On Thu, 16 Oct 2008 06:36:34 -0700 (PDT), Denny
wrote:

Plumbers power snake for sewers... Rent it at the rent it shop... It
will auger up through that duct tape and sand like it is tissue
paper...

denny/ k8do

Ummm.... this is through 3/4" schedule 40 PVC with at least two right
angles. The augers I've seen are for much larger sewer drain pipe and
will not fit inside 3/4" PVC. Anything that can drill through sand
can probably also do some real damage to the PVC. A much smaller
diameter "snake" is probably safer. With only 1ft of sand to push
through, a solid "tape" type electricians snake can be pushed through
by hand. The only down side is that the pipe will fill with sand when
the duct tape is breached, so cleanup may be a problem. If dry sand,
a small hose on the end of a vacuum cleaner should work.

Incidentally, the frequencies used by commerical cable finders are
815Hz, 8Khz, and 82KHz at 2-3 watts.
http://www.rycominstruments.com/3-8879-Cable-Utility-Locator.asp
However, that's good for 15 ft depth and many miles of cable. Higher
frequencies will probably work for 1ft of sand and only 100ft of wire.


--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

Ummm.... this is through 3/4" schedule 40 PVC with at least two right
angles. The augers I've seen are for much larger sewer drain pipe and
will not fit inside 3/4" PVC. Anything that can drill through sand

Ouch! Unless you are trying to fish a phone line, you (might/might
not/want) WILL dig it all up and go to 2" with 45 degree bends and bevel the
inside edges. Once above ground you can break out to pull boxes.

You have my sympathy.

"Ed" wrote in message
. 192.196...


How about one of those 'stage' smoke machines pumped into the open
end?

VK5JE


That's a good one, too, but in my case, I KNOW that I duct taped the
end of the conduit in such a manner that it is truly air tight... even
possibly under pressure. Thanks anyway.

Ed

Hi Ed

Will the taped end will not leak with 80 PSI air in the conduit?

Jerry KD6JDJ

On Thu, 16 Oct 2008 16:37:22 GMT, "JB" wrote:

Ummm.... this is through 3/4" schedule 40 PVC with at least two right
angles. The augers I've seen are for much larger sewer drain pipe and
will not fit inside 3/4" PVC. Anything that can drill through sand

Ouch! Unless you are trying to fish a phone line, you (might/might
not/want) WILL dig it all up and go to 2" with 45 degree bends and bevel the
inside edges. Once above ground you can break out to pull boxes.

You have my sympathy.

Thanks for the sympathy but it's not my conduit or problem. The
plumbing belongs to Ed, K6AAT.

Question: What's the difference between conduit and plumbing?
Answer: Plumbing holds water. Otherwise, they're the same.

I'm not sure what might be going inside a 3/4" conduit, but if it's
for a tower, it's way too small. The original question does not
indicate what manner of wiring goes inside. With 3/4", you can get
perhaps one run of LMR400 plus some flat rotator cable and you're
full. Hard to tell from here.

It's also possible to place a diplexer (or triplexer) at both ends of
the single coax run for splitting out HF, VHF, and UHF. I've done
that when running multiple coax cables was impossible.
http://www.rfparts.com/diamond/Product_Catalog/plexers.html

It's been a long time since I've done any tower construction, but for
commercial installs, I never used buried coax runs. AC power for the
tower lights were in 3" steel threaded conduit (not EMT), but the coax
was all above ground. That shortened the coax runs about 25ft which
was well worth the effort.

Incidentally, a good trick is to *NOT* lay the conduit perfectly
horizontally plumb. Put one end lower than the other so that water
well drain into that end. Shove a PEX sprinkler line down to the low
point of pipe and pump out the water once a year. I prefer
pressurized conduit, but a water sump works fairly well.

I discovered, the hard way, why using steel pipe instead of PVC was a
good idea. With everything underground, the obvious parking location
for the crane, cherry picker, or propane truck was directly on top of
the buried PVC. After a few cracked pipes, I decided that steel was a
good idea.

I like to pressurize the conduit slightly to keep the water out. It's
really not necessary as most coax will survive when immersed. However,
everyone re-uses coax, which has cuts in the outer jacket, and which
might not be fully waterproof. A pressure gauge, bicycle valve,
bicycle pump, some putty, and a few PSI are good enough.

I almost forgot.... a slow death to the installer that shoved a coax
barrel splice down a stuffed conduit, thus insuring that all
subsequent coax runs will jam up against the coax connectors.

