Definition: riser (irrigation). A riser is a set of pipes that connect and/or support a piece of irrigation equipment on or to the irrigation system. Typically the equipment is mounted at or above ground level and the riser connects it to pipes or tubes located below ground. Thus the source of the name riser, as it “rises” up above ground to the equipment. Risers are typically used to support sprinklers, drip emitters, valves, backflow preventers, air vents, and just about anything else.
This article is specifically about types, as well as the pros and cons, of risers used for sprinklers and drip emitters.
Risers for Drip Irrigation: On most drip irrigation systems the emitters plug directly into the drip tubing without using risers. Some drip systems, where the emitters are attached to threaded outlets, also use risers to attach the emitters. These are often called “hard piped” drip systems. The following article on sprinkler risers would also apply to a hard-piped drip system. Just substitute the term “drip emitter” for sprinkler.
There are any number of ways you can attach a sprinkler head (or drip emitter) to the lateral pipe/tube. (Lateral pipe/tube is the term used for the piping/tubing that carries water from the zone control valve to the sprinkler heads.)
Before we get into risers let’s quickly cover the related topic of sprinkler placement or positioning in relationship to adjacent objects or surfaces.
Sidewalks: 4 to 6 inches is the normal distance a sprinkler should be from the edge of a sidewalk. (Before you ask, no, a 6 inch distance does not cause a dry spot along the edge of the sidewalk. Sprinklers are designed to be installed 4-6″ away and allow sufficient “back-spray” to water these areas.) If closer than 4″ lawn edgers and string trimmers will tend to damage the sprinkler.
Fences and Walls: Keep sprinklers at least 12″ away from fences or freestanding walls. If the sprinklers are within 36″ (3 feet) of a fence you most likely will see water stains from the sprinkler spray on the fence or wall. This can look pretty bad. In areas with strong winds a wall or fence will be discolored with water stains even if it is as much as 5 feet away.
Building Foundations and Walls: Keep sprinklers at least 18″ away from foundations and building walls. No water should spray onto a building wall. For this reason any sprinkler that sprays water should be at least 36″ away. Bubblers or “flat” spray sprinklers may be closer if unavoidable and soils are suitable. The water must not spray onto the wall or foundation and the soil must not be expansive (see next paragraph.)
Expansive Soils: If you have expansive soils (wet soil cracks when it dries) there are special rules and precautions regarding sprinkler placement around buildings and structures. If you get expansive soil near your foundation wet it can break your foundation! Read the Sprinklers and Expansive Soils Tutorial.
How can I water grass next to a wall or fence if the sprinklers are 36″ away?!! You can’t if you use sprinklers. This is one reason why professional landscapers put a foundation planting of low shrubs around the perimeter of buildings and along fences. The shrubs are watered using drip irrigation or bubblers that minimize the water volume and do not spray water in the air where the wind can blow it around. Another option is to use subsurface drip irrigation for the lawn watering. Even then it is not a good idea to put the volume of water needed by a lawn right up against a foundation. It is just asking for structural problems like moisture damage, rot, and termites. Plus it is not considered good esthetic landscape design to put lawn directly against a building, unless the building has a significant architectural feature at ground level that needs to be highly visible. Nothing says “amateur design” like lawn planted up against the wall of the typical home. OK, to be clear, if it is your house, do as you wish. Maybe you think it looks great, that’s fine, I’m just letting you know that every pro who passes by is going to snicker!
But I WANT lawn against my house you landscape design snob!!! OK, I am being a bit of a design snob. Sorry. If you do want lawn installed right up to a building foundation you should put a concrete apron (or other non-irrigated surface like rock or gravel) between the lawn and the foundation. Typically an apron at least 18″ wide is needed to keep water away (if the sprinkler heads are 6″ out from the concrete edge that is a 24″ distance to help minimize water on the wall.) I like a concrete apron because it gives a clean sharp edge to the grass that is easy to trim and goes well visually with the building’s hard edge. Make sure the concrete surface is sloped away from the building so rain and any irrigation over-spray water flows away from the building.
