Irrigation Winterization Mistakes to Avoid (and What Certification Candidates Should Know)

Every fall, somebody hooks an air compressor to a sprinkler system, cranks the regulator up “to be safe,” and finds out the hard way that more air isn’t better. A blown fitting, a nozzle launched across a parking lot, or a cracked valve can turn a routine shutdown into a spring repair bill.

If you work in irrigation, or you’re studying for an Irrigation Association (IA) certification, winterization is worth understanding at the “why” level, not just the “how.” The Irrigation Association lists startup and winterization procedures among the core skills it expects of irrigation technicians, the same people its Certified Irrigation Technician (CIT) credential is built for.

Here are the mistakes that cause the most trouble, and the reasoning behind each fix.

1. Treating air pressure like water pressure

This is the big one. Many people assume that if a system handles 100-plus psi of water, it can take the same pressure in air. Rain Bird’s winterization guide calls that a common misbelief: air behaves very differently from water in a pipe and can put far more stress on components.

The published limits are lower than most people expect:

• Hunter Industries and Colorado State University Extension both say not to exceed 50 psi for polyethylene pipe or 80 psi for rigid PVC.
• Rain Bird’s guide is more conservative and says air pressure must not exceed 50 psi during the blowout.

When sources differ, the safe answer is the one an exam will usually reward too: use a pressure regulator, follow the manufacturer’s instructions, and never exceed the rating of the weakest component in the system. CSU Extension also points out that pressure above what the nozzles are rated for can blow them right off.

2. Chasing pressure when you really need volume

The fix for a stubborn system isn’t more psi. It’s more air volume, measured in cubic feet per minute (CFM).

CSU Extension explains why: with too little air volume, the air pushes some water out and then rides over the top of what’s left. That water drains back into low spots, right where it can freeze. Hunter offers a sizing rule of thumb: divide the GPM of the largest zone by 7.5 to estimate the CFM you need at the point of connection.

Both Hunter and Rain Bird warn against a shortcut some people try: letting an undersized compressor fill its tank and the closed mainline with high-pressure air, then opening a valve and hoping the surge clears the line. That’s exactly the high-pressure, low-volume combination that damages systems.

3. Running the compressor with no open valve

Air needs somewhere to go. Rain Bird’s guide says not to run the compressor without at least one zone valve open, from startup all the way to shutdown. If the controller fails to open a valve and the compressor keeps pushing air into a closed mainline, pressure builds with nowhere to escape.

The habit worth building: confirm a zone is actually open, not just “on” at the controller, before air goes in. When you finish, leave a zone open while you shut the compressor down, as K-Rain’s winterization instructions recommend.

4. Blowing air through the backflow preventer

Hunter is direct about this: connect the compressor to the mainline downstream of the backflow device, and don’t blow compressed air through any backflow device. Backflow assemblies protect the drinking water supply, and they aren’t built to have air forced through them. Drain and protect them according to the manufacturer’s directions and local requirements instead.

5. Parking on one zone too long

It’s tempting to hold air on a zone until it runs bone dry. The problem is heat and friction. K-Rain advises against blowing any zone for more than about a minute at a time, noting that sustained heat from compressed air can damage pipe, and that many gear-driven rotors rely on water for lubrication and cooling.

The better approach is short cycles: move from zone to zone, then go back through them again until only a fine mist comes out of the heads. Rain Bird and K-Rain both suggest starting with the zone farthest from the air connection.

6. Ignoring basic job-site safety

Rain Bird’s guide tells you to wear eye protection and not to stand over pipes, valves, or heads during a blowout, because over-pressurized parts and debris can fly. On commercial sites, think about where people walk, too. A hose or fitting failing under pressure near a building entrance is a real hazard. Irrigation & Lighting magazine recently ran a good piece on this kind of costly field mistake, and it’s worth a read if you run crews.

Bonus: use the shutdown as an inspection

Fall shutdown is one of the few times you’ll walk every zone on purpose. Note broken heads, leaks, and sunken boxes while you’re there. A short written punch list makes spring startup faster and gives the property owner a clear picture of what needs attention.

Why this matters for certification

Winterization questions reward the same thinking the field does: understand how pressure, volume, and components interact, and follow manufacturer guidance over habit. The IA’s Certification Candidate Handbook also lists winterization and start-up in the maintenance and operations content candidates are expected to apply. If you can explain why 50 psi with plenty of CFM beats 120 psi from a shop compressor, you’re thinking like a certified professional.

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Guidance in this post comes from Hunter Industries, Rain Bird, K-Rain, Colorado State University Extension, and the Irrigation Association, checked October 30, 2026. Always follow the manufacturer’s instructions for the specific equipment on your site.