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PVC Pipe: SCH vs. Class

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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.


Pressure Loss in Sprinkler Risers

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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.

 

How to Remove a Valve Zone from Sprinkler system

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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 Find Your GPM & PSI – Municipal Water Source

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If your water comes to you from a water company, you’re on the right page.

However…
If your water supply is from a pump and/or well on your property, skip this page and go to How to Measure the GPM & PSI from a Pump or Well page.  If your water comes from a tank or other gravity fed system, skip this page and go to How to Measure the GPM & PSI from a Gravity Fed Water System.

Tip

If you have a printer, there is a  Sprinkler System Design Data Form that will make things easier for you.  There is also a PDF version of the Sprinkler System Design Data Form.

The path ahead viewed dimly through the fog??? What we’re about to embark on here is known as “doing it the right way”. We are going to start by figuring out what the maximum water supply would be if you had perfect conditions, such as a very short pipe from the water meter to your house, lots of water pressure, a small yard, a happy family, a low interest rate mortgage, and good neighbors! Then we are going to modify that number later in the tutorial to reflect your actual conditions (long pipe, lousy water pressure, bad neighbors, whatever.)

The end result is that we will determine what the exact, optimum water supply is for designing your sprinkler system. What that means for you is that your sprinkler system will use less water, last longer, and there won’t be dry spots! Now it’s going to be a little more work than “guesstimating” would be, but it will be worth it. Don’t get discouraged, be patient, and it will all come together. The worst thing you could do right now is to try deciding what sprinkler you want to use. That would be “putting the cart before the horse”. Trust me, I know what I’m doing. Now let’s get on with it…


A. Find your water supply pipe.

Hopefully you already know where the water service pipe comes onto your property, or at least where it enters your house.

Mild Winter Climates:  In milder climate areas there is typically a shut-off valve and or a water meter at the location where the pipe enters the property. From there the pipe generally goes to the house, then surfaces above ground where a house shut-off valve is located, then the pipe turns and runs into the side of the house. Often this location where the pipe enters the house is where the tap for the irrigation system will be made.

Water meter near curb.
Water meter near curb.

Note the “W” etched in the curb in front of the concrete water meter box in the photo above. Often there will be some type of mark on a curb at the location that the water supply pipe to the house runs under it.

Pressure regulator at house entry point.
Pressure regulator at house entry point.

The photo above is of a typical mild-climate water supply line where it enters the house.  This one has a rather unusual model of pressure regulator (the gizmo with the white adjustment knob on top) to reduce the water pressure.  Many houses do not have a pressure regulator.  A ball valve (with a blue handle, the handle is in the “off” position) is on the incoming water supply pipe. The pipe going into the wall is the house supply. The pipe exiting the photo at the lower left goes to a hose bib.

Cold Winter Climates:  In colder climates the water line often enters directly into the basement or crawl space under the house from underground.  This water pipe to the house is often buried very deep to keep it below the frost line. The shut-off valve, and possibly a water meter, are often located in the basement or crawl space to help protect them from freezing.

Water meter in basement.
A pressure regulator & water meter in a basement.

The photo above shows a typical water supply line in a cold-winter climate.  A copper water pipe enters through floor, goes up into a ball valve (yellow handle), then through a pressure regulator, then a remote-reading water meter. You would tap in for the sprinklers after the water meter. The mainline supply size would be measured on the copper pipe coming out of the floor. The water pressure in this case could be measured at any water faucet after the regulator (probably any faucet in the whole house would work). Photo credit and thanks to Ed Pletsch.

What type of pipe is it?

Once you find your supply pipe you need to know what type of pipe or tubing it is.  Keep in mind that there may be more than one type of pipe or tubing used at different locations!  Often copper is used under concrete slabs and then it converts to PEX for other locations.

Steel Pipe. Steel pipe comes in two types, black steel (used mostly for gas lines) and galvanized steel (galv. steel) which is used for water pipes. Galvanized steel pipe will be a silver gray color, and a magnet will stick to it. It will have threaded joints. Steel pipe is made in conformance with IPS (iron pipe size) standards.  Galvanized pipe is often found on homes in inland areas, especially on less expensive tract homes.

Brass Pipe. Brass pipe is sometimes used for homes. Like copper it can take on a greenish tint with age. A magnet will not stick to it. It will have threaded joints. Brass pipe is made in made in conformance with IPS (iron pipe size) standards.  Brass is not very common except for short sections of pipe, due to cost.

PVC Pipe. PVC plastic pipe is almost always white or gray, and is more rigid than the other commonly used types of plastic water pipe. Standard PVC pipe is made in conformance with IPS (iron pipe size) standards. It should have the letters “PVC” printed on the pipe. PVC is fairly rigid, and it is not easily scratched with your fingernail. PVC tends to be more commonly used in mild climate areas. Another type of PVC called CPVC is sometimes used inside homes and often is found in older mobile homes. It is similar to regular PVC, but will be labeled “CPVC”. Most often it is a yellowish, gold, or tan color. CPVC in homes is usually made to copper tube sizes (look for “SDR-11” printed on the pipe), but is also sometimes iron pipe size (labeled IPS).  PVC is often used for house supply pipes in mild winter areas.

Copper Tube. Copper tube is very common in homes. It takes on a dirty green color as it ages. A magnet will not stick to it. Most joints will be soldered, look for silver color solder at the joints to identify it. Copper tube has a different diameter than iron pipes, and is made in sizes known as CTS (copper tube size).  Copper has been the standard “high quality” tube used on better homes for decades.  Often used in areas near the coast where salt air causes rapid corrosion of steel.

PEX and PE Tube. Both are both polyethylene (poly) products. Both tend to be used in areas with severe winters and/or rocky soil. There is a lot of confusion over these two poly-based products. Be careful, both are sometimes called “poly”, especially by the sales people in the big home improvement stores. True PEX is a stronger form of cross-linked polyethylene that has become popular in recent years. Both PEX and PE are flexible, and both have a glossy appearance and slick surface. So how do you tell which one you have? Older PE is almost always black, and in most cases PEX is not black. PE is almost never used inside a house if the house was built to code. The surest thing to look for are the letters “PEX” printed on the tubing. Making things even worse, white PEX looks a lot like PVC, especially if it is old or dirty! PEX is easily scratched with a fingernail, PVC scratches, but not easily. PEX was not invented until the ’70s, and it is seldom found in homes built before 1975. (It wasn’t officially sold in the USA until 1985. Of course, if your house has been remodeled, you could still have it in a older house.) PEX is almost always made to conform with CTS sizes. The heavy duty PE tube used for plumbing is most often made to a uniform size standard (labeled “SDR-7”), but many different PE products used for irrigation do not conform with this size standard. Be careful when working with PE tube, if possible take a sample with you when you go shopping for parts so you can test fit them at the store.  PEX is quickly becoming the default tube for piping new homes due to low cost and ease of installation.

Warning: PEX pipe has a very thick wall, thus it has a smaller inside area for the water to flow through. This means it has much higher pressure losses when the water passes through it. For this reason you need to be careful when replacing a copper or PE tube with a PEX tube. Often when replacing a copper or PE tube with a PEX tube it is necessary to use PEX that is one size larger than the tube it is replacing. So if you are replacing a 3/4″ copper tube with PEX, you should consider using 1″ size PEX tube for the replacement. Otherwise you may notice a drop in water pressure after the replacement is made.

