it needs all the sealer for a good seal.   If the wires still pull out after another try you are probably using the wrong size connector.
  6. Finally make a visual inspection of the splice.  The insulation on the wire should be fully inserted into the sealer gel or grease.  No bare wire should be visible.  That’s all there is to using twist on wire connectors, they are very quick and easy.

The connector size is important when using twist on connectors!   Be sure you buy and use the correct size connector for the wire sizes you are splicing. The package will list the various wire size combinations that the connector works on.  The connector colors indicate the connector’s size and most are standardized.  Here are some general guidelines.  Warning: There are some brands that do not follow these color guidelines so double check the instructions on the package!

Connectors for #18 wire.  Most residential irrigation systems use #18 size wire, this is the size of most of the multi-wire underground irrigation cables sold in hardware stores.   Unfortunately the colors for these connectors are not standardized.  Most I have seen are dark blue or black.  Make sure it says it will connect 2- #18 wires.

Connectors for #14 & #12 wire.  Larger irrigation systems and commercial irrigation often use individual #14 wires.  Sometimes #12 will be used for irrigation systems with very long distances between the controller and the valve.  Most often these connectors are yellow.   Note: Most of the yellow connectors I have seen will NOT connect a single #14 wire to a typical valve solenoid wire.  For this you will probably need the smaller #18 wire connectors above.

Twist-On Waterproof Wire Connectors. Wing Style on left (blue), Nut Style on Right (black).




Mechanical Clip Style Non-Stripping Connectors

Clip style is a catch-all name I use for the various types of connectors that use a mechanical clamping system to grab and bite into the wire.  Typically with this type of connector you push the wire into a round slot on the connector, and then squeeze some type of clamp that bites into the wire to hold it in place.  Some require pliers to squeeze the clamp into the wires.   The most popular of these types of connectors for irrigation use is the Blazing Snaploc BVS Series wire connectors and the 3M Scotchlok 314 series connectors.  These connectors are more expensive but make a very secure connection almost always on the first attempt.  You won’t need to buy nearly as many extras for bad splices.


Container Type Connectors

These connectors are a two piece, two step system.  You connect the wires together using either a standard twist type wire connector, a crimp sleeve, or even soldering the wires together.  Then you shove the splice into a container filled with a water-proofing grease or jell and snap a retainer lid closed to hold the splice inside the container.

A variation on this type of connector is the original waterproofing method used back when I started in the business.   You mixed a 2-part epoxy resin in a small plastic envelope and then shoved the splice into the envelope so it was covered in resin.  The resin was allowed to harden creating a solid water-proof seal.  Unfortunately the resin was a carcinogen.   I don’t think these are sold any longer.


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.


PVC Pipe: SCH vs. Class

SCH Rated Pipe

PVC pipe types labeled “schedule” (abbreviated “SCH“) are made based on the traditional dimensions used for steel pipe.  Unfortunately steel has very different strength characteristics from plastic, so it is a system that isn’t very logical for use with PVC pipe.  But when plastic first came along it was made to the same size standards that were already in use for steel.  The common PVC pipe schedules you will see in stores are SCH 40 and SCH 80.  As the pipe sizes rated SCH increase, the strength and pressure rating of SCH pipe decreases.  So 1/2″ SCH 40 PVC pipe is very strong, while 2″ SCH 40 PVC has comparatively a low pressure rating, and is more easily damaged.  In sizes 1/2″ to 1 1/2” SCH 40 is a thick wall pipe with a reasonably high pressure rating and good resistance to physical damage.  It is often used for mainlines and other situations where a tough high pressure pipe is needed.  Sch 80 is generally used for making threaded plastic nipples because the plastic walls are thick enough to have threads cut into them (although most now have molded threads rather than threads “cut” with a die.)

