[TowerTalk] Buring Bury-Flex

[Patrick Greenlee]

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 at verizon.net>
> To: "Tower Talk" <towertalk at 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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