How to winterize an irrigation system by blowing out lines and insulating backflow devices
Preparing your irrigation system for winter prevents burst pipes, damaged sprinklers, and costly repairs in spring. This guide walks you through a straightforward, step-by-step blowout of the lines and how to insulate and protect the backflow device. You’ll need common tools, an air compressor, and about 1–2 hours for a typical residential system.
Step 1: Turn off water supply
Shut off the main irrigation valve at the meter or the dedicated supply line. Leave the domestic water supply alone; confirm the irrigation isolation valve is fully closed to prevent pressurizing household plumbing. Turning off the water stops flow into the system while you purge remaining water.
[Illustration: hand turning an outdoor irrigation shutoff valve near a water meter in cold weather]
Step 2: Shut down the controller and batteries
Power off the irrigation controller and remove batteries to prevent scheduled cycles during blowout. Label the controller and note current settings if you need to restore them later. This avoids accidental activation that could damage lines when compressed air is applied.
[Illustration: close-up of irrigation controller with batteries being removed and power button off]
Step 3: Attach compressor to blowout port
Locate the blowout or test port, typically near the backflow or at the mainline connection, and connect an adapter and 50–80 psi-rated hose from a compressor. Set the compressor to 40–80 psi for PVC systems and no more than 50 psi for older poly tubing; using correct pressure prevents pipe or head damage.
[Illustration: air compressor hose attached to irrigation blowout adapter near backflow assembly]
Step 4: Open manual valves and bleed zones
Open any manual isolation valves, then run each zone valve manually from the controller or the valve box using the solenoid or by turning the valve. Blow out one zone at a time for 1–3 minutes until only a fine mist or no water is expelled, which ensures lines are dry without over-pressurizing.
[Illustration: person opening valve box while running a single sprinkler zone with water mist from heads]
Step 5: Cycle through all zones carefully
Repeat the blowout process for all zones, starting furthest from the compressor and moving toward the supply to push water out efficiently. Monitor pressure on the compressor gauge; reduce to 20–30 psi when clearing small drip or low-flow lines. Completing every zone clears trapped water that could freeze and expand.
[Illustration: sequence of labeled valve boxes with person switching zones and watching compressor gauge]
Step 6: Drain and inspect backflow device
Open the backflow test cocks and drain ports to let trapped water escape, then operate the relief valve briefly to purge remaining water. Inspect the assembly for cracks, corrosion, or loose parts and replace any worn rubber seals; a dry, intact backflow prevents freeze damage and contamination risk in spring.
[Illustration: hand opening backflow test cocks and draining water into a bucket while inspecting components]
Step 7: Insulate and secure backflow assembly
Wrap the backflow with foam insulation, pipe wrap, or an insulated box rated for outdoor use, sealing gaps with waterproof tape and adding a heat cable if temperatures regularly drop below 10°F (-12°C). Secure the insulation with UV-resistant straps and label the box for spring service; proper insulation keeps internal temperatures above freezing.
[Illustration: backflow assembly wrapped in foam insulation with a small removable insulated box and labeled exterior]
- Schedule blowout before the first hard freeze; aim for daytime temperatures above 25°F (-4°C) for safer working conditions.
- Use an air compressor with a moisture trap and a regulator; drain compressor tank and trap after use to prevent rust and contamination.
- Wear hearing protection when using compressors; long exposure to 85 dB+ can damage hearing during 30–90 minute jobs.
- Mark and record zone numbers on controller and valves to speed the blowout process and avoid missing zones.
- Take photos of valve and backflow setups before disassembly to help reassembly or spring service calls.
- If you have drip irrigation sections, either isolate them and use lower pressure (20–30 psi) or remove and store emitters to avoid damage. Drip lines are more delicate than sprayheads.
- Never connect compressor directly to household potable plumbing; always isolate the irrigation supply to avoid backflow into drinking water.
- Do not exceed manufacturer-recommended pressure limits—pressures over 80 psi can burst PVC and older polyethylene lines.
- Avoid standing near sprinkler heads during blowout; high-pressure air can eject debris or frozen slugs that can injure you.
- If you detect cracks, heavy corrosion, or unclear valve operation on the backflow, stop and call a licensed irrigation or backflow tester to avoid contamination or system failure.
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