TipOne good hint to the type of pipe is the way the pipes are connected to each other. PEX and PE are never glued at the joints. Sometimes PEX & PE are heat welded together, but most of the time they are connected together with fittings using clamps, teeth, or compression-nuts that hold the tube onto or into the fitting. (“Fittings” is the term we use for the various connectors that are used to join two or more pipes together.) If the pipe has glued joints it is almost always going to be PVC or ABS. (ABS plastic is typically black rigid pipe, almost always 3″ or larger in diameter, and is mostly used for sewer and drainage pipes.  ABS can be other colors so don’t assume a pipe is PVC just because it is white or gray!) Another hint is that poly pipe tends to be used in colder climates, and PVC tends to be used in warmer climates. If you have to regularly shovel snow from the driveway, chances are the pipe is PE or PEX. Copper pipe is often soldered to the fittings. Look for the silver color solder at joints. Steel and brass pipe have threaded connections, a few threads almost always are visible at the joints. Confused yet? Your best bet is to find lettering on the pipe that says what type it is.


B. Find your Water Meter:

Now we need to know if you have a water meter. Most, but not all, water companies use a water meter to measure the amount of water you use. If you don’t have a meter, there will almost always be a shut-off valve at the point your house water line connects to the water provider’s pipes.  Often the valves are buried, sometimes several feet down, and a sleeve comes up to the surface with a small lid or box over it. The water company uses a special tool that can reach down and open or close the valve. Often grass has completely grown over the lid and you can’t find it. Try probing the ground with a pitchfork, metal rake, or screwdriver to find the hard cover of the box.

The water meters are normally installed in an underground box as close as possible to the property line. This is usually at the street or alley. Most of the time the box will have “water meter” or the water company name stamped on the lid. In areas with severely cold winters the water meter is often installed in the house basement or a utility room of the house. If you still can’t find it, call your water company and request their assistance.

Try to find a size stamped on the meter. If you can’t find a size, ask your water company or just assume the meter is the next size SMALLER than the pipe running to the house. It is common for the meter to be one size smaller than the pipe. Standard water meter sizes are: 5/8″, 3/4″, 1″, 1 1/2″.

Spiders and snakes: If the meter is in a box, watch out for spiders and ants in the meter box! Most of the “pro” irrigation repair guys I know carry a can of spider spray with them! Sometimes we find snakes, rats, gophers, and other beasts in the boxes too! I found a turtle shell in a box once.  No tunnels or holes into the box that I could find.  I have no idea how it got in there.

pencilEnter the meter size on your Design Data Form.  If you don’t have a meter, enter 0 (zero).


C. Measure Your Water Pressure

Water pressure is the energy that powers your sprinkler system, so it is very important. If you work with it, it will make your sprinklers do the “rain dance”. If you ignore it, it can bite you hard in the wallet! For this tutorial I use the pressure units “PSI” which means “pounds per square inch”. When pros talk about pressure readings we almost never say the words “pounds per square inch”, we just say the letter names “P. S. I”. Outside of the United States pressure is most often measured in “bars”.

First off, grab the phone and call up your water supplier. Ask them for the “static water pressure” for your neighborhood. Don’t be shy, people call them all the time to ask! They may give you a pressure range, like 40-60 PSI. If so, write down the LOW number of this range. You can also measure your own water pressure using a pressure gauge that attaches to a hose bib on your house (you can purchase a 0-120 PSI gauge with a hose adapter on it at pretty much any hardware store).

Pressure regulators (also called pressure reducing valves)

Pressure regulators are devices used to reduce the water pressure and are commonly found on home water supplies in towns with hills. It takes lots of water pressure to lift water uphill. So in order to get the water to the houses on top of the hill the water pressure in the water system has to be very high. But this causes the pressure at the homes at the bottom of the hill to be too high.  So pressure regulators are installed on the water supply pipes to homes in the lower areas of town, where the pressures are very high. The pressure regulators are generally set to someplace between 50 and 65 PSI.

If the water company tells you your neighborhood pressure is over 65 PSI, you probably have a pressure regulator installed someplace on the water supply line to the house. The pressure regulator reduces the water pressure in your house, so that it doesn’t damage your plumbing fixtures. Look around and see if you can find it (see the pressure regulators in the pictures above). The regulator may be installed near the water meter or at the point where the water supply pipe enters the house. This is important, because if you have a regulator and you tap into the water supply for your sprinklers after the regulator, the pressure will be a lot lower.

If you have a pressure regulator on your house you must use a gauge to test the water pressure yourself. Most pressure regulators are adjustable, so the water company has no idea what pressure the regulator is set at.  When in doubt, test the water pressure with a gauge.

At this point you should make at least a preliminary decision as to where you want to tap into the house water supply pipe for the irrigation system water. Typically, the closer you can tap to the point the water enters your property, the better. Of course, you must tap into the pipe after the water meter. In areas where it gets very cold some people like to tap into a pipe in the basement or someplace else inside a heated building. That way they don’t have to worry about the shut-off valve for the irrigation freezing. (Be sure to install a drain valve after the shut-off valve to drain the water out of the irrigation pipe during freezing weather!) If you have a pressure regulator, consider if it would be better to tap before or after it.

A static water pressure higher than 70 PSI can damage the fixtures and appliances in a household.  If you measure a static water pressure higher than 70 PSI when you do your water pressure check as described below, then you should consider installing a pressure regulator on your house water supply if there is not one already. It will help your faucets, pipes, washing machine, dish washer, etc. to all last a lot longer.  Make sure it is a good quality brass-body pressure regulator.

TipFor a pressure regulator to work accurately the pressure setting on it must be at least 15 PSI lower than the inlet pressure. So if your static pressure is 70 PSI, the highest pressure you should set on the pressure regulator would be 55 PSI. 55 PSI is a good pressure for both the needs of a house and a sprinkler system.

Hose Bibs as a Water Supply Source = BAD!

Using a hose bib or even a “sprinkler system stub-out pipe” provided on the side of the house for sprinklers is not a good idea. There are often unknown restrictions in the house piping that cause the water supply from these hose bibs to be severely limited. The water running through the house pipes can also be very noisy at night and disturbs some people’s sleep. Do this only as a last resort, when there is no other reasonable way to get water for your sprinkler system.  I would suggest you assume the pipe is 1/2″ size, even if it appears larger.   If you have concrete that prevents running a new pipe around the house, call a boring contractor and find out how much it would cost to bore a 1″ pipe under the concrete.  It may be worth the price.  Directional boring technology now allows them to bore and install curved pipes around obstacles.

 

How to Measure the Water Pressure with a Gauge

caution

Important: If you want to test the pressure yourself, everything that uses water in your home: faucets, ice makers, toilets, etc., MUST be turned off when you take the measurement (that’s why its called “static” water pressure, the water isn’t moving.) Everything! This is critical or you will get a false low reading! You can test the pressure at any faucet that is at about the same height as the proposed irrigation tap. If all the water is turned off, the pressure will be exactly the same regardless of where you test it. (Try it and see!)  The easiest place to test the pressure is usually a hose bib or garden valve on the outside wall of the house.

To test the water pressure using a gauge, attach the gauge to a water outlet, like a hose bib or washing machine connection. The place where you attach the gauge can be anywhere in the house, as long as it is about the same height (elevation) as the place where you will tap in the sprinkler system supply. Ie; don’t check it on the 3rd floor if you plan to attach the sprinklers at the first floor! (It is one of those weird, hard to understand hydraulic laws that as long as the water is not flowing the pressure is the same at any point on a pipe that has the same elevation above sea level.) Double check that all the water so water is turned off and not flowing in the house pipes. Then turn on the valve the gauge is connected to and allow the water to enter the gauge. Read the pressure on the gauge. That’s all there is to it, it’s very easy to do! Turn off the water and disconnect the gauge, you’re done!

OK, I realize I may have confused you, because earlier I told you not to use a hose bib to tap the sprinklers into, and now I just told you that you can use a hose bib to measure the static pressure.  This is because you can get an accurate pressure measurement from a hose bib– if the water is not flowing, as described.  The small pipe can’t restrict the flow if the water isn’t flowing!  Confused?  Hydraulics is hard to understand.  I may sound crazy but I know what I’m doing!  Often users of the tutorial have an “ah ha!” moment when they get about 95% done with their first design and suddenly it all makes sense.

pencil

The static water pressure that you were given (or you measured with a gauge) is your Design Pressure. Write down the “Design Pressure” on your Design Data Form!