Also, this is what happens when a monopole tower is stuffed full of
coax cables, and some idiot decides to enlarge the hole with a cutting
torch.
http://802.11junk.com/jeffl/pics/drivel/slides/monopoleBurn.html
http://odessaoffice.com/wireless/priceless.jpg


--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

On Thu, 16 Oct 2008 17:17:05 GMT, "Jerry"
wrote:

Will the taped end will not leak with 80 PSI air in the conduit?
Jerry KD6JDJ

Well, if it does leak, the sand above the duct tape will dribble down
into the 3/4" conduit creating a rather awkward clean up exercise.
That's why conduit runs usually terminate above the ground, not below.
The trick is to find the conduit end without blowing off the seal.

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

"Jeff Liebermann" wrote in message
...
On Thu, 16 Oct 2008 17:17:05 GMT, "Jerry"
wrote:

Will the taped end will not leak with 80 PSI air in the conduit?
Jerry KD6JDJ

Well, if it does leak, the sand above the duct tape will dribble down
into the 3/4" conduit creating a rather awkward clean up exercise.
That's why conduit runs usually terminate above the ground, not below.
The trick is to find the conduit end without blowing off the seal.

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

Hi Jeff

It may be of little interest to the OP, but the sand might have difficulty
leaking back into a conduit with air blowing out of it. In addition, the
air might leak from a small rupture below the oipen end of the conduit.
The OP may have no access to compressed air anyway.

Jerry KD6JDJ

On Thu, 16 Oct 2008 20:31:56 GMT, "Jerry"
wrote:


"Jeff Liebermann" wrote in message
.. .
On Thu, 16 Oct 2008 17:17:05 GMT, "Jerry"
wrote:

Will the taped end will not leak with 80 PSI air in the conduit?
Jerry KD6JDJ

Well, if it does leak, the sand above the duct tape will dribble down
into the 3/4" conduit creating a rather awkward clean up exercise.
That's why conduit runs usually terminate above the ground, not below.
The trick is to find the conduit end without blowing off the seal.

Hi Jeff
It may be of little interest to the OP, but the sand might have difficulty
leaking back into a conduit with air blowing out of it. In addition, the
air might leak from a small rupture below the oipen end of the conduit.
The OP may have no access to compressed air anyway.

Jerry KD6JDJ

Welcome to rec.radio.amateur.antenna.physics

Ok, let's do the math. Dry sand weighs 100 lb/cubic-foot. There's
about 1 ft of sand above the end of the 3/4" conduit. The weight
action is roughly conical, so the volume of sand involved is (my
guess) about:
100 lbs/ft^3 * 1/3 = 33 lbs of sand.
All that it acting on a 3/4" diameter pipe, with a cross sectional
area of about:
Pi * 0.75" = 2.4 in^2
Therefore, the pressure exerted by the sand is:
33 lbs / 2.4 in^2 = 14 PSI
So, if he can pressurize the pipe to more than 14 PSI, he can lift the
column of sand sufficiently to keep it from dribbling into the pipe.

Of course, it's not that simple. Laminar air flow, pressure gradients
across the conduit, and the effects of the duct tape will ruin my
simplistic guesswork. Worse, the back pressure created by the
immovable column of sand will force some sand particles into the
conduit around the edges with the "reflected" air pressure. In the
middle of the conduit, the air flow is all out of the conduit, but
near the edges, it could easily be the other direction. I'm also
assuming that the sand is a perfect air seal, which it's not. To
prevent all this from happening, the minimum air pressure should be
about twice the 14 PSI, which is easily achievable with an air
compressor, but not a vacuum cleaner.

I'm also trying to imagine how the process will work. I see an air
compressor pumping madly away as the neighbors kids furiously dig
around the resultant sand volcano, as sand rapidly refills the conical
hole. In my never humble opinion, there's no way to prevent sand from
dropping into the conduit if the duct tape seal is broken before
excavating the end of the conduit.

Once the sand is in the conduit, just blowing air through the pipe
isn't going to magically elevate the sand particles 1ft or more in the
air. The air does not have sufficient mass to convey enough momentum
to move the sand particles, much less eject them vertically. For
that, one needs a denser medium, such as water. Shoving a plunger
through might work, but it's equally likely to jam sand particles into
the PVC conduit walls.




--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

On Thu, 16 Oct 2008 13:57:44 -0700, Jeff Liebermann
wrote:

Worse, the back pressure created by the
immovable column of sand will force some sand particles into the
conduit around the edges with the "reflected" air pressure.

H E R E S Y

Reflected waves do NOT have power in them - or so goes the catechism.

