It’s getting cold again, and we’re getting a lot of calls on sprinkler blowout compressors. Air Compressors Direct customer and sprinkler system owner, Tony Weir, shared this great info on the procedure:
"This is in the operator’s manual of my Hunter irrigation system:
'Use an air compressor with a Cubic Foot per Minute (CFM) rating of 80-100 for any mainline of 2" or less, and do not exceed 80 PSI on PVC piping or 50 PSI on polyethylene piping.'
This is what a rental shop supplies, or what sprinkler companies use to blow out 99% of water and vapor from the sprinkler lines.
Anything less, like a 60-gallon unit producing 15 CFM, will only remove around 50% of water. Keep in mind that water expands by 9% when it freezes. This means that if it freezes, there may be enough water left behind to cause a break in the line or a break in a sprinkler head.”
I had been blowing out the system at my old house with a 60-gallon air compressor and only had one break in eight years. Elevations were very flat and I got lucky, but I had to let the tank recover after each zone. Furthermore, I went through all 10 zones 3 times each to get as much water out as possible. We need to have this information circulated to everyone. We don't want people to buy inadequately powered equipment with high expectations."
Here’s my "boilerplate" answer to this question. The same one that I have shared with you through the seasons:
Blowing water out of lines requires the largest capacity (CFM @ psi) compressor possible. So we recommend the compressor that has the highest rating that fits your storage area & budget. More CFM is always faster.
Tony’s information above is very helpful in demonstrating the right way to do it, however some people are still resistant when it comes to purchasing a 60 gallon air compressor unless they plan to use air tools. It's important to remember that even if you're not using air tools, higher CFM is necessary for many other tasks - especially those like blowing out sprinkler systems.