[TowerTalk] Buring Bury-Flex

[Larry Banks]

Hi Patrick,

You have partially answered my question, thank you.  Many others have sent 
good ideas but no one has answered my question yet.  Some additional 
comments about this installation:

    * Given that Bury-Flex is fine under water, and I will only be 
protecting part of the run, the ends will be open and underground. 
Therefore I can guarantee that there will be water in the conduit which by 
itself is not an issue. I don't even plan on cementing the connections 
between the 10' sections, elbows, etc.
    * I'm not worried about heat.
    * Your statement "If your PVC filled with water, froze, and burst the 
coax would likely not be harmed" is key .  If it were true I would have my 
answer.  I have seen no information that shows that the PVC would burst 
before the coax was crushed.
    * I must have some protection where the coax comes out from the ground 
and up the mast for weed-whackers, etc., so some amount of conduit is a 
must.  Granted, being vertical, this portion would most likely drain. just 
fine.

Thanks again to everyone who has sent ideas.  I may just do it and see what 
happens over the next few years!


73 -- Larry -- W1DYJ







-----Original Message----- 
From: Patrick Greenlee
Sent: Saturday, May 10, 2014 9:51
To: towertalk at contesting.com
Subject: Re: [TowerTalk] Buring Bury-Flex

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