How to Blow Out a Sprinkler System, With or Without an Air Compressor

Your sprinkler pipes still hold water from the last cycle, and the forecast drops below 32°F this weekend. Colorado State University (CSU) says freezing water can burst pipes and crack valves. Rain Bird says to blow out one zone at a time at 50 psi, 2 minutes at a time, until only mist comes out. CSU says never push air through a PVB or RP backflow device; the seals can melt.

Quick pick: a blowout adapter with a shut-off valve, plus eye protection.

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How much air pressure to use

Rigid PVC pipe (white): 80 psi maximum, per CSU.

Flexible black polyethylene pipe: 50 psi maximum, per CSU.

Not sure: use 50 psi, Rain Bird's limit.

Nozzles: CSU says pressure above a nozzle's rating can blow it off.

Compressor size: the CFM math

CSU's formula: zone gallons per minute (GPM) ÷ 7.5 = CFM needed. Add up the GPM of each nozzle on the zone.

12 GPM zone (say, 6 heads at 2 GPM): 1.6 CFM

20 GPM zone: about 2.7 CFM, CSU's own example

CSU says too little air rides over the water and leaves it in low spots. Rain Bird recommends a 50 to 70 gallon compressor that delivers 185 CFM or more, and says to call a pro if you lack the equipment.

Without a compressor: what actually works

Manual drain valves: Rain Bird says to shut off the mainline, open a zone valve to relieve pressure, then slowly open each drain valve, wearing eye protection; it's under pressure.

Automatic drains: they empty each time the water shuts off, Rain Bird says; puddles can mean one is stuck open.

The catch: CSU says not to trust drain valves: buried pipes shift and leave water in low spots, and electric valves need air. PlantTalk prefers a pro blowout.

Step by step: the blowout

☐ Put on safety glasses and never stand over a head, valve or fitting while air is on (Rain Bird, CSU).

☐ Shut off the water at the stop-and-waste valve. CSU says it may need a long key; don't force it.

☐ Run the zone farthest from the air connection to relieve pressure (Rain Bird).

☐ Hook the compressor to the blowout fitting downstream of the backflow device and close the downstream ball valve (CSU).

☐ Set the regulator to 50 psi, then open the air slowly until the heads pop up (Rain Bird).

☐ Blow each zone no more than 2 minutes at a time, then move on; repeat two or more rounds until only mist shows (Rain Bird). Don't re-blow a dry zone; friction heat can damage pipe (CSU).

☐ Leave one zone on while you shut off the compressor, then unhook it. Let the air bleed out of the tank and lines before touching the hose or valves (Rain Bird).

☐ Set the backflow ball valves and test cocks half open for winter (CSU).

Blowout adapter and a compressor (#ad)

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Vibrant Yard Co. Sprinkler Winterize Adapter with Valve, 14 in: 3/4 in garden hose threads, a 1/4 in industrial quick-connect plug and a forged brass shut-off valve, per the maker. Check that it fits your port. See it on Amazon

ECOMAX 6 Gallon Pancake Air Compressor: rated 3 CFM at 90 psi, per the maker. It meets CSU's math for zones up to about 22 GPM, far below Rain Bird's 185 CFM. CSU's test: if heads stay up while air flows, the compressor is big enough; if they drop, it's undersized; Rain Bird says to call a pro. See it on Amazon

Sprinkler blowout FAQ

What PSI should I use to blow out sprinklers?

50 psi is Rain Bird's limit. CSU puts the maximum at 80 psi for rigid PVC and 50 psi for black polyethylene.

Can I winterize a sprinkler system without an air compressor?

Only by drain valves, and CSU says that is not reliable. Systems with electric valves need air.

Do I blow air through the backflow preventer?

No. CSU says PVB and RP devices must never be blown out with air.

More fall prep: dormant seeding, frost cloth and fall lawn fertilizer.

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Sources: Colorado State University Extension, Home Sprinkler Systems: Preparing Your Sprinkler System for Winter, Fact Sheet 4.719; CSU Extension PlantTalk Colorado, 2205 Winterizing Sprinkler Systems; Rain Bird, Fall is Blow-Out Season: Tips for Winterizing Your Sprinkler System, October 20, 2025.