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dbennett
10-07-2005, 05:25 PM
I work for a water utility. We have a system on a mountain where people pay fixed rates for water. Most of the homes are seasonal use. In the winter, people leave water running to avoid burst pipes, putting lots of undesired demand on the infrastructure.

A couple of years ago I read some research proving that pipes burst because the ice blockage acts like a piston, compressing the water in the closed end of the line. Eventually, the high pressure causes a leak at the weakest point. Leaving the faucet dripping protects the system by relieving pressure, not so much by keeping the water moving.

I now hear that Watts makes a pressure relieving toilet valve that releases system pressure into the toilet tank. Could the use of this valve eliminate the need for people to run a faucet in cold weather? What are the risks?

Any other ideas on this issue?

neili
10-07-2005, 06:22 PM
Thermodynamic equations include energy and velocity. Thinking of frozen water as a particular state of energy for water adding velocity would change that state of energy. With out going to the text books, I would say that the movement of the water has more to do with keeping the water from freezing than does the relief of pressure. I am too lazy to get of the couch and look, so this is just my opinion.

plumber1
10-07-2005, 06:50 PM
From where I sit, those folks on the mountain should drain there places when the leave.
I would never trust that toilet with a relief here in Michigan.
I've spent more time thawing and repairing both plumbing and heating pipes.
Any where there is a dip, there is a place to freeze.
Piston or not, that ol ice moves sideways too..........

hj
10-07-2005, 07:49 PM
The relief valve sounds good in theory, the problem is that pipes can freeze in two different areas and then the rupture can take place between them.

alhurley
10-07-2005, 11:56 PM
the reason the freezing action is so destructive has to do with the physics of water as it cools. As one would expect, as water cools the molecules move less and the volume decreases. That is true up to about 26 deg F. Somewhere around there water starts expanding again. But now you are dealing with a solid (ice) and the expansion has no place to go because it is literally blocking itself from doing its job. KABOOM! The force of the expanding water easily breaks through copper or plastic. That's fine until things start to thaw and the ice no longer blocks the water behind it. Suddenly you have a leak - usually big.

One thing that I used in our house in MI was the heat tape with a built in temp sensor. This allowed you to leave the tape on all the time and it would regulate itself. Never had a problem after we started using it. :D

hj
10-08-2005, 07:02 AM
The expansion actually starts at about 30 degrees, and if the ice can "push" the water out of the way at either end then it may expand longitudinally and may not crack the pipe. If it is trapped then it will expand in all directions.