There is nothing magic about using grey, sold as conduit, PVCinstead of
white water line PVC. Water line PVC can be purchased in various
strengths such as schedule 40. Here is a chunk of a Google hit: PVC
Pipe-Schedule 40. Corrosion resistant pressure pipe, IPS sizes 1/8”
through 24”, for use at temperatures up to and including*140 °F*.
Pressure rating (*120 psi*to*810 psi*) varies with schedule, pipe size,
and temperature...
Why assume the "conduit" will fill with water? When installed properly
PVC is used in domestic water supplies successfully with NO LEAKS for
decades and decades after installation, including being under pressure
and or with water temps into the 120's (not all PVC is specked for high
temp but your underground temps will not likely exceed 100F and
certainly not 120F..
If after installation you seal the ends (entry and exit points of your
coax) with RTV or other long lasting waterproof material, why would you
assume the PVC will fill with water?
I have some buried 3 in PVC conduits for coax, control wires, and power
wires and a shop air line and after a couple years no water.
How can I test? I always leave a stout cord run through the conduit so
pulling yet another cable is easier. I can use it to pull a small rope
through the conduit run and then use the small rope to pull through a
balled up dry rag. The rag comes out dry indicating no water in the
conduit run. Admittedly your conditions may be harsher than mine with a
greater freeze depth but without water in the conduit freeze depth isn't
so important.
A different angle. The coax is bury flex and OK to run underwater. If
your PVC filled with water, froze, and burst the coax would likely not
be harmed and the now leaky conduit would still provide armor protection
to deflect the errant gardening trowel or spade.
Patrick NJ5G
On 5/9/2014 10:14 PM, Jim Thomson wrote:
Date: Fri, 09 May 2014 15:00:32 -0400
From: "Larry Banks" <larryb.w1dyj@verizon.net>
To: "Tower Talk" <towertalk@contesting.com>
Subject: [TowerTalk] Buring Bury-Flex
Hi all,
I am running Davis Bury-Flex out to a new 40M vertical in my back yard. (Maine
coast.) As it is going across gravel walkways and near garden beds, and will
not be that far below ground level, I am worried about it getting cut or nicked
in the future from yard work, etc.
My plan is to use 1? sched 40 PVC conduit ? the gray stuff ? for protection.
(I will not be adding additional coax, wires, etc., ever, so this should be big
enough.)
My Concern: the conduit will obviously become full of water ? will freeze
cycles and the expansion of ice inside the conduit compress and therefore
damage the Bury-Flex in any way?
73 -- Larry -- W1DYJ
## The problem with the 4 inch od stuff is the holes are opposite each other...
IE... N-S... or E-W. No point in orienting the pipe so the holes are E-W
either. Otherwise it will have to have one
helluva lot of water in it b4 it spills out the holes that will be 2” up each
side. Better to mount the pipe N-S. Problem with that is... you will let in
water through the N hole..at the top.
## A better solution is to use smaller pipe.... like 1”-2” OD...with no
holes in it.... and just drill some .25 inch holes every foot or so..down the entire length
of the pipe. Then install the pipe so all the
newly drilled holes are all facing DOWNWARDS. Then install some sand + gravel
into the bottom of the trench...b4 you drop the pipe in. Any water that gets
in...will simply run out the holes at the bottom of the
pipe.
## The gray stuff is UV resistant...and found in the electrical dept of your
local home depot etc.
Jim VE7RF
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