When you have to cut a water line in a situation where it’s impractical to shut off the water, surround the pipe on each side of the cut with dry ice. The water adjacent to the ice will freeze. Make the cut, insert the fitting and thaw the pipe.
Jack H. Gillow, Highland, MI
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That is slick! Granted, one has to go find and purchase the dry ice, but I have seen this kind of situation.
That's one of the best plumbing hacks ever, top ten at least. Curious how much dry ice packing needed for typical residential supply line. Ingenious.
There are commercially available pipe freezing kits available that do much the same thing with freon (the propellant used in aerosols) and pipe lagging. I've had some success with these kits (about 10-15 mins working time), but I suspect dry ice will have a longer working time. However, I am a little concerned about the temperatures involved with dry ice and the possibility of damage to the skin should accidental contact occur.
Maybe you should specify what type of pipe you are talking about. How do you not incur frost damage to the pipe itself? I have done a lot of repairs on pipes that froze and split open. Are we talking PEX as opposed to copper, and is it really more efficient to try and find dry ice than turning off the water?
I appreciate the gist of this tip, but it really should read "...when it's IMPOSSIBLE to shut the water off...", because I think this technique should only ever be a last resort. Yes it will work - if very carefully planned and executed - but the potential for disaster is very high. Imagine an ill-formed ice plug letting loose in someone's home while the line is still under full city pressure, and the now fully open water line gushing full force while you scramble around in full panic mode trying to figure out what to do next. Not pretty. We do routinely freeze copper water lines in the course of our work (residential plumbing contractor), but with a special carbon dioxide powered kit designed specifically for the purpose (and years of experience) - and even then it can often be tricky business in the wrong circumstances. We've seen and heard enough tales of enough freeze jobs gone wrong to never advise a non-professional to attempt it with dry ice and a prayer.