Winterizing

[LarryJB]

Originally Posted by Concord

Density Anomalies of Water

Best I can find.

Whew! this also explains that water's freezing point decreases with pressure. So does this imply that we could fudge a little by somehow increase the pressure in the water lines? like maybe turning on the water pump? Or even connecting water to compressed air? Not that I would do it, but theoretically?

[grindstone01]

Originally Posted by LarryJB

Whew! this also explains that water's freezing point decreases with pressure. So does this imply that we could fudge a little by somehow increase the pressure in the water lines? like maybe turning on the water pump? Or even connecting water to compressed air? Not that I would do it, but theoretically?

Another way to look at this is to assume that 150 PSI would burst your RV pipe. If you start out with the pipe water pressure at 60 PSI from a city hook up, then the freezing ice only has to build up 90 PSI before the pipe would burst. Whereas if the pipe PSI were at 0, then the freezing water needs to build up 150 PSI before busting a pipe.
This is why city water mains will burst at relatively warm temps like mid 20's due to them already being at high pressure before the freezing expansion begins.
If I keep my RV water at 0 PSI (unhooked), I have survived temps in the low 20's w/o draining the water system.

[LarryJB]

Originally Posted by grindstone01

Another way to look at this is to assume that 150 PSI would burst your RV pipe. If you start out with the pipe water pressure at 60 PSI from a city hook up, then the freezing ice only has to build up 90 PSI before the pipe would burst. Whereas if the pipe PSI were at 0, then the freezing water needs to build up 150 PSI before busting a pipe.
This is why city water mains will burst at relatively warm temps like mid 20's due to them already being at high pressure before the freezing expansion begins.
If I keep my RV water at 0 PSI (unhooked), I have survived temps in the low 20's w/o draining the water system.

I love this discussion!

[Bobby F]

Concord: "Between 0 and -4 C water expands as it crystalizes. The rest of the temperature spectrum it behaves a other elements... Expands with heat, contracts with cold."

This. It's the phase change that causes expansion. Once water has frozen completely into ice, the crystalline formation which causes the 9% expansion is done, and ice then shrinks as it gets colder.

[FL420]

Originally Posted by Concord

http://www1.lsbu.ac.uk/water/density_anomalies.html

Best I can find.

I admit I didn't read the whole article because frankly, it made my brain hurt. The gist of it that I noticed, perhaps inaccurately, was that increased pressure on the water can affect its compressibility and/or expansivity.
From my perspective talking about water in RV plumbing and sewage systems I didn't consider any pressure on the water other than the normal atmospheric pressure or temperatures outside of the range of temperatures normally experienced by RVers in North America.
grindstone01 brought up the point of lowering pressure in the water supply plumbing. From my perspective I never use campground water for any purpose other than to fill my fresh water tank so I never leave a hose hooked up to my coach. I always turn my water pump off when I leave the coach or go to bed. Perhaps I should drain a little water from the lines for expansion space by draining my sink faucets of residual water after turning off the pump.
Another thought I had is adding a small expansion tank(or 2 if the hot water side needs one too) to the water system. Most people use them to handle hammering in copper pipes due to pressure changes and sometimes due to temperature changes.
The RV hot water heater already functions as an old fashioned style expansion tank. That is if the water heater is routinely maintained by draining, cleaning and refilling the tank. When refilling the tank the T&P valve should be open and when water flows from it the filling should stop and the T&P valve closed. This re-establishes the compressible air space at the top of the tank that over time had been diminished by the air being absorbed and removed by the water.
Modern expansion tanks use a rubber diaphragm that is certified safe for potable water to separate the compressible air section of the tank from the incompressible section.

https://en.m.wikipedia.org/wiki/Expansion_tank

Your thoughts welcome.

[Concord]

It's hard to find evidence of the obvious, but I did find this...

The only thing I added is the conversion chart to Fahrenheit at the bottom.

[Concord]

Here it is.

[grindstone01]

Originally Posted by Bobby F

Concord: "Between 0 and -4 C water expands as it crystalizes. The rest of the temperature spectrum it behaves a other elements... Expands with heat, contracts with cold."

This. It's the phase change that causes expansion. Once water has frozen completely into ice, the crystalline formation which causes the 9% expansion is done, and ice then shrinks as it gets colder.

If ice shrinks when it gets colder, then why are we worried about bursting pipes??

[Bobby F]

"If ice shrinks when it gets colder, then why are we worried about bursting pipes??"


In the phase change - liquid to solid - the crystallization causes it to expand about 9%.


Once it's all frozen, the expansion stops. Just like almost all substances, it then shrinks in the cold - but nowhere near as much as it expanded with the phase change.

[LarryJB]

Originally Posted by grindstone01

If ice shrinks when it gets colder, then why are we worried about bursting pipes??

Wouldn't the damage already be done before it starts to shrink? It has to expand before it can shrink.

[grindstone01]

Originally Posted by Bobby F

"If ice shrinks when it gets colder, then why are we worried about bursting pipes??"


In the phase change - liquid to solid - the crystallization causes it to expand about 9%.


Once it's all frozen, the expansion stops. Just like almost all substances, it then shrinks in the cold - but nowhere near as much as it expanded with the phase change.

Originally Posted by LarryJB

Wouldn't the damage already be done before it starts to shrink? It has to expand before it can shrink.

Based on what you guys are saying then is once your pipes survive the water freeze stage at 32F, then you don't have to worry any more about pipes bursting as the temp drops. Attached is a good article which talks about 20F being a typical pipe bursting point due to expanding ice.
https://inspectapedia.com/plumbing/F..._Water_Ice.php

[Bobby F]

"Based on what you guys are saying then is once your pipes survive the water freeze stage at 32F, then you don't have to worry any more about pipes bursting as the temp drops."

Once everything is completely frozen through - once the entire rig is completely cold-soaked so that everything is a uniform 28-29 degrees or so with no warm spots - you're correct. Leave water in your pipes for a week at that temp, and, mostly, what's going to be blown is blown.

Once you get down into the much lower temps, though, you start dealing with decreased plasticity/elasticity of pipe materials, such that a pipe that barely didn't split at 30 will then split.

But, mostly, you're correct. The main effect of really colder temps is the speed with which you can attain that complete cold-soak. The article speaks of 20 degrees as a burst point - but it also says this:

" . . . expansive forces generally do not cause water pipes to burst until temperatures further fall to around 20°F or until temperatures remain below freezing for some protracted time period."

20 degrees gets you that complete cold-soak faster than 30 does. But if you let everything hit 30 for enough time, you'll get the same bursting.

(Do you know how depressing it is to realize that you know all of this stuff about really lousy weather? I'd much rather be able to discuss the dangers of suntanning than the dangers of freezing your butt off. )