This page addresses the installation of valves in underground boxes. For installation of anti-siphon type valves see the previous page of this tutorial Anti-Siphon Valve Installation, but you should read this page too. There is some useful information here on other items you may need to address while installing your irrigation system. The detail below shows a typical underground valve installation for a commercial irrigation system.
The first question do-it-yourselfers ask is "do I really need a box?" The answer is no, you can directly bury the valve in the soil. But it's not a terribly smart thing to do. If the valve breaks and you buried it without a box you are going to have one nasty job repairing it. Chances are if it's an electric valve you will cut the wires trying to dig down to the valve, and those wires are not fun at all to try and find and splice back together! As an added bonus a good sharp shovel will cut clean through a plastic valve before you even realize you hit it! So put it in a box. If you really need to save money you can make a box out of something laying around the house, like an old 1 or 5 gallon plastic container. The new plastic one gallon paint cans that showed up on the market in the last few years also work pretty well. You'll need to completely bury it, so be sure to mark the location somehow so you can find the valve later.
You will note that the valve box is sitting on a 4" deep layer of crushed rock and that all openings in the box need to be sealed. This is very important. Sealing the openings keeps dirt from washing in. Plastic tape works pretty good for most of the smaller openings, a piece of plastic milk jug can be taped in place to seal any bigger openings. The rock layer under the box serves three purposes. First it supports the box to keep it from sinking, so put the rock in before you install the box so the box sits on top of the rock. Don't pour rock into the box after it's installed, that's no help at all! Without some form of extra support most boxes sink into the ground with time, usually leaving the box sitting at an odd angle. The rock also provides drainage for any water which gets into the box. But one of the most important purposes of the rock is to keep out critters such as moles and gophers. They love these boxes! They won't make their home in the box but they will fill the box completely with dirt (toads, spiders, and snakes will move into the box, however, if they can find a way in). Here's an experiment you can do for a little fun. Find an active gopher hole and remove the dirt piled around it. Place a medium size cardboard box with the top removed upside down over the hole and anchor it in place. Seal out any light that gets into the box. Leave it for a day or two. When you return the box will be completely filled with dirt! This is an old gardener's trick for getting nice pulverized soil for use around the garden. Hey, if you've got gophers you may as well put them to work for you!
Why Only One Valve per Box?
Why only one valve per box? You can install more than one valve in a box if you want to. In commercial irrigation work we only install one valve per box because it makes future maintenance much easier. If you ever need to work on the valve, it is much easier if it isn't crammed into the same box with another valve. A common mistake I see homeowners make is installing valves too close to each other. When gluing pipe it is very easy to install the valves side-by-side with almost no space between them. But what happens if you ever need to remove one? Did you leave enough room to unscrew the valve? Often valves on PVC pipes need to be cut out to remove them (which is OK, that's the way professionals do it). After repair they are then glued back in using a special repair coupling. But if the section of pipe is too small, you won't have anything to glue the new fitting to! So the rule-of-thumb is that all pipe lengths that may need to be cut in the future should be at least 6" long. And when cutting out a valve, always make your cut at least 2" from any fittings. That leaves a short section of pipe sticking out of the old fitting that you can glue the new repair coupling onto.
What are the plugs for?
You may have noted the two plugs on either side of the valve in the detail. These allow access for installing a future liquid fertilizer injector for applying fertilizer using the irrigation system. These plugs are optional, however I strongly recommend installing them, especially if the valve controls a drip system. Calcium and other minerals in the water can build up on the emitters and plug them with time. A weak acid solution can be injected into the water to dissolve the mineral deposits by using a fertilizer injector . Some people also like to place a hose bib on the upstream side of the valve where the plug is. This allows a garden hose to be attached for supplemental watering or whatever. Make sure you install the hose bib on the inlet side of the valve or the hose will work only when the valve is on!
I can't stress enough that the wire splices must be completely waterproofed! Simply wrapping them in plastic tape is not sufficient. Here's why: Take a look at the wire attached to the valve. You will notice that it is multi-strand (several small wires twisted together into one wire). Multi-strand wire can carry more voltage than single strand wire and is more flexible, making it idea for the short leads on the valve where both of these features are useful. But multi-strand wire has one big disadvantage in this situation. Capillary action causes water to be drawn up the small spaces between the multiple wires, right into the valve's solenoid! When the water gets into the solenoid it destroys it. Leaking wire splices are the cause of 90% of electric solenoid failures. So you almost eliminate the chances of a valve failure simply by taking the time to water-proof the wire splices immediately. That means before ANY water gets near the valve! Don't wait a day or two before you water-proof the splices, do it now! All it take is one drop of water on the wire and you can kiss that solenoid good-bye!
There are several special connectors made for underground wire splices which create a waterproof splice and are the best way to seal the splices. Most of these are simply a special wire connector and/or container filled with a very thick grease gel. The splice is pushed into the grease and the grease flows around it sealing it. Do-it-yourselfers who are cheap or can't find these connectors can make their own. Use a standard wire connector to make the splice. Make sure the wire connector is the correct size for the wires you are splicing. Do not try to "make do" with the next wire connector size smaller or larger or you will regret it, that's a promise! After making the splice fill the wire connector cavity with kitchen and bath type 100% silicon sealer, making sure no gaps or holes are present and no bare wire is exposed. Next coat the entire wire connector and the wire for 2 inches away from the connector with a layer of the sealer (yeah it's messy, that's the price you pay for being cheap). After the sealer dries wrap the whole thing in a couple of layers of electrical tape. Do not shortcut on the wire sealer or you will curse yourself later when the valve fails! You've been warned.
Did I mention previously that snails also like to live in valve boxes that aren't sealed? If you look closely at the detail you will see that it shows "pig tails" in the wire, created by wrapping a 24" length of wire around a 1/2" pipe then removing the pipe. Everything in that detail has a purpose! In this case the pig tails provide some extra wire for the future should you need it to make repairs. You will appreciate it if you ever have to remove the valve. But there is another purpose for those piggy parts. As everyone knows, lightning sometimes strikes the ground. And of course, lightning is electricity and electricity likes to follow wire! Guess what you're burying in the ground with your irrigation system? Lots of wire for the lightning to follow! O.K., realistically a direct lightning strike on your valve or wire is going to fry it to a crisp. But in an electrical storm tremendous amounts of static electricity builds up in the ground which can surge through the wires and damage the valves. The pig tails literally throw off this static electricity surge when it hits them, offering a small but significant amount of protection for the valve. There is some debate as to whether this really works, but my position is it's cheap insurance, you need the extra wire anyway, and it looks cool, so why not? This brings up a related subject which is protecting your controller. Most controllers are built to take the electricity surge and pass it through to the ground without damage. Note well that it passes it on to the ground, as in a ground wire connected to a grounding stake driven deep into the ground. If you don't install a ground wire on your controller it has nowhere to pass the surge to. This means a separate ground wire, not the third so-called ground wire in the building's electrical wiring circuits. If you are installing this irrigation system in an area with frequent lightning storms you better install that separate grounding rod shown on the controller details or you're liable to be buying a new controller one of these days!
There are additional valve details with this tutorial, showing different types of valves and applications. Most of the above items also apply to those details too. You should find a valve detail appropriate to your situation. Don't neglect those drain valves if you're installing the irrigation system in an area where the water in the pipes could freeze and break the pipes!
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