De-winterizing a sprinkler system is the controlled process of safely returning water pressure to the irrigation lines after they have been drained and protected from freezing temperatures. This reactivation prevents structural damage to pipes, valves, and sprinkler heads caused by a sudden rush of water. The goal is to fill the empty system slowly, allowing trapped air to escape and providing time to check for leaks. This procedure is typically performed in the spring, once the threat of a hard frost has completely passed.
Reestablishing the Main Water Supply
The first step involves locating and carefully reopening the internal shut-off valve, which controls the water flow from the main supply into the irrigation system. This valve is often located in a basement, crawlspace, or near the water meter, and must be opened slowly to prevent a high-pressure surge.
Next, attention must shift to the backflow prevention device (BFP), which protects the potable water supply from irrigation system contaminants. The BFP assembly typically has two main ball valves and two or four small test cocks. The test cocks, which were likely left open for drainage during winterization, must be closed by turning the flathead screw slot perpendicular to the valve body. The main ball valves should initially be kept in the off position, perpendicular to the pipe.
Introducing water to the BFP starts by slowly turning the first ball valve (closest to the water source) a quarter-turn to the on position, parallel with the pipe. This slow opening prevents water hammer, a destructive pressure wave caused by water abruptly hitting a closed fitting in the empty pipes. The initial rush of water must be gentle enough to avoid “dry line shock” that can damage components.
Slowly Pressurizing the System and Leak Check
With the first BFP ball valve open, the backflow preventer is pressurized, but the underground system remains closed off by the second ball valve. Visually inspect the BFP for any immediate leaks, cracks, or sprays, especially around the body and test cocks, which are vulnerable to freeze damage. A persistent drip or spray indicates a failed seal or burst component, requiring immediate shut-off and repair.
Slowly introduce water into the underground pipe network by gradually opening the second ball valve on the backflow preventer. Open this valve in small increments, allowing the water to slowly fill the main lines. The slow rate of fill displaces trapped air, pushing it out gradually through the sprinkler heads and preventing the air from causing a damaging pressure spike when it reaches a closed zone valve.
After opening the second ball valve slightly, pause for 15 to 30 minutes to allow the air to fully bleed out of the system. The sound of rushing water should diminish, and any sputtering from the highest sprinkler heads should stop. Once the system has stabilized and no immediate leaks are apparent, the second ball valve can be fully opened, completing the pressurization of the main line.
Testing and Adjusting Zones and Sprinkler Heads
With the main lines pressurized, activate the system using the irrigation controller, starting with the first watering zone. Manually running each zone sequentially allows for a thorough inspection. As each zone cycles on, confirm that all sprinkler heads are fully extending, indicating sufficient water pressure.
Observe the spray pattern for proper coverage, looking for areas that are not receiving water or sections that are oversaturated. Low pressure across an entire zone may point to a significant underground leak. An erratic spray from a single head suggests a clogged nozzle or a broken seal. Minor adjustments, such as changing the spray arc, can be made using a small flathead screwdriver while the zone is actively running.
After confirming mechanical components are working correctly, program the controller for the season. Set the initial watering schedule based on current plant needs and local watering restrictions. This ensures the system is ready for automatic operation, though the schedule will require adjustment as the weather changes.
Troubleshooting Common Issues
Immediate activation may reveal several minor issues that are simple to address without professional assistance. If all zones exhibit noticeably low pressure, the most frequent cause is the internal shut-off valve or one of the backflow preventer ball valves not being fully open. System-wide low pressure may also indicate a major leak, typically evident by a distinct hissing sound or a localized area of standing water.
If water is continuously trickling or flowing out of the backflow preventer, especially from the relief valve or test cocks, it often signals a failure in the internal seals or springs, which are susceptible to damage from freezing. This issue prevents the system from holding pressure and generally requires replacing the internal components or the entire backflow assembly. A professional certified in backflow prevention is typically required for this type of repair.
Should a single watering zone fail to turn on when commanded by the controller, the problem is usually electrical, specifically a faulty solenoid or a wiring connection issue at the valve box. While a broken solenoid can be replaced, major problems like a burst pipe along the main line, which manifests as a significant and sustained leak, are best handled by an experienced irrigation technician.