The annual practice of winterizing an irrigation system is a necessary seasonal maintenance task in regions where temperatures drop below freezing. Water left inside the pipes expands as it freezes, generating immense pressures that can easily rupture plastic piping, damage sensitive valve components, and shatter the backflow prevention device. Draining the system completely removes this risk, protecting the entire network from catastrophic failure and expensive springtime repairs.
Pre-Drain Preparation
Before beginning any draining procedure, the main water supply feeding the irrigation system must be completely shut off. This is typically accomplished by turning a dedicated ball valve located near the main water meter or the backflow preventer. Closing this valve prevents new water from entering the system, which would otherwise repressurize the lines during draining.
Simultaneously, the system’s electric controller or timer needs to be deactivated. This prevents the system from automatically attempting to cycle through the zones during draining. If the controller is not turned off, a valve might unexpectedly open, causing water to spray or introducing confusion.
Identifying Your Sprinkler System’s Draining Method
Not all irrigation systems are drained in the same manner; identifying the correct method is necessary. Systems are categorized into three types: manual drain, automatic drain, or blowout required. The choice often depends on the climate and the depth of the buried pipes.
Manual drain systems require physically opening small valves or drain plugs located at the lowest points of the main and lateral lines. Automatic drain systems utilize specialized valves installed beneath the sprinkler heads or in the piping. These valves automatically open to release water once the internal line pressure drops below a certain threshold.
The third method, the blowout, is common in colder regions with deep frost penetration and involves forcibly removing water using compressed air. Inspecting the system can help determine the type. Look for small, quarter-turn drain valves near the end of the lines or a dedicated connection port for an air compressor. If neither is visible, the system likely employs automatic drain valves.
Step-by-Step for Manual and Automatic Draining Systems
For systems with manual drain valves, the process begins by locating the main drain valve, usually situated near the water shut-off valve or the backflow preventer. Opening this valve allows the water in the main supply line to drain out via gravity. Once the main line is empty, locate and open the smaller drain valves positioned at the lowest points of each zone’s lateral lines.
These lateral line drain valves are typically small, screw-type fittings that must be turned or unscrewed to allow water to escape. Open each valve fully and allow the water to run until it completely stops dripping. This method relies entirely on gravity and the slope of the land. Consequently, any dips or low spots in the piping may retain small amounts of water.
Systems utilizing automatic drain valves simplify the process, requiring only a simple pressure release to activate the draining mechanism. With the main water supply shut off, the system pressure must be relieved by momentarily opening one sprinkler zone valve. This is achieved by briefly turning on the irrigation controller to activate a single zone for about 30 seconds.
As pressure is relieved, the spring-loaded, pressure-activated automatic drain valves will open beneath the ground. These valves remain open until the pressure inside the pipe equalizes with atmospheric pressure, allowing the water to drain passively. This method is quicker but, like the manual process, depends on pipe slope and may not fully clear all moisture, making it less suitable for the coldest climates.
Regardless of the system type, the backflow prevention device requires special attention and is nearly always drained manually. This device contains chambers and test cocks that must be opened to release trapped water. Because it is located above ground, it is particularly susceptible to freezing damage. The test cocks should be opened and left at a 45-degree angle to ensure complete drainage.
The Air Compressor Blowout Procedure
The blowout method is the most comprehensive way to clear water and is the only recommended procedure for areas experiencing deep or prolonged freezing temperatures. This technique requires an air compressor capable of delivering a high volume of air (10 to 25 cubic feet per minute, or CFM). However, the pressure must be strictly controlled.
Before beginning, confirm the compressor’s pressure regulator is set to a maximum of 80 PSI for rigid PVC pipe systems, and no more than 50 PSI for systems using polyethylene pipe. Exceeding these pressures can cause internal seals to fail or rupture the pipe. The compressor is connected to the dedicated port, often found near the backflow preventer, using a specialized quick-connect adapter.
Safety is paramount during this procedure. Appropriate eye protection must be worn at all times, as air and debris can be ejected from the sprinkler heads at high velocity. Never stand directly over any system component while it is being pressurized. The procedure must be carried out one zone at a time, starting with the zone located furthest from the compressor.
Slowly introduce compressed air into the system until water begins to discharge from the sprinkler heads in that zone. Once the water stream changes to a fine mist or vapor, the zone is clear, and the air supply should be immediately shut off. Running the compressor for too long on a dry line can generate heat that damages the internal components of the sprinkler heads.
Repeat this process for every zone, moving sequentially closer to the compressor connection point. Once all zones are cleared, disconnect the compressor. All main and zone valves should be left slightly open. This final step allows any residual moisture that may condense or collect over the winter to evaporate or drain away, preventing potential freeze damage.