RadioBanter - View