How to Blow out a Sprinkler System with an Air Compressor

With each season comes certain responsibilities and necessary projects to do around the home and yard to keep everything running smoothly and in good order. Before winter, one such project is blowing out the sprinkler system using an air compressor. Investing a little time to properly winterize the sprinkler system can prevent problems and costly repairs.

Air Compressor Sizing

For the most part, you’ll need an air compressor that provides the appropriate CFM (cubic feet per minute) for the equipment you’re using. Consult the owner’s manual for the recommended rating for CFM and psi (pounds per square inch) or speak with a representative at your local home improvement center about adjusting/regulating the air pressure. Usually, 80 psi is used for rigid PVC pipes and 50 psi is the standard for black polyethylene pipes.

As a general rule, using a pressure regulating valve prevents excessive air pressure, which can cause damage if not kept in sync with the air volume.

If you don’t own an air compressor, the equipment is available at home improvement centers or you can rent the compressor from a local equipment rental shop. Before buying or renting, be sure you choose a machine that has the power to do the job for the size and type of sprinkler system you’re working with.

Using an Air Compressor With a Sprinkler System

Step 1 - Shut off Water Supply

Turn off the water supply to the irrigation system.

Step 2 - Release Pressure in the Line

Open the hose bib at the sprinkler’s mainline to release pressure on the pipes, and allow any water to drain.

Step 3 - Prep Compressor

Turn on the compressor and follow the manufacturer’s directions for setting/charging the air compressor's psi. Once the psi is set, turn off the compressor and close the compressor valve.

Step 4 - Connect the Hose

Attach the compressor hose to the hose bib at the sprinkler’s mainline. This may require using a connector or adapter since the fitting between the hose bib and the air compressor hose may not align properly and result in a non-secure seal.

Step 5 - Start Compression

Activate the compressor to set the system timer/controller so the sprinkler located furthest away from the compressor and at the highest elevation will be the first zone activated.

Step 6 - Stop Backflow

Next, shut off the backflow isolation valves.

Step 7 - Man the Valve

Carefully open the compressor’s valve, allowing air to enter the system gradually.

Step 8 - Monitor

Monitor the blow out pressure to keep it below the specified operating pressure.

Step 9 - Move Zones

When complete, move on to the next sprinkler/zone location.

Step 10 - Stay in the Zone

Blow out each zone/sprinkler location, one by one, until there is no evidence of water emerging from the sprinkler heads. Activate the air compressor for approximately two minutes at each sprinkler zone. Repeat several times, if necessary.

Step 11 - Stop on Time

Once there is no longer any water emerging from the sprinkler system, discontinue the blow out process. Sending compressed air through the dry pipes will cause damage.

Step 12 - Disconnect

When all of the water is removed, it’s important to disconnect the equipment to release any remaining air pressure in the line.

Step 13 - Finish up

Follow the instructions for the specific equipment you’re using to address any additional steps necessary to complete the process.

Safety Issues

Keep in mind that with an air compressor doing its job properly, any debris near or around the area can easily become mobile, due to the pressure the water is under as it's blown out of the line. As the pressurized water comes into contact with movable items, they can cause serious damage and/or injury to your eyes.

Additionally, do not stand near or over any of the components of the irrigation system such as sprinkler heads, valves, or pipes.

When working with an air compressor, keep everyone safe from harm, including outdoor pets, by staying indoors until the blow out process is completed.

As with any home improvement project, if you're in doubt about any of the procedures, contact a professional who specializes in irrigation systems to ensure a safe process.