Fall Irrigation System Blowout Procedure
A seasonal blowout procedure for the irrigation system to evacuate standing water from all lines, valves, and heads using compressed air, protecting the system from freeze-related damage during the fall and winter months.
Spokane County Library District
09/09/2026
Fall Irrigation System Blowout Procedure
This procedure ensures that the irrigation system is safely and thoroughly purged of all residual water using compressed air prior to the onset of freezing temperatures, preventing pipe bursts, valve damage, and component deterioration caused by ice expansion, and preserving the structural integrity and operational readiness of the system for the following season.
Personal Protective Equipment (PPE) Safety glasses Hearing protection Work gloves High-visibility vest when working near parking lots or roadways Safety Precautions Only trained personnel or licensed irrigation contractors shall perform blowouts. Never stand over sprinkler heads during operation. Use regulated compressed air pressure appropriate for the irrigation system. Ensure all bystanders remain clear of the work area. Do not exceed manufacturer-recommended air pressure limits.
Maximum Air Pressure Guidelines
System Type Maximum Pressure PVC Mainline/Lateral Lines 50 PSI Polyethylene Pipe 80 PSI Drip Irrigation 30 PSI
Air compressor capable of producing sufficient CFM for system size Compressor hose and fittings Irrigation system keys/tools Lockout/Tagout materials Winterization tags or documentation forms Hand tools Site irrigation maps
Notify branch management of scheduled irrigation shutdown. Review irrigation maps and controller locations. Inspect the system for damaged heads, leaks, or exposed piping. Verify compressor pressure settings. Ensure water supply shutoff valve is accessible.
Locate the irrigation system isolation valve. Close the irrigation water supply valve completely. Confirm no water is feeding the irrigation mainline. Open a downstream drain valve, if equipped, to relieve pressure.
Shut off upstream and downstream isolation valves. Open all test cocks approximately 45 degrees. Leave test cocks in the partially open position after winterization. If district policy requires removal of backflow assemblies, remove and store in a secure heated location.
Connect compressor hose to the designated blowout connection downstream of the backflow preventer. Start compressor and allow pressure to stabilize. Verify pressure does not exceed specified limits.
Important Operate only one irrigation zone at a time. For each irrigation zone: Activate Zone 1 manually through the controller. Apply compressed air until: Water discharge changes to a fine mist. Sprinkler heads stop expelling visible water. Run air only long enough to clear the line. Shut off the zone. Allow compressor pressure to recover. Proceed to the next zone. Repeat for all zones. Drip Irrigation Zones Reduce compressor pressure to a maximum of 30 PSI. Open zone manually. Blow out until water is removed. Avoid prolonged air discharge that may damage emitters.
Conventional Controllers Turn controller to: "Off" "Rain Mode" Or manufacturer winter shutdown setting Leave power connected unless manufacturer guidance states otherwise. Verify all scheduled watering programs are disabled. Smart Controllers Place controller in winter mode. Verify no automatic watering schedules remain active.
Confirm supply valve remains closed. Open test cocks to 45 degrees. Open bleed valves as applicable. Verify no trapped water remains in exposed components.
Verify: All irrigation zones have been blown clear. Water supply remains shut off. Controller is disabled. Backflow device is winterized. Valve boxes are closed and secure. Equipment and hoses have been removed. Site is clean and safe.
Documentation
Winterization Record Example Site: ___________________________ Date: ___________________________ Completed By: ___________________ Number of Zones: ________________ Backflow Winterized: □ Yes □ No Deficiencies Noted:
Source: Spokane County Library District (Community Member)