Draining an irrigation system, known as winterization, is an annual process that removes standing water from pipes and components before freezing temperatures arrive. As water turns to ice, it expands, generating immense pressure that can fracture plastic pipes, sprinkler heads, and sensitive valve components. Protecting the system’s infrastructure from structural damage extends its lifespan and prevents costly repairs.
Essential Pre-Draining Steps
Before any water is intentionally released, the primary water source must be completely isolated to prevent repressurization during the draining process. Locate the main shut-off valve, typically found near the backflow prevention device or where the irrigation line branches off the main domestic supply. Turning this valve to the closed position prevents any new water from entering the network. Simultaneously, the irrigation controller must be fully deactivated to prevent the system from cycling on. Disconnecting the controller’s power source, whether by unplugging the unit or flipping the dedicated circuit breaker, ensures that all solenoid valves remain closed.
Draining Method: Using Manual and Automatic Valves
Many simpler irrigation systems rely on the force of gravity for water removal, utilizing either manual or automatic drain valves installed at the lowest points of the piping network.
Manual Drain Valves
For systems equipped with manual drain valves, the process involves locating these specific fittings, which are often marked with a cap or a small lever. Opening these valves allows the water to exit the lines due to the natural slope of the ground, assuming the pipes have a continuous pitch toward the drain point.
Automatic Drain Valves
Automatic drain valves are designed to open mechanically when the water pressure within the main line drops below a set threshold, typically around 10 to 15 pounds per square inch (psi). These valves are spring-loaded and remain closed under normal operating pressure. Once the main water supply is shut off, the internal pressure dissipates, causing the spring to relax and the valve to open, initiating the water removal.
This passive draining method is effective only in regions where the ground slopes consistently away from the water source and the climate is less severe. Gravity drainage may not remove all residual water, especially from horizontal sections or higher elevation components, which can still pose a freeze risk.
Draining Method: The Compressed Air Blowout
The compressed air blowout method is the most reliable way to achieve complete water removal, especially in regions that experience hard, sustained freezes, as it actively forces standing water out of the entire network. This process requires specialized equipment, including an oil-free air compressor capable of producing a consistent volume of air and a proper quick-connect fitting to link the compressor to a designated point, usually a winterization port or the backflow device. Selecting the right compressor is based on the system’s pipe volume, requiring a unit rated for a high cubic feet per minute (CFM) output, rather than just high pressure.
Safety is paramount when using compressed air, as the forces involved can be hazardous if components fail or air is improperly handled. Eye protection, such as industrial-grade safety goggles, is mandatory for anyone near the system during the blowout process to guard against flying debris or water spray. It is necessary to maintain a low pressure setting on the compressor, keeping the air pressure below the maximum operating pressure of the system’s components, which is typically no more than 50 psi for standard residential lines.
The procedure begins by connecting the compressor hose to the designated inlet point and slowly introducing air into the system. The air should be added gradually, allowing it to displace the water through the furthest zones first. Only one zone or valve should be opened at a time to maximize the air pressure and velocity directed through that specific section of piping.
Once a single zone is opened, the air will push the water out of the sprinkler heads, often resulting in a forceful mist or geyser of water. The zone should be allowed to run until only a fine mist remains, which indicates the bulk of the liquid water has been successfully cleared from those lateral lines. Never stand directly over any component while the system is under air pressure.
After the first zone appears clear, the valve must be closed before moving to the next zone, ensuring that the air pressure remains focused on the section being cleared. This sequential process is repeated for every zone in the system, moving methodically from the furthest valve back toward the compressor connection point. Running the compressor for too long after the water is cleared can generate heat from friction within the piping, potentially damaging PVC components.
The backflow prevention device, which often contains small, sensitive internal components like check valves and seals, requires particular attention during the blowout. The air pressure must be introduced carefully to prevent damage to these assemblies. Many professionals recommend purging the backflow device separately or ensuring the pressure is minimized when clearing this specific component.
Due to the precise pressure regulation and potential dangers associated with compressed air, anyone who is not completely comfortable with the equipment or the procedure should consider hiring a certified irrigation professional. Professionals possess the proper industrial-grade equipment and training to execute the blowout safely and ensure the system is completely dry.
Securing the System After Draining
Once all the water has been expelled from the lateral lines, the final steps involve securing the system for the winter season. The backflow prevention device, which is often located above ground and contains metal components, must be insulated to protect its casing and internal mechanisms from freezing air temperatures. Using specialized insulation blankets or custom-fit foam covers provides a necessary thermal barrier against frost.
A final consideration is the position of all drain valves and the system’s main shut-off valve. Consult local winterization guidelines to determine the best practice for valve positioning, as some regions leave manual drain valves slightly open to allow seepage to escape, while others close them to prevent debris entry. Confirm the main water supply remains closed, and the irrigation controller remains powered off or disconnected.