Winterizing a home irrigation system is a necessary annual task in any region that experiences freezing temperatures. Water left inside the pipes, valves, and sprinkler heads expands as it freezes, exerting pressure that can rupture components made of plastic or metal. This leads to costly repairs and system downtime in the spring. Draining all water from the system before the first hard freeze is the only reliable way to prevent this damage.
Preparing the Sprinkler System for Draining
The process begins by isolating the irrigation system from the main water source. Locate the dedicated shut-off valve for the sprinkler line, typically a ball or gate valve near the water meter, in a basement, or in a utility box outside. Turning this valve to the closed position stops the flow of water into the system.
Once the main water supply is secured, relieve the residual pressure within the mainline. This is accomplished by briefly running a sprinkler zone from the controller or by opening a hose bib downstream of the main shut-off valve. Allowing the pressure to drop helps prevent a forceful release of water when opening drain valves or connecting a compressor.
The backflow prevention device, often located above ground, is highly susceptible to freezing damage and must be drained. First, close the isolation valves on both its inlet and outlet sides. Next, open the small test cocks, typically equipped with slotted screws, using a flathead screwdriver to allow trapped water to escape. Leaving the backflow device full of water can cause internal components to crack, requiring replacement.
Draining Systems with Manual and Automatic Valves
Some irrigation systems drain passively using gravity, but this is only effective if the lines slope toward designated drain points. Systems with manual drains feature small, screw-type valves or removable caps located at the lowest points of the main and lateral lines. Opening these valves one by one allows the water to exit the system.
After opening the main drain valve, also open the drain caps or valves on the lateral lines, which feed the individual sprinkler heads. This ensures water is removed from both the primary and secondary piping networks. Once the flow slows to a trickle, leave the drain valves open to prevent a vacuum lock, which can trap pockets of water.
Systems equipped with automatic drain valves require minimal intervention. These spring-loaded valves are installed at low points and open automatically when the line pressure drops below a threshold, typically 10 to 15 PSI. For these systems, shutting off the main water supply and relieving mainline pressure is usually sufficient to initiate drainage. However, since this method may not remove all water, the compressed air blowout method is often preferred in areas with severe winter conditions.
The Compressed Air Blowout Method
The blowout method is the most thorough way to remove water, using a portable air compressor to force moisture out through the sprinkler heads. This requires a compressor with sufficient volume, ideally delivering 20 to 50 cubic feet per minute (CFM) for a typical residential system. Connect the compressor to a dedicated blowout port or a hose bib on the system’s side of the backflow preventer.
Safety is important, and air pressure must be regulated to prevent damage. For flexible polyethylene pipe, pressure should never exceed 50 PSI. Rigid PVC lines can handle up to 80 PSI, but staying below 60 PSI is recommended to protect sprinkler heads and seals. Eye protection must be worn, as air and debris eject forcefully from the heads.
Perform drainage one zone at a time, starting with the zone farthest from the compressor connection point. This sequencing pushes the maximum amount of water through the longest sections first. Once the compressor is connected, activate the farthest zone via the controller, and gradually introduce the air into the system.
Allow the zone to run until the spray turns into a fine, white mist, indicating most water has been expelled. Immediately shut off the air supply to that zone and repeat the process for the next closest zone. Running compressed air through a completely dry pipe can generate friction heat, potentially melting plastic components and seals. Repeat the entire cycle two to three times, allowing the compressor to fully recharge between zones.
Final Steps for Winterizing the System
Once the lines are cleared, switch the irrigation controller or timer off or place it into “rain mode.” This prevents the system from activating zone valves during the winter, which could cause a dry run and damage internal solenoid components. Disabling the controller ensures the system remains dormant until spring.
Insulate any above-ground components, particularly the backflow prevention device, to protect them from temperature drops. Wrapping the device with foam insulation tape or a purpose-built cover shields the metal from the cold. Although the backflow device was drained earlier, insulation provides extra protection against freezing where small amounts of water may remain.
Finally, ensure all manual drain valves and the test cocks on the backflow device are left partially open. For ball valves, leave the handle at a 45-degree angle to the pipe. This slightly open position prevents water from becoming trapped and allows any residual moisture that condenses within the lines to escape, securing the system for winter.