[TowerTalk] Water in Conduit...
akozak at hourglass.com
Thu Mar 5 10:06:07 EST 2015
I am amazed at the number of hams who don't understand basic physics.
First of all, condensation requires a supply of air with a dew point above the temperature inside the conduit. The total amount of moisture in the volume of air per running foot of even large diameter conduit is at most a few grams. For condensation to be a problem, there has to be a constant resupply of air - where would it come from? Can't be from convection. If it was, that means it's warmer underground than above and you'd actually lower the RH. If it is being forced in from the ends, that is very easy to mitigate - terminate the conduit with a box.
But put that aside for a minute. If you're going to use any kind of drain pipe, it doesn't matter where the holes are. On the top, on the bottom, sides, it matters not. Water seeks it's own level. If you bury a drain hole riddled pipe so that it is below the water table at any time of year - even shallow during a rainstorm - that pipe will completely fill with a quantity of water that eclipses anything you might get from condensation.
Only hams think that holes in buried pipe let water out and not in.
From: TowerTalk <towertalk-bounces at contesting.com> on behalf of Patrick Greenlee <patrick_g at windstream.net>
Sent: Thursday, March 5, 2015 9:22 AM
To: towertalk at contesting.com
Subject: Re: [TowerTalk] Water in Conduit...
Jim, put on your flame retardant longhandles. I posted similarly and
took incoming fire for quite a while. Seems some folks refuse to
believe that PVC pipe that can hold over 100 PSI on the inside can't
stop a PSI or two from the outside toward the inside. I use 4 inch S&D
(cheaper, lighter, and strong enough) for several runs for power, coax,
control lines etc. I have one small section with a leak due to improper
back fill (by me) which I regret but fixed. I use the one inch ID low
pressure (good for 100 PSI) plastic irrigation tubing to sleeve the
lines just in the region of the aforementioned leak. Yes, a band aid,
but I was overcome by a gust of laziness and didn't want to dig it up,
replace it, and bury correctly.
My glue joints don't leak. I have string in the runs to pull a rope to
pull more cables. I can tie it such it is continuous, half inside the
conduit and half outside, Tie on a rag and pull it through a hundred
feet plus of pipe and it comes out dry. (not the run with the leak)
I was warned that I would get condensation but years later it hasn't
happened yet. If I got any I would put a small muffin fan to circulate
air when the humidistat said it was dry enough and let it shut down when
conditions were favorable to condensation. Alternatively I could slide
some bags of desiccant in on the pull string and check them periodically.
Those of you unable to keep water out of your conduit have my sympathy.
I know how irritating it could be. If your conduit is assembled properly
and doesn't leak leaving the airborne moisture as your target then put
desiccant bags in the conduit and plug the ends of the conduit where the
cables enter/exit. Various ways to plug include duct tape, spray foam,
wadded up paper coated with silicon caulk or...
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