This new and dangerous introduction of a side topic can only lead to
endless debate about the superposition phase properties of sand in
vacua (particel theories inhabiting the crevices in the science of
Equal Librium)

73's
Richard Clark, KB7QHC

"Jeff Liebermann" wrote in message
...
On Thu, 16 Oct 2008 20:31:56 GMT, "Jerry"
wrote:


"Jeff Liebermann" wrote in message
. ..
On Thu, 16 Oct 2008 17:17:05 GMT, "Jerry"
wrote:

Will the taped end will not leak with 80 PSI air in the conduit?
Jerry KD6JDJ

Well, if it does leak, the sand above the duct tape will dribble down
into the 3/4" conduit creating a rather awkward clean up exercise.
That's why conduit runs usually terminate above the ground, not below.
The trick is to find the conduit end without blowing off the seal.

Hi Jeff
It may be of little interest to the OP, but the sand might have
difficulty
leaking back into a conduit with air blowing out of it. In addition, the
air might leak from a small rupture below the oipen end of the conduit.
The OP may have no access to compressed air anyway.

Jerry KD6JDJ

Welcome to rec.radio.amateur.antenna.physics

Ok, let's do the math. Dry sand weighs 100 lb/cubic-foot. There's
about 1 ft of sand above the end of the 3/4" conduit. The weight
action is roughly conical, so the volume of sand involved is (my
guess) about:
100 lbs/ft^3 * 1/3 = 33 lbs of sand.
All that it acting on a 3/4" diameter pipe, with a cross sectional
area of about:
Pi * 0.75" = 2.4 in^2
Therefore, the pressure exerted by the sand is:
33 lbs / 2.4 in^2 = 14 PSI
So, if he can pressurize the pipe to more than 14 PSI, he can lift the
column of sand sufficiently to keep it from dribbling into the pipe.

Of course, it's not that simple. Laminar air flow, pressure gradients
across the conduit, and the effects of the duct tape will ruin my
simplistic guesswork. Worse, the back pressure created by the
immovable column of sand will force some sand particles into the
conduit around the edges with the "reflected" air pressure. In the
middle of the conduit, the air flow is all out of the conduit, but
near the edges, it could easily be the other direction. I'm also
assuming that the sand is a perfect air seal, which it's not. To
prevent all this from happening, the minimum air pressure should be
about twice the 14 PSI, which is easily achievable with an air
compressor, but not a vacuum cleaner.

I'm also trying to imagine how the process will work. I see an air
compressor pumping madly away as the neighbors kids furiously dig
around the resultant sand volcano, as sand rapidly refills the conical
hole. In my never humble opinion, there's no way to prevent sand from
dropping into the conduit if the duct tape seal is broken before
excavating the end of the conduit.

Once the sand is in the conduit, just blowing air through the pipe
isn't going to magically elevate the sand particles 1ft or more in the
air. The air does not have sufficient mass to convey enough momentum
to move the sand particles, much less eject them vertically. For
that, one needs a denser medium, such as water. Shoving a plunger
through might work, but it's equally likely to jam sand particles into
the PVC conduit walls.




--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

Wow, Jeff, you are a really smart guy. It sure is nice to know that you
are able to analyze this sand over conduit problem so thoroughly. Heck, I
thought the air would blow out thru the sand. I didnt even consider the
sand above the air leak to be immovable. I thought the air would find a
path to leak out somewhere between the tape and the conduit. I hadnt
thought about using neighbor kids. Why would you consider using kids for
this project?
I'll assume you wont recommend the OP use water or air to locate the far
end of his conduit.

Jerry KD6JDJ

On Thu, 16 Oct 2008 14:19:05 -0700, Richard Clark
wrote:

On Thu, 16 Oct 2008 13:57:44 -0700, Jeff Liebermann
wrote:

Worse, the back pressure created by the
immovable column of sand will force some sand particles into the
conduit around the edges with the "reflected" air pressure.

H E R E S Y

Hershey Bar (Chocolate Rules). Besides, following the orthodoxy lacks
entertainment value.

Reflected waves do NOT have power in them - or so goes the catechism.

This new and dangerous introduction of a side topic can only lead to
endless debate about the superposition phase properties of sand in
vacua (particel theories inhabiting the crevices in the science of
Equal Librium)

Yeah, but I like playing in the sand. Try this experiment next time
you have an air compressor and nozzle handy. Find a cardboard,
plastic or metal tube at least 3 ft long. A vacuum cleaner extension
pipe will suffice. Plug up the other end with whatever is handy. Blow
air into the center of the tube. Run your fingers around the edges of
the tube and note which way the air is flowing. That's what will
happen if the compressed air is not sufficient to blow 30 lbs of sand
into the air. The air and the sand will flow back into the pipe in
the opposite direction as the compressed air.

73's
Richard Clark, KB7QHC

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558