Use a 10-25 CFM Air Compressor to Blow Out Sprinklers

To safely blow out sprinkler systems, use an air compressor with 10-25 CFM (cubic feet per minute) and 50-80 PSI. A 10-15 CFM compressor works for residential systems (≤10 zones), while 20+ CFM is ideal for larger setups. Never exceed 80 PSI to avoid damaging pipes.

Key Factors to Determine Compressor Size

  • System size: Small (≤5 zones) = 10 CFM; Large (10+ zones) = 20-25 CFM.
  • Pipe diameter: ¾" pipes need less CFM than 1" or larger.
  • PSI limit: Stay below 80 PSI (most systems max at 50-60 PSI).
  • Tank size: 20-30 gallon tanks provide steady airflow for longer blows.

Compressor Size Comparison by System Type

System Type Zones Recommended CFM PSI Range Estimated Blowout Time
Small Residential 1-5 8-12 CFM 40-50 PSI 5-10 mins/zone
Medium Residential 6-10 15-20 CFM 50-60 PSI 10-15 mins/zone
Large/Commercial 10+ 20-25+ CFM 60-80 PSI 15-20 mins/zone

Step-by-Step Blowout Process

  1. Turn off water supply and set the system to "blowout" mode.
  2. Attach compressor to the mainline valve via a proper fitting (no duct tape).
  3. Start with the farthest zone and work backward to the closest.
  4. Open one zone at a time and blow until water stops (30-90 seconds per head).
  5. Repeat for all zones, then drain backflow preventers and valves.

Safety Risks of Undersized or Oversized Compressors

  • Too small (≤8 CFM): Incomplete water removal → frozen pipes.
  • Too large (>25 CFM): Risk of bursting pipes or fittings if PSI isn't controlled.
  • No pressure regulator: PSI spikes can damage sprinkler heads or valves.
  • Improper connections: Hose whipping or dislodging under pressure.

Alternative Methods (If No Compressor)

  • Manual drain valves: Only works for systems with automatic drains (ineffective for low spots).
  • Compressed air rental: Home improvement stores rent 15-20 CFM compressors.
  • Professional service: Best for complex systems or first-time blowouts.

Signs Your Compressor Is Too Weak

  • Water still sprays after 2+ minutes per zone.
  • Compressor overheats or cycles constantly.
  • Sprinkler heads drip water after blowing.
  • PSI drops below 30 when opening a zone.