Preparing an underground sprinkler system for winter is necessary maintenance in areas subject to freezing temperatures. When water freezes inside the pipes, it expands, cracking pipes, fittings, and delicate components, leading to costly repairs. The most effective winterization method is using compressed air to “blow out” the remaining water from the lines. Using compressed air requires specific knowledge of the maximum pressure the system can handle to prevent internal damage. This article provides the necessary pressure specifications and procedural steps to perform this task safely and effectively.
Determining the Safe Pressure Range
The primary concern when blowing out a sprinkler system is the maximum pressure the system’s internal components can withstand. The safest pressure to use is between 30 and 50 pounds per square inch (PSI). This range provides enough force to expel the water without risking the integrity of the plastic components. Exceeding this pressure, particularly above 80 PSI, can cause catastrophic failure in the system’s valves, seals, and pipes.
The maximum safe pressure depends on the type of pipe material used. For rigid PVC (polyvinyl chloride) pipe, common in residential mainlines, the absolute maximum pressure should not exceed 80 PSI. However, flexible polyethylene (poly pipe) tubing, used for lateral lines, generally tops out at 50 PSI. Delicate components such as drip irrigation or micro-sprinkler systems require even less pressure, often needing only 30 PSI to clear water effectively.
Applying excessive pressure can cause damage through friction heating, where rapidly moving, highly compressed air heats the inside of the pipe. This heat can weaken or melt internal plastic fittings and seals, causing them to fail or leak once the system is repressurized. It is better to use a low-pressure, high-volume approach to gently evacuate the water, minimizing the risk of heat damage and structural failure.
Essential Equipment and Compressor Requirements
The correct equipment is necessary to ensure a safe and thorough blowout, especially concerning the volume of air delivered, measured in Cubic Feet per Minute (CFM). While the pressure (PSI) is regulated to be low, the compressor must provide a high CFM to physically push the entire volume of water out of the pipes. A common residential system requires a compressor capable of delivering between 10 and 25 CFM to be effective.
Many standard home-use compressors may reach 50 PSI but often only deliver 2 to 5 CFM, which is inadequate for moving the water volume. An undersized compressor will only push air over the top of the water, leaving significant moisture trapped in the lower sections where it can still freeze. For a typical residential system, a minimum of 20 CFM is recommended, often necessitating renting a commercial-grade unit.
In addition to a properly sized compressor with an adjustable pressure regulator, certain accessories are needed for safety and connection. Safety glasses are mandatory, as water and debris will be expelled from the sprinkler heads at high velocity. An adapter fitting is required to connect the air compressor hose to the system’s designated blowout port, usually located near the backflow preventer or the main shutoff valve.
The Step-by-Step Procedure for a Safe Blowout
Before connecting the air compressor, turn off the main water supply to the irrigation system. This prevents additional water from entering the pipes during the clearing process. Next, set the pressure regulator on the air compressor to the determined safe pressure, ideally between 30 and 50 PSI, before attaching it to the system’s blowout port. Ensure the connection is secure to prevent the air hose from detaching under pressure.
Once the air is ready, activate the system one zone at a time. Start with the zone highest in elevation or the one furthest from the compressor connection. Allow air to flow into a zone only until the water expelled from the sprinkler heads turns into a fine mist. Once only mist or clear air is visible, immediately shut off the zone to prevent the compressed air from running too long.
Each zone should be blown out in short cycles, typically no longer than two minutes at a time. Running the air for prolonged periods generates excessive friction heat, which can damage the internal components of the pipes and heads. After the first pass, the entire sequence of zones should be repeated two or more times to ensure all residual water has been pushed out. Turn off and disconnect the compressor only after confirming every zone has been thoroughly cleared.