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Andy Champ[_2_]

On 23/01/2013 09:59, wrote:
In article ,
Peter Clinch wrote:
Bad phrasing on my part. What I'm getting at is that in order to /be/
staurated you need over a 4m water column providing pressure, and that
other words, the hydrostatic head will be maintained precisely because
the pore structure cannot get saturated until you exceed it.
The pore structure won't be saturated however much the face is.

Well, maybe. I accept that is true under simple conditions, but
real life isn't that simple. Inter alia, one of the reasons that
Goretex says that its fabrics must be kept clean is that 'dirt'
can act as a flux. Also, rubbing causes transient overpressure
which can cause 'breakthrough' - and, once that has happened and
both sides of the pores are wet, the surface tension effect is
(mostly) lost.

There is also the question of what the overpressure is for pouring
rain being driven by a force 7 gale :-)

I'm cross-posting this to uk.rec.motorcycles, because they are rather
familiar with the problems of high wind speeds and rain.

Its claims are nonsense (a
water molecule is NOT much larger than a steam molecule), and my
understanding is that the hydrostatic head is due to hydrophic
material.

It's surface tension, but you can't break the surface tension until you
exceed the hydrostatic head, which you won't do because it's too big.
So it won't leak until you've got a lot more pressure forcing the water
through than will happen in practical application.

I am not convinced, though I have been unable to measure any flow.
What I have seen is water on one side, in conjunction with rubbing
and probably dirt cause darkening and a feeling of damp on the
other. This matches with what I know of the physics involved.

Most examples of "leaking" are condensation on the other side, which is
remarakably difficult to get rid of.

That is true. As we both know, perfect waterproofing is a complete
waste of time for UK conditions, for that reason alone.

If it's easy to measure percolation through goretex then it would fail
the hydrostatic head tests that Gore use as the basis of their guarantee.

Not at all. Those tests almost certainly require a maximum level of
leakage, which can be regarded as negligible. That's reasonable, but
NOT the same as claims of perfect waterproofness.

Regards,
Nick Maclaren.

See embedded.... Andy