How to Blow Out Sprinkler System: Protecting Your Irrigation Investment Before Winter's Wrath

The first time I watched my neighbor's sprinkler head explode like a tiny geyser after the first hard freeze, I understood viscerally why winterizing matters. That crystalline moment—water shooting fifteen feet into the air at 7 AM while he stood there in his bathrobe, coffee mug frozen mid-sip—taught me more about frozen pipe damage than any manual ever could.

Blowing out your sprinkler system isn't just another tedious fall chore to check off your list. It's an act of preservation, really. Water expands roughly 9% when it freezes, and that seemingly small percentage translates to about 2,000 pounds of pressure per square inch inside your pipes. Your PVC pipes? They can handle maybe 400 PSI on a good day.

The Physics Behind the Process (And Why Garden Hoses Won't Cut It)

I spent years thinking I could just drain my system and call it good. Water flows downhill, right? But here's what nobody tells you: water clings. It pools in the low spots, hides in the elbows, and lurks in your backflow preventer like an unwelcome houseguest. Even a tablespoon of water in the wrong spot can split a fitting wide open when January rolls around.

The only reliable way to evict every last drop is compressed air. And before you drag out that pancake compressor from your garage—the one that barely fills your car tires—let me save you some heartache. You need volume, not just pressure. Think of it this way: you're not trying to power-wash the inside of your pipes; you're creating a sustained wind tunnel effect that pushes water ahead of it like leaves before a storm.

Most residential systems need somewhere between 80-100 PSI, but more importantly, they need 20-25 cubic feet per minute (CFM) for smaller yards, and up to 50 CFM for larger properties. That dusty compressor that came free with your nail gun? It's probably pushing 2-4 CFM at best.

Reading Your System Like a Map

Every sprinkler system tells a story through its components, and learning to read yours can mean the difference between a successful blowout and an expensive spring surprise. Start at your backflow preventer—that brass contraption that looks like it belongs on a submarine. It's usually within three feet of where your main water line enters the house, though I've seen creative installations in crawl spaces that would make a contortionist weep.

Your system likely falls into one of three categories, and each demands a slightly different approach. If you've got black polyethylene pipes (poly pipe to its friends), you're in luck—this stuff is forgiving, flexible, and handles air pressure like a champ. PVC systems, those white rigid pipes, need a gentler touch. They're strong but brittle, especially after a few years of UV exposure. Then there's the oddball: galvanized steel systems in older homes. If you've got one of these dinosaurs, treat it with the respect you'd show your grandmother's china.

The real trick is identifying your zones. Most systems have between 4-8 zones, each controlled by a valve that's either in a mysterious green box in your yard or lurking in your basement looking like something from a steampunk novel. You'll blow these out one at a time, and the order matters more than you'd think.

The Actual Process (Where Theory Meets Muddy Reality)

First things first: shut off the water. Sounds obvious, but you'd be amazed how many people skip this step and wonder why their compressor sounds like it's trying to inflate the Hindenburg. The main shutoff is usually inside your house, and there's often a second valve outside near the backflow preventer.

Now comes the part where you'll question your life choices: draining the backflow preventer. These devices have test cocks (stop giggling) that need to be opened to release trapped water. Turn them about 45 degrees—they'll hiss and spit like angry cats. This is normal. The water that comes out will be rusty, smelly, and will stain your driveway. I learned to put a bucket under mine after explaining to my wife why our concrete looked like a crime scene.

Here's where I diverge from conventional wisdom: start with your highest elevation zones first. Water wants to flow downhill, and by clearing the high ground first, you're working with gravity instead of against it. Most people start with Zone 1 because, well, it's Zone 1. But if Zone 1 is your front yard that slopes down to the street, and Zone 4 is that side yard up by the house, you're making extra work for yourself.

Connect your compressor to the blowout port—it's usually a quick-connect fitting downstream from the backflow preventer. If you don't have one, you'll need to install one, or remove a sprinkler head and use a fitting to connect there. Fair warning: the first time you do this, you will cross-thread something. It's a rite of passage.

Set your compressor to about 50 PSI to start. Yes, I know I said 80-100 earlier, but trust the process. Turn on Zone 1 (or your highest zone) at the controller, then slowly increase the pressure. You'll hear it before you see it—a rumbling, gurgling sound like a dragon with indigestion. Then the sprinkler heads will start spitting, first water, then a mix of water and air, and finally just air with a fine mist.

