How to Blow Out a Sprinkler System Yourself (Safe PSI)

The number that matters is 50 PSI. Keep the air at the compressor's regulator between 40 and 50 PSI, never higher, and you can clear most residential lines without splitting fittings or launching a sprinkler head across the yard. The rest is a matter of order: water supply off, backflow preventer drained, then one zone at a time.

Finish before your first hard freeze. In many northern states that arrives in October or November, but it varies by region and even by neighborhood. Your local Cooperative Extension office can give you average first-frost dates. The USDA Plant Hardiness Zone Map shows average coldest winter temperatures rather than frost dates, but it tells you how seriously to take winter.

What do you need before you start?

You need an air compressor that moves enough volume, a fitting that matches your system's blowout port, and eye protection. Volume, measured in cubic feet per minute (CFM), matters more than tank size or the maximum PSI printed on the box.

• Air compressor: many irrigation pros suggest a rented towable compressor rated at 10 CFM or more at 40 to 50 PSI. A small pancake compressor can work on a small system, but it refills constantly and you'll spend a long afternoon waiting.
• Pressure regulator with a gauge: most compressors have one. Confirm it reads sensibly at the hose outlet.
• Adapter: a quick-connect fitting that matches your blowout port, often 3/4 inch or 1 inch. Photograph the port and take the photo to the hardware store.
• Short air hose and plumber's tape for the threads.
• Eye and ear protection: safety glasses at minimum. Compressed air throws grit and fragments.
• Screwdriver and adjustable pliers for the backflow test cocks and shutoff valves.
• Tags or a marker to note which valves you changed so you can reverse them in spring.

Can your system be blown out, and how do you shut off the water?

Most buried systems with a blowout port can be blown out at home: close the irrigation shutoff valve first, then find the port. The port is a threaded or quick-connect fitting on the mainline, downstream of the backflow device and the shutoff.

1. Locate the irrigation shutoff, usually a ball valve in the basement, crawl space, or a buried box near the meter, and close it (handle perpendicular to the pipe).
2. Find the blowout port. If you can't, don't improvise by tapping into the line. A plumber or irrigation contractor can add one, and if that means digging, call 811 first so buried utilities get marked.
3. Identify your zone valves in the green boxes or manifold, and note whether you have a master valve. The controller has to open each in turn so air can pass.
4. Treat drip irrigation separately. Drip tubing, filters, and regulators are low-pressure parts and usually can't take 40 PSI. Remove the filter and regulator and follow the manufacturer's instructions, or leave those zones for a pro.

How do you drain the backflow preventer and above-ground parts?

Close the backflow preventer's supply valve, open its test cocks, and let gravity do the work. Never push compressed air through it, because spinning air can damage the seals and poppets that keep irrigation water out of your drinking supply.

1. With the shutoff closed, open the test cocks. On a pressure vacuum breaker, these are small slotted screws on the body. Loosen them and let the water run out.
2. Turn the assembly's ball valves to a 45-degree half-open position, unless the manufacturer says otherwise, so trapped water can drain instead of freezing and cracking the body.
3. Open every manual drain valve in the system, and drain any above-ground pipe or hose bibs tied to the irrigation line. Tag what you opened.
4. In cold climates, wrap the assembly with an insulated cover after draining.

Double-check and reduced-pressure assemblies are bulkier and often covered by local rules about who may remove or service them. Some municipalities also require certified testers for backflow work. Check with your water utility or building department before you touch one.

How do you connect the compressor and set the pressure under 50 PSI?

Connect the hose to the blowout port with the regulator turned down, then raise the pressure slowly to 40 PSI and never past 50. Rigid PVC may tolerate more, but fittings, glued joints, poly pipe, and sprinkler bodies are the weak points, and they are what split.

1. Turn the pressure regulator to its lowest setting before you attach anything.
2. Wrap the adapter threads with plumber's tape, thread the quick-connect fitting onto the blowout port, and snug it with pliers.
3. Start the compressor and let the tank build.
4. Open the regulator slowly while watching its gauge, and stop at 40 PSI. The tank gauge reads stored pressure, which is much higher and not the number that matters.

How do you blow out each zone one at a time?

Set the controller to manual, start one zone, run air until the water turns to a fine mist, then shut it off and move to the next. Never open more than one zone at once, because splitting the airflow leaves every zone with too little volume to push the water out.

1. Start with the zone farthest from the blowout port or at the highest elevation, if you can tell which that is. Otherwise any zone will do, since the second pass catches what the first misses.
2. Use the controller's manual start to open that zone's valve. Confirm the water supply is still off.
3. Watch the heads. They pop up, spit water, then spit mist. The farthest head on the zone clears last.
4. Cut the air after about two minutes, even if heads are still spitting. Running air through heads with no water to cool them can overheat and wear them, and a compressor can't hold pressure while you wait on a stubborn zone.
5. Let the compressor recover to 40 PSI, then start the next zone.
6. When every zone is done, go back through all of them again. Water collects in low spots and runs back to the heads after the first pass.

Finish by setting the controller to off or rain delay so it doesn't try to run in January.

How do you check that every head and valve has cleared?

Wait about ten minutes after the second pass, then walk every zone and look for fresh water at the heads and in the valve boxes. Dry heads and dry boxes mean the lines are clear. A head that dribbles again shows you where water is still pooled.

Press each popped-up head down and look for a seep around the riser. Open each valve box, and treat any valve body that is still dripping as a reason for another pass. Check every manual drain valve at low points, and close or leave open each one according to your system's instructions, tagging any you leave open so you remember them in spring. Then disconnect the compressor, cap the blowout port, and close the boxes.

What are the common mistakes that crack pipe or leave water behind?

The most common mistakes are too much pressure, too much run time on a single zone, and skipping the second pass. Each one saves a few minutes now and can cost you a repair in April.

Cranking the regulator to speed things up doesn't clear water faster. It splits fittings. An undersized compressor is the quieter problem: if the pressure collapses every few seconds, the lines won't clear, so rent a bigger unit. Running one zone for five or ten minutes is harder on heads than short bursts across several passes.

Opening several zones at once drops the volume and leaves water behind. Forcing air through the backflow preventer risks its seals. Leaving the shutoff open refills the line as fast as you blow it out. And waiting too long means a pipe can crack in the first hard freeze without your knowing until spring.

When should you stop and call a licensed irrigation pro?

Stop and call a licensed irrigation pro if a zone won't clear after three passes, a valve keeps weeping, or you can't identify where to connect the compressor safely. Any of these can mean trapped water, a leak, or a layout you can't read from the surface, and each can crack pipe in the next freeze.

• One zone keeps pushing water after three or more passes. Water may be sitting in a sagging section, or the line may be broken.
• A zone valve keeps weeping after the system is blown out.
• You hear air hissing underground, or the compressor can't hold pressure.
• There is no blowout port and you aren't sure how the mainline is plumbed.
• You have a reduced-pressure backflow assembly, or a local rule limits who may handle it.
• Your system uses a pump, a well, or a large drip network.

A professional blowout typically runs $60 to $200 depending on zone count, region, and backflow type. Book early, because good contractors fill up in the weeks before the first freeze. Licensing requirements for irrigation work vary by state. The EPA WaterSense program is a reasonable place to look for irrigation professionals certified through WaterSense-labeled programs.

Next step: look up your average first-frost date this week, line up a compressor, and run a test on one zone before you commit to the whole system.