A Quick Primer on Sprinkler Systems

Please Read This!

Reading this page is going to help you more than you can imagine at this point. Unless you know how to design a sprinkler system (why are you reading this?) or have training in hydraulics, it will save a lot of questions if you understand just a little of the basic principles behind irrigation system design. I’ll try to keep it light and easy on the brain cells.

Sprinklers Need Energy

A sprinkler requires two things to operate- water flow and water pressure. When a sprinkler system design fails, it is almost always due to a lack of water pressure at the sprinklers. This is important because, if you are like 99% of the people using this tutorial, you are thinking solely in terms of water flow. “How much water do I need (or have available) for my sprinkler system?” That’s an important question to ask, but it must go hand in hand with its sister question, “How much pressure will I have at the sprinkler?” The “at the sprinkler” part of that question is critical! Allow me to demonstrate by means of a simple, if not somewhat stupid, example:

Go get a sprinkler, any sprinkler will do fine, even one you put on the end of a hose. Now get a big bucket of water. 5 gallons is an ideal size. Now place the sprinkler on the ground (somewhere outside is strongly recommended) and pour the water into the sprinkler inlet. Did the sprinkler operate correctly? Did it water a good size area? NO? Why not? It had plenty of water. Ahh… but it didn’t have any water pressure! The water you poured into it didn’t have enough pressure to make the sprinkler operate.

Water pressure is the ENERGY that makes the sprinkler do its thing. Water pressure is like the gasoline for the car. Flow is like the distance the car travels. No gas, no travel. No water pressure, no water flow. (Yes, Ms. Ph.D. in hydraulics, that’s not a perfect analogy- but it works for most people.)

We understand that water requires pressure to push it through the pipes. It also stands to reason that just as a car uses up gas when it travels, the water also uses up the pressure as it flows! So from the moment the water starts flowing through the pipes of your water system, it is using up the pressure. We refer to that as “losing pressure” when designing. Some pressure is lost when the water goes through a water meter. It loses some more pressure as it moves through the various pipes in your yard and house. Squeezing through valves and/or a backflow preventer eats up more pressure. Everything the water encounters as it moves from the water source to the sprinkler uses up a small amount of the water pressure.

So here is the key to a good sprinkler system design: After the water gets through all those pipes and valves and reaches the sprinkler head, there still must be enough pressure left to make the sprinkler head operate correctly. If there isn’t, it’s just like the sprinkler you poured water onto in the example above. All the water in the world won’t make it work without pressure! By using the correct sizes of pipes, valves, etc. you can control how much pressure is lost in the irrigation system, and that, my friends, is what sprinkler system design is all about!

So here’s sprinkler design in a nutshell: Sprinkler design is simply manipulating how much water pressure is lost between the point the water enters your yard and the sprinkler head. That’s right, you are about to learn how to manipulate! (Come on, you’ve always had a secret desire to be able to manipulate, right?)

TipAt the bottom of each page of the tutorials is a link to a glossary. If you run into a term you don’t know, click on glossary and look it up. Warning: The glossary has a lot of my bad puns and weird humor in it.

The Sprinkler System Design Process:

Step #1: You’ll learn how to accurately measure your yard and then sketch out the area to be irrigated. Next some information needs to be obtained. Don’t worry, I’ll tell you how and where to get it. We’ll also make an “educated guess” at an Initial Flow Rate, which will serve as a starting point for the flow and pressure manipulations mentioned earlier.
Step #2: We’ll take a look at those things that will “eat up” your water pressure as the water moves to the sprinklers. I’ll show you how to find out how much pressure each one of those items will use. While we’re at it, you’ll learn about sprinkler heads, valves, backflow preventers and all the other equipment that will go into your new sprinkler system. You’ll learn how to tell a good product from a bad one, regardless of brand names. Then we will manipulate those pressure losses and end up with the actual flow and pressure values you will use for your sprinkler system. Don’t panic, there’s a lot of information to cover, but I will lead you through it item by item. It will be easy if you take it one thing at a time and don’t freak out on me!

