[TowerTalk] water in EMT conduit

[TexasRF at aol.com]

Patrick, the problem here is that it is not possible with the usual  
materials available to hermetically seal the conduit on the ends where the  wiring 
enters and exits.
 
If it were possible, then one would do that while there was a positive  
pressure inside the conduit and all would be fine. 
 
Theoretically a hermetic seal can be done. Practically, it can't be  done.
 
The small amount of water vapor present in the also small air exchange from 
 heat/cool cycles is a source of condensation. True, only a little day by 
day but  over time it accumulates and that is the problem.
 
This problem is so insidious that it can happen inside a hollow coax center 
 conductor and accumulate inside the coax connector. In North Texas, in the 
Fall  of the year, several droplets of water can accumulate in a couple of 
weeks.Cable  manufacturers now offer rubber "bullets" to install inside 
hollow center  conductors to stop the flow of vapor laden air and water 
condensation. This is  as close to a hermetic seal as one can hope for.
 
73,
Gerald K5GW
 
 
 
 
In a message dated 2/27/2013 1:55:30 P.M. Pacific Standard Time,  
patrick_g at windstream.net writes:


Lets  see if I followed the gist of the thread...

If a conduit with no water  in it is hermetically sealed it will promote 
condensation.

Conduits  should be left open so they can dry out.

Sealed conduits will breathe  with changes in temp and barometric pressure 
and thus admit  moisture.

...and so on and so  forth...

********************************************************

I'm  still wondering how a conduit properly installed and sealed admits 
more  
and more moisture over time.    Ideas?  (Porosity of PVC  increased by 
electromagnetic forces, intervention by space aliens, or  what?)

I can't help going back to the question of how PVC pipe that can  hold over 
100 PSI successfully without any leaks, when partially filled  with cables, 
can't withstand changes in ambient pressure rarely reaching  or exceeding 
5PSI. Max swings in barometric pressure from high pressure  weather 
phenomena 
to lows of cyclones shouldn't exceed this level much if  at all. Excluding 
critters and sealing the end of the conduit can be as  simple as drilling 
nicely fitting holes in an inexpensive PVC pipe cap to  let the wires exit 
and sealing the wire/hole interstices with silicone  rubber or Excel.  If 
you 
want to go to Herculean lengths then  bulkhead feed through fittings with 
rubber stoppers of compression sealing  design will surpass the 
requirements.

Patrick AF5CK  

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