Irrigation Desain : sprinklers (1)

2 Feb

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?)

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.


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