How to Install Underground Sprinklers

Introduction: How to Install Underground Sprinklers

About: The official instructable for Popular Mechanics magazine, reporting on the DIY world since 1902.

If you’re tired of dragging that old lawn sprinkler around every few days, you may want to consider installing your own underground sprinkler system. By doing the job yourself, you can save 30 to 40 percent of the cost of a professional installation, and today’s sprinkler components are easier than ever to assemble. Once your system is in place, you can program it to water your lawn on a regular schedule, and also set the startup time and watering duration. You can allocate more water to some areas than others, and rain sensors are available to override the program on rainy days.

As you might imagine, much of the heavy lifting is in the planning. Manufacturers know that helping you feel comfortable with the installation is the best way to sell their products, so they offer plenty of help. You’ll find installation videos next to sprinkler parts in home centers, and most companies that sell retail offer a custom-design service. To start this process, measure your water pressure at an outdoor faucet with a simple pressure gauge available at home centers (Photo 1). Then, use a 5-gal. bucket to measure how much water the system delivers per minute. Send this information to the manufacturer, along with a scale drawing of your property with all landscape features. In return, you’ll receive a detailed system layout with all components sized and color-coded.

Along with the diagram, you’ll get a complete materials list, including essential items not sold by the manufacturer. Some companies charge for this service, others don’t. Rain Bird, the company we used for the primary sprinkler components, charges $30. But, from Rain Bird you get a plan with an engineer’s stamp, which means preapproval if you live in a state with water conservation requirements (Rain Bird Irrigation Corp., 7590 Britannia Ct., Suite A, San Diego, CA 92154-7403; 800-426-7782; Your system layout will divide your lawn into zones, each controlled by a zone valve. We installed one set of three valves in the front yard and two sets in the back for a total of eight zones and 48 sprinkler heads.

While you can install the entire system yourself and dig everything by hand, we installed the piping with a pipe-pulling machine that uses a heavy blade to drag the pipe through the soil with minimal surface disruption. We paid about $150, plus the cost of materials, to have the job done. You also can rent a pipe puller and do the work yourself. In addition to the valves, heads and control panel from Rain Bird, we used a clever, self-tapping saddle valve called the Blazing Saddle (Tom King Harmony Products Inc., 2129 Barrett Station Rd., No.143, St. Louis, MO 63131; This bright yellow valve snaps onto polyethylene pipe without a wrench. The fingertight tap bores a hole that seals immediately.

In warm climates, you can run the entire system in PVC pipe (not CPVC). PVC can’t take a freeze, however, so cold-climate installations usually include some polyethylene pipe and must be drained in the winter. We used PVC pipe between the house and the zone valves and finished the job with polyethylene pipe, plus some copper to go through the rim joist and down to ground level. Every system needs a backflow preventer to keep the lawn from contaminating the potable water system. One type is a standard, surface-level backflow preventer (about $150), which must be installed 12 in. above the highest point of the yard. We installed a reduced-pressure backflow preventer (about $300) because it’s allowed below grade. We put it in the basement and will drain the system to this point each winter. As you might suspect, the cost of an in-ground sprinkler system can vary widely. As a reference point, our eight-zone system ran about $1500.

This project was originally published in the April 2002 issue of Popular Mechanics.  You can find more great projects at Popular Mechanics DIY Central.

Step 1: Running the Pipes

If you plan to dig the entire system by hand, dig the main runs first, then the branch lines. They should be at least 6 in. deep, but 8 to 10 in. will give you better fitting room.If you’ve rented a pipe puller, begin by attaching the pipe to the machine’s blade (Photo 2). When running a main feed line, it’s best to wrap the low-voltage cable around the pipe and pull it at the same time. With the piping connected, start the machine moving forward and lower the blade into the ground (Photo 3).

Bore through your home’s rim joist and run copper pipe and cable through the hole and to the ground. Make the conversion from copper to PVC at ground level with a threaded connector. Run the main PVC line, along with the cable, to the first zone-valve location. Assemble the valve sets above-ground, then cement them to the underground piping (Photo 4). Install a plastic, inline drain fitting on the downstream side of each valve and connect the cable wires.

