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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