Irrigation access boxes get no respect
Of all the parts needed to install an irrigation system, the valve box is perhaps the most underestimated and under-appreciated. Some of the earliest residential irrigation systems consisted of nothing more than a 4-inch diameter tin cover over a 4-inch pipe that was placed over the valve. The lid rested slightly under the turf. On service calls, it was not uncommon to find a valve, buried, with no valve box at all. Without valve boxes, these irrigation systems worked fine--until it was time to service them. Without a set of plans, it could take hours using a wire locator to find the valve. Then, the trick was digging up the valve without damaging it.
Simply put, the valve box's purpose is to protect the valve, as well as to allow for convenient adjustment or service. Additionally, valve boxes protect other parts of an irrigation system that may need service, including: wire splices, gate valves, ball valves, certain types of backflow preventers, multiple drip emitters, flush valves, air-relief valves and the like.
Valve-box materials and sizes vary Typical irrigation valve boxes are made of a strong, thermoplastic material, especially suitable for underground use. They are light in weight, easy to handle and ideal for enclosing key parts of an irrigation system that encounters only light-to-medium traffic. When a valve box needs to withstand a larger load, such as the weight of cars or trucks, concrete or cast-iron boxes are a better choice. Standard sizes include 6-inch round economy, 6-inch round deluxe, 10-inch round, standard square and jumbo. Check with local distributors to meet special applications or to investigate other options.
One type of a specialty valve box is the emitter box. Manufacturers specifically designed it to cover multi-outlet drip emitters. These differ from standard boxes in that they have long slots up the sides to accommodate the quarter-inch distribution tubing that you can feed up the sides. These boxes not only protect the emitter but also help to prevent potential vandalism.
Concealing the box: color The box's color and placement can make it more or less noticeable. The most common color used for valve boxes in the irrigation industry is green--for the distinct purpose of matching the color of turf and blending with the natural surroundings. Recently, however, many irrigation consultants and owners have started to specify black boxes. General consensus is that the black color seems surprisingly less noticeable than green, even in turf. Plus, in planting beds, the black color blends well with mulch.
In terms of placement, the obvious objective is to install valve boxes in areas where they will be less noticeable, or hidden from view entirely, so as not to detract from the beauty of a landscape. Often, if possible, it is best to install the box in a planting bed vs. a lawn area where it may be more visible. Clearly, if you install the irrigation system before you install the landscape, it may be more difficult to identify which areas may be less conspicuous.
Installation at the proper height The actual installation of the box and valve is quite simple. And, with a few additions, a valve box will serve its intended purpose for an extended period. In turf, set the top of the valve box at grade. In shrub beds, set it 1- to 2-inches abovegrade to allow for mulch.
Typically, when installing a valve box over a valve, you should adjust the depth and width of the hole dug for the box to accommodate the valve. Cut the bottom of the box so that it does not rest directly on the pipe or wire. In an installation where the weight of vehicles or mowers could damage the piping under the box by compressing it, place bricks underneath the box to increase its strength. In instances where you have more than one box or extensions to a box, place one row of bricks in the bottom corners for added support. (Generally, two bricks should accommodate an economy-sized box. Use up to eight bricks for a jumbo-sized box.)
When installing a box over multiple valves or manifolds, you'll need to cut more of the box. For this reason, most valve boxes come with knock outs to provide easy installation. This is done by placing the box over the assembled valve and pipe and scoring those areas of the valve box. You'll then trim these areas with a pipe saw. When estimating the cut, remember that the valve box will need to sit flush with the grade. Once you've marked the box, cut from the bottom uptoward the lid in at least two places. Make these cuts long enough so that there is at least 1 inch between the box and any pipes. Using the pipe saw, cut across these two cuts just enough to score the piece. Then use pliers to break off the piece.
Special considerations Whenever you install a valve box over any type of valve, it is important to keep in mind the underlying purpose of the valve box: to access the valve. Therefore, make sure you center the valve in the box with its top about 4 inches from the bottom of the lid. When grouping valves together, be careful not to force too many into one box. Often, they can become so tight that the box actually has to be dug up to service the valves, defeating its original purpose.
The same rules that apply to setting sprinkler heads also apply to valve boxes. Don't install them against sidewalks, curbs or up against buildings, because you can damage them during edging operations or vehicles can damage them. Also, beware of setting boxes next to bed lines. These areas tend to "creep" over the years and may end up creating an eyesore if half the box lies in turf and the other in a bed.
On commercial projects, it is common for contracts to specify gravel (1 to 4 inches) and filter fabric for the inside of the valve box. This keeps the inside of the box neat and provides adequate drainage. The gravel should be about 4 inches thick from the bottom of the valve to the bottom of the box. When servicing the system, be aware that errant gravel pieces can enter the valve when you open it. A recent specification our firm followed also called for the valve box itself to rest on a 4-inch gravel base.
Some irrigation contractors use filter fabric to prevent soil from settling back into the box. Wrap the fabric under and around the valve box and secure it with duct tape. The tape will hold the fabric in place until you've completed backfilling. With the combination of gravel and filter fabric, a valve box can more easily fulfill its objective for the life of the project.
Protect the box You can purchase valve boxes with locking covers to protect against vandalism. This typically consists of a nut that is molded into the box to bolt down the top. For this device to be successful, it is important that you reinstall the bolts each time you service the valve. If you have large commercial or golf installations, consider branding valve boxes with the number identifying the controller and zone. Doing so can be a big time-saver when troubleshooting large systems. Both propane and electric branding irons are currently available, providing the installer with the option of branding boxes in the field or at the shop.
In short, thermoplastic valve boxes aren't simply an extra charge that gets needlessly added on to the bottom line of an irrigation installation. Rather, they provide the means for a quick system repair or adjustment and they are instrumental in "finishing off" a professional-looking job. With proper installation, they will last the life of an irrigation system, increase the system's efficiency and add to the aesthetic integrity of the project.
John Helander, who lives in Gainesville, Va., is a certified water auditor and manager for Ruppert Landscape Co.'s irrigation services department. Ruppert Landscape is a full-service, commercial landscape contractor based in Ashland, Md., specializing in landscape installation, maintenance, irrigation and environmental restoration.
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