D. Measure the Maximum Available Flow (GPM)

Flow is the traveling companion of water pressure. Pressure is the “energy” that moves the water through the pipes. Flow is the measure of how much water is moved in a given amount of time. Flow is measured in this tutorial using Gallons per Minute (GPM). Other common units used to measure flow include cubic feet per second (commonly used to measure river flows here in the USA), liters per minute, cubic meters per hour, and many others. Now that you know your Design Pressure you need to determine how much water you can use at a time, or your available flow.

Measure Your Supply Pipe Size

You need to find the water supply pipe and measure it’s size. Grab a piece of string about 6″(152mm) long, then find the location where your water supply pipe enters the house. Strip away any insulation, so you can get at the pipe and wrap the string around it. Measure how many inches of string it takes to go around the pipe once.

The string length is the circumference of the pipe (yikes, bad memories of high school geometry!). Using the circumference we can calculate the diameter of the pipe, which allows us to look up the pipe size, from which we can calculate the flow of water using the formula… zzzzzzzzzz….. Let’s forget all those calculations! Based on the string length use the table below to find your pipe size.

For Copper Pipe & PEX Tube

2.75″ (70mm) = 3/4″ pipe

3.53″ (90mm) = 1″ pipe

4.32″ (110mm) = 1¼” pipe

5.10″ (130mm) = 1½” pipe

For Steel, Brass or PVC Plastic Pipe

3.25″ (83mm) = 3/4″ pipe

4.00″(102mm) = 1″ pipe

5.00″(127mm) = 1¼” pipe

6.00″(152mm) = 1½” pipe

For most PE Tube

2.96-3.33″ (75-85mm) = 3/4″ pipe

3.74-4.24″ (95-108mm) = 1″ pipe

4.90-5.57″ (124-141mm) = 1¼” pipe

5.70-6.28″ (145-160mm) = 1½” pipe

Your string length will vary a little, depending on such unavoidable variables as string stretch, dirt on pipe, manufacturing tolerance, what kind of mood you’re in, etc.

pencil

Enter the supply pipe size on your Design Data Form! Also make a note of the type– copper, brass, steel, PVC, PEX, or PE.


 

Find Your Maximum Available GPM:

Your maximum available GPM is the maximum flow of water you have available for your sprinkler system. Actually, it would be more accurate to call this the Maximum Safe GPM. In most cases it is possible to push a higher flow (GPM) through the pipe. However, at high flows the water actually damages the inside of the pipe.

Use the smallest pipe to determine the Maximum Available Flow. Often the water supply coming into your property will not be a single type and size of pipe. You may have a plastic pipe running underground from the water company to your house. When the pipe enters the house it might switch from plastic to copper pipe, or possibly it might be galvanized steel. Then as the water supply pipe runs through the house it likely branches off in several directions with the pipe becoming smaller and smaller in size as it goes. When determining your Maximum Available GPM you will need to check the Maximum Available Flow for each of the types of pipe that the water will pass through, then use the lowest value as the Maximum Available GPM for your sprinkler design. You only need to be concerned about the pipes the water will pass through before it reaches the point where you are going to tap into it for the irrigation system.

There is an exception to the statement above. Often a short section of a smaller pipe size will be present on the water supply for one reason or another. Maybe the plumber didn’t want to drill a larger hole in the wall for the pipe. As long as this smaller pipe section is less than 5 feet long, you can ignore it and use the larger pipe size to determine maximum flow. The higher flow will be able to squeeze through the smaller pipe. The smaller pipe may wear out faster over time, but typically these short pipes are in places where they are easy to replace. Plus, the smaller pipe is often brass or steel, which has a higher resistance to wear than copper or plastic. You have to make a judgement call on this. In most cases I choose to ignore the small section of pipe.

Small Valves. It is not uncommon to find that a shut-off valve installed on the water supply pipe is a smaller size than the pipe. Don’t worry about it. It will not impact the available flow and valves are constructed to handle higher flows than the pipe.

Example 1: You find the water supply pipe entering the house, examine and measure it, and find that it is 1″ copper pipe. But you’re an ambitious type, so you also have done some digging around in the yard and discovered that the pipe going to the house through the yard is 1 1/4″ PE plastic. It just changes to copper about 6 feet away from the house (this is actually a fairly common situation.) After the copper pipe enters the house it quickly branches off in multiple directions and becomes smaller, but this doesn’t matter to you, because you have already decided that you are going to tap your irrigation system into the 1″ copper pipe right where it enters the house. So the irrigation water will not pass through any of those smaller pipes inside the house and you can ignore them.

Looking at the table you find that 1 1/4″ PE gives a flow of 23 GPM. But looking at 1″ copper pipe in the table shows a flow of only 18 GPM. Since the copper pipe is over 5 feet long you can’t just ignore it. This means you must use the lower 18 GPM value. But wait a minute! What if instead of tapping into the copper pipe, you decide to tap into the PE pipe out in the yard before it switches to copper? Now you can use the higher 23 GPM value because the water will no longer go through the 1″ copper pipe!

Example 2: You found you have a 3/4″ copper pipe that comes into the basement but you have no idea where or what type of pipe is used in the yard. It’s 0 degrees outside, and you couldn’t get a shovel into the frozen ground even if you wanted to, which you don’t! In this case it’s reasonably safe to assume the pipe in the yard is 3/4″ copper also. So you would use 11 GPM from the table.

Example 3: You have no idea where the water pipe enters the house, you have no idea where it is in the yard, and you have no desire to try to find out. In this case you must face reality, it’s time to hire a sprinkler contractor!

Maximum Available GPM Table (Maximum Safe GPM)

Maximum Available GPM (Maximum Safe GPM)
Pipe Size Steel Pipe Copper Pipe PVC Pipe PE (poly) Tube PEX (CTS) Tube
1/2″ 6 GPM(7 ft/sec) 6 GPM(7 ft/sec) 6 GPM(7 ft/sec) 6 GPM(7 ft/sec) 3 GPM(7 ft/sec*)
3/4″ 11 GPM(7 ft/sec) 11 GPM(7 ft/sec) 11 GPM(7 ft/sec) 11 GPM(7 ft/sec) 7 GPM(7 ft/sec*)
1″ 18 GPM(7 ft/sec) 18 GPM(7 ft/sec) 18 GPM(7 ft/sec) 18 GPM(7 ft/sec) 12 GPM(7 ft/sec*)
1 1/4″ 23 GPM(5 ft/sec) 23 GPM(5 ft/sec) 23 GPM(5 ft/sec) 23 GPM(5 ft/sec)
1 1/2″ 32 GPM(5 ft/sec) 32 GPM(5 ft/sec) 32 GPM(5 ft/sec) 32 GPM(5 ft/sec)
2″ 52 GPM(5 ft/sec) 52 GPM(5 ft/sec) 52 GPM(5 ft/sec) 52 GPM(5 ft/sec)
Important Notes:
  • CTS = Copper tubing size.
  • Caution: The values in the table above are the maximum safe flows for the given size and type of pipe.
  • These values are NOT the amount of flow you actually will use for your sprinkler system! Step #2 will show you how to modify these values to reflect your actual flow.
  • Velocities (ft/sec) are shown for reference only.
  • * PEX tube has an extremely small inside diameter when compared with the other pipe/tube types, this limits flow.  Some manufacturers suggest that PEX will not be damaged by higher flows, up to 10 ft/sec.  I don’t feel there is sufficient evidence yet to warrant damaging your plumbing by using flows that are too high, so I am sticking with the old industry standard for plastic pipe of 7 ft/sec maximum velocity.  If you wish to take the chance, values at 10 ft/sec are
    1/2″=6 GPM, 3/4″=11 GPM and 1″=18 GPM.  Use these higher values at your own risk.  They could cause serious damage to your both your house plumbing & irrigation piping.  Read More on Water Hammer.

