Once you have your irrigation materials and installation tools together, you're ready to layout, or "stake", your new irrigation system. Start by marking each of the sprinkler head locations (well, only if it's a sprinkler system!). Place a stake, flag, long nail with a ribbon tied to it, tin can, rock, or whatever, at the location of each sprinkler head. 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. For most sprinkler heads there will be at least 3 other sprinklers that should each be about the same distance away. Make sure that none of these distances are more than the maximum spacing allowed for that sprinkler head. (See the Sprinkler Design Tutorial for more information on maximum sprinkler spacings.)
Rule of thumb guidelines for do-it-yourselfers:
- If the distance between spray type sprinklers is more than 18' 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 the sprinklers are too far apart you will need to either adjust the sprinkler locations, 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! Remember that it is easier and cheaper to redesign everything at this point than it will be to fix problems later! For drip systems you will want to double check that you have enough emitters and tubing to reach all the areas/plants to be irrigated.
Now you need to mark the pipe locations on the ground. You can use chalk, white paint, or just drag a shovel to mark the ground where the trenches will be. For do-it yourselfers I recommend that you mock-up the pipes at this point. Lay the pipe 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 they will need to be at. This will help you visualize how the whole thing will fit together and will identify any missing fittings you need. Don't push the PVC fittings and pipe together, they are extremely difficult to get apart. Just lay them next to each other. If you plan to use swing risers for the sprinkler heads you can preassemble them at this time, and screw them into the PVC tee or ell that will be glued onto the lateral pipe. This will save time later as it is easier to screw them into the fittings before the pipe is glued together.
How to make leak-free threaded joints. When joining male and female threaded fittings, put a nice thick layer of Teflon tape on the male threads before you screw them into the fittings. Pull the tape tight onto the male thread so that the tape molds into the threads. Wrap it in the direction of the threads so it doesn't unwind off when you screw the fitting on. (If you are looking at the end of the male fitting that would be clockwise.) When you have enough tape on it, the shape of the threads will be just barely visible through the tape. Then screw the male thread into the female threaded fitting. If the joint is between two metal pieces put a wrench on it and tighten it as tight as you can get it. For plastic fittings just tighten it by hand. If you are an average guy or gal you can add one more full turn using a wrench after it is hand tight. If you have ever been called a gorilla, stop at hand tight. Over-tightening plastic fittings splits the female fitting, resulting in a leak. But not tightening them enough also gets you a leak.
Applying Teflon tape to male threads.
Note the direction the tape is wrapped around the male threads.
Marlex street ells often don't need Teflon tape to seal, but I still use a little on mine. Marlex is a shiny, black, plastic that is slightly softer than PVC. The black fittings used for "Funny Pipe" are not Marlex. Use Teflon tape on them. If you can't scratch the plastic with your fingernail, use Teflon tape!
Marlex Street Ell
Don't attach the sprinklers to the risers 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 they 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 step on it when trenching.
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 use Teflon tape or another sealer on all the threaded joints so they won't leak. Now, when I'm ready to install the manifolds later, I can 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 years.
One last tip. When you dig the trenches, all the sprinkler head flags (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 one nail to each end of the string. With the flag at the sprinkler head location, stretch out the string to form a V 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!
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