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@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@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
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