Flow Test

A flow test is optional, but suggested if you are not positive about the size or type of water supply pipe. The flow test should be run at a faucet as close as possible to the point you will tap into the water pipe for your irrigation system.

Get a 5-gallon bucket. Old paint buckets work great. Since most 5-gallon buckets actually hold more than 5 gallons of water, you will need to calibrate the bucket as follows: Find an accurate measuring container, and measure out 5 gallons of water into your bucket. Then mark the water level on the side of the bucket with a marking pen so you can easily see it. ?The test is simple. Put the bucket under your water outlet pipe and time how long it takes to fill the bucket to 5 gallons.  The formula for calculating the flow in GPM is: 300 divided by the seconds it takes to fill a 5 gallon bucket = GPM.

If the result of the bucket test is lower than the Maximum Available GPM from the table above, something is restricting the flow. It may be the faucet you are using for the test, or there may be a restriction someplace in the house water supply pipe. You can try to find the restriction and get rid of it, or you can simply use the lower flow test GPM for your Initial Design Flow below.

caution

If the result of the bucket test is higher than the Maximum Available GPM you determined in the table above, use the lower value from the table. The Maximum Available GPM Table gives you the maximum SAFE flow. The bucket test is only used to determine if there is an unseen restriction in the water supply pipe that reduces the flow below the level given in the table. Yes, many sprinkler tutorials and sprinkler salespersons may tell you a bucket test should be used for the design flow, they are wrong! In most cases a bucket test like this one gives you an unsafe flow. See the answers to common questions at the bottom of this page for details on why this happens.

pencil

Enter your Maximum Available GPM on your Design Data Form.


E. Initial Design Flow

Your Design Flow is the maximum amount of water you will design your sprinkler system to use. For now, use the same number as the Maximum Available GPM, or use the actual Flow Test GPM, whichever is lower.

You will probably need to reduce your Design Flow later, so additional lines are provided for Adjusted Design Flows on the Design Data Form. The initial flows here are very optimistic, 20 to 30% too high for most situations. You will make the adjustment, if needed, later in step #2. Don’t worry about it now. This is just an advanced warning so you won’t be surprised when you need to change the flow later.

pencil

Enter your Design Flow on your Design Data Form. Use a pencil so you can change it later!!!!


F. 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). So 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, so 20 GPM would water 2 acres of shrubs.

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 be willing to water as many as 10 hours per day. If you are willing to water more hours per day you can increase the area irrigated by a similar percentage.

If you don’t have enough water I can suggest a few ideas for you to look into.

  1. You can consider pushing the limits and using a higher Minimum available GPM than I recommend in the table above. If you want to try using a higher flow than recommended above, then go to http://irrigationtutorials.com/faq/increase-irrigation-gpm.htm for full instructions on how to proceed.
  2. Another option is to use drip irrigation for shrub areas. 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.
  3. Consider reducing the amount of lawn and replacing it with shrubs. Shrubs use about half the amount of water as lawn.
  4. Another option for getting a higher flow is to install a larger water supply pipe. A description of how to do that is at the bottom of this page.

If you’re happy with your Maximum Available GPM value, you can skip down to the end of this page.


Answers to common questions:

why

Why is the flow you measured with a bucket often too high? The GPM rates in the Maximum Available GPM Table above are based on a SAFE water velocity. When you do the bucket test, there are few restrictions on the flow, so the water velocity may easily exceed that safe limit. If you design your sprinkler system to exceed these flows some really bad things can happen. The first of these is called “water hammer”. Water hammer is a pressure surge which declares its presence by destroying the weakest point in your plumbing. The weakest point is usually that little water tube that runs between the shut off valve and the toilet in your bathroom, or possibly the ones that go to the sink faucets. The result is a flooded house, and that’s something you don’t need. Water hammer is exponentially related to water pressure. The higher the water pressure, the greater the water hammer danger. If your water pressure is over 80 PSI, I suggest that you reduce your maximum flow found in the table above by 20% and read carefully the High Pressure Alert below! The other bad thing that happens at high flows is called “scrubbing”. Scrubbing is what happens when the high water velocity actually scrubs molecules loose from the inside of the pipe. Eventually it wears away enough that the pipe develops a leak. The higher the velocity, the more scrubbing you get. A little scrubbing may take 20-30 years to create a leak.  With a higher velocity the problem becomes much worse.  I have seen 7 year old homes need a total replacement of all the copper pipes due to scrubbing damage. This is extremely expensive to repair! In my 30-year-old neighborhood, most of the homes have now had to replace the water supply pipes to the house due to scrubbing damage caused by sprinkler systems installed back in the bad old days before any of us realized the dangers of high flows. There are still a lot of old tutorials and literature being published that were written before the dangers of high flows were discovered, so be careful when comparing advice on this topic. A lot of industry professionals still haven’t gotten the word on this either!

But, but, but… you didn’t hear any water hammer when you did the bucket test, and nothing broke, so what’s the deal? After all, that higher flow could save some serious money on sprinkler parts! The deal is that you are only human. You can’t close the valve fast enough by hand to create water hammer, but don’t worry, an automatic sprinkler valve can! It can snap that valve closed almost instantly. The higher the water pressure, the faster the valve closes. When that valve snaps closed, it sends a shock wave through the pipe (water hammer). It may take weeks or even years for it to wear down the weak point in your plumbing and break, but it will! Then the cost savings on sprinkler parts will seem trivial. Do it right the first time! Water hammer and scrubbing are insidious and relentless. They just keep working away, little by little, day after day. Clunk, clunk, clunk, chew, chew… until the day you come home to a flooded house.

why

Clunk, clunk, clunk? Pipe noise!!! I hear those loud noises every time the washing machine or dishwasher runs! Is that water hammer??? You bet it is, and you better do something about it!  First, if the water pressure in your house is over 65 PSI, install a pressure regulator to lower the pressure. If that doesn’t get rid of it, go down to your local hardware store and buy a water hammer arrestor. You can get one that screws onto the washing machine or dishwasher fill pipe. They cost about $10-15 and they work pretty well for water hammer caused by appliances. They don’t work nearly as well for water hammer caused by sprinkler systems. This is because many sprinkler systems exceed the maximum water velocities by so much that the arrestor is over-whelmed by it. I’ve written a whole tutorial on this topic: Water Hammer and Air in Pipes.


This article is part of the Sprinkler Design Tutorial Series
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Sprinkler Head Risers

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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.)

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

One of the most common sprinkler risers used for residential systems is a simple short section of pipe called a “nipple”.  Nipple is the standard plumbing term used for any short section of pipe 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 or rigid pvc plastic the nipple won’t easily break.  Now this may seem like a good thing, as we don’t generally want things to break. But think for a moment, which would you prefer to break?  An expensive sprinkler head, a hard to repair underground lateral pipe… or a cheap, easy to replace riser?  A nipple is also non-adjustable.  The sprinkler head can’t be moved from side-to-side or tilted if it is installed on a simple nipple.

If you want to go the really cheap route and use a nipple for the riser I suggest that you use a polyethylene (“poly”) nipple.  Most people opt for a clever molded poly nipple called a “poly cut-off riser“.  A poly cut-off riser is a short pipe section (typically 6” long) with multiple sets of threads on it (see photo below.) You simply cut it off to the desired length with a knife or a pipe cutter.

Why use polyethylene?  Because the poly material is very soft, the nipple will bend under stress and spring back to the original location when the stress is removed.  It also will break under less stress than a PVC or metal nipple, so it is likely to break before either the sprinkler or the lateral pipe breaks. When cutting the poly cut-off riser to the desired length 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 are very inexpensive.  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.

Poly Cut-Off Riser
Poly Cut-Off Riser. The arrows show where to cut the riser to shorten it.