Pressure ratings of SCH 40 PVC pipe:

1/2″  =  600 PSI
3/4″ = 480 PSI
1″ = 450 PSI
1 1/4″ = 370 PSI
1 1/2″ = 330 PSI
2″ = 280 PSI
2 1/2″ = 300 (not a typo, 2.5″ pressure is an oddity)
3″ = 260 PSI
4″ = 220 PSI

As you can see, the pressure ratings drop as the pipe size increases.  Note that the industry standard rule is that your normal operating pressure should not exceed 1/2 of the rated pipe pressure.  In other words, you shouldn’t use 1 1/2″ pipe for pressures higher than 165 PSI (330 x 0.5 = 165 PSI).  This is because pressure surges created by closing valves can easily double the water pressure in the pipe.  This rule applies to all PVC pipe, including that labeled SCH and CL.

Class rated pipe

PVC pipe types labeled “Class” (abbreviated “CL“) are based on the pipe’s pressure rating.  So Cl 200 PVC pipe is rated for 200 PSI of water pressure.  Cl 315 PVC pipe is rated for 315 PSI of water pressure.  The strength of CL labeled pipe is directly related to the pressure rating.  The standard “Cl” pipes are Cl 125, Cl 160, Cl 200 and Cl 315.  Of these Cl 200 and Cl 315 are most common.  Cl 125 is sold as a low cost pipe for use in sprinkler laterals for those for whom low price is everything.  It has a very thin wall and breaks easily if not handled carefully or nicked with a digging tool.

1/2″ size pipe is generally only available in SCH 40.  This is because of the thin wall of 1/2″ pipe makes it very easy to break.  I don’t recommend using 1/2″ PVC pipe at all, however if you must, you should use SCH 40.  Sometimes you will find 1/2″ Cl 125 PVC pipe at discount stores due to the very low price.

The Class system is obviously a more logical system for labeling pipe as you know immediately how strong the pipe is based on the label.  Unfortunately the more confusing “SCH” system became entrenched in the industry and remains.

What Pipe Type to Use

All PVC pipe labeled for a given size in the USA has the same outside diameter.  So any pipe labeled as 3/4″ will be the same diameter, whether it is SCH 40 or Cl 200 or any other type.  That allows the same fittings to be used to join the various pipe types together.  Most fittings are made to SCH 40 standards, although SCH 80 fittings are available, typically only at specialty plumbing and irrigation stores.  Technically most codes require SCH 80 fittings for pipe sizes 2″ or over.  In practice I’ve noticed that  SCH 40 fittings are often used up to 3″ size.  When dealing with sizes 4″ and above the use of non-glued “rubber ring-joint” fittings is recommended and usually required by code as well.  Glueing joints on 3″ and larger PVC pipe is very, very difficult.

“Mainlines” are all of the pipes that are under constant pressure, that is, the pipes that are before the sprinkler zone valves.   In most of the industry SCH 40 PVC pipe is used for irrigation mainlines up to 1 1/2″ size.  For 2″ size and larger Cl 315 PVC is used.  Most building codes prohibit the use of 2″ and larger SCH 40 PVC pipe for pressurized water lines.  Depending on the jurisdiction, this rule may or may not be applied to irrigation systems.  Those same codes generally require that all pressurized PVC pipes (mainlines) be buried at least 18″ deep to protect them from accidental damage, regardless of the type or size of pipe used.

“Lateral” pipes are the pipes after the sprinkler zone valve.  These pipes are only pressurized when the sprinklers are operating.   For lateral pipes the standard is to use Cl 200 PVC pipe.  Where budget is a concern and you can find it, sometimes Cl 160 is used.  As previously mentioned I recommend you avoid Cl 125 PVC pipe.  Laterals can be buried any depth, but I generally recommend at least 10″ deep to avoid a lot of maintenance problems with broken pipes.

Why Not Use 1/2″ Pipe or Tube for Irrigation

Well, if you have been reading my tutorials, I guess it’s pretty obvious that I’m not recommending you use 1/2″ pipe. I have a number of reasons for this.

  • 1/2″ PVC pipe is generally not available in most areas except in SCH 40 type.
  • The water capacity of 1/2″ pipe or tube is very low.
  • 1/2″ PVC pipe is hard to glue together without using too much glue. The glue piles up on the inside of the pipe when you insert it into the fitting and blocks the water flow. Too much glue also weakens the wall of the pipe and a leak develops after a few years.
  • Using 1/2″ pipe means you have to have another size of spare pipe and fittings on hand for repairs.
  • But the biggest reason is that 1/2″ pipe leaves no flexibility for future changes or additions to your sprinkler system. If you ever need to add another sprinkler to the pipe you’re screwed.

