Winterization, the process of draining a sprinkler system, is mandatory to protect your irrigation investment from freezing temperatures. When water freezes, it expands by approximately nine percent, creating immense pressure inside pipes, valves, and sprinkler heads. This force can crack PVC or polyethylene pipes and split brass components, leading to costly damage that only becomes apparent when the system is turned on in the spring. Removing all water from the underground lines before the first hard freeze prevents this extensive repair.
System Preparation Before Draining
Before physically removing water, stop the supply from entering the irrigation lines. Locate the dedicated isolation valve for the sprinkler system, which is typically separate from the main house shut-off and may be found in a basement, crawlspace, or underground valve box. Turn this valve off completely to prevent new water from flowing into the system during draining.
Next, set the electronic controller or timer to the “Rain” or “Off” position. This prevents the system from automatically running scheduled cycles, which would cause control valves to open without water pressure. Deactivating the controller is necessary because running the system dry can damage components like the master valve or a pump.
Detailed Draining Methods
The correct draining method depends on the original design of your irrigation system. Homeowners typically use three primary techniques, and identifying the applicable method is the first step toward successful winterization.
Manual Drain Systems
Manual drain systems rely on gravity and the operator opening valves located at the lowest points of the piping network. These drain valves are typically threaded caps or small gate valves found at the ends and low points of the main and lateral lines. After shutting off the water supply, systematically open each valve to allow trapped water to escape.
This method requires the pipes to be installed with a continuous downward slope. Because underground pipes can shift, this method does not guarantee complete water removal and is often not recommended in regions with severe freezing. Once water stops flowing, the valve must be left open to allow residual moisture to continue draining.
Automatic Drain Systems
Automatic drain systems use special spring-loaded drain valves placed at low points within the piping. These valves open automatically to release water when the pressure within the pipe drops below a certain threshold, often around 10 PSI. To initiate draining, shut off the water supply, and then momentarily activate a zone on the controller to relieve system pressure.
As pressure falls, the internal valves open and drain the water by gravity without manual intervention. If a sprinkler head contains a check valve, the head may need to be physically lifted to allow water to escape. This method is more reliable than a manual system but still depends on the pipe’s slope and the proper function of the automatic valves.
The Blowout Method (Compression)
The blowout method uses a large-volume air compressor to physically force all water out of the irrigation lines, making it the most thorough technique. A specialized compressor, ideally delivering 20 cubic feet per minute (CFM) or more, connects to a dedicated port downstream of the backflow preventer. Wear ANSI-approved safety glasses, as pressurized air can eject debris or water with force.
Air pressure must be carefully regulated to prevent damage. For residential systems with PVC piping, pressure should not exceed 80 PSI, with a recommended operating range between 40 and 60 PSI. Pressures above this limit can rupture pipes, damage seals, and destroy sprinkler heads.
The process involves clearing one irrigation zone at a time, starting with the zone farthest from the air connection or the highest elevation zone. Turn the compressor on slowly, introducing air gradually to push water out through the sprinkler heads.
Once a zone sprays only a fine mist, immediately shut off the air supply to prevent heat buildup and damage from dry air friction. Due to the specific air volume and pressure requirements and the potential for serious damage, homeowners often hire a certified irrigation professional for this procedure.
Final Steps and System Safety
After the main lines are cleared, attention must turn to above-ground components, especially the Backflow Prevention Device (BPD) or Pressure Vacuum Breaker (PVB). These assemblies contain intricate internal parts highly susceptible to freezing damage. The BPD must be drained by manipulating its test cocks and ball valves to release all trapped water.
Set the two ball valves on the backflow device to a 45-degree angle. This prevents water from being trapped behind the ball, which can occur if they are fully open or closed. The small test cocks should also be opened, typically using a flathead screwdriver, to allow any moisture to escape.
Finally, any remaining manual drain valves in the system should be left slightly open, or the drain cap removed, to relieve pressure that might build up from residual moisture or air.