While a simple poly nipple will work for a riser on an economically challenged install, there are better ways.  So let’s move along and look at the better options.

 


Swing Joint Risers

A much better solution for risers is to use something designed to allow the sprinkler to move slightly. The riser most professionals use is referred to as a “swing joint” or “swing riser”.  (Swing joint is an older name used, swing riser seems to be replacing it.) 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! By the way, 4 to 6 inches is the normal distance a sprinkler should be from a sidewalk. (Before you ask, no, a 6 inch distance does not cause a dry spot along the edge of the sidewalk.)

Flexible Arm Swing Risers:

Don’t use these flexible arm swing risers with sprinklers that have a 3/4″ or larger inlet.  See the rigid riser below for 3/4″ and larger inlet size sprinklers.

Flexible Swing Joint Sprinkler Riser
Sketch of a Flexible Swing Joint Sprinkler Riser

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 ®” which is 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 it yourself.

While you can still buy the parts to assemble the riser yourself, most of these are now cheaper to buy as preassembled units.  The preassembled swing risers often have 3 or even 4 ells which makes them much easier to install.  4 ells makes them a lot easier to install and position.  If the swing joint you purchase has only 3 ells you can duplicate this 4 ell feature by adding street ells to the 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! The threads on high density polyethylene do not seize up like PVC does, which allows the threaded joint to stay flexible.

If you are building your own flexible swing joint risers 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 riser do not bend the flexible pipe to help position the sprinkler. Poly pipe has what we call “memory” in the pipe industry- it tries to return to its original shape in a few hours. When it does, it will pull your sprinkler along with it and the end result will be a sprinkler that leans at a weird angle. I have even seen the pipe pull the sprinklers underground! 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! 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 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 insert 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. 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.

OK, I confess it is often not as easy to get the insert ell in as it is to install a light bulb. So if it’s cold, the flexible pipe is stiff, and the insert ell just doesn’t want to go in, here’s a trick– use KY Jelly on the insert ell barbs. Don’t use any other type of oil or soap, they can damage the plastic. Thanks to marketing, most people seem to know what KY  is, unlike back when this tip was passed along to me.  KY Jelly is a water-based lubricant. Don’t head for the hardware store like I did. (Now that was an embarrassing incident!  Fortunately the clerk at the hardware store didn’t know what it was either, or if he did, he wasn’t letting on.) Buy it at the drugstore or supermarket, you’ll find it on Women’s hygiene aisle or near near the condoms.  ‘Nuff said guys?

 

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

 

The photo above is a preassembled flexible pipe swing riser attached to a PVC fitting and a pop-up sprinkler.  The riser in this photo is made by Hunter and features 4 ells for ease of installation and added flexibility.

 


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.  Rigid risers are what I use on all my higher-end systems, as well as parks and golf courses.

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. Before you ask, no, a 6 inch distance does not cause a dry spot along the edge of the 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 Funny Pipe ® risers mentioned earlier are not Marlex! If you can’t scratch it with your fingernail, it is not Marlex.

Marlex St Ell
High-Density Poly Street Ell (“St Ell”)

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.

swing riser or swing joint
Sketch of a Rigid Arm Swing Riser

 


Flexible Risers

What if you really need to bend the riser pipe? 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. I find it is especially useful for broken sprinkler replacements as it can be contorted to fit into a tight hole.  It looks like a flexible electrical conduit. (In fact that’s exactly what it is, a flexible electrical cable protector with a length of vinyl tubing inside it!) Don’t use it for anything other than small 1/2″ inlet spray heads. It can’t withstand high pressures and the flow through it is very limited. I usually put a threaded high-density poly street ell on one or both ends which makes it much easier to install.

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

This article is part of the Sprinkler Irrigation Installation Tutorial Series
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Drip Irrigation Design Guidelines – Basics of Measurements, Parts, and more

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Index to the Guidelines:

If you wish to print out the entire Drip Guidelines Package for reading off-line, print this page and each of the ones listed in the links above.

Background:

Drip irrigation is the most efficient method of irrigating. While sprinkler systems are around 75-85% efficient, drip systems typically are 90% or higher. What that means is much less wasted water! For this reason drip is the preferred method of irrigation in the desert regions of the United States. But drip irrigation has other benefits which make it useful almost anywhere. It is easy to install, easy to design, can be very inexpensive, and can reduce disease problems associated with high levels of moisture on some plants. If you want to grow a rain forest however, drip irrigation will work but might not be the best choice!

Drip irrigation (sometimes called trickle irrigation) works by applying water slowly, directly to the soil, bloop, bleep, bloop, bleep. The high efficiency of drip irrigation results from two primary factors. The first is that the water soaks into the soil before it can evaporate or run off. The second is that the water is only applied where it is needed, (at the plant’s roots) rather than sprayed everywhere. While drip systems are simple and pretty forgiving of errors in design and installation, there are some guidelines that if followed, will make for a much better drip system. The purpose of this tutorial is to guide you toward materials and methods that will increase the benefits of your new drip system, while steering you away from some common misconceptions and practices that can cause you trouble.

“What’s with the Metric measurements? !!” Come on, quit whining, the rest of the world uses metric without problems!!! OK, don’t flame me, I give up, I’ll compromise… While a lot of drip irrigation research has occurred in the USA, most of the credit for making drip irrigation what it is today really should go to Israel and South Africa. So I’m going to honor that contribution by using the metric system as the primary measurement units for these guidelines. After all, metric is really the “native” measurements of drip irrigation. When I started using drip irrigation (back in the dark ages of irrigation) all drip data and products were in metric! But because I’m such a nice guy (inflated ego alert!! Dump some ice water on this guy!), I will provide English measurements also. So don’t panic.

This tutorial is setup in a multilevel format. Each of the guidelines below describes a basic rule for drip irrigation design, the guidelines follow in the logical order for creating a design. You can think of the guidelines as design steps if it helps. This page is the top level, here you will find a brief description of each design guideline. For many of the guideline topics there is a link to another page with expanded information on the guideline topic. There may be additional links from there to allow you to dig even deeper into the drip irrigation knowledge base. So you choose how much you want (or need) to learn. My recommendation is that if you want to print out something, print this page. Then refer to the other levels (and print them if necessary) as needed. That will save you a lot of unnecessary wear and tear on your printer. It might also save a tree from going to the paper mill!

Parts of a Drip system:

If you don’t know a lateral from a pressure regulator start by learning about the basic parts of a typical drip irrigation system. I strongly suggest that even if you are familiar with drip irrigation you start be reading through The Basic Parts of a Drip System page now. It contains a lot of tips and recommendations.

A simple drip system.
Illustration of a very simple drip system.
Complex home drip system
A more complex home drip system.
Suggestion: Click on the image above for a pdf version of the drawing that prints better.

Prescriptive Drip Design Guidelines:

These guidelines will provide you with all the information necessary to design a residential drip system for a typical yard. These guidelines are what is termed a “prescriptive standard” in the building industry. A prescriptive standard is a set of rules and/or methods that, when followed, allow you to skip the engineering calculations for a design. Obviously this saves a lot of time and effort in preparing a design. The downside to a prescriptive standard design is that it tends to “over-design” in order to make the design “one size fits all”. Unlike sprinkler irrigation, drip irrigation systems are much more forgiving of design error, the cost of over sizing the materials is minimal, and so a prescriptive design method works very well for almost everyone. To prepare a fully engineered drip irrigation design requires a massive number of difficult mathematical calculations. If there was ever a great place to use prescriptive standards for the design, it is drip irrigation!

Emitter Type and Flow:

Use pressure compensating emitters if you have an elevation difference of over 1,5 meters (5 feet) in the area you are irrigating. For more level areas turbulent flow emitters will work great and are often less expensive. For gravity flow systems use short-path emitters, they typically work better than the others at very low water pressures.

For most soil types 2,0 l/hr (0.6 gph) emitters work well and are more economical. For sandy soil use 4,0 l/hr (1 gph) emitters.