My conclusion: The small amount of money saved by using 1/2″ pipe just isn’t worth the hassle and risk.

Irrigation Lateral Sprinkler Pipe Size

Friction Loss:
As water moves through a pipe it loses pressure due to a phenomenon commonly called “friction loss”. Much of this loss is caused by turbulence, but we call it friction loss for simplicity. The amount of friction loss is determined by the type of pipe, the diameter of the pipe, the amount of water flowing through the pipe, and the length of the pipe. A complex formula (called the Williams/Hazen Formula) predicts the amount of pressure that will be lost due to friction loss.  The water also loses pressure each time it passes through a valve, a backflow preventer, or anything else it encounters on it’s way to the sprinkler head. Even a bend in the pipe causes pressure loss!  Don’t panic over the formula, we’ll use a pipe sizing chart or a friction loss calculator!

You need lots of pressure at those sprinkler heads!
The sprinkler head needs a minimum amount of water pressure to work properly. The manufacturer’s performance charts tell you how much pressure is required to achieve a specific radius for the water.  As the pressure increases so does the flow (GPM) and the radius of the throw. So in order to assure that there is enough pressure to make the sprinklers operate as they should, we need to calculate the pressure losses between the water source and the sprinkler head.  If the pressure loss is found to be too great, then we must reduce.  The easiest way to do that is to use a larger size pipe.



There are several methods used to determine pipe sizes of sprinkler system lateral pipes.  I’m going to explain two methods.  One method is faster but less accurate, the other is very accurate but takes more time.

Chart Method:

Pros: The fastest and easiest method.  Requires a single, simple calculation and uses a chart to determine the sizes.
Cons:  The learning curve to use it is a bit more difficult to understand.  It uses an averaging system to arrive at pipe sizes.
See step-by-step tutorial for the Chart Method

Trial & Error:

Pros:  Very accurate, calculates the pressure loss in each pipe section using a spreadsheet.  Easier to understand.
Cons:  Time consuming, need to enter data into the spreadsheet, uses trial and error to establish pipe sizes.
See step-by-step tutorial for the Trial & Error method

Which method should you use?  For a beginner with a small irrigation system probably the Trial & Error system will be easier.  Below are overviews of each method for experienced designers to use.  Unless you are experienced you should probably read the full tutorial for the method you select.


See Determining Sprinkler Pipe Size Using a Pipe Sizing Chart for detailed step-by-step instructions.

Calculate the PSI/100 value:

( ____ PSI x 100) / ____ Feet Total Length = PSI/100

____ PSI.  Insert the maximum PSI loss for the valve circuit laterals into the formula where it says “____PSI.”

____ Feet.  Insert the distance from the valve to the farthest sprinkler on the valve circuit  in the space labeled “____ Feet Total Length” in the formula.

Remember that the maximum total pressure loss between the valve and the last sprinkler may NOT exceed 20% of the sprinkler head operating pressure.

The Pipe Size Table or Chart:

Sprinkler Pipe Sizing Chart for Laterals
PSI/100 = Desired PSI Loss in Lateral x 100 / Total length of Lateral















































































































 Flows shown red are over 5 feet/second. Use caution!


    1. Find your PSI/100 value in the top blue row.
    2. Read down the column to the value equal to, or higher than, the GPM in the pipe section.
    3. Read across to the pipe size for that section in the right column.
    4. Repeat steps 2 & 3 for next pipe section.

This table uses an averaging formula based on the assumption that all flows for any given size of pipe will not be at the maximum GPM for that size of pipe. In rare cases the PSI loss for the entire lateral may exceed the desired loss by up to 10%. This table assumes the use of Cl 200 PVC pipe, adjustments to the pipe sizes are required for other pipe types, such as poly or SCH 40 PVC.

Pipe Sizing Chart, Copyright 1979, Jess Stryker, All rights reserved.