Step #3: Here’s where we actually start drawing the sprinkler system on paper. Finally! You will learn a lot more about sprinklers in step #3. It’s a long wait, but if you had started trying to figure out where to put the sprinklers back in step 1 or 2, like some tutorials do, you’d be erasing them now!

Step #4: Here’s where you’ll divide your sprinkler system up into zones and lay out the piping routes. This is where we’re going to make the right decisions to create a sprinkler system that uses less water than most and gives you healthier plants. Bad sprinkler design is a major cause of turf disease and wasted water.

Step #5: Finally, we will determine the size of each pipe and clean up a few small details. We’ll look at how to automate the sprinkler system if you want to.

Congratulations, you are now a sprinkler system designer!

Other Stuff:

If you’re in a hurry you can skip the rest of this page. The remaining topics on this page answer a few common questions asked at this point:

Free Designs:

Irrigation design is a deceptively simple looking task. A great number of over-simplified “design it yourself” pamphlets have not helped the situation. A few of those pamphlets have even been scanned onto web pages (I was hoping they would be allowed to die a merciful death!). The current industry trend is toward offering homeowners free “computerized” designs in place of the oversimplified guides. I’m not opposed to these free design offers; however you should be aware that there is usually a condition attached (such as buy your irrigation materials from the designer). I will offer the following warning: I have yet to see a computer program that can perform “hands off” irrigation design. They are getting better each year, but every irrigation design software package I have encountered requires tweaking of the completed design to obtain a good irrigation system. So here’s what to do. Go ahead and get the free design if you want, then sit down with this tutorial and make sure the free design measures up! A free design is often a good way to get a running start for your own design. The most common error I see on free designs is stretching the distance between sprinkler locations, many have small areas where the sprinklers don’t provide good coverage. The theory they are using is that you won’t mind a small yellow area if it saves you money. (A reasonable conclusion; you ordered a free design so saving money is obviously a priority for you.)

Irrigation Design Software

Most irrigation software assumes you know at least the basics about how to design irrigation. The really good ones that do calculations for you cost way more than you would pay to have a professional design a moderate size irrigation system for you. The less expensive boxed programs I have seen at retail stores only provide basic drafting tools used to create pretty looking plans. They do not automate any of the tougher design tasks like figuring out pipe sizes or sprinkler head locations. However, there are a lot of them and I admit I have not looked at all of the programs available. If you come across a reasonably priced program (under $500 US) that claims that the software will determine the best sprinkler locations, route the pipes, and give you the correct pipe sizes let me know! Technology is advancing rapidly and I believe the day will come when such a program will be available.

A “behind the scenes” look at the tutorial.

So what is it that makes irrigation design so difficult that even the best artificial intelligence computer programs stumble on it? Part of the reason for the difficulty is that some of the hydraulic principles are rather abstract and hard to understand and apply. The primary difficulty, however, is that there are many, many variables involved in even the simplest irrigation design. This also creates a problem for me when writing a tutorial like this one: “How do I create a tutorial which can get you through all those variables without frying your brain?”

My answer to the problem of making a top-quality tutorial is to attempt to simplify the design process, so that it will take a minimum of time and learning, while not over-simplifying it to the level of those almost useless pamphlets you get at the hardware store. What I have done for this tutorial is simplified the mathematical equations, used charts and tables where possible, substituted constant values for a few variables, thrown in some sample drawings, and glossed over much of the complex hydraulic theory. That eliminates a good portion of the problem. In some instances, however, I simply can’t make assumptions without sacrificing quality. So you will be asked from time to time to provide data. I will do my best to guide you toward quick and accurate sources from which you can obtain that data. When possible, I will provide data values for you to choose from. In a few instances, I have made an estimation of the value for you. In those cases I have used a “somewhat conservative” value. In other words, I have not used the most conservative value available, as to do so would result in gross over-design most of the time. Rather I have used a relatively conservative value, which will work in the vast majority of situations. The goal is that when one of these estimated values is too conservative, it will be balanced by another elsewhere which is too liberal. In the interest of accuracy, I will provide a technical note whenever I make an assumption. I don’t want to do anything behind your back!

Now, let’s get started with your own sprinkler design!

This article is part of the Sprinkler Design Tutorial Series
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