The practice of “blowing out” an irrigation system involves using a high-volume air compressor to force all standing water from the underground pipes, valves, and sprinkler heads. This winterization process is necessary because water expansion when temperatures drop below freezing can rupture the system’s components. Even a small amount of residual water can lead to expensive repairs to pipes, fittings, and the internal mechanisms of valves. Performing this task correctly protects the entire investment in the irrigation infrastructure.
Assessing DIY Feasibility and Necessary Equipment
A homeowner can certainly perform a sprinkler blowout on a residential system, but this task requires a high degree of technical comfort and the correct specialized tools. Smaller, less complex systems are well-suited for a do-it-yourself approach. However, large properties with extensive piping networks or commercial-grade systems are generally better left to professionals. Attempting to clear a large system with inadequate tools will inevitably lead to an incomplete blowout and subsequent freeze damage.
The most important factor in equipment is the air volume, measured in Cubic Feet Per Minute (CFM), rather than the pressure (PSI). A system needs a continuous volume of air to effectively push a column of water out of long pipe segments. Residential systems typically require a compressor capable of delivering at least 20 to 50 CFM. Small household compressors may not have the necessary CFM volume to clear the entire length of the pipe, even if their PSI rating is high.
The pressure regulator on the compressor is a non-negotiable component for this task. Pressure must be strictly controlled to prevent catastrophic system failure. Safety gear is also mandatory, including ANSI-approved eye protection. Finally, a specialized quick-connect adapter is necessary to securely link the compressor’s hose to the system’s dedicated blowout port, which is often located near the backflow preventer.
The Step-by-Step Procedure for Clearing Sprinkler Lines
Before connecting any equipment, the water supply to the irrigation system must be completely shut off at the main isolation valve. This prevents new water from entering the lines while the air is being introduced. The backflow prevention device should also be drained according to local codes, often involving opening the test cocks to release trapped water and pressure.
The air compressor is then connected to the designated system port, typically found downstream of the main shutoff valve. It is crucial that the air regulator is set to a low pressure, ideally between 30 and 50 PSI, before the air is introduced. Pressure must never exceed 80 PSI for rigid PVC piping or 50 PSI for more flexible polyethylene lines, as excessive force can cause pipe fracture or seal failure.
The actual blowout is performed zone by zone, beginning with the zone located farthest from the air compressor connection. Activating the farthest zone first ensures that the maximum pipe length is cleared before proceeding to shorter segments. Air should be introduced in short, controlled bursts, generally no longer than one to two minutes per zone. This intermittent application prevents heat buildup within the pipes, which can melt internal plastic components of the sprinkler heads.
A zone is considered sufficiently cleared when the water spray from the heads reduces to a light, dry mist or only puffs of air are visible. Once this dry air is confirmed, the zone is shut off, and the process is immediately repeated for the next zone in sequence. After all zones have been cleared, the air compressor is disconnected, and any remaining residual air pressure in the mainline is released by briefly opening the system’s drain valves. The valves can then be left slightly ajar for the winter.
Safety Protocols and Avoiding Costly Errors
The power of compressed air necessitates strict safety measures to prevent personal injury and system damage. The most important protocol is the mandatory use of safety glasses, as debris, dirt, and water can exit the sprinkler heads at high velocity. Operators must avoid standing directly over the sprinkler heads or other system components while the air is running. High-pressure air can cause serious bodily harm if it enters the bloodstream through a cut or skin puncture.
A common and costly error is failing to regulate the air pressure, which can instantly ruin the system. Using a standard tire compressor without a proper regulator often delivers pressure well over the 50 PSI limit, which can shatter PVC pipes or destroy the seals and gears inside rotary sprinkler heads. Another frequent mistake is blowing air directly through the backflow preventer, which contains delicate internal check valves and springs that are not designed to withstand high-volume air flow. Damage to this component is often the most expensive single repair in the spring.
Blowing out a zone for too long is also a significant error, as the friction of compressed air passing through the pipes generates heat. This heat can warp or melt the plastic components within the sprinkler heads and valves. The most critical failure is the incomplete blowout, where residual water remains in a low spot or a lateral line. Even a small pocket of water will freeze, expand, and guarantee a cracked pipe.