For more information see Drip Irrigation Emitters.

How Many Emitters are Needed?

1 or 2 emitters per plant, depending on the size of the plant. Trees and large shrubs may need more. Obviously, using two allows for a backup if one clogs up (which happens now and then, even on the best designed and maintained drip systems.) But just as important, more emitters also wet more soil area. This results in more roots, and a healthier, happier plant. Exception: if the plants are very close together you may need to use less than 2 per plant in order to maintain the minimum spacing between emitters. Minimum spacing for emitters: In most situations install emitters at least 450mm (18″) apart. A good default spacing for quick and dirty design is to space the emitters 600mm (24″) apart. For supplemental watering of low-water-use plants, use one emitter per plant. Supplemental watering is used for establishment of drought tolerant plants that are not likely to need irrigation once they have developed a good root system, or might be used to apply a little extra water now and then to make them a bit more lush. Use of low-water plants with supplemental drip irrigation is considered very “green” and is the current trend in landscape design.

Rule of thumb- install emitters 600mm (24″) apart under 80% of the leaf canopy of the plant. That’s where the roots are, and the roots need water. If the soil is very permeable install emitters 300mm to 450mm (12-18 inches) apart. For more information and a better method of determining spacing see Drip Emitter Spacing.

Backflow Preventer:

Drip emitters rest directly on the soil so it is especially important to have a backflow preventer to prevent water contamination by soil-borne disease. There are several types that will work depending on your situation and local codes. For more information see Irrigation Backflow Preventers.

What valve type and size to use:

Use a 20mm (3/4″) valve for most systems. Any type of valve may be used. For more information see Drip Irrigation Valves.

How many emitters per valve?

Use the charts below to determine how many emitters to install on each valve circuit. If you don’t know what size your water supply pipe is, see How to Find the Size of a Pipe.

Emitter volume used Any water supply that comes out of a building, such as a hose bib. Any system with a pump*. 20mm (3/4″) water supply. Use a 20mm (3/4″) valve. 25mm (1″) water supply. OK to use a 20mm (3/4″) valve.
2,0 l/hr (0.6 gph) 300 300 700
4,0 l/hr (1 gph) 180 180 420

*Pumps can be tricky. This is a conservative figure in order to make it work with the majority of pump fed systems. You may be able to use a larger number of emitters by calculating the actual output of your pump. See the Irrigation Pumping Systems tutorial for more information about using pumps.

Water supplies coming out of a building are also a problem. The piping in buildings is almost never designed to carry large amounts of water such as is used by irrigation systems. To be safe I assume you have significant restrictions. 95% of buildings have these restrictions so don’t increase the flow unless you really know what you’re doing. Increasing the flow could cause extreme damage to the plumbing in the building!

Mainlines & Laterals.

Use 25mm (1 inch) PVC, PEX or polyethylene irrigation pipe for mainlines (“mains”) and laterals. The total length of the mainline and the lateral together should not be more than 120 meters (400 feet). So you could have 100 meters of mainline and 20 meters of lateral, for a total of 120 meters of both. But you should not have 80 meters of mainline and 60 meters of lateral because the total of both would be more than 120 meters. Remember mainline is the pipe before the control valve, lateral is pipe after the control valve. Many drip systems won’t need mainlines or laterals. Or they may need just a mainline, or just a lateral. For more information see the sections on mainlines and laterals in the The Basic Parts of a Drip System.

Maximum drip tube length.

The length of drip tube (or drip hose) may not exceed 60 meters (200′) from the point the water enters the tube to the end of the tube. Thus you could have 120 meters (400′) of tube if the water entered the tube in the middle (that would be 60 meters from the point the water enters the tube to the end of the tube in each direction, which would be OK). You can extend one tube off of another as long as the total length of the tubes that are connected is not more than 60 meters (200′). For more information see the drip tube section of The Basic Parts of a Drip System.

Buried Emitters

Never bury emitters underground unless they are made to be buried. If you bury the emitter roots will grow into it and clog it. If you do want to bury the emitters do a search for “subsurface drip irrigation” to find specialty drip products designed to be buried. Follow the manufacturer’s recommendations for those products as they must be designed and installed to very exacting standards to avoid problems.

Buried Tube.

Don’t bury the drip tube. If you do bury drip tube don’t complain to me if gophers, moles or other rodents chew it up. I’ve seen them gnaw to pieces a buried drip system over night. One day it works, the next, it’s garbage. It only takes one gopher (or mole, squirrel, etc.), and one evening! You’ve been warned! Other wildlife (and most dogs), will also chew the tubes. It helps if you provide a water source for them to drink from if possible. A water bowl with an emitter over it to keep it full sometimes will distract wildlife from the tubes. You may need to train your dog not to chew the tubes, dogs seem to chew on the tubes for no real reason other than to annoy you. If you want to hide the tube, dig a shallow trench for it, so that it is just below the level of the surrounding soil. Don’t put dirt over the tube. Throw some mulch or bark over the top to hide the tube, or plant a low spreading plant that will grow over it and hide it.

Feeder, Spaghetti, and Distribution Tubing

Avoid using feeder, spaghetti, or distribution tubing if possible. For more on this topic see the section on spaghetti tubing on The Basic Parts of a Drip System page.

Hard-Piped Drip Systems

A type of drip system used in commercial and high quality landscapes called “hard-piped” uses buried PVC pipe rather than poly drip tubing. The PVC pipe is installed underground and a pipe goes to each plant location, so it takes a lot of pipe. At each plant the emitters are installed above ground on short poly tubes called “risers”. Hard pipe systems can be pretty expensive due. For a detail drawing of this click here. The design of a hard-piped drip system is essentially the same as shown here, except you would use PVC or larger size poly irrigation pipe in place of the inexpensive drip tubing.

Fittings- Use the correct size!

This is really important! There are many different sizes of drip tubing sold, and the fittings have to be made for the exact size tube you are using! If they aren’t, they will either be very hard to install, or the tube will blow off the fitting. Sometimes it takes a week or so for the tube to come loose, but if the fitting is even 1mm too large, the tubing will come off eventually. Never heat the drip tube or use oil on it to make it easier to insert into or onto the fittings. See the section on drip tube in The Basic Parts of a Drip System for more information on fittings and tips and tricks for installing fittings.

Stake down the Drip Tubes!

Stake the drip tubes to the ground once every meter (about 3 feet). This keeps the tubes from wandering. No kidding, they tend to move around by themselves! Staking them also helps protect them from damage. I prefer to use metal stakes as the plastic ones I’ve tried pull loose too easily. Wire that rusts holds even better, as the rust binds the wire to the soil. After a few days they can be almost impossible to remove. They will rust away in a few years, but by then the tubing has adapted to its position and stays in place pretty well. Standard 12 gauge wire works well, as does pieces of wire coat-hangers. Buy some coat-hangers at a yard sale or thrift store and help recycle! Bend a 300mm (12 inch) length of wire into a”U” shape to make a tubing “staple”. Or you can buy metal staples that are made for holding down erosion control blankets, they work great.

Check Valves, Slopes, Hillsides:

Install check valves if the drip system is on a hillside of slope to prevent the water in the tubes from draining out through the lowest emitter each time the system stops running. For more information see the drip tube section of The Basic Parts of a Drip System.

Air Vents:

Install an air vent at the highest point on each drip valve circuit. If there are multiple high points you an air vent installed at each one. Air vents should always be used for drip systems on sloped areas. Air vents are often not installed on small homeowner drip systems without any slopes. If air vents are not used be sure the emitters at the highest points are not installed where dirt could be sucked into them. For more information see Drip Systems for Slopes and Hillsides.

Flush Valves and End Caps

Install a flush valve or end cap at the end of each drip tube. Automatic flush valves are available, however my personal preference is for manual flush valves. See the section on flush valves in The Basic Parts of a Drip System for more information.

