Blowing Out a Sprinkler System Takes at Least 40 PSI, but HGTV’s Guide Warns Polyethylene Pipe Has to Stay Below 50

Two numbers decide whether a sprinkler blowout protects an irrigation system or damages it. HGTV’s winterizing guide says the compressor has to deliver at least 40 PSI to push water out of the pipes, while polyethylene pipe should stay below 50 PSI. Rigid PVC pipe, according to the same guide, should not go past 80 PSI.

The guide, written by Julie Martens Forney and Kamron Sanders and last updated March 12, 2026, is one of several that home gardeners can check before the first hard freeze. Extension services and gardening sites agree on the main limits but differ on how much air volume a compressor needs.

Why 40 PSI is the floor and 50 PSI is the ceiling for flexible pipe

HGTV’s irrigation winterizing guide says the compressor has to reach at least 40 PSI for the air to clear water from the lines. The same guide sets the upper limits by pipe type: no more than 80 PSI for PVC and below 50 PSI for polyethylene.

Colorado State University Extension gives a slightly different framing in its fact sheet on preparing a home sprinkler system for winter, written by C.E. Swift and M. Higgins and reviewed in August 2025. It puts the working range at 40 to 80 psi and lists a maximum of 80 psi for rigid PVC and 50 psi for flexible black polyethylene pipe. HGTV says polyethylene should stay below 50, so a homeowner who wants a margin can set the regulator a few pounds under that mark.

The Colorado State sheet also warns that the nozzle manufacturer’s rating matters. Excess pressure can blow nozzles off, it says, so the compressor’s regulator should be set before any zone is opened.

How much air a compressor needs to move

Pressure is only half of the equation. HGTV notes that an ordinary compressor cannot supply enough air volume to blow out an entire system at once, which is why the work is done one zone at a time.

Colorado State Extension offers a formula for the volume: divide a zone’s gallons per minute by 7.5 to get the cubic feet per minute of air needed. Its example is a 20 GPM zone at 30 psi, which needs about 2.66 CFM. The sheet says a compressor is sized correctly if sprinkler heads stay up while air is still flowing after the water is gone, and that too little air leaves water in low spots where it can freeze.

Other guides name specific compressor sizes, and they do not match. Gardening Know How contributor Tyler Schuster, in an article published Oct. 6, 2026, recommends a compressor rated at 5 CFM at 40 PSI and says airflow matters as much as pressure. Angi’s blowout guide says compressors around 100 CFM handle most systems and lists a general range of 40 to 80 PSI, with the same 80 PSI cap for PVC and 50 PSI for polyethylene. Because the figures vary so widely, the zone-by-zone formula from the extension sheet is the one tied to an actual system.

The zone-by-zone order HGTV lays out

HGTV’s steps start with shutting off the water supply at the main line valve, then draining the main line by opening its valve over a bucket or routing the water out through a hose attached to a hose bib. Next comes closing the backflow preventer valves so compressed air does not reach and damage the device.

Only then does the compressor go on. The guide says to set its pressure to at least 40 PSI while staying within the limit for the pipe type, connect through a quick-connect adapter on the blow-out port or a built-in quick coupler, and open the blow-out port valve if the system has one.

Zones are cleared one at a time, beginning with the farthest from the compressor. Each zone is closed once water stops flowing, and the next one down the line is opened. HGTV warns to stop the air once the water stops so plastic components do not overheat, and says a tiny amount of leftover water is unlikely to cause damage.

Angi’s guide gives the same far-zone-first order and adds that on hilly yards the highest points should go first. It also says to cycle each zone to clear remaining water and then release trapped air by opening and closing the manual drain and backflow valves for 5 to 10 minutes. Colorado State’s sheet recommends two short cycles per zone rather than one long one, and says not to re-blow a zone that is already clear.

What the extension services say about backflow devices and doing it alone

Colorado State Extension is blunt about the backflow assembly: PVB and RP backflow devices must never be blown out with compressed air, because the heat can melt their internal rubber seals. It also says gravity drain valves are not recommended since they cannot confirm the system is clear, and that eye protection is required. Gardening Know How gives matching cautions: never force air against a closed valve and never run air through dry pipes for long, since friction heat can damage heads, fittings and seals.

Not every extension office treats the blowout as a homeowner job. Oklahoma State University Extension, in its tips for winterizing a home irrigation system, says compressed-air blowing “isn’t something a homeowner should do on their own” and notes that improper pressure can damage the system. It lists draining backflow preventers and exposed pipes, opening manual valves, turning off the timer and insulating the main shut-off valve and other above-ground parts.

Utah State University Extension’s irrigation maintenance fact sheet, by Candace Schaible, Kelly Kopp and Jennie Hoover, lays out a shorter path. It says to shut off the main valve, relieve pressure by turning on each zone valve, open drain valves if the system has them, and use an air compressor only if it does not. The sheet also suggests having an irrigation professional blow out the system.

Timer settings and the last steps before freezing weather

Other cold-weather chores follow the same logic of getting water and fuel out before freezing weather, as in this look at the steps Nebraska Extension lists for putting a lawn mower away for winter.

HGTV ends with releasing remaining pressure by opening the backflow valves and the main drain valve once the compressor is disconnected, then closing all the valves after the air has cleared. The timer should be turned off, the guide says, and it suggests rain or standby mode so nothing has to be reprogrammed in spring.

Gardening Know How says to finish before the area’s first hard freeze, which in colder regions usually means early to mid-fall, and to give each zone two passes. It also recommends leaving the backflow ball valves and test cocks half-open over winter. In mild-winter regions, the site says, shutting off the water, turning off the controller and draining exposed parts may be enough.

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This article was produced with AI assistance and edited for accuracy against the sources linked above.

Image: Famartin – CC BY-SA 4.0/Wikimedia Commons