"Phil L" wrote in message
...
Franz Heymann wrote:
:: "Phil L" wrote in message
:: . ..
::: Franz Heymann wrote:
::::: "Phil L" wrote in message
::::: . ..
:::::: Sue wrote:
:::::::: ........ how can I protect my outside tap from freezing up?
::::::::
:::::::: Sue
::::::
:::::: Turn the water off at it's supply...draining it is unnecesary
:::::: as any water which remains inside it will expand out of the
:::::: tap if you leave it in the 'on' position.
:::::
::::: That depends on whether it freezes solid at the tap end first.
:::::
::: The water at the tap end will expand though the outlet...unless
::: there's a long pipe (half a metre or more)outside, this will not
::: cause any problems.
::
:: Not if the water freezes solid at the tap end before the water in
:: the rest of the pipe begins to expand as it gets cold.
::
:: It is of the essence to realise that water starts expanding when
:: its temperature drops below 4 deg C, long before it freezes.
::

Yes, it's the 'long before it freezes' which needs understanding...
once it
has expanded enough to freeze solid, excess water has been pushed
out
through the open tap.

Not if it freezes at the tap end before the water higher up the pipe
has finished expanding.

It can only burst the pipe if it has nowhere else to go!

Thsat occurs immediately after the water in and near the tap has
solidified.

- if there is an
outlet it will go through this (the tap).

Not if the tap contains a solid plug of ice

...to suggest that the tap is
colder than the pipework is false, the copper is less than a
millimetre
thick while the brass is up to 10 mm, ergo the pipewater will freeze
first,
pushing the rest of the water towards the outlet.

That argument is as full of flaws as a colander is full of holes.
Also, you forgot that the tap will be wet if it is left open.
Evaporation will then help to cool the tap and promote local freezing.
The tap will have more roughnesses than the pipework itself, thereby
providing local nucleii for the onset of freezing.
The free droplets at the tap will be moved around by air currents,
thus preventing them from becoming a supercooled liquid and promoting
freezing.
I could go on for a very long time yet, but this is getting to be
boring.

Franz