OK, back to our discussion of risers.
Simple Pipe Risers (i.e.; Pipe Nipples):
One of the most common sprinkler risers used for residential systems is a simple short section of pipe called a “nipple”. Actually a nipple is the standard plumbing term used for any short section of pipe, usually with male threads on the ends, regardless of where it is used. While a nipple is the least expensive riser type, it also has some very distinct disadvantages. If the nipple is made of metal the nipple won’t easily break. A rigid PVC plastic nipple (like the gray SCH 80 PVC nipple) is not easy to break either (although I have seen it happen.) Now this may seem like a good thing, as we don’t generally want things to break. However, when the sprinkler mounted on a rigid nipple is hit hard by a mower or car tire, something probably WILL break! So what do you want to break? The sprinkler head is expensive to replace if it breaks, but fortunately it doesn’t usually break. If you use a hard plastic or metal nipple for the riser it won’t likely break either. Unfortunately, what usually does break is the fitting on the lateral pipe that the nipple is screwed into. While not expensive, this fitting is going to be a real pain in the behind to replace if it breaks. You’ll have to dig up several feet of pipe, bail out several gallons of water that drain out of the broken pipe, cut the broken section out of the pipe, repair it, put the sprinkler back in place, then backfill the muddy hole. You’re talking at least an hour of hard, dirty work. The better solution is to use soft polyethylene (poly) nipples for your risers.
Poly Cut-Off Risers:
If you want to go the really cheap route and use a nipple for the riser I suggest that you use what is typically called a “poly cut-off riser” or some other similar name depending on the brand. A poly cut-off riser is a short pipe section (typically 6″ long) with multiple sets of threads molded into it (see photo below.) You simply cut it off to the desired length with a knife or a pipe cutter. Because the poly material is very soft, the nipple will bend under stress and will break before either the sprinkler or the lateral fitting break. While it is not fun to replace the broken poly nipple, it is a lot easier and faster than replacing the lateral pipe fitting below it and much cheaper than replacing a broken sprinkler head!
Poly Cut-off Riser
The arrows show where to cut the riser to make it the correct length.
When cutting the poly cut-off riser always cut it at the top of one of the sections of thread, as shown by the arrows in the photo below. Cut-off nipples generally cost less than a dollar a piece, which is pretty inexpensive to replace. Keep in mind that sooner or later you are going to have to replace a few of them. After all, they’re designed to break! So buy a few extra when you install your system. You don’t need to use thread sealants like Teflon tape on poly risers, the soft plastic will seal itself. Amateurs should never use liquid or paste thread sealers on sprinkler systems, if some of it squeezes through the threads to the inside of the pipe the water will take it straight to the sprinkler nozzle where it will clog the nozzle.
Swing Joint Risers
A much better solution for risers than the simple nipple system described above is to use something designed to allow the sprinkler to absorb an impact without anything breaking. The riser most professionals use for this is a “swing joint” or “swing riser”. In addition to deflecting to prevent breakage, most swing risers also allow the sprinkler head location to be easily adjusted. With the swing riser types known as “flexible arm swing risers” and “quadruple swing risers” the sprinkler head doesn’t need to be directly over the lateral pipe fitting, so it is not nearly as critical that the pipe be installed in the right place. Thus the trenching and pipe installation is going to be much easier and faster. I don’t know about you, but I like methods that are easier and faster– especially when they also give better results!
Flexible Arm Swing Risers:
The flexible arm swing riser is cheap and easy to install but not as durable as a rigid arm swing riser (but it is still much more durable than the cut-off riser mentioned above). This is the method I recommend for a residential or even a light commercial application, and it is what I use on the majority of my fast-food restaurant irrigation systems. It provides a good balance between cost, ease, and durability. The flexible arm swing riser consists of a length of flexible pipe (sometimes referred to as “Funny Pipe ®” a trademarked name of the Toro Company) with a insert ell on both ends. One ell attaches to the sprinkler, the other to the lateral pipe fitting. You can buy these swing risers preassembled, or you can buy the flexible pipe and insert ells separately and assemble them yourself.