Notes about the Pipe Sizing Chart:

  • Warning:  The sprinkler pipe sizing chart is based on using Cl 200 PVC pipe.   It also works for Class 125 (not recommended) and Class 160 (hard to find).
  • Schedule 40 PVC: If you plan to use Schedule 40 PVC pipe (“SCH 40”) for the laterals you need to make an adjustment before using the chart. Reduce the PSI/100 value you just calculated for the valve circuits to 1/2 the original values.
  • Polyethylene, Polybutylene: After you obtain your pipe size from the chart you need to increase it by one size to get the proper size for poly pipe. In other words, if the chart says ¾” PVC pipe, then you should use 1″ poly pipe. 1″ would become 1¼”, 1¼” becomes 1½”, 1½” becomes 2″, etc.
  • Where’s the 1/2″ pipe?  See “why not 1/2″?”

CONFUSING?  DON’T PANIC:   For detailed instructions see the page Irrigation Pipe Sizing Chart for Laterals.



See Calculating Sprinkler System Pipe Size Using a Spreadsheet for detailed step-by-step instructions.

This method involves trying various pipe sizes until a good combination is found.  A spreadsheet does the calculations.

You will need a spreadsheet friction loss calculator:  Friction Loss Calculator Spreadsheets

Remember that the maximum total pressure loss between the valve and the last sprinkler may NOT exceed 20% of the sprinkler head operating pressure.

Use the spreadsheet friction loss calculator to determine the pressure loss:

  1. Download and open the Friction Loss Calculator.
  2. There is a line on the spreadsheet for each section of pipe.
  3. Start with the pipe section after the control valve and work out to the farthest sprinkler.
  4. Select 3/4″ pipe for the pipe or tube size. (See “why not 1/2″?”)
  5. Enter the GPM for the section of pipe.
  6. Enter the length of the section of pipe.
  7. Use an error factor of 1.1
  8. Go to the next line down and repeat steps 4-7 for the next pipe section.
  9. The spreadsheet calculator will tell you the velocity and PSI Loss for each pipe section.
  10. At the bottom of the calculator it will tell you the pressure loss total of all sections combined.
  11. Change the pipe size if the velocity or total pressure loss is too high.

You must calculate the pressure loss for each of the possible water paths in the valve circuit.

Here is an example of the possible water paths for a valve circuit, shown in red, blue, and magenta.

Start with the water route that is the longest.  In this case that would be the red route.   There are 9 pipe sections in this route labeled 1-9.  Enter the data from this route into the calculator.  Use a larger pipe size if the velocity is not safe.   Check that the friction loss “Total of All Sections” does not exceed your maximum allowable amount.

Write the pipe size for each section on your plan.
Now repeat the process for the blue water route and then the magenta color route.

Confused? For detailed instructions on using the spreadsheets see What Size Pipe for Sprinkler System Laterals?

This article is part of the Sprinkler Irrigation Design Tutorial
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Using A Smaller Pipe to Increase Water Pressure

There is a very persistent misconception in the lawn sprinkler industry that using progressively smaller pipe sizes in a sprinkler system will help keep the water pressure high.   The argument is that as the water moves through the pipes past the sprinklers, the pipe must get smaller in order to squeeze the water so that the pressure stays high enough to operate the sprinklers.  Unfortunately, it’s not true.  It would be nice if it was, because we could eliminate pumps.  Plus think of all the money you would save on pipe.  The smaller the pipe you used, the better your system would work!  So why not use 1/4″ or even 1/8″ tube for the pipes?  That would really pump up the pressure!  Sounds a little silly when you look at it that way, right?  OK, enough with the sarcasm.  I’ll explain this whole mess.

Squeezing the water into a smaller pipe will not increase the water pressure!

Part of the reason this misconception persists is that it does seem logical.  The example most often given to support this idea is what happens when holding your thumb over the end of a hose.  As you press your thumb over the opening, making it smaller, you can feel the water pressure against your thumb increase.  Pushing your thumb even tighter against the end of the hose, makes the opening even smaller, and you feel the pressure increase even more.  That would seem to prove that decreasing the opening size is increasing the water pressure.  So logically, using a smaller pipe would also increase the water pressure.

