[TowerTalk] [Bulk] Fwd: where the condensation comes from

[Roger (K8RI) on TT]

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 at pacbell.net>
>   To: Hans Hammarquist <hanslg at aol.com>; towertalk at 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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