Winterization is the process of protecting an underground lawn irrigation system from winter weather. This involves removing water from the pipes, valves, and sprinkler heads to prevent damage from freezing temperatures. Water expands by about 9% when it freezes, generating immense pressure within confined spaces. This expansion inevitably leads to burst pipes, cracked fittings, and destroyed backflow preventers. Winterizing the system is a necessary preventative measure to avoid costly repairs and ensure the system operates correctly when spring arrives.
Determining the Optimal Time for Winterization
The ideal moment to drain a sprinkler system is directly tied to local climate and the forecast for a “hard freeze.” Water begins to freeze at 32°F, but the surrounding soil provides temporary insulation for buried pipes. A brief dip below freezing overnight typically does not cause damage to underground components.
The danger arises with a sustained drop in temperature, defined as a hard freeze, which occurs when the air temperature falls to 28°F or lower for several consecutive hours. This prolonged exposure allows the cold to penetrate the insulating soil layer and reach the water inside the pipes. For many northern regions, this window often closes by late October, requiring winterization before then.
Homeowners in areas with moderate winters may be able to wait until late November or early December, but those in colder climates often need to act earlier in the fall. The system must be fully drained before the first anticipated overnight hard freeze to eliminate the risk of damage. Relying on historical averages is risky; instead, monitor long-range weather forecasts for the first predicted period of sustained temperatures below 28°F.
Preparatory Steps Before Draining
Before any water removal method is employed, the water supply to the irrigation system must be shut off completely. This prevents water from flowing into the system while the draining procedure is underway. The main shut-off valve is typically located near the water meter or in a basement and must be closed first.
It is also necessary to turn off the sprinkler system’s controller or timer. If the controller is accidentally activated during the draining process, it could cause mechanical valves to open or close unexpectedly, potentially leading to damage or making the procedure ineffective. Turning the controller off ensures the system remains inactive until it is repressurized in the spring. After the water supply is off, the pressure must be relieved by briefly running a zone or opening a drain valve.
Comparing Different Draining Methods
The method used to remove water depends on the system design and the severity of the winter climate. Systems in the mildest climates may utilize manual drain valves, which are installed at the low points of the piping. These require a homeowner to physically open the valves to let water drain out by gravity. However, this method is unreliable because the underground pipes can shift over time, creating pockets where water is trapped, making it insufficient for regions with consistent freezing.
Some systems are equipped with automatic drain valves, which are spring-loaded components that open automatically when the pressure in the line drops below a certain threshold. These are also installed at low points and rely on the principle that when the main water supply is turned off, the drop in pressure causes the valves to open and drain the line. Like the manual method, automatic valves do not guarantee complete water removal, leaving the system vulnerable to freeze damage in harsh climates.
The most comprehensive method for regions that experience hard freezes is the Air Blowout Procedure. This technique uses a large air compressor to force air through the lines, pushing residual water out through the sprinkler heads. For any location where the ground freezes consistently, the blowout method is the only way to ensure the water is fully evacuated from all components, including the valves and backflow preventer.
Step-by-Step Guide to the Air Blowout Procedure
The air blowout procedure is the most effective method for winterization but requires careful attention to safety and equipment specifications. Before connecting any equipment, put on safety glasses to protect your eyes from debris expelled by the high-pressure air. A specialized air compressor with a high volume, typically 30 to 50 cubic feet per minute (CFM), is necessary to move the water through the pipes.
The air compressor is connected to a dedicated blowout port, usually located near the backflow preventer. The pressure must be carefully regulated to avoid damaging the system: for PVC piping, the pressure should not exceed 80 pounds per square inch (PSI), and for polyethylene pipe, it should be kept below 50 PSI. Excessive pressure can cause pipes to rupture or fittings to fail.
The process requires working through the system zone by zone, starting with the one furthest from the compressor connection. Each zone should be opened individually via the controller to allow the compressed air to flow through the pipes. The air runs until only a fine mist, or no water at all, is seen exiting the sprinkler heads.
Avoid running the compressed air through a completely dry line for more than a few seconds, as the friction can generate heat that melts plastic components. Once a zone is clear, it should be closed before moving to the next zone, cycling through the entire system. Finally, the air pressure should be bled off, and the backflow preventer must be depressurized. Homeowners uncomfortable with the high-pressure equipment should hire a professional for this procedure.