Rotors: Don’t use these flexible arm swing risers with rotors that have a 3/4″ or larger inlet. That means don’t use them with most rotors! See the rigid riser below for 3/4″ and larger inlet size rotors. The small flexible tubes used on these swing risers restrict the higher water flow that most rotors need for proper performance.
The preassembled swing risers often have 3 or even 4 ells which makes them much easier to install. You can duplicate this feature by adding street ells to the build-it yourself risers. A street ell is just an ell that has female threads on one end and male threads on the other (see photo below.) I suggest adding a street ell to one or both ends of your swing riser to make it easier to install. The street ells you use should be high density polyethylene, which is black in color and has a slightly oily feel. “Marlex” is a common brand name of high density poly that you may encounter. Do not waste your money on white PVC street ells, they are worthless for swing risers! PVC threads seize up which defeats the whole idea of a flexible joint.
Do not use more than a 18″ length of flexible pipe for your riser! The flow through this pipe is very restricted. Longer lengths cause a high amount of pressure loss and this can mess up the performance of the sprinkler head. If the head is more than 18″ away you should run a branch pipe over to it using the same size and type of pipe as the lateral.
When installing the flexible swing riser do not bend the flexible tube to help position the sprinkler. Position the sprinkler by turning/twisting the ells to move it into position. Poly tube has what we call “memory”- it tries to return to its previous shape when bent. Chances are the tube was coiled or curved slightly when you purchased it and that is the shape it will want to remain. When it does try to return to the previous shape it will pull your sprinkler along with it and the end result will be a sprinkler that leans at a weird angle. If the pipe is curved when you buy it, work with the curve of the pipe. Twist the ells around on the end of the pipe until the sprinkler is in the position you want without bending the pipe. Cut the pipe length shorter if need be. (I recommend starting with a 12″ to 18″ length of flex pipe and then cutting it shorter as needed to position the sprinkler.) One more time; do not bend the flexible pipe. Believe me when I tell you that it will save you a lot of headaches later!
Clamps: You do not need to use clamps on the special insert ells that are made for swing risers. These ells are made differently than the ones used for standard poly pipe. They have a self-locking ridge on the ell that seals it and locks the flexible tube on. Most of these swing riser insert ells also have spiral barbs, so you need to twist them into the pipe– just like screwing a light bulb into a socket. You do know how to install a light bulb, right? Finally, you should use Teflon tape on the male threads of the ells to seal them. You don’t have to use a lot of Teflon on these, a little leak here isn’t a huge problem. While they shouldn’t, my experience is they tend to leak if not sealed with Teflon tape. Again, unless you are a professional pipe fitter, I would recommend that you not use a liquid or paste type thread sealer. See my rant on that topic above in the Simple Pipe Riser section.
Inserting the ells into cold tubing: OK, I confess it is often not as easy to get the insert ell into the tube as it is to install a light bulb. So if it’s cold, the flexible tube is stiff, and the insert ell just doesn’t want to go in, here’s a trick– use original KY Jelly (not the “warming” variety) on the insert ell barbs. Don’t use any other type of oil or soap, they can damage the plastic. (Don’t know what KY Jelly is? It is a water-based lubricant. Don’t head for the hardware store like I did when I was first given this tip. Now that was an embarrassing incident! Go to the drugstore or supermarket. It’s in the women’s hygiene section– ’nuff said guys? Try not to have a silly grin on your face when you check out.) You can also soften the tube by dipping it into hot water. WARNING: Do not heat the tube with a heat gun, torch, etc. as the uneven heating that results from directional heat will severely weaken the tube.
(The riser in the photo above 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.
