When water freezes, it expands by approximately nine percent in volume. This expansion generates immense pressure, often exceeding 50,000 pounds per square inch in a confined space. This force is sufficient to crack PVC pipes, shatter plastic fittings, and rupture metal components within an irrigation system. Protecting your system from freeze damage is a yearly necessity in cold climates to avoid costly repairs. This guide details the necessary steps to remove water and secure hardware before sustained freezing temperatures arrive.
Preparing the System for Winter
The first step in winterization is isolating the irrigation system from its water source. Locate the main shut-off valve, typically installed near the main meter or where the line branches off to feed the sprinkler system. Turning this valve to the closed position prevents water from entering the system once draining begins. This ensures that lines cleared of water do not refill accidentally during the winter.
The electronic controller that manages the watering schedule must also be deactivated. Switch the controller’s setting to the “off” or “rain mode” position to prevent accidental activation of the solenoid valves. If the controller is easily accessible, physically disconnect its power source. This prevents the solenoids from attempting to open while the system is depressurized or being serviced.
Methods for Removing Water from Lines
Once the water supply is secured, water removal can begin using either gravity or forced air.
Gravity Draining
Systems designed with manual drain valves at the low points of the mainline and lateral lines can be partially drained by opening these valves. Gravity allows the majority of the water to exit the system through the lowest elevation points. This method is effective for removing bulk water but often leaves residual moisture trapped in dips and bends within the piping.
Compressed Air Blowout
The most complete and reliable method for clearing the lines is the compressed air blowout. This technique requires an air compressor capable of delivering a sufficient volume of air, measured in cubic feet per minute (CFM), to push water through the entire length of the piping. The compressor’s CFM rating should ideally match the system’s pipe volume to ensure rapid water evacuation.
A specialized connection point, often installed downstream of the backflow preventer, is used to connect the air hose to the irrigation mainline. It is necessary to regulate the air pressure applied to the system. For standard PVC or polyethylene residential systems, the pressure must be kept below 50 pounds per square inch (PSI). Pressures exceeding this limit can fracture the piping or damage internal seals, causing catastrophic failure.
The blowout process involves opening only one irrigation zone valve at a time, starting with the zone furthest from the compressor connection point. Air is run through the zone until a fine mist, rather than a heavy spray of water, is observed exiting the sprinkler heads. ANSI-approved eye protection must be worn throughout this procedure due to the high-velocity discharge of debris and water. Once a zone is clear, its valve is closed before moving to the next zone to maintain adequate pressure.
Safeguarding Vulnerable Components
Even after the lines are cleared, specific hardware components remain highly susceptible to freeze damage due to their complex internal mechanisms. Backflow prevention devices (BFPs) are particularly vulnerable because they contain tight chambers, springs, and moving parts designed to hold water under pressure. If water freezes within the main body of the BFP, the resulting expansion often shears the internal components or cracks the brass housing.
For maximum protection, completely drain the BFP by opening its test cocks and shut-off valves to allow trapped water to escape. In areas with prolonged, deep freezes, the device should be detached from the piping and stored indoors in a temperature-controlled environment. If removal is not feasible, the BFP must be heavily insulated using specialized foam covers, ensuring all sides and connections are sealed from cold air exposure.
Other components requiring attention include control valves and manifolds, which are often housed in underground boxes. While the surrounding earth offers some insulation, water trapped inside the valve body or solenoid housing can still freeze and damage the plastic casings. Adding a layer of insulating material, such as fiberglass batting, inside the valve box provides an additional thermal barrier.
Any external pump or filter housings should also be completely drained and disconnected, or removed entirely. This prevents cracking of the plastic or metal casing during freezing temperatures.
Post-Freeze Inspection and Startup
When the threat of freezing temperatures has passed, the irrigation system must be brought back online through a careful sequence of actions. Reinstall any removed components, such as the backflow preventer or pump parts, following the manufacturer’s guidelines. Remove insulation covers from vulnerable areas, and reconnect the controller to its power source.
The process of repressurizing the system is important for preventing immediate damage. The main water supply valve must be turned on very slowly, opening the valve over a period of several minutes rather than instantly. This gradual introduction of water minimizes the effect of water hammer, a pressure surge that can rupture seals or crack components weakened by the winter cycle.
Once the system is fully pressurized, program the controller back to its desired watering schedule. Before setting it to automatic, manually run each zone briefly to visually inspect all sprinkler heads and underground connections for leaks. Observing the system under pressure ensures that any damage missed during winterization is identified and repaired before the growing season begins.