Draining your pipes before the winter freeze prevents springtime floods.

How to Flush Out a Sprinkler System for Freezing Temps

by Chris Deziel

Sprinkler pipes and heads, like the components of any water system, are vulnerable to freezing temperatures. When residual water turns to ice in the pipes, it expands and blocks them, creating excessive pressure between the blocked section and the shutoff valve. If the pipe bursts, it usually does so in that section, not the one in which the ice is located. You can prevent bursting pipes by draining them for the winter. The procedure is easiest if you have a drain valve installed in an appropriate location on the mainline. If not, drain the system with compressed air.

Manual Draining

Look for a drain valve. If there is one, it will be located at the lowest point of the sprinkler mainline. It may be a ball valve, a compression valve or even a plug or cap screwed to a fitting.

Turn off the main water supply and open the valve controlling flow to one of the zones in the system. You may be able to work the valve manually, or you may have to open it electronically through the controller.

Open the drain valve slowly -- the water may be under pressure. Use a wrench to unscrew a cap or plug. Let it drain into the ground, or if it's in the house, into a bucket.

Close the drain valve, and then close the zone valve and open the next one and repeat the draining procedure. Drain the water from all the zones in the same way.

Blowing with Compressed Air

Turn off the main shut off valve and open one of the zone valves, either manually or electronically from the control panel.

Attach a compressor hose to a quick-connect air fitting attached to the sprinkler mainline. If your system doesn't have such a fitting, you may need to install one. Cut into the mainline near the shut-off valve with a hacksaw and glue in a tee with plastic pipe cement. Glue a threaded female adapter to the perpendicular port and screw the quick-connect fitting to the adapter.

Turn on the compressor and let the pressure build until all the sprinklers in the zone pop up. Do not exceed 50 psi, or you could damage the pipes. Leave the zone pressurized for two minutes, and then turn off the compressor. Wait for the air to purge from the zone, close the zone valve, open another one and repeat the procedure.

Blow each zone at least twice. The pipes are purged of water when only a fine spray emerges from each sprinkler head when they are pressurized.

Leave one zone open while you shut down and unhook the compressor. Close the valve when the compressor is disconnected. If the system has an electronic control, turn it to "Off."

Items you will need

  • Wrench
  • Bucket
  • Hacksaw
  • Plastic tee
  • Plastic pipe cement
  • Threaded female adapter
  • Quick-connect air fitting
  • Air compressor


  • Complete the drainage procedure by unscrewing the tops of all the zone valves and wiping out all the water from inside with a sponge. Leave the valves open for the winter.
  • You need a compressor that delivers 10 to 25 cubic feet of air per minute rather than an inexpensive compressor for car tires.


  • Never stand over a sprinkler head while the system is pressurized with compressed air. Because it has lower viscosity than water, pressurized air can burst pipes and fittings.
  • Wear eye protection while flushing a system with compressed air.

About the Author

Chris Deziel has a bachelor's degree in physics and a master's degree in humanities. Besides having an abiding interest in popular science, Deziel has been active in the building and home design trades since 1975. As a landscape builder, he helped establish two gardening companies.

Photo Credits

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