Irrigation 101

PART 3: IRRIGATION SYSTEM INSTALLATION

In many states, the law requires that only licensed plumbers install backflow preventers and tap into the potable water supply. Many times, an irrigation contractor purchases the backflow preventer and has a plumber install it; a large irrigation contractor may have a full-time plumber on staff.

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Each type of backflow preventer has strict installation requirements. Some types of preventers (pressure vacuum breakers and reduced-pressure type) will dump water when contaminated. Therefore, you need to install the device outside, with a catch drain or in a drainable room so flooding does not occur. For smaller systems, install backflow preventers with copper pipe inlets and outlets. Units larger than 3 inches are installed on steel or ductile iron piping.

You can install pipe either by pulling or trenching. This again will depend on the size, type of pipe and geographical preferences. Pipe 2 inches and less is often pulled. Polyethylene is piped more commonly than PVC.

Install pipe deep enough so that maintenance practices will not damage it, but not so deep that you can't service it. The trench you use should be free from rock and other debris. Install the pipe in a consistent manner with no sharp turns. Glue the fittings per the manufacturer's requirements. It is a good idea to double-clamp polyethylene fittings.

Wire is not pulled, but laid. Never pull wire directly off the roll; it will go in too tight. It is important to install the wire with plenty of slack, especially at valve boxes to allow for servicing. Install wire beside or below the pipe to prevent damage. Place 24-volt wire and 120-volt wire on separate sides of the trench.

Install valve boxes at grade and, where possible, in landscaped areas where you can cover them with mulch. Make sure covers are intact and securely fitted to the box.

Height of sprinklers

Install sprinklers flush to grade so that mowing or other maintenance will not damage them. Sprinklers installed too low will have their streams affected by the turf. Sprinklers installed too high are subject to damage from traffic and mowers, and can pose a tripping liability.

You can install sprinklers on a number of support devices, but it is important that there not be a rigid connection between the sprinkler and the pipe. This causes the force of any weight going over the sprinkler, such as the mower, to be transmitted directly to the pipe, which can cause the pipe or fitting to break. Use a flexible connection such as a swing joint or swing-pipe assembly.

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