There are various types of rigid arm swing risers depending on how many ells the swing riser has. The double swing riser has two ells at the bottom of the rigid arm and is pretty much worthless for most situations in my (not so humble) opinion. It allows the head angle to be adjusted, but does not allow the head to be moved up or down. Double swing risers are used primarily for shrub style sprinklers mounted on a pipe above ground.
The triple swing riser is much better and is the standard swing riser used by most professionals. The triple swing riser allows the head to move up and down and allows it to be angled in any direction (i.e.; you can install the head at an angle so that it is perpendicular to a slope.) But you still can’t move the sprinkler head from side to side with a triple swing riser. That’s why I use quadruple swing risers when I use a rigid arm swing riser.
The quadruple swing riser allows the sprinkler head to be moved in any direction. It can be adjusted up or down, angled in any direction, plus it can swing from side to side. For example, lets say you install your lateral pipe parallel to a sidewalk and for whatever reason, the pipe winds up being 10″ away from the edge of the sidewalk. With a triple swing riser your sprinkler is also going to be 10″ away from the sidewalk unless you install a small branch pipe over to the sidewalk from the lateral. With a quadruple swing riser you simply swing the sprinkler over so it is as close to the edge of the sidewalk as you want it to be. (Again, 4 to 6 inches is the normal distance a sprinkler should be from a sidewalk.) A quadruple swing riser costs about a dollar more than a triple swing riser, but gives you total flexibility– which is important if you want a really efficient sprinkler system! A typical rigid swing riser is constructed using a 12 inch long SCH 80 PVC nipple for the rigid arm (generally SCH 80 is gray colored) and high density polyethylene street ells (see photo of a street ell above.) High density polyethylene is typically referred to as “Marlex”. Marlex is black in color, softer than PVC, and works better for swing risers than PVC because it has a naturally oily surface. Do not use standard threaded white or gray PVC ells on swing risers! The threads on standard PVC ells tend to stick to each other and keep the swing riser arm from moving as it should. I recommend that you use a small amount of Teflon tape on the male threads, even when using Marlex street ells. By the way, the black plastic used for the swing pipe risers mentioned earlier are not Marlex! If you can’t scratch it with your fingernail, it is not Marlex.
Several manufacturers make preassembled rigid swing risers for sprinklers. Most of these preassembled swing risers are very high quality and use special PVC ells with o-ring sealed swivels built into them. Unlike standard threaded ell joints these swivels allow very free movement of the swing riser and are superior to swing risers made with standard threaded ells. They are often used with the large, expensive sprinklers used on golf course and park irrigation systems. The large, heavy tractor mowers used on parks and golf courses make it essential that the swing risers be able to move freely.
What if you really need to bend the riser tube? There is a very flexible pipe riser product that is now sold at most irrigation supply stores and home improvement stores. It is durable and can be bent to pretty much any position you want. Tie it in a knot if you wish. I have been very pleased with this product so I feel I can recommend it for situations where you need a really flexible riser pipe. It is especially useful for sprinkler replacements. It looks like a flexible electrical conduit. (In fact that’s exactly what it is, a flexible plastic electrical cable protector with a length of vinyl tubing inside it!) Don’t use it for anything other than small spray head risers. It can’t withstand high pressures and will not work with high flow sprinklers. I usually put a threaded street ell on one or both ends to make it easier to install. The vinyl tube used in these risers is very small and creates high pressure loss. Do not string multiple riser tubes together to make a longer riser. The resulting high pressure loss will make your sprinkler not work very well.
Riser Pressure Loss
The amount of water pressure lost through the risers varies greatly. Some manufacturer’s provide pressure loss data for their risers, most do not. If you are using my Sprinkler Design Tutorial to design your system you don’t need to worry about pressure loss in the risers. As long as you use one of the riser types as described above you are covered. I have included compensation for the riser pressure loss in the lateral pipe sizing tables and spreadsheets.
This article is part of the Sprinkler Design Tutorial Series
<<< Previous Page ||| Tutorial Index ||| Next Page >>>