garyemunson wrote:
The best tool to own is a battery powered compressor with a regulator you can set at 40 lbs.
With all due respect, that's VERY dangerous advice.
The pressure the air is under has very little to do with clearing the water out of the lines compared to the VOLUME of air you put through the system.
In theory, a 1/4" air fitting running wide open, like when blowing out a water system, with the feed pressure at 40 psi will flow a little over 25 CFM.
A decent small 120 volt compressor with a 2 gallon tank might be able to make 5 or 6 CFM at 40 psi.
The only way you'd get enough volume of air with a battery powered compressor would be to fit an air tank inline with the hose and create a reservoir of pressure to give you full pressure for a much longer period of time, however you'd likely burn up the compressor in no time doing that.
It would also take all day doing it that way.