Unfortunately there is a lot more happening with this “thumb over the hose end” example than you realize.   As water moves through a hose or pipe there is a lot of resistance caused by the hose or pipe surfaces.   The water moves through the hose at the maximum speed it can while still overcoming this friction.  When the water reaches the end of the hose it has close to zero pressure left as it exits.  So if you have, say, 50 PSI of water pressure at the hose faucet, the  water will move as fast as it can through the hose, such that it will use up almost all that 50 PSI of pressure by the time it reaches the end of the hose.  If there were 60 PSI of pressure, the water would just move a little faster through the hose so that it used up almost all 60 PSI by the time it exits.  So basically regardless of the pressure, almost all the water pressure is used up by the time the water flows through the hose.  The nature of water is that it will reach the most efficient balance between flow rate and pressure loss that it can.  (Note, I am oversimplifying this to make it digestible for the average person.  If you have a degree in hydraulics you already know all the other related stuff about open vs. closed channels and nozzling effects.)

When you put your thumb over the end of the hose you change the flow dynamics in the hose.  Your thumb restricts the flow of water through the hose.   With your thumb over the end, the water is flowing much slower through the hose, and as a result, there is a lot less pressure loss due to friction.  So with less pressure being lost in the hose, the pressure at the end of the hose where your thumb is increases.  The tighter you squeeze your thumb, the more the flow is reduced, and the greater the pressure you feel will be.  But you haven’t created any NEW pressure.  You have simply traded reduced flow for increased pressure.    You can easily test this yourself.  Take a bucket and time how long it takes to fill it using an open end hose.  Now time how long it takes to fill the same bucket with your thumb firmly pressed over the hose end.  It will take longer to fill, because your thumb has reduced the flow!  The same thing would happen in your sprinkler system if you used smaller pipe to increase the pressure.  The smaller pipe would restrict the flow of water.   The reduced flow would reduce the pressure loss in the pipes, resulting in more pressure.  But of course the sprinklers would not work because they won’t be getting the flow they require!    Sprinklers require both flow and pressure.

OK, that’s the layman’s explanation.  But there are also some much more complex scientific theory that I have been asked about in relation to this topic.   So here’s some very scientific explanations.

Bernoulli’s Principle, Venturi Effect, & Flying Pigs

Grab your thinking caps for this.  As you well know, Bernoulli’s Principle essentially says (paraphrased) that as the speed of a fluid increases, the pressure of that fluid decreases. If it didn’t, pigs wouldn’t fly.*   Obviously as you force a given amount of water through a smaller size pipe, the velocity of the water must increase for it to get through the smaller pipe.  According to Bernoulli’s Principle that will decrease the water pressure!  This is called the Venturi effect.  By suddenly forcing the water through a narrow passage you can actually create enough of a pressure decrease that it creates suction.  This is how many fertilizer injectors work.  It also is another reason why using a smaller pipe would not increase the pressure– it would actually decrease it!

Another less common argument is the pipe size must be decreased because the flow is decreasing at each sprinkler head location along the pipe route. Thus if the pipe were to remain the same size, the velocity in the pipe would decrease, resulting in an increase in pressure (according to Bernoulli’s Principle again.)  This is actually a good, scientifically based point, and accurate too!  So the argument is that the pipe sizes must become smaller in order to keep the velocity constant and avoid an increase in water pressure. (Are you bored yet?) Unfortunately when used as an argument for using smaller pipe, this one falls flat when you do the actual math.  At a flow of 7 feet per second, which is the maximum recommended safe flow for PVC pipe, the maximum possible pressure increase  due to velocity change would be a whopping 1/3 PSI.  So in theory, using a smaller pipe would eliminate that 1/3 PSI pressure gain.  But using a smaller pipe probably would also increase the pressure loss due to friction, as previously mentioned.   The drop in pressure due to friction loss likely will offset most if not all of any gain that might have occurred due to decrease in velocity.  Even if it didn’t the maximum possible pressure gain of 1/3 PSI is simply not significant and would not be noticed.  So I stand by my statement that the only reason to decrease pipe size is to save money.

