Water left inside an outdoor sprinkler system during cold weather presents a serious risk of damage. When water freezes, it expands by about one-eleventh of its volume, which is enough force to crack pipes, fittings, valves, and sprinkler heads. This process, known as winterization, involves using compressed air to “blow out” the remaining water from the underground lines before the first hard freeze. The compressed air blowout method is the most effective way to ensure the system’s longevity and avoid costly spring repairs, since relying on manual or automatic drain valves alone is often insufficient.
Essential Equipment and Safety Measures
Proper execution of the blowout method requires specialized equipment and strict adherence to safety protocols. A suitable air compressor must be used, focusing on both its pressure (PSI) and volume (CFM) capabilities. For most residential systems, the compressor should deliver a minimum of 10 to 25 CFM to ensure the air has enough volume to push the water out. Insufficient CFM may only push air over the top of the water, leaving a significant amount in the lowest points to freeze.
The pressure must be carefully regulated to prevent damage to the irrigation components. The maximum safe pressure for rigid PVC piping is typically 80 PSI; flexible polyethylene pipe requires a lower limit of 50 PSI. It is recommended to set the regulator between 40 and 50 PSI to start and never exceed 80 PSI, as excessive pressure can rupture pipes or cause sprinkler heads to fly off. A specialized air fitting adapter screws into the designated blow-out port or near the backflow preventer. Safety glasses are mandatory, as pressurized air and debris can eject unexpectedly from the sprinkler heads.
Step-by-Step Guide to Blowing Out Sprinkler Lines
The winterization process begins with shutting off the main water source that feeds the irrigation system. Locate the isolation valve, typically found before the backflow prevention device, and turn the water off. Once the water is shut off, open a drain valve or the test cocks on the backflow device to relieve static pressure in the mainline. Next, attach the air compressor hose to the system’s designated connection point using the specialized adapter.
Before turning on the air, confirm the compressor’s pressure regulator is set to a safe PSI level, typically 50 PSI or below. The system’s controller should be activated to open the zones sequentially, starting with the zone highest in elevation or furthest from the compressor connection. As compressed air enters the line, water will spray from the sprinkler heads in the active zone. Run the compressor only until a fine mist appears from the heads, indicating the majority of the water has been expelled.
Avoid running the air “dry” for more than a few seconds after the water is gone. The friction from the compressed air can generate heat and damage the plastic internal components of the sprinkler heads. Once a zone is clear, switch the controller to the next zone and repeat the process until all zones are cleared. Repeating the cycle two or three times ensures any remaining pockets of water are removed from the lowest points in the system.
Securing the System for Winter
After the sprinkler lines have been cleared, the backflow prevention device must be addressed to prevent freeze damage. The above-ground backflow assembly is vulnerable to freezing temperatures. The shutoff valves should be turned to a 45-degree angle, or halfway open, to allow for expansion space and prevent water from being trapped in the ball-valve mechanisms.
The test cocks, small ports on the backflow device, should be opened using a flat-head screwdriver to allow residual moisture to drain. These test cocks should be left slightly open for the duration of the winter to allow for ongoing drainage and pressure relief. Finally, the main irrigation controller should be turned to the “off” or “rain delay” setting to prevent accidental activation of the system during the winter.