How to Blow Out a Sprinkler System Yourself: PSI Limits, Steps and the Mistakes That Crack Pipes

Water left in sprinkler lines over winter freezes, expands and splits pipes, fittings and valves. The damage doesn’t show until spring, when you turn the system on and find a geyser in the lawn. Colorado State University Extension puts it plainly: fall winterizing is “much less costly and much less labor intensive” than repairing freeze damage in spring.

This guide covers the pressure limits, a step-by-step blowout, the mistakes that cause damage, and whether your compressor is up to the job, using Colorado State Extension and Rain Bird guidance. MowReview quotes no prices and hasn’t tested the products mentioned. How we research explains why.

The numbers that matter

Step by step

1. Pick a dry day before the first hard freeze.
2. Shut off the water supply to the system. Colorado State notes the stop-and-waste valve may be in a basement, crawlspace or an underground valve box as deep as about 5 feet. Don’t force it.
3. Relieve pressure by briefly running one zone from the controller.
4. Connect the compressor to the blowout port downstream of the backflow preventer, using a blowout adapter. Set the regulator to your pipe’s limit before you start.
5. Open one zone before starting the air. Rain Bird stresses this so pressure doesn’t build against closed valves and blow heads apart.
6. Blow the zone in bursts of two minutes or less. Water sprays, then sputters, then turns to mist.
7. Move to the next zone, then come back for a second pass on each one, as both Rain Bird and Colorado State advise.
8. Shut off the compressor before disconnecting, and never close every zone while the compressor is still feeding air.
9. Deal with the backflow preventer. For a pressure vacuum breaker, Colorado State says to leave its ball valves and test cocks half-open over winter. Rain Bird recommends insulating valve boxes and backflow preventers.
10. Set the controller to off or rain mode for winter.

Five mistakes that cause damage

1. Blowing air through the backflow preventer. Colorado State says pressure vacuum breakers and reduced pressure devices “must never be blown out with compressed air,” because the heat can melt their rubber seals.
2. Too much pressure. Colorado State says excess pressure can blow nozzles off. Flexible poly pipe takes much less than PVC.
3. Running air too long. Rain Bird says compressed air heats up and can damage components. Keep bursts under two minutes.
4. Trusting drain valves alone. Colorado State doesn’t recommend gravity-based manual or automatic drains, because there’s no way to see that the lines are empty.
5. Adding antifreeze. The American Red Cross warns against it unless directed, because it’s dangerous to people, pets, wildlife and landscaping.

Do you need to winterize at all?

If your ground freezes, yes. In the warmest parts of the South, many systems stay in use year-round, but lines can still freeze in a hard cold snap. If you’re unsure, follow your installer’s instructions. The Red Cross advises draining sprinkler supply lines according to the manufacturer’s or installer’s directions. Your outdoor faucets need attention too: see how to keep an outdoor faucet from freezing, and robot mowers and sprinkler systems if you run both.

The picks

Questions

What PSI should I use to blow out sprinklers?

Colorado State University Extension says to keep compressor pressure between 40 and 80 psi, with no more than 80 psi for rigid PVC and 50 psi for flexible black polyethylene pipe. Rain Bird’s guidance says air should not exceed 50 psi.

Can I blow out sprinklers with a small air compressor?

Often not well. Rain Bird recommends a compressor that can supply 185 cubic feet per minute or more, roughly a 50 to 70 gallon unit, which is far more than typical home compressors deliver. A small compressor may move air through the lines without clearing all the water.

How long should I blow out each sprinkler zone?

In short bursts. Rain Bird says not to blow any zone for more than two minutes at a time, because compressed-air heat can damage components, and to repeat at least twice per zone until only a fine mist comes from the heads.

Should I blow air through the backflow preventer?

No. Colorado State University Extension says pressure vacuum breakers and reduced pressure backflow devices must never be blown out with compressed air, because the heat can melt their internal rubber seals. Connect the compressor downstream of the backflow device.

Can I just drain my sprinkler system instead of blowing it out?

Colorado State University Extension doesn’t recommend relying on gravity-based manual or automatic drain valves, because there’s no way to confirm the lines are empty. It calls compressed-air blowout the reliable method.

Should I put antifreeze in my sprinkler lines?

No. The American Red Cross warns against putting antifreeze in water lines unless directed, because it’s dangerous to people, pets, wildlife and landscaping.

The short version

Water off, compressor connected downstream of the backflow preventer, one zone open, bursts under two minutes, two passes per zone, and pressure at or below 80 psi for PVC and 50 psi for poly pipe. Never blow through the backflow device, and skip the antifreeze. If your compressor is a small home unit, rent a bigger one or call a pro.