The first step in physically installing your sprinkler system is to layout, or “stake”, your new irrigation system on the ground. Start by marking each of the sprinkler head locations in the irrigated area, using your sprinkler system plan as a guide. (Don’t have a plan? Stop here. Don’t make trouble for yourself. You NEED a plan!)
Place a stake, a flag (they sell flags for this purpose at irrigation supply outlets), a long nail with a ribbon tied to it, or whatever, at the location of each sprinkler head. (At this point I suggest you NOT use paint as a sprinkler location marker, you may need to make adjustments and paint makes that difficult.) Now carefully double check the distances between each of the sprinkler heads. You don’t want to find out that the sprinklers are in the wrong place after they are buried in the ground! Measure the distance from each sprinkler head to the next head in each direction. If your system is properly designed there should be at least 2 other sprinklers (usually 3) about the same distance away. Make sure that none of these distances are more than the maximum spacing allowed for that sprinkler head model. (See the Sprinkler Design Tutorial for more information on maximum sprinkler spacings.)
Rule of thumb spacing guidelines:
- If the distance between spray type sprinklers is more than 18′ there’s a problem.
- If the distance between rotary nozzle type sprinklers is more than 35′ there’s a problem.
- If the distance between rotor type sprinklers is more than 35′ there’s a problem.
- If the distance between any 3 adjacent heads varies more than 20% there is a problem.
- If you don’t know what spray, rotary nozzle, and rotor type sprinklers are read the article on Types of Sprinklers.
The spacings shown above are maximums! The best spacing is probably less than these distances! Remember, the water from one sprinkler should spray all the way to the adjacent sprinkler. Sprinklers are designed to require 100% overlap. You will have dry spots without that required overlap. (This is not greed on the sprinkler manufacturer’s part, there is a scientific, mathematical reason for this overlap. See the article on Sprinkler Spacing for details. )
If the sprinklers are too far apart you will need to adjust the sprinkler locations, another solution is to adjust the perimeter of the area to be watered to make it smaller, or redesign the system. Never stretch the spacings between sprinkler heads beyond the maximums, you will get very noticeable dry spots! Remember that it is easier and cheaper to redesign everything at this point than it will be to fix problems later! Adding more sprinkler heads to a system later in an attempt to get rid of dry spots generally does not work out well, is a lot of work, much more expensive, and almost always just creates new problems. (Right now it may seem like you need to rush to get this sprinkler system in the ground, but waiting a few weeks to fix the problems is nothing compared to the grief of living for years with a horrible sprinkler system that doesn’t work. Many, many regretful owners of bad sprinkler system have told me that this is advice they wish they had heeded.)
Now you need to mark the pipe locations on the ground. You can use chalk, white paint, or just drag a shovel over the ground to mark where the trenches will be.
For do-it yourselfers I recommend that you mock-up the pipes at this point. Lay the pipes on the ground (don’t cut it yet, just use full lengths to get a feel for the layout) and then lay the fittings next to the pipe at the locations of the sprinkler heads, drain valves, junctions (tees), and bends (ells.) This will help you visualize how the whole thing will fit together and will identify any missing fittings you need to buy. Don’t mock up fittings and pipe by actually fitting them together, they are extremely difficult to get apart. Just lay them next to each other on the ground. If you plan to use swing risers for the sprinkler heads you can preassemble them at this time, and screw them into the tee or ell that will be attached to the lateral pipe. This will save time later as it is easier to screw them into the fittings before the pipe or tube is assembled.
Don’t attach the sprinklers yet. After you have everything laid out, get a bunch of plastic bags. Place the fittings along with the sprinklers and risers for each location together in a bag and label it. I use small plastic trash bags. Then I write a number on the bag and write the same number on my irrigation plan at the location where the fittings in the bag go. Now I won’t have to search for the correct fittings later when I’m hot and tired. A little preparation now saves lots of time and frustration later! Be sure to move the pipe out of the way when you’re finished so you don’t break it when digging trenches or pulling tube.
Next, mock-up the valve assemblies to make sure you have all the proper parts you will need for them. Make sure the manifolds will fit into the space allotted. I actually do the final assembly of most of the valve manifolds at this point and set them aside. If the manifold is made of metal pipe and will be connected to another metal pipe in the field, I use a special fitting called a “union” at the point where the two sections will connect. The union allows the preassembled manifold to be installed much quicker and easier. If you’re not familiar with unions ask your supplier to show you how they work. They aren’t cheap but they are worth every penny you pay.
Make sure you follow the instructions for making leak-free threaded joints. Now, when your ready to install the manifolds later, just grab the preassembled manifold and slap it into place. I like to assemble the manifolds in my garage where its cleaner, cooler, and I have a vise to hold the pipe while I thread it together. Warning: if you use a vise never squeeze PVC pipe to the point that it’s shape deforms! You may create invisible hairline fractures that will begin to leak in a few months.
One last tip. When you dig the trenches or pull the tube into the ground, all the sprinkler head markers (flags or stakes) will get moved. So here’s a trick to help you find the locations again later. For each sprinkler head get a 20 foot long piece of string and two large nails about 4″ long. Tie the string around the sprinkler flag so that the flag is in the middle of the length of string. Now tie a nail to each end of the string. With the flag at the sprinkler head location, stretch out the string tight to form a V with the nails about 5 feet apart from each other and shove the nails into the ground. Now you can move the flag and dig the trenches. Don’t pull the nails out! To find the sprinkler location again just stretch the string back out tight from the nail locations to create the V again. The flag will be at the same location it was before!