A sprinkler blowout is the seasonal process of removing all residual water from an in-ground irrigation system using highly pressurized air. This procedure is a fundamental part of winterizing any sprinkler system in regions that experience freezing temperatures. The goal is to completely clear the underground pipes, valves, and sprinkler heads to prevent damage during the winter months. This preventative maintenance ensures the system remains intact and ready for operation when warm weather returns.
Why Sprinkler Blowouts Are Necessary
Sprinkler blowouts are necessary because water expands upon freezing. When water transitions to a solid state, its volume increases by approximately nine percent. Even small amounts of water left in the confined spaces of an irrigation system exert tremendous pressure when they freeze.
This expansive force can easily crack polyvinyl chloride (PVC) pipes, rupture polyethylene lines, and destroy internal components, especially the backflow preventer. The backflow preventer, often located above ground, is vulnerable due to its complex seals and mechanisms. Repairing burst pipes and replacing specialized parts costs significantly more than a yearly blowout.
The Blowout Procedure and Required Equipment
The process begins by completely shutting off the main water supply line to the irrigation system to ensure no additional water enters the pipes during the procedure. Next, a specialized air compressor is connected to a designated access point, often a quick-connect fitting near the system’s main shutoff valve. This connection allows the compressed air to be injected into the system’s piping network.
The air compressor is the most critical piece of equipment; a standard home garage unit is usually inadequate. Effective water removal requires a compressor with a high volume of air flow (CFM), generally ranging from 20 to 50 CFM for a residential system. The compressor must also be equipped with an adjustable pressure regulator to prevent damage to the system components.
Maintaining a safe pressure level is paramount, as excessive force can cause immediate and catastrophic damage to the pipes, fittings, and sprinkler heads. For most residential systems, the air pressure should be regulated to a maximum of 50 to 80 pounds per square inch (PSI), with polyethylene piping requiring the lower end of this range.
The technician manually or electronically opens one zone valve at a time, allowing the compressed air to push the water out through the sprinkler heads until only a fine mist appears. Cycling zones individually is essential as it concentrates the air volume, ensuring all water is expelled. The air should run only until the water is cleared, typically no more than a couple of minutes per zone, to prevent heat buildup that can warp plastic components. Once the last zone is cleared, the compressor is disconnected, and the system is left depressurized for the winter.
Timing, Safety, and Professional Considerations
The timing of the blowout depends entirely on local weather patterns. The procedure should be completed just before the first “hard freeze,” when temperatures drop below 28 degrees Fahrenheit for a sustained period. Scheduling too early means the system cannot be used if late-season watering is needed, while waiting too long risks the pipes freezing before maintenance is performed.
Safety during a sprinkler blowout cannot be overstated, as compressed air is extremely dangerous. Anyone performing the procedure must wear appropriate eye and hearing protection to guard against debris and noise. A major safety risk is attempting to turn on the air compressor while all zone valves are closed, which can lead to a dangerous pressure buildup and potential system failure.
Many homeowners hire a professional service due to the high cost of specialized equipment rental and inherent safety risks. Professionals possess commercial-grade tow-behind air compressors that provide the necessary high CFM and expertise to regulate pressure correctly. Using a professional minimizes the risk of costly damage to the irrigation system and ensures the system functions reliably come spring.