The Art of Knowing When to Stop

This is where experience trumps instruction manuals. You'll read that you should blow each zone for 2-3 minutes. That's like saying you should cook a steak for 5 minutes per side—technically true, but missing all the nuance. A zone is done when the mist stops and you're getting nothing but air. For my front yard, that's about 90 seconds. For the back forty with its long runs and elevation changes, it's closer to 4 minutes.

But here's the crucial bit: don't overdo it. Running air through dry pipes generates heat through friction. I once watched a professional (who should have known better) melt the internal seals in a valve by running air through it for ten minutes straight. The zone worked fine until the following July, when it decided to water continuously until manually shut off. The repair bill was... educational.

The Zones Nobody Remembers

After you've blown out all your regular zones, you're not done. Remember that drip irrigation for your wife's roses? That's a zone. The bubbler for the Japanese maple? Also a zone. These low-flow zones are particularly vulnerable because they use smaller diameter pipes and micro-tubing that can split if you look at them wrong.

For drip zones, drop your pressure to 30-40 PSI. Any higher and you'll blow the emitters clean off the tubing, turning your precisely designed irrigation system into a modern art installation. I speak from experience here—nothing says "amateur hour" quite like drip emitters scattered across your mulch like confetti after a particularly exuberant blowout.

The Backflow Preventer Finale

Once all zones are clear, you need to winterize the backflow preventer itself. This is where most DIY attempts go sideways. Those test cocks you opened earlier? They need to stay at 45 degrees—not closed, not fully open. The ball valves should be at 45 degrees too. This position allows any residual water to drain and prevents the ball from creating a water trap.

If you have an older pressure vacuum breaker (PVB) style backflow preventer, you might notice it has a canopy on top. Resist the urge to wrap it in insulation or cover it with a bucket. These devices need to breathe, and trapped moisture will do more damage than cold air ever could. I've seen well-meaning homeowners create perfect terrariums for mold growth by overwrapping their backflow preventers.

When to Call It Quits (And Call a Pro)

Let me be brutally honest: if you have a large property with multiple elevation changes, zones running over 300 feet, or a system installed before you were born, hiring a professional might be the smartest $75-150 you spend all year. I'm all for DIY, but there's no shame in recognizing when you're outgunned.

Similarly, if your compressor can't maintain pressure when a zone is running, you're fighting a losing battle. Inadequate air volume doesn't just make the job take longer—it can leave water trapped in low spots that you'll discover come spring in the form of split pipes and geysering heads.

The Morning After

Once you've completed the blowout, resist the temptation to test your handiwork by turning on a zone. I know it's satisfying to see those heads pop up and spray nothing but air, but each cycle wears on components that are designed to work with water as a lubricant, not air.

Instead, take a victory lap around your property. Look for any heads that didn't fully retract—sometimes debris prevents them from seating properly, leaving them vulnerable to freezing. Check for any pooling water around heads or valve boxes that might indicate a problem you'll want to address come spring.

Finally, turn off your controller or switch it to "rain mode" if it has one. There's no point in it sending signals to valves all winter, and some older controllers can damage solenoids with repeated dry firing.

The Bigger Picture

Winterizing your sprinkler system is really about respecting the infrastructure we usually ignore. These networks of pipes and valves faithfully deliver water all summer, asking nothing in return but this one annual favor. In our throwaway culture, there's something deeply satisfying about maintaining a system that, with proper care, can last decades.

I've blown out my system every fall for fifteen years now. The process has become a ritual that marks the transition from the frenetic growth of summer to the quiet dormancy of winter. There's a meditative quality to working your way through each zone, watching the water give way to mist, then to nothing but air. It's a reminder that even the most reliable systems need our attention, that prevention really is worth a pound of cure, and that sometimes the best way to preserve something is to empty it completely.

Plus, you'll never have to stand in your bathrobe watching your sprinkler system do its best Old Faithful impression while your neighbors pretend not to notice. Trust me on that one.

Authoritative Sources:

Hunter Industries. Residential Irrigation System Design Handbook. San Marcos: Hunter Industries Incorporated, 2019. Print.

Irrigation Association. Landscape Irrigation Best Management Practices. Fairfax: Irrigation Association, 2020. Print.

Mecham, Brock. Landscape Irrigation Scheduling and Water Management. Water Management Committee of the Irrigation Association, 2018. Print.

Rain Bird Corporation. Irrigation Design Manual. Azusa: Rain Bird Corporation, 2021. Print.

United States Environmental Protection Agency. "WaterSense: Sprinkler Spruce-Up." EPA.gov. United States Environmental Protection Agency, 2021. Web.

Whiting, David, et al. Irrigation Management in the Home Landscape. Colorado State University Extension, 2019. Print.