>From my experience, the principle way water gets into conduit is via ground
>water migration due to improper conduit joints.
I have two runs of 3", one of 2.5", and one of 1.25" all near 100' long. Both
ends terminate in NEMA 4 rated boxes. All coax exits at the tower via bulkhead
lightning arrestors and signal cable exit by watertight nipples. On the house
end, the NEMA box mounted on the side of the house has a cutout through the
house wall in its back where all coax and cables enter the garage area.
In the six years the conduit and cables have been installed, all I've ever
found when running new lines is dust. You can feel air flow through the
conduit and the conduit ends are not sealed.
I did take care when installing the conduit to lightly sand the areas to be
joined, use primer, and generous amounts of glue. You also need at least two
people to force the joints of the larger sizes together while rotating the pipe
in opposite directions. Then leave it alone until the glue dries.
Perry K4PWO
-----Original Message-----
From: TowerTalk [mailto:towertalk-bounces@contesting.com] On Behalf Of Tom_N2SR
via TowerTalk
Sent: Monday, February 01, 2016 1:43 PM
To: towertalk@contesting.com
Subject: Re: [TowerTalk] [Bulk] Fwd: where the condensation comes from
One could rent a tank of nitrogen from their local gas supplier. Purchase (or
rent) a reduction control valve (they typically have two pressure gauges, one
for the tank supply, and one for the lower pressure output). Run a small hose
from the gauge to the conduit, and seal the ends of the conduit. Once the
nitrogen floods the conduit, it only takes a few psi to maintain it. When the
tank goes empty, replace it. Nitrogen is a cheap gas. It shouldn't cost that
much to rent a tank. Dry nitrogen is used in aerospace testing all the time.
We use it to drive out air from thermal cycling chambers, which are used to
cycle units to extreme temperatures. Tom, N2SR
From: Grant Saviers <grants2@pacbell.net>
To: Hans Hammarquist <hanslg@aol.com>; towertalk@contesting.com
Sent: Monday, February 1, 2016 10:59 AM
Subject: Re: [TowerTalk] [Bulk] Fwd: where the condensation comes from
What matters most is the temperature of the buried conduit vs the wet
bulb of the air entering the conduit.
One end plugged stops the flow, and both ends plugged are usually not
hermetic so changing atmospheric pressure brings in moisture. (in trying
to make gas pressure seals, I found it surprising how much flow goes
down inside regular stranded wire).
So, plugging the outside end of the conduit and leaving the inside end
open is maybe sometimes possibly better than both ends plugged.
IMO, the only "sure thing" for a dry conduit is a low flow or slight
pressurization of very dry air. Since both ends of my conduits are
outside, I use direct burial cables and don't worry about condensation.
In fact, a plus of condensation is it keeps the wire pulling lubricant
active, so removing cables/coax is much easier. Nice when I was
salvaging about a thousand feet of LDF4 and LDF5 from conduit with
condensation.
Grant KZ1W
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