*Oh, by the way, Bernoulli’s Principle is why airplane wings create lift, which helps airplanes fly.  Therefore, it is also the reason that people, and yes, even pigs, can fly!

Spreadsheets for Calculating Pipe Pressure Loss

Here are some spreadsheets I have created to help you calculate the capacity and water pressure loss through pipes and tubes of various types and sizes. These should be useful for both figuring pressure loss in mainlines and laterals. Each spreadsheet allows for multiple sections of pipe of various sizes and flows. All you do is select the proper spreadsheet for the type of pipe you are going to use, select the pipe size from a drop down list, enter the flow through the pipe in GPM, then enter the length of the pipe in feet. The spreadsheet calculator will then do the math to give you the water velocity in the pipe along with the pressure loss in PSI for that section of pipe. If there are multiple sections of pipe the spreadsheet will also total all of them for the total pressure loss.

Full instructions for using the spreadsheets are included on the spreadsheets.


Please read this paragraph before you try to use the spreadsheets.

These spreadsheets use Apache Open Office.   That means you need to have the Open Office program installed on your computer for them to work.  I use Open Office because it is a free, safe program that is available for just about every desktop and laptop computer make and model.  That means just about everyone can use it, and nobody has to make a major software investment just to use the spreadsheets.  If you don’t already have Open Office you will need to install it on your computer before you can use the spreadsheets. You can uninstall it when you are done using it if you want.  Download it free from .  It does take a while to download Open  Office.  It is a full office productivity suite.  (Check it out, there are some cool apps in it!)

Your browser may try to “open” the spreadsheets if you left click on the links, even if you don’t have Open Office installed.  This is because most computers have some type of minimal spreadsheet reader installed on them, so the reader will try to open these spreadsheets.  If they were just simple spreadsheets they would probably work with the readers.  But they aren’t.   In most cases you will get a corrupted version of the spreadsheet that does not work.  This is because these friction loss calculators use very complex formulas that the “stripped down” spreadsheet readers can’t handle.  You need to install Open Office.   I may have already mentioned this. 🙂

Remember, you can un-install Open Office when you are done if you don’t like it.

If you try to open the spreadsheets directly using your Internet browser they will probably open as Read Only and the spreadsheet won’t work.  This is because the browser will not open an executable file directly.  (It is trying to protect you from possible viruses.) 
Solution:  Right click on the link and “Save” the file to your hard drive.  The actual wording varies, so depending on your browser you may select “Save link as..”, “Save Target as…”, etc.   This should save the spreadsheet file to your hard drive.  Then open it directly from your computer without using the browser plug-in.  Tablet and phone users:  you may need to get to a real computer to use the spreadsheets.

If the spreadsheets don’t work for you..

  1. Do you have Open Office installed?  If not, install it.
  2. Are you using Open Office to read the spreadsheet?  Sometimes another spreadsheet program will try to open it instead of Open Office.
  3. Have you tried saving the spreadsheet file to your desktop, starting up Open Office, then opening the spreadsheet with Open Office?
  4. If the spreadsheet says it is “Read Only” you probably are using a non-compatible plug in.  Install & use Open Office.
  5. Just dragging the spreadsheet link to your desktop may not actually save the file.  You need to right click on the link and select Save as…
  6. If you have an older version of Open Office you may need to upgrade it.
  7. Try rebooting.  I’ve experienced a problem where if I try to open one of these spreadsheets in a browser the computer gets messed up and won’t start Open Office.  Rebooting fixed the issue.


Do not try to open these spreadsheets by left clicking on the links.  Save the spreadsheets to your hard-drive first.  See the explanation above.

Cl 125 PVC pipe Calculator Spreadsheet for Velocity, Friction Loss or Pressure Loss.

Cl 160 PVC pipe Calculator Spreadsheet for Velocity, Friction Loss or Pressure Loss.

Cl 200 PVC pipe Calculator Spreadsheet for Velocity, Friction Loss or Pressure Loss.

Cl 315 PVC pipe Calculator Spreadsheet for Velocity, Friction Loss or Pressure Loss.

