How to Blow Out a Sprinkler System: Step-by-Step Guide (PSI, CFM & Compressor Size)

Every October, New Jersey homeowners ask the same question: can I blow out my own sprinkler system? The honest answer is yes — if you have the right compressor, know your pipe type, and follow the sequence carefully. Here is exactly how professionals do it, what equipment you actually need, and where DIY blowouts most often go wrong.

What You Need Before You Start

• Air compressor with 20–25 CFM minimum for small residential systems. Professional rigs are tow-behind units pushing 80–185 CFM. This is the make-or-break spec — see below.
• Quick-connect adapter matching your system blowout port (usually a 1" or 3/4" threaded fitting near the backflow preventer).
• Eye protection. Heads can pop and spit debris under air pressure.
• Your controller accessible, so you can cycle zones manually.

CFM vs. PSI: Why Your Pancake Compressor Will Not Work

This is the most misunderstood part of a DIY blowout. Clearing irrigation lines is about air volume (CFM), not pressure (PSI). A 6-gallon pancake compressor can hit 150 PSI, but it only moves 2–4 CFM — it will push a slug of air into the line, stall, and leave water sitting in every low spot while appearing to "work." The heads hiss, you feel productive, and the water that stayed behind cracks your lateral lines in January.

Rule of thumb: if your compressor fits in a car trunk, it cannot properly blow out an in-ground system.

Step-by-Step: How to Blow Out a Sprinkler System

1. Shut off the irrigation water supply at the main shutoff valve (usually in the basement or a valve box near the meter).
2. Relieve pressure. Open a zone briefly or crack the drain to bleed off line pressure.
3. Set your compressor regulator: 50 PSI maximum for polyethylene (black poly) pipe, 80 PSI maximum for PVC. More pressure does not clear more water — it blows fittings apart and destroys valve diaphragms.
4. Connect the compressor to the blowout port — downstream of the backflow preventer. Never blow compressed air through the backflow device itself.
5. Open one zone at a time from the controller, starting with the zone farthest from the compressor.
6. Run air until heads spray only mist — usually about 2 minutes per zone. Do not run dry heads for long stretches; heat from friction can melt gears and seals.
7. Cycle every zone 2–3 times. Water settles back into low spots between passes. One pass per zone is the classic DIY mistake.
8. Winterize the backflow preventer: drain it and set the ball valves and test cocks to a 45° angle. Full guide here: How to Winterize a Backflow Preventer.
9. Set the controller to off or rain mode. Smart controllers can simply be left plugged in over winter.

Common DIY Blowout Mistakes

• Using an undersized compressor (see above — the #1 cause of "but I winterized it!" spring repairs)
• Running PSI too high and splitting poly fittings
• Blowing air through the backflow preventer instead of around it
• Single pass per zone instead of 2–3 cycles
• Forgetting drip zones — they winterize differently: How to Winterize Drip Irrigation
• Waiting past mid-November — in NJ the first hard freeze does not send a calendar invite

When to Just Call a Pro

If your system has more than 4–5 zones, a well feed, or any backflow device you are not 100% sure how to handle, professional winterization costs less than renting a proper tow-behind compressor for the day. Freeze damage repairs start around $300 and climb fast.

📌 Related winterization resources:

• Professional Winterization & Blow-Out Service
• Sprinkler Winterization FAQ
• Monmouth County Winterization Guide

Skip the Compressor Rental — Book a Blowout

Coastal Mist Irrigation winterizes systems across Ocean, Monmouth, and Atlantic County every fall. Call or text 609-548-5187 or schedule online.