Two things:
1. I find it difficult to believe that condensation is a major problem. The
volume of water in the water vapor contained in the air trapped in a conduit is
pretty small even if the air was warm and saturated when sealed in. There
shouldn't be an enormous amount of air "turnover" to replenish the water vapor
- it's not like there are large volumes of air circulating in a closed (though
not airtight) space. There are literally hundreds of thousands of miles of
buried electrical conduit in the world with no special care taken to prevent
condensation that one would have to expect a high failure rate if it was a
major problem.
2. Maybe in the desert it makes sense to drill holes in perfectly watertight
conduit. But anyplace that has a normal rainfall and soil that retains any
moisture, all that would accomplish is to make sure the conduit is always
filled with water.
IMO. YMMV. LSMFT.
Al
AB2ZY
________________________________________
From: TowerTalk [towertalk-bounces@contesting.com] On Behalf Of Patrick
Greenlee [patrick_g@windstream.net]
Sent: Tuesday, February 26, 2013 11:34 AM
To: towertalk@contesting.com
Subject: Re: [TowerTalk] more pulling cables
What is special about PVC when used as conduit rather than water supply?
You glue up a run of PVC with maybe 50 or 100 PSI and it doesn't leak for
decades or forever. You glue up PVC as conduit with no pressure and water
leaks in???? What is wrong with this picture? How does glued PVC as
conduit know to leak? I suggest if done correctly PVC conduit does not
leak. Condensation might rear its ugly head though. You might get water
running down a cable into the conduit. In extreme circumstances (commercial
boats and ships) I have seen water travel down a coax shield (inside the
jacket) and run out at the lower end. Of course the braid turned to green
mush later.
If you don't let water get into the conduit in the first place you don't
have to worry about draining it or having any water caused problems. Seal
it up and prevent air flow and condensation caused by that flow.
I repeat for emphasis: If you can install PVC pipe that doesn't leak with
domestic water pressures then you can install it as conduit with no leaks
with no pressure.
Blowing water out of conduit with shop air or a shop vac. Small diameter
conduit maybe but 3 inch or larger? I'd like to see that. Rags on a string
work. Blowing warm dry air through cinduit will dry it out after the heavy
lifting is done (rag on a rope.)
Patrick AF5CK
-----Original Message-----
From: Gene Smar
Sent: Tuesday, February 26, 2013 9:22 AM
To: k7awbgoog@gmail.com ; towertalk@contesting.com
Subject: Re: [TowerTalk] more pulling cables
Steve:
A few Conduit Rules of Thumb (based on my own experience; YMMV):
o Don't install elbows - use sweeps for turns. Sweeps are larger-radius
bends than elbows and permit easier pulling through these bends.
o Don't pull cable through as you assemble the conduit. This is way too
messy.
o Use glue. Slip-fit conduit connections are neater but could become
dislodged if the ground heaves during freeze-thaw cycles. Then you'll have
to pull future cables through misaligned underground conduit ends.
o You may bury/cover the conduit system before pulling cables. After all,
the intent of a conduit system is to permit change in conduit contents -
adding and removing cable - over the life of the installation.
o Water WILL get into your conduit system. Therefore, you ought to permit it
to drain. I drilled holes in the underside of my conduit at the low points
in the run. Underneath these low points I dug a small pit and filled the pit
with crushed concrete; you also can use gravel. Conduit water will drain out
of the low points in the run and into the pit where it will percolate into
the earth. I sealed the drilled holes with ladscaping material - the kind of
stuff that permits water to flow through it in only one direction. I tied
pieces of this fabric onto the conduit with solid wire. (See
http://s83.beta.photobucket.com/user/ersmar/media/45degreeelbow.jpg.html?sort=2&o=4#/user/ersmar/media/45degreeelbow.jpg.html?sort=2&o=4&_suid=136189100743809135445073939117
.)
o Instead of a continuous conduit run you may also install pullboxes at
intervals. Pullboxes have no bottoms and are buried along the conduit route;
the tops are at grade level. Therefore, you should install pullboxes over
gravel pits as above and slope conduits so that they drain into the
pullboxes. You can use pullboxes to transition from one conduit run into
another underground, e.g., your Tower 1 and Tower 2 cables enter the pullbox
from one side and split into Tower 1 and Tower 2 conduits on the opposite
side, etc.
o "Critter-proofing" is important, especially if you use pullboxes. I
suggest steel wool stuffed into the accessible ends of conduits. Fiberglass
insulation is too attractive for nesting material, plus it gets soggy when
the aforementioned conduit water tries to drain past it. Landscaping
material is adequate critter screening for drilled holes.
o Leave a pulling rope inside the conduit for (inevitable) future installs.
You can install this rope along with the last coax pull.
73 de
Gene Smar AD3F
On 02/25/13, Steve K7AWB<k7awbgoog@gmail.com> wrote:
This April, I will install my conduit and pull the cables to the existing
towers. From the shack
wall, its about 100 feet to Tower #1 and an additional 130 feet to Tower #2.
I live on 20 acres.
The cables to Tower #1 will terminate in a steel enclosure at the bottom of
that tower. Also, the cables to the far Tower #2 will terminate in a steel
enclosure at the base of Tower #1 and then continue to Tower #2 in their
conduit.
I probably will use three of the 4" PVC conduits for all the cables
to get to Tower #1. One will contain the cables for Tower #1 use; another
for Tower #2 use; and the third for future projects in the back field. Then
one additional conduit goes from Tower #1 to Tower #2. Ands one additional
goes in another
direction also from Tower #1 for future area in the back field.
I figure to glue and bury the conduit in the ground first and put sand,
dirt, & rock on top of it so pulling cables will not pull the conduit out of
the
ground rather that gluing each section, one at a time, around the cables.
Is burying the conduit before pulling a good idea like I suggest? After all,
once it is buried, it is impossible to remove it economically. I will use
sand to create a smooth bottom for the conduits to rest on and then cover
them with dirt. Its all fractured basalt out there, but the back hoe that
was used managed to make the trenches. The trenches are about 24" deep or
so.
I know this has been discussed before, but I still have not decided on
drilling or not a few water holes in the bottom every so often, or at least
at the lowest spots, to drain water from condensation. Holes bring bugs
which may or may not matter. I don't want a small hole to become an
enlarged entrance hole for a Vole which I have out there.
Any suggestions would be welcome.
Steve Sala
K7AWB
DN17es
Nine Mile Falls, WA
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