SCH 40 PVC pipe Calculator Spreadsheet for Velocity, Friction Loss or Pressure Loss.

SCH 80 PVC pipe Calculator Spreadsheet for Velocity, Friction Loss or Pressure Loss.



Do not try to open these spreadsheets by left clicking on the links.  Save the spreadsheets to your hard-drive first.  See the explanation above.

Polyethylene Tube Calculator Spreadsheet for Velocity, Friction Loss or Pressure Loss.



Do not try to open these spreadsheets by left clicking on the links.  Save the spreadsheets to your hard-drive first.  See the explanation above.

PEX Tube Calculator Spreadsheet for Velocity, Friction Loss or Pressure Loss.



Do not try to open these spreadsheets by left clicking on the links.  Save the spreadsheets to your hard-drive first.  See the explanation above.

Type K Copper Tube Calculator Spreadsheet for Velocity, Friction Loss or Pressure Loss.

Type L Copper Tube Calculator Spreadsheet for Velocity, Friction Loss or Pressure Loss.

Type M Copper Tube Calculator Spreadsheet for Velocity, Friction Loss or Pressure Loss.



Do not try to open these spreadsheets by left clicking on the links.  Save the spreadsheets to your hard-drive first.  See the explanation above.

SCH 40 Steel Pipe Calculator Spreadsheet for Velocity, Friction Loss or Pressure Loss.  (also use for galvanized steel)




Using a Looped Mainline for Irrigation

Looping your mainline often allows you to use a smaller pipe size for it, so using a loop system can be financially advantageous on a large irrigated area.  A looped mainline also provides maintenance advantages on larger sprinkler systems, and almost all large landscape irrigation systems, like parks and golf courses, utilize a loop mainline layout.  For smaller sprinkler irrigation systems they often provide little or no advantages.   As a general rule if you have less than 10 valve zones you are not going to get much of an advantage from a looped mainline.

What is a Looped Mainline?

The irrigation mainline is the pipe that runs from your water source to the individual valves that turn on a group of sprinklers or a drip irrigation circuit.   When the mainline is looped that simply means that all or part of it creates a continuous loop.  Typically a looped mainline starts with a single pipe coming out from the water source (pump, water meter, etc.) then the single pipe splits into two pipes.  the two pipes loop around the irrigated area and then rejoin each other to create the “loop”.   Zone valves would be located at various points along the loop to supply groups of sprinklers.   Normally you would put a isolation ball valve on each leg of the loop at the “split”, the location where the pipes separate into the loop.  A third isolation ball valve is placed on the far side of the loop, allowing the loop to be divided into sections.  (see the sketch of a looped mainline below)   Additional isolation valves may be added anywhere along the loop if desired, to divide it into more segments.  The isolation valves allow you to shut down sections of the mainline for repairs while the rest of it may still be operational.  For a large irrigation system being able to shut down only a portion of the system for repairs can be very advantageous.   Very large irrigation systems may have multiple loops, sometimes one loop will even be inside of another loop.

Plan View Sketch of a Looped Mainline
Plan View Sketch of a Looped Mainline

How to Design a Looped Mainline

When using a loop you should use the same size pipe for the entire looped portion of the mainline.  (This is not a hard and fast rule, just a strong suggestion unless you really understand hydraulics!)  The pipe leading from the water source to the loop may need to be a larger size than the loop pipe.  It is also OK to have mainline “spurs” off of the loop leading to other valves or faucets.  While unusual, the pipe size of the spurs may also be larger than the size of the loop pipe if they need to be.  Valves for sprinkler zones, faucets, quick coupler valves or any other equipment may be placed anywhere along the loop, as well as on the mainline leading to the loop or even on spurs off of the loop. Normally drinking fountains would be on a separate pipe and not connected to the irrigation system due to the possibility of water contamination from the sprinklers.  See the article on use of backflow preventers for more information on contamination.

Multiple Loops

You can have multiple loops, but I suggest that if you do, you size the pipe using the outside perimeter (largest) loop, as if there were not any cross pipes within the loop (using the method that follows below.)  Then after you have determined what size the outside loop pipes need to be,  use the same pipe size for any smaller loops or cross pipes inside the perimeter loop.  (Technical note: The pipe sizes of inside loops and cross pipes do not necessarily need to be the same size as the outside loop, it is just that using the same pipe size will almost always work.  Using a smaller size pipe may work, but it may not.  So it is  advisable for non-experts to stick with the same size!)

Loop Mainline Calculations

You must calculate both the friction loss AND the velocity for a looped mainline.  We’ll go through the process step-by-step.  You calculate the pressure loss for the non-looped mainline section from the water source to the beginning of the loop in the normal way (as described in the Irrigation Mainline Tutorial), using the pipe size, flow rate, and length of the pipe section.  I suggest that you use one of the  the Friction Loss Calculator Spreadsheets I’ve created, they are easier for non-mathematically oriented folks to use than the old manual calculations using charts.  Choose the proper spreadsheet for the type of pipe or tube.   Then enter the  size, the GPM, and the length of the loop.  Pressure loss for spurs off of the loop are also calculated using this same method.

Pressure Loss in the Loop:

To calculate pressure loss for the looped section we simply will assume that the water flow splits, and 1/2 of the water is going around 1/2 of the loop and the rest of the water is going the other way around.  To do this start by determining the “highest flow GPM” that is found on the looped section.  If you are planning to operate only one valve at a time that would be the flow for the largest zone valve to be installed on the loop section.  If you will be running more than one valve at a time then the “highest flow GPM” will be the combined flow rate for the largest group of valves that will operate at the same time. Once you have the “highest flow GPM” you calculate pressure loss in the pipe using the calculator.  But for the looped portion you will enter 1/2 of that “highest flow GPM” for the flow in the looped pipe and 1/2 of the total loop length (all the way around and back to the beginning) as the length of the pipe.  The calculator result is the pressure loss in PSI for the entire looped section.

Total Pressure Loss for the Mainline:

Just total up the pressure loss for the mainline leading to the loop, the pressure loss for the loop, and if you have any spurs add to your total the pressure loss for the single spur having the largest loss value.  The total of those is the pressure loss for your entire mainline network.

Velocity Problems:

As mentioned, this method of calculating pressure loss uses an averaging system that assumes that half the water goes one direction to the valve, and the other half goes the other direction.  While this is not a perfect method, it works good enough for figuring out the pressure loss.  However, the flow doesn’t really split evenly in both directions.  In reality the flow balances in each direction based on pressure loss, with most of the flow in the loop going the shortest distance to a valve.  So if one of the zone valves is just a few feet from the split point on the loop, almost all the flow will go through that short distance rather than going the long way around and back to the valve.  Also in the event you make a repair you may close those isolation valves mentioned earlier.  This will force all of the flow in a singe direction through one side of the loop.  So we come to the second rule of loops, the pipe size for the looped section must be large enough to handle ALL of the flow in one direction.  If it is not, you may create excessive velocity of flow in a section of pipe which can cause major, and very expensive, problems.  This means you must check the velocity of the flow while assuming all the flow may go in a single direction around the loop.  If the velocity is over 7 feet per second you may create excessive pipe wear and water hammer.  Pipe wear can seriously shorten the life of your system, water hammer is much worse, let’s just say you don’t want it.  (Look it up if you really are curious.)

Calculate the Velocity:

Using the Friction Loss Calculator Spreadsheets mentioned above enter the pipe size, the “highest flow GPM”, and any random value for the length of the loop.    Ignore the pressure loss it gives you, just check the ft/sec velocity result it gives you.  The velocity MUST be less than 7 ft/sec.  If it is not, you will need to use a larger size pipe for the loop.

That’s it!  You should now know how to create a looped mainline.  If it seems confusing try rereading it, it is admittedly a bit confusing after the first reading!  It really is simpler than it first sounds, be patient, grab some coffee, take your time.  Go back and actually work through it one sentence at a time, study the sample sketch of a looped mainline and try sketching your own on paper.    Practice a bit with the Pressure Loss Calculator to see what happens when you change the input values.  It should start to make more sense.