Water left inside a sprinkler system during cold weather poses a serious threat because of the unique property of water to expand when it freezes. When water reaches 32 degrees Fahrenheit, it expands by approximately nine percent, creating immense pressure within the rigid pipes and components of the irrigation system. This pressure can easily cause pipes to crack, valves to split, and backflow preventers to rupture, leading to expensive repairs. Proper winterization is a preventative maintenance step that removes all water from the lines, safeguarding the entire system against freeze damage.
Preparation Steps and Optimal Timing
The process of draining the system should begin just before the first hard freeze is expected in your region. A hard freeze is defined as temperatures dropping below 32 degrees Fahrenheit for several hours, which can cause significant damage to an unprotected system. The first step involves locating and shutting off the main water supply valve, which is frequently found near the water meter or where the line enters the house.
Once the water source is closed, you must relieve any residual pressure remaining in the lines. This is accomplished by momentarily running one of the sprinkler zones on the controller or by slightly opening a manual drain valve. Depressurizing the system prevents potential damage when you begin the drainage process. Finally, the irrigation controller should be turned off completely or set to a “rain mode” to prevent accidental activation during the winter.
Draining the System Using Valves
For systems in regions with milder winters or those specifically designed for gravity drainage, water can be removed using drain valves located at the lowest points of the piping. Systems with manual drain valves require a user to physically locate and open each valve, allowing gravity to pull the water out of the pipes. Leave these valves open until all the water has completely drained away.
Other systems utilize automatic drain valves, which operate independently when the water pressure in the line drops below a set point, typically around 10 PSI. When the main supply valve is shut off, the resulting pressure drop causes these automatic valves to open, expelling the water. While these drainage methods work in certain conditions, they often leave small amounts of water trapped in uneven pipe sections, which is why the pressurized air method is recommended for climates where the ground freezes deeply.
The Sprinkler Blowout Procedure
The blowout method uses compressed air to force all water out of the irrigation lines, providing the most complete protection against freezing. This procedure requires an air compressor with enough volume, typically rated for at least 20 to 50 cubic feet per minute (CFM) at 50 to 80 pounds per square inch (PSI), to effectively move the water. Smaller compressors often lack the necessary air volume to properly clear the lines, creating a false sense of security.
Before connecting the equipment, wear safety goggles to protect the eyes from debris or dislodged sprinkler heads. The air compressor is connected to a dedicated blow-out port, which is often located near the backflow prevention device. Ensure the ball valves on the backflow preventer are closed before introducing air, as high-pressure air can damage its internal components.
Air pressure must be introduced gradually. The pressure regulator should be set to a maximum of 80 PSI for PVC piping and lower, around 50 PSI, for polyethylene pipes, to avoid rupturing the lines. The process is performed one zone at a time, starting with the zone farthest away from the compressor connection. Run air through each zone only until a fine mist appears from the sprinkler heads, indicating that the bulk of the water has been expelled.
Post-Drainage System Shutdown
Once the main lines are confirmed to be completely dry, a few final actions are necessary to prepare the system for the cold months. If your local codes permit, the backflow prevention device should be drained by turning its test cocks and ball valves to a 45-degree angle, which prevents water from being trapped within the valve body. In some areas, or for certain models, it may be required to completely remove the device and store it indoors.
The irrigation controller should be fully powered down by shutting off the circuit breaker or unplugging the unit. If manual drain valves were used, they should be left slightly open to allow any remaining moisture to evaporate or escape. This final step ensures that any residual water does not freeze and cause damage.