The process of winterization, often called “blowing out” a sprinkler system, is necessary to prevent damage when temperatures drop below freezing. Water expands by about nine percent as it turns to ice, and this expansion can rupture underground pipes, valves, and sprinkler heads. The professional method involves using a high-volume air compressor to force water out of the irrigation lines. For users without this specialized equipment, several viable alternative methods rely on different mechanical principles to clear the system.
Essential Pre-Drain Steps
Before removing water from the pipes, completely halt the flow from the main supply line. Locate the primary shut-off valve for the irrigation system, typically found near the water meter, the backflow preventer, or inside a basement or crawlspace. Turning this valve perpendicular to the pipe isolates the sprinkler system from the home’s water source, preventing new water from entering the lines.
Next, turn off the system controller or timer, or set it to a “rain” or “standby” mode for the season. This prevents the solenoid valves from unexpectedly opening and closing during draining. Once the water is shut off, release the pressurized water remaining in the pipes by opening a drain valve or test cock downstream of the shut-off point. Depressurizing the lines prevents a sudden surge or “water hammer” when the main drain valves are opened.
Utilizing Gravity and Manual Drains
The most common non-pressurized method relies on simple gravity, requiring the system to have manual drain valves installed at all low points of the piping. Locate these low-point drains, often situated at the end of each irrigation zone line or at the bottom of a slope. Slowly opening these valves allows the water to trickle out until the line is empty at that point.
This method is only effective if the entire underground piping network has been installed with a continuous slope toward these manual drain valves. If the lines run level or have dips, water will collect in those low spots, which can still lead to freezing damage. After draining the main lines, you must address the backflow prevention device, which holds a significant amount of water above ground.
Draining the backflow preventer requires using its dedicated test cocks and shut-off valves, not the main system drains. Turn the main shut-off handles on the backflow device to the closed position, and then open the small, slotted test cocks to allow the trapped water to escape. Leaving these test cocks and the main ball valves set at a 45-degree angle for the winter helps ensure any residual moisture can expand without cracking the assembly.
Specialized Alternatives and System Limitations
Some irrigation systems are designed with automatic drain valves (ADVs) that eliminate the need for manual intervention at low points. These ADVs are spring-loaded valves that open automatically when the line pressure drops below a specific threshold, typically less than 10 pounds per square inch, allowing water to drain. If your system has this feature, shutting off the main water supply and relieving the system pressure should cause these valves to cycle open and drain the lines passively.
A less conventional alternative involves using a wet/dry shop vacuum to pull water from the pipes. This technique is applied by removing a sprinkler head or accessing an exposed pipe end and creating a tight seal with the vacuum hose. While the vacuum can remove standing water near the connection point, its limited suction and air volume make it ineffective for long runs of pipe or complex, multi-zone systems.
Using a vacuum to clear the lines is time-consuming and offers no guarantee of complete water removal deep within the piping network. For systems with deep-set pipes or extensive lateral lines, the suction power is often insufficient to overcome the resistance and friction of the water. This method should only be considered for very small, simple systems or for removing surface water from valve boxes after the primary draining.
Evaluating the Effectiveness of Non-Pressurized Methods
The limitation of all non-pressurized drainage methods is that they rely on gravity and cannot overcome the surface tension of water or minor imperfections in the pipe slope. Even when a system is designed for perfect drainage, underground pipe shifts over time can create small sags or “bellies” where water pools. This residual water, even in small amounts, poses a risk because water’s volume expansion upon freezing can destroy components.
These non-compressor draining methods are generally considered appropriate only for very mild climates where the ground does not freeze deeply or for short-term protection before a light frost. In regions with sustained below-freezing temperatures, the presence of residual water in the valves, sprinkler heads, or low-lying pipe sections will inevitably lead to damage. If your system is complex, lacks proper low-point drains, or if you live in a cold climate, the risk of a burst pipe is significantly higher.
In situations where a gravity drain or vacuum is used, it is advisable to rent a high-volume air compressor or hire a professional to perform a proper blowout as a final, protective measure. The cost of a professional blowout or a rental is minimal compared to the expense of replacing burst underground pipes and broken backflow preventers in the spring. For maximum protection against freeze damage, the complete removal of all water via forced air remains the most reliable strategy for winterization.