The annual winterization of an irrigation system is a necessary maintenance task in regions where temperatures drop below freezing. Water trapped within pipes expands by approximately nine percent upon freezing, generating immense pressure that can rupture pipes, valves, and sprinkler heads. The only reliable method to prevent this extensive freeze damage is the “blowout” procedure, which uses compressed air to physically expel water from the entire system. This guide provides the detailed instructions required to safely and effectively complete this process using a portable air compressor.
Gathering the Necessary Equipment
The process begins with securing the correct tools, particularly an air compressor with sufficient volume, measured in Cubic Feet per Minute (CFM), to move water through the lines. Compressors with low CFM ratings often lack the sustained air volume needed for efficient water removal, causing air to ride over the top of the water instead of pushing it out. For typical residential systems, an air compressor delivering at least 15 to 20 CFM at the working pressure is recommended for a quick and effective purge, though higher volumes are faster.
The compressor must feature an adjustable pressure regulator and a functioning gauge, since controlling air pressure is necessary to prevent damage. Because the system’s pipes and fittings are not designed to withstand high-pressure air, the regulator ensures the pressure remains within safe limits during the blowout. An air adapter is also required to securely link the compressor hose to the system’s designated connection point, often a threaded fitting near the backflow device. Robust eye protection, such as safety goggles, must be worn throughout the process due to the risk of pressurized debris and water discharge.
Preparing the System for Air Injection
Before introducing any compressed air, the system must be fully isolated from the home’s water source to prevent water from flowing back into the lines. The main water supply valve should be located and turned completely off, typically found downstream of the main house shutoff or near the backflow preventer. This isolation step ensures that once the water is expelled, the pipes remain dry for the winter months.
Next, address the backflow prevention device, which often contains standing water that can freeze and damage internal components. If the device has isolation ball valves, turn them to the closed position to protect the device from the air pressure being introduced downstream. Any drain valves or test cocks on the backflow device should then be opened to allow trapped water to drain according to manufacturer’s specifications.
With the water supply secured and the backflow device drained, set the air compressor’s pressure regulator to the appropriate level before attaching the hose. The compressor hose is then securely connected to the system, typically at a designated blowout port located after the backflow device, using the adapter. Ensure this connection is tight to prevent air leaks, which compromise the efficiency of the blowout.
The Step-by-Step Blowout Procedure
The regulated pressure must be carefully determined based on the pipe material, as exceeding safe limits can instantly rupture the lines. For systems utilizing flexible black polyethylene pipe, the pressure must not exceed 50 PSI. Systems built with rigid white PVC pipe can generally tolerate slightly higher pressure, but it is recommended to stay below 80 PSI to protect the weaker sprinkler heads and fittings.
Once the regulated pressure is set, the blowout process begins by activating the zone valve furthest from the compressor connection point. This sequencing allows the air to push the maximum volume of water through the longest path first. After activating the zone via the irrigation controller, the compressor’s output valve should be gradually opened to introduce air into the system.
Air should be introduced in short, controlled bursts rather than a continuous stream to protect the system from damaging heat buildup. Friction from compressed air moving through dry pipes can quickly raise the internal temperature of plastic components. Each burst should last only until water flow from the sprinkler heads is replaced by a fine mist or vapor, indicating the majority of the liquid has been cleared.
Allow the air pressure to drop between each short cycle before reintroducing the burst of air; this further mitigates heat accumulation. Once the first zone is cleared, use the controller to close that zone valve and immediately open the next zone in sequence. Repeat this sequential process for every zone, moving steadily closer to the compressor connection point.
Each zone should ideally be blown out twice to ensure that residual water, which may have pooled in low spots, is fully expelled. A fine mist, not a steady stream of water, confirms the zone is adequately purged. After the final zone is cleared, shut off and disconnect the compressor before proceeding to the final safety checks.
Critical Safety Warnings and Pressure Management
The use of compressed air introduces significant hazards, making adherence to safety protocols non-negotiable. Never stand directly over any pressurized component, especially the backflow device, as components or debris could be ejected with dangerous force. Eye protection must be worn at all times while the compressor is connected and operating, safeguarding against flying dirt, debris, and water.
Avoid exceeding the maximum pressure limits for the pipe material, as this is the primary cause of system damage during winterization. Even if the main line can handle a higher PSI, the delicate internal mechanisms of sprinkler heads and valves are the weakest link and can be destroyed by over-pressurization. Remember that it is the volume of air, the CFM, not the pressure, that effectively removes the water.
After the system is blown out and the compressor is disconnected, the final steps ensure any remaining moisture does not cause damage. Any drain valves or test cocks on the backflow device that were opened should be left in a partially open position, often at a forty-five-degree angle. This practice allows any minimal residual water to expand without cracking the device if it freezes, completing the winterization process.