Don't forget a flow meter. (rotometer). the flow rate is so little you
can't hear it and can just feel it against your face. Typically, for
anything other than a short rental, you provide the pressure regulator,
gauges, and flow meter. They are not expensive, BUT each set fits
"*ONLY"* one type of gas cylinder.
Leasing might be the only way some providers do it. You can purchase
the tanks, but then, you have to take care of and pay for periodic
pressure testing of the cylinder. Look it up in high pressure tank
thread regulations.
NOTE: Ideally for a purge, the conduit should be pressurized only a few
inches above atmospheric pressure which means a sealed conduit with a
"tiny" leak at the far end. Purging properly can be a real PITA for the
individual and expensive if not done correctly. Blowing dry air through
the conduit is the easiest and cheapest (relatively speaking) for the
individual. There are also different ways of doing that with varying
efficiencies.
Purging an open conduit takes a much higher flow, making all but
"relatively" dry air a bit on the expensive side. The air only needs to
be dry enough to be below the dew-point anywhere in the conduit at the
lowest temperature it will experience. OTOH the dryer the air, the
better for removing moisture/water. I don't know the proper terms, but
any refrigeration, or H&V man should
IIRC the last tank of N2/CO2 (MIG Welder) was about $125, but that was
so long ago, I since, had to renew the lease. OTOH, refills are
relatively inexpensive.
I'd think dry air would be cheaper, particularly if you already have a
suitable compressor and tank. If you do any spray painting you should
already have a dryer. On a monthly "blow-down", a lot of water comes
out of that 80 gallon tank. In the summer, I blow down that tank every
day before use. That lost air saves a lot of dryer cartridges, unless
you have a heated commercial dryer.
73,
Roger (K8RI)
On 2/1/2016 Monday 2:42 PM, Tom_N2SR via TowerTalk wrote:
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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73
Roger (K8RI)
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