A Quick Primer on Sprinkler Design

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 reading this, 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!

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