[TowerTalk] Buring Bury-Flex

Sat May 10 14:21:15 EDT 2014

I still don't understand the assumption that the pipe will fill with 
water.  Isn't that like assuming the PVC used to deliver water under 
pressure will always fail and leak which flies in the face of our 
experience?   It doesn't leak in pressure applications over 100 PSI.  A 
rough rule of thumb is one PSI of hydraulic pressure for every two feet 
of water depth.  If your water depth plus bury depth in your back yard 
is say 2 ft  in total then you will have a maximum of 1 PSI of pressure. 
   Don't you think a system used successfully to deliver water at over 
100 PSI should be able to take 1 PSI in the rigors of your subterranean 
backyard situation?

A good seal can be made with a length of shrink tubing and some silicon 
rubber (I like the GE II 50 year type.)  If you use the nozzle on the 
caulking gun size container of GE II to inject a good quantity into the 
pipe, maneuvering to get some on all sides of the coax and then place a 
generous quantity at the end of the pipe and all over the coax and then 
slide the heat shrink down over the end of the pipe overlapping thle end 
of the pipe for a few inches when you shrink the tubing you will get a 
water tight seal.  You may need to use a smaller diameter piece of 
shrink tubing to overlap the first larger diameter piece of shrink in 
order to get a tight seal to the coax.

If you put in an elbow (use a sweep for easier installation of coax) you 
can then have the PVC extend out of the ground vertically into the air 
where the sealing is even easier.

Do not depend on the PVC to withstand the Weed Whacker.  I have seen PVC 
fail many times in that situation. Drop a length of steel tubing or pipe 
over the vertical conduit taller than the tallest you anticipate weed 
whacking.

If you remain convinced that pipe made and used for pressure water at 
over 100 PSI can't withstand your water at less than 1 PSI and you 
further are concerned that the bury flex will implode as ice forms in 
the flooded conduit then run a skill saw down the pipe and cut a slot 
lengthwise down the PVC.  Then when ice forms the PVC will expand at a 
low level of force and the bury flex will not be crushed.  Just drilling 
holes to drain the pipe will not stop ice from forming and putting 
pressure on the coax.

In addition to the two each 3 inch conduits running over 100 ft from my 
shop to barn, and staying dry, I have a one inch conduit from the shop 
to my overhead diesel fuel tank.  Thisi little conduit is for 120VAC and 
it stays dry inside.  I am currently burying two each 4 inch conduits (4 
inch PVC sewer and drain pipe) from my barn out into a pasture to 
service 3 towers.  These two runs of PVC are a bit over 350 ft.  They 
come to the surface and connect to a 2x2x1 ft J-box at the endo of the 
run and 142 feet short of the end where there is a similar J-box.  
Another J-box with the same configuration is about 80 ft out from the 
barn.  I do not anticipate these runs filling with water anymore than 
the previous hundreds of feet of 3 and 1 inch runs have which is NOT AT 
ALL.  I;m not using bury flex. Some of my current runs are standard LMR 
400 but the new runs described above (4 inch sewer and drain) are 1/2 
inch hardline., romex 10-2 plus ground, and various control lines.

Patrick NJ5G

On 5/10/2014 9:13 AM, Larry Banks wrote:
> 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
>
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