Winterizing a residential sprinkler system is a preventative measure against freeze damage that can cause extensive and costly repairs. Water expands by about nine percent when it turns to ice, creating immense pressure that can exceed the structural integrity of the pipes and lead to rupture. Water left in underground pipes, valves, and sprinkler heads is the primary risk factor, making complete removal of the liquid the goal of the winterization process.
Stopping the Water Source
The first step is isolating the irrigation system from the main water supply. Most systems have a dedicated shut-off valve, often a ball or gate valve, located on a branch line splitting off from the main household plumbing. This valve is typically found in a basement, crawlspace, or an underground box near the water meter. A ball valve is off when the handle is perpendicular to the pipe, while a gate valve is closed by turning the circular handle clockwise until it stops.
Once the dedicated valve is closed, the short length of pipe between this shut-off point and the backflow prevention device must be drained. This section often contains a small drain valve or spigot designed for this purpose. Placing a bucket beneath this point and opening the valve allows the trapped water to escape, preventing a freeze-related burst in the main supply line.
Draining the System Using Gravity or Drain Valves
For systems installed in areas with minimal freezing or those specifically designed for passive drainage, the use of manual or automatic drain valves is a simpler alternative to the compressed air method. Manual drain systems feature valves, usually simple turn-cocks or caps, located at the lowest points in the piping network. Opening these valves allows gravity to pull the water out of the pipes.
Activating each sprinkler zone for a brief period can help release pressure and encourage water flow toward these low-point drains. Some systems incorporate automatic drain valves positioned downstream of the zone valves, which open automatically when the internal water pressure drops below a certain threshold. While effective for simple systems, this gravity-based approach may not remove all water from complex or unevenly sloped lines, especially in colder climates.
The Compressed Air Blowout Procedure
The most thorough and widely recommended method for winterizing a system is the compressed air blowout, which forces all remaining water out of the lateral lines and heads. This procedure requires an air compressor and a specialized adapter that connects the compressor’s quick-connect fitting to the system’s blowout port, which is often a threaded hose connection. Safety is paramount during this process, and users must wear eye protection and never stand directly over any component while the system is pressurized.
It is important to regulate the compressor’s output pressure to prevent damage to the irrigation components. A maximum pressure of 50 pounds per square inch (PSI) is a conservative limit for most residential polyethylene piping and components, though rigid PVC pipe can tolerate slightly higher pressures. The process involves attaching the compressor, manually opening one zone valve at the controller, and slowly introducing air until water begins to spray from the sprinkler heads.
Each zone must be cleared individually, starting with the one farthest from the compressor connection point to minimize the required air volume and pressure. The zone is considered successfully purged when the water spraying from the heads changes to only a fine, intermittent mist. Once this mist appears, the compressor must be immediately shut off, as running dry compressed air through the system for too long can generate friction heat and damage the plastic gears within the sprinkler heads.
Protecting the Controller and Backflow Preventer
The irrigation controller, which manages the system’s schedule, should be set to “rain mode” or turned off completely to prevent it from cycling the valves during the off-season. This action ensures the automatic valves remain closed and do not attempt to run the system while the water supply is disconnected.
The backflow prevention device (BFP), typically located above ground, is susceptible to freeze damage. After the main water is off, the two small test cocks, or petcocks, on the BFP should be opened using a flathead screwdriver to drain the water trapped inside its chambers. Additionally, the main ball valves on the BFP should be positioned at a 45-degree angle—neither fully open nor fully closed—to prevent residual water from becoming trapped and freezing inside the valve body. Depending on local climate and code, the entire BFP unit may also need to be insulated with specialized blankets or removed entirely and stored indoors.