[TowerTalk] Tower design question

[KA6AMD]

I'll take a whack at this since I have had to deal with it recently. 

I live out in the Mojave desert where the relative humidity is usually 
in the teens.Even with that and 100+ daytime temperatures, I was able to 
drain water out of my mast sections when they got plugged up.  The day 
to night temperature differences pumped water into the mast sections.  
As it cooled down at night, the water condensed in the tube.  It 
collected there faster than it could evaporate during the day.

What we are dealing with here is a powerful force of nature: vapor 
pressure.  When there are more water molecules outside a space than 
inside, the water wants to migrate to the lower vapor pressure.  
Stopping it is very difficult.  Hence hermetically sealed containers are 
very expensive and hard to make.  The way it is done in industry is to 
use welded seams and complicated gasket seals. 

So what you would have to do is put a seal on every penetration of the 
tower tubing and make sure that seal is not damaged or compromised 
during assembly.  This would be almost impossible on a tower and would 
cost an arm and a leg. 

An alternative would be to pump dry air through the tower to maintain 
the interior relative humidity below the condensation temperature of 
water.  This is a maintenance headache and costly as well.  The best bet 
(and by far the cheapest) is to let the water drain out.

Erich N6FD
(ex KA6AMD)

Pat Barthelow wrote:
> Perhaps I have missed this in the thread, but has anyone described the 
> mechanism of accumulation of water at the base of the corner tubing, of Rohn 
> 25-Like towers?
>
> Some outside the box thinking...
>
> If you did something liike seal each joint/bolts assembly with liberal 
> amounts of externally applied RTV material, after assembly,  that would 
> eliminate water entering through capillary action through the joints.
> I wonder if when the tower cools a lot, at night, if that can cause a 
> significant, but  slight vacuum, inside the legs that would draw moisture in 
> that is sitting on outside joints.
> Water entry may not only be through joints, but may be condensation.  Does 
> the "Pointy Top" close off the top ends of the corner posts?  Could you 
> perhaps tap into the top sections of a tower, where stresses and weight are 
> low, and apply a blast of pressurized air, into the whole length of the leg, 
> to clear/blow out any accumulated crud at the base, and to check that the 
> base tips of the legs are clear.   That might be a good idea when setting 
> the base, if the effort is made to place the buried legs on gravel which 
> allows drainage, to put some air pressure insde  the vertical tubes to 
> continuously blow out ingress of wet concrete during base setup.   How about 
> some sort of electic thermal wrap around each leg, as it enters the ground, 
> to periodically evaporate accoumulated water?
>
> Sincerely, Pat Barthelow     aa6eg at hotmail.com
> http://www.jamesburgdish.org
> Jamesburg Earth Station  Moon Bounce Team
> http://www.cq-vhf.com
>
>
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