Our cable had 10 wires and each zone valve had two lead wires. Connect one of each pair of valve lead wires to a common (white) cable wire that will service all of the valves. Join a different color-coded wire to the other lead of each zone valve. Continue making connections in this way until you’ve reached the last set (Photo 5). With all the valves connected and wired, install valve boxes and backfill (Photo 6). The feed line also needs to have a drain fitting at its lowest point.

Thread a brass drain fitting into the threaded branch of a PVC tee and install the tee at a downward 45˚ angle (Photo 7). Dig a small depression under the drain and fill it with sand and gravel. If you’ve hired an operator or rented a machine, you’ll be able to bore under sidewalks and driveways with the boring attachment. Otherwise, tunnel under these obstacles by hand or use a homemade sluice pipe. Attach a pointed sluice nozzle, available at home centers, to one end of a length of PVC pipe. Join a hose connector to the other end of the pipe, and dig shallow trenches on opposing sides of the sidewalk. With the hose connected and the water turned on, repeatedly push the pipe forward and back under the sidewalk to create the hole (Photo 8).

Polyethylene pipe is joined by barb fittings. These can be secured by hose clamps, but stainless steel crimp rings (Oetiker clamps) are a better choice. They’re inexpensive ($16 for 100) and are a snap to use. Cut the pipe with a scissor-style pipe cutter (Photo 9). Slide a stainless steel crimp ring onto each pipe and insert the barb fittings (Photo 10). Slide the rings in place and crimp them tight with the pliers (Photo 11). Installing The Heads

Step 2: Installing the Heads

The sprinkler heads can be connected to the pipes in several ways. If drainage is not a problem, the simplest method is to install a 90˚ ell with a barb fitting on one end and a female thread on the other (Photo 12). If you’re at a low spot and need seasonal drainage, install a 90˚ drain ell instead (Photo 13).

From there, you can connect a head to the ell with a threaded riser, or make an offset swing pipe. Swing-pipe connections offer a few advantages. First, you don’t need a supply pipe directly under each head, and second, offset fittings make the connection more durable. To make a swing-pipe connection, thread one 90˚ ell into the drain fitting and another into the bottom of a sprinkler head. Use Teflon tape on the threads. Then, join the two ells with a length of 3⁄8-in. polyethylene swing pipe (Photo 14). This fit is so snug that it doesn’t need a crimp ring. Finish by filling the hole while tamping the soil with a rubber mallet every 4 in. (Photo 15). When tapping into a continuous piping run, use the self-tapping saddle valve mentioned earlier.

Open the collar and press the saddle onto the pipe until you feel the bottom of the valve’s collar snap together (Photo 16). Then, thread the tap into the saddle until it pierces the pipe and clicks tight (Photo 17). To connect the head, install either a swing pipe or a threaded riser in the top of the fitting (Photo 18). We equipped our entire system with three types of heads: spray heads for small areas, rotary heads for the large areas and a bubbler for the flower garden. The bubbler sends a trickle of water through 1⁄8-in. tubing to various spots in the garden (Photo 19).

Step 3: Final Touches

Local plumbing codes will dictate how you tap into your household water system, but our installation was fairly typical. We cut into the 3⁄4-in. waterline just beyond the meter and upsized to 1-in. pipe for the sprinkler system branch line. Soon after the tap, install a full-flow ball valve (Photo 20). After the ball valve, install a brass nipple and the reduced-pressure backflow preventer (Photo 21). Run piping from the backflow preventer to the pipe installed through the rim joist.

This type of backflow preventer will occasionally back surge, so you’ll need a catch basin with an air gap underneath it. Pipe the basin to a nearby floor drain with 1-in. pipe (Photo 22). The piping after the backflow preventer will also need a drain valve so you can drain the overhead line in winter. Install the control panel on a convenient wall. Run the cable into the panel, strip the wires, and connect them according to the manufacturer’s instructions (Photo 23). Outside, pull the plugs from the sprinkler heads and flush the dirt from each zone. When the water runs clear, install the grit strainers and nozzles, and make angle and volume adjustments at the heads.

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