Patios with Potted Plants and Trellises:

You will probably want 6mm (1/4″) feeder/spaghetti/distribution tube running to the plants if they are in pots just to make it less obtrusive visually. Try to use as little 6mm (1/4″) distribution tube as possible, keep the tube lengths short as much as possible, and only put 2 emitters on a single 6mm (1/4″) tube. If a 6mm (1/4″) tube is longer than 5 feet, use only one emitter on it. I like to staple the tubes to something to keep them in place if possible (like stapling the tube to a trellis for hanging plants.) Use a wire stake to hold the emitter in place in a pot. Don’t pull any of your tubes tight, snake them a little, leaving some slack in them to allow movement. The tubes will expand and contract with temperature changes, you don’t want them to tear or pop the fittings off.

So for example, I run standard 15-16-17mm (1/2″) tube along the patio perimeters, trying to put it in places it will be out of the way or I can hide it. I also run it up onto the trellis if there are lots of hanging plants, putting it on the back side out of view and clamping it to the trellis using standard conduit or pipe clamps. (I’ve found conduit clamps are cheapest, look in the electrical dept at any hardware store.) From the 15-16-17mm (1/2″) tube I run short lengths of 6mm (1/4″) tube to the potted plants. Remember: more 6mm (1/4″) tube = more problems.

Backflow preventers are always an issue if you have hanging plants and trellises. Vacuum breaker or anti-siphon type of backflow preventers must be installed above the trellis or they won’t work. Both those types of backflow devices must be installed at least 150mm (6″) higher in elevation than any of your emitters. This is generally not very practical to do. I have seen people run copper pipe up a trellis and put an anti-siphon valve 150mm (6″) above the trellis. But in most cases you need to use a double check, or preferably a reduced pressure type of backflow preventer. Those can be installed at any elevation (a reduced pressure type should be above ground.) I recommend a reduced pressure type. See the backflow preventer page for more detailed information.

Beyond these issues, the other basic drip guidelines in this tutorial all apply to patio and trellis drip systems.

Gravity Flow Systems:

If you are using a gravity flow water source like a rain barrel see the suggestions on the Gravity Flow Drip Systems page.

Drip System Sample Detail Drawings:

I have put together a few sample drawings of drip system parts and assemblies that you might find useful. See Drip System Sample Detail Drawings.

 


Technical Data:

This is just for those who want to know all the little details. Everyone else can ignore this information. Here are the assumed pressure losses for the prescriptive drip system design used in these guidelines:

  • Valve 0,4 bars
  • Backflow Preventer 0,8 bars
  • Pressure Regulator 0,0 bars
  • Filter 0,2 bars
  • Mainline & lateral 0,4 bars
  • Drip Tube 0,2 bars
  • Emitters 1,0 bars

Total Pressure required 3,0 bars (44 PSI)

Based on 0,2 l/s flow for 20 mm valve with smaller supply, 0,4 l/s flow for 20 mm valve, and 0,9 l/s for 25 mm valve.

How to Find the Size of a Pipe

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Measure Your Supply Pipe Circumference:

Grab a piece of string about 6″(152mm) long. Strip away any insulation so you can get at the pipe and wrap the string around it. Measure how many inches of string it takes to go around the pipe once. This is the circumference of the pipe (yikes, bad memories of high school geometry!). Using the circumference we can calculate the diameter of the pipe. But school’s out so let’s forget about doing geometry calculations! Based on the string length use the table below to find your pipe size.

For Copper or PEX Pipe

  • 2.75″ (70mm) = 3/4″ pipe
  • 3.53″ (90mm) = 1″ pipe
  • 4.32″ (110mm) = 1 1/4″ pipe
  • 5.10″ (130mm) = 1 1/2″ pipe

For Steel Pipe or PVC Plastic Pipe

  • 3.25″ (83mm) = 3/4″ pipe
  • 4.00″(102mm) = 1″ pipe
  • 5.00″(127mm) = 1 1/4″ pipe
  • 6.00″(152mm) = 1 1/2″ pipe

For Flexible Polyethylene Pipe

  • 2.96-3.33″ (75-85mm) = 3/4″ pipe
  • 3.74-4.24″ (95-108mm) = 1″ pipe
  • 4.90-5.57″ (124-141mm) = 1 1/4″ pipe
  • 5.70-6.28″ (145-160mm) = 1 1/2″ pipe

Your string length will probably not be exactly the same as the lengths in the chart. Measurements vary a little, depending on how much the string stretches, dirt on the pipe, manufacturing tolerance of the pipe, how accurate you are at measuring, etc.

Connect Sprinkler System to Water Supply

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Where and How to Connect Your Irrigation System to Your Water Supply:

This page provides some specific rules, tips, and techniques for tapping into a house water supply pipe for a new irrigation system.   Where and how you tap into the water supply can be critically important, not just for the proper operation of the irrigation system, but also for the preservation of your sanity!

The first thing you need to do is to contact your water provider (assuming you have one) and find out if they have any specific requirements on where to tap irrigation systems into the water supply.  Most of the time the only requirement they have will be that the irrigation tap needs to be after the water meter, meaning the water needs to go through the meter to reach your irrigation system (so that you pay for the irrigation water!)

In some places you will be required to install a second water meter for the irrigation water (ie;  at the time I am writing this the state of California (USA) is considering a state-wide requirement that all new irrigation systems must have a second, separate water meter that measures only irrigation water.  Some local water companies already require separate meters.)  If that is the situation the water provider will likely have a very specific place, method, and brand of meter you must use for the irrigation water tap.  The location of the tap will depend on what kind of water meter they require, so they will need to help you.  They may require that a professional certified by the water provider install the meter.

Typical Irrigation Water Tap Location:  If a separate water meter is not required the general rule-of-thumb is that the irrigation tap is installed someplace on the water supply pipe after any water meters and before the house emergency shut-off valve.  That allows the irrigation to still work even if you need to shut off the house water for an emergency.  A second emergency shut-off valve is installed on the irrigation system water supply after the tap.  I like to install a hose outlet on the house water supply pipe before the house emergency shut-off valve.  That way it the house water has to be shut-off in an emergency the homeowner will still have a source of water!

Warm Climates:   A typical warm climate home has a water supply pipe that goes underground from the water source to the house.  Typically this pipe is buried about 18 inches deep.  At the house the supply pipe comes up out of the ground, makes a right angle, then goes into the house wall.  The emergency shut-off valve for the house is almost always located on this above ground section of pipe where it is convenient to get to it.   The normal method of installing a irrigation tap is to cut into this supply pipe anyplace between the water meter (if there is one) and the house emergency shut-off valve.  The cut and tap may be made into either the below ground part of the pipe or in the section where the pipe is above ground.  Whatever is easiest and most  convenient for you.

If the tap is going to be made underground, it may be possible and easier to install a tap by cutting into the water supply pipe and installing a special tee called a “compression tee” (see How to Use Compression Tees & Couplings.)

Cold Climates:  In cold winter climates the water supply for the house typically goes from the water supply to the house underground, often buried several feet deep to protect it from frost.  It typically enters the house through a basement or crawl space below the house floors.   A water meter is often installed on the water supply pipe in the basement or crawl space.  The irrigation tap has to be after the water meter (if you have one.)  Because the water supply pipe is usually buried very deep, most people install the irrigation tap in the basement or crawl space where it is easier to reach.  If you are tapping into a water supply in a basement or under a house you may want to hire a plumber to install the tap if you are not experienced at plumbing work.  You don’t want a flooded basement if you mess it up.

If the tap is to go outside the house and underground, it may be possible and easier to install a tap by cutting into the water supply pipe and installing a special tee called a “compression tee” (see How to Use Compression Tees & Couplings.)

Don’t Route Irrigation Water Through the House Pipes!

If at all possible do not tap into a pipe or use a stub-out where the water will need to flow through the house to get to the irrigation system (other than through the basement.) In other words, you do not want the water to go through pipes inside the house walls to get to the irrigation system.  I see a lot of homes where the builder has provided an irrigation outlet on the back of the house, with the water running through the house to reach it.  Most people who utilize one of these outlets regret it! There are a few reasons for this:

  1. Flow Restrictions.  First, there may be restrictions in the piping as it goes through the house that you can’t see and don’t know about. This includes multiple turns, small size pipe sections, crimps in the tube, and all kinds of things.
  2. Noise!  The second reason is that it is likely that the irrigation will be running at night. Often the irrigation water will make a lot of noise as it moves through the house pipes and it sounds a lot louder during the quiet of night.
  3. Damage to Pipes.  The 3rd reason is the worst one of all, a phenomenon called “scrubbing.”  Scrubbing is when excessive water velocity in a pipe causes extreme wear on the inside of the pipe.  Water is abrasive and it will eat away the inside of a pipe or tube over time!  (Feel free to look up scrubbing on the Internet. Repairing the damaged pipes is a huge industry in some parts of the USA.)  Houses with copper pipe and tube are especially vulnerable to scrubbing damage.
  4. Water Softeners.  If you have one (or ever plan to install one) the irrigation water can’t go through it.  Chances are any water that goes through the house also is softened if there is a softener.  This includes the exchangeable tank softeners that water quality services bring out to your house, chances are they use salt/sodium to soften the water.  Even if you use a potassium salt type of softener that is easier on plants, the cost of using soft water for irrigation is going to be enormous.

So I recommend that if you need to get water from one side of the house to the other, that you install a new pipe around the house. If you decide to use an outlet on the side of the house, perform a simple test. If there is a hose on the outlet remove it (the hose will restrict the flow.) Wait until late at night and then open up that faucet all the way. Then go inside and see how loud it sounds inside the house. The noise will likely be even louder when the irrigation system is installed.

I realize sometimes you have no choice but to route the water through the house.  If so I suggest you reduce the flow for each valve zone.  Lowering the flow reduces the water velocity in the pipes.  With a lower velocity, there is much less chance you will have any of these problems occur.  Try to keep it under 4 feet/second.  (The Pressure Loss Spreadsheets will give you the velocities for various flows and pipes.)  You may need to double the number of valves to lower the flow, but it is better than listening to the noise, or worse, having to spend thousands of dollars to replace the pipes in the house walls because they were destroyed by scrubbing!

Shut-Off Valve

Its a good idea to install an emergency isolation or “shut-off” valve on the irrigation water pipe as close as possible to the point where you tap into the water supply. That way you can easily and quickly shut-down the irrigation system for emergencies or repairs. In areas where it freezes in winter this valve should be protected from freezing. The standard is to use a ball valve for the isolation valve. Inexpensive “gate valves” have a tendency to fail after just a few uses.  This is a good place to spend more money for a quality valve.  Nothing is worse than having an emergency and discovering your emergency shut off valve doesn’t work!

Backflow Preventers

You must have a backflow preventer on your irrigation system if it is connected to any water system that is used for drinking water. In some places this includes well water, even if your well is not used for drinking.  In most places this is the law, everywhere else its just the smart thing to do.  THE IRRIGATION VALVES ARE NOT SUFFICIENT TO STOP BACKFLOW.   This website has a very detailed article on backflow preventers that will help you figure out why, where, and guide you step-by-step in selecting which one to use.   See Everything You Need to Know About Backflow Preventers.


This article is part of the Sprinkler Irrigation Installation Tutorial Series
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By using this tutorial you agree to be bound by the conditions and limitations listed on the Terms of Use page.


Compression Tees and Couplings

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A compression coupling or tee is a special fitting designed for joining existing metal and PVC pipes or tubes.  They are sometimes sold as “pipe repair couplings”.  They are primarily used for underground connections.  Other types of compression fittings, such as threaded adapters, are also available for situations where something other than a coupling or tee is needed. Compression couplings are primarily used for pipe repairs, compression tees are used to tap a new pipe/tube into an existing one. A compression fitting may be constructed of PVC or metal.  PVC should only be used for connections that will be hidden from sunlight, like underground or in a box.

A PVC Compression Coupling
A PVC Compression Coupling

A compression fitting works by using a rubber gasket. This gasket is compressed against the existing pipe when you tighten a nut on the end of the fitting. This makes a leak-free seal without the need to thread, glue, or solder the pipe connection. Use metal body compression fittings above ground level, PVC may be used below ground but must be installed below the frost level. Compression fittings may leak if used on heavily corroded, rusty, or pitted pipe. For this reason some professionals do not recommend that they be used on older steel or galvanized steel pipe.  The pipe or tubes attached to a compression fitting must be firmly held in place, if not buried they should be strapped down tightly.  If the pipes or tubes can shift or move the compression fitting will not hold!

Note: some drip irrigation fittings are also called “compression” fittings. They are not the same thing as these tees and ells shown here!  Also “compression fittings” are sometimes used for copper, polyethylene and PEX tubes, they are similar to these, but also are not the same thing.  These compression fittings are only for rigid pipes, like PVC or metal.

To use a compression tee to tap into an existing pipe:

Installing a Compression Tee
Installing a Compression Tee
  • First, the pipe you want to install the compression tee or coupling on must be firmly anchored in place. It is particularly important to make sure the pipe will not be able to slide back and forth in the lengthwise direction. If the pipe can slide, it will blow out of the end of the compression fitting! The rubber gasket will NOT hold the pipe in place.  This often happens if the pipe has an ell (change of direction) within a few feet of where you install the compression fitting. If there is an ell in the pipe near the compression fitting, the ell must be “blocked” in place. For underground pipes a brick behind the ell wedged between the ell and undisturbed soil can be used as a block to keep the ell from moving. Do not use wood as a brace underground, the wood will rot out. You can also use concrete to hold the pipe in place. The official term used for the brick or concrete that holds the pipe in place is a “thrust block”. If the pipe is above ground, it needs to be firmly strapped in place so it will not move.
  • Make sure you buy the correct size compression tee! It will leak if you use the wrong size. The size will depend on both the size of the pipe you are installing it on AND the material the pipe is made out of.  Read the sizes carefully!  For example: the same compression fitting size fits 1/2″ PVC, 1/2″ iron-steel pipe, and 3/4″ copper tube! Often this compression fitting is simply labeled as “1/2 I, 3/4 C” which can seem a bit cryptic to most people. If in doubt ask the salesperson to help you select the proper size and hope the salesperson knows what they are talking about.
  • Once you have the tee, shut off the water in the pipe you are going to tap into. Now cut a small section out of the pipe you wish to tap into. The section you cut out will need to be about half the length of the compression tee. Remove any burrs from the cut end of the pipe. Clean the pipe surface to remove any dirt, rust, scale, or oil from the pipe. A wire brush should be used to clean metal pipe.
  • Each end of the compression tee has a nut (or ring) that is used to tighten it onto the pipe. Between the compression tee body and the nut is a rubber gasket. Slide the compression tee onto one end of the pipe. Note: the drawing below shows the compression tee sliding onto the pipe, however, you may find that you need to remove the nut and gasket and put them onto the pipe ends first and then reassemble the whole thing on the pipe. The gaskets fit very snug. You may need to wiggle it around a bit to work them into place, or you may need to tap the fitting with a rubber mallet to get them into place. Do not use soap to lubricate them! If you must use a lubricant, use original KY Jelly (not the warming type) it is an excellent water-based lubricant, plumbers use it all the time.
  • Now slide the compression tee so it is centered between the two pipe sections.
  • Tighten the rings down to seal the rubber gasket onto the pipe. That’s all, you’re done! Install the new pipe going to your irrigation system into the side outlet of the tee.

 

How to Use Pressure and Flow Switches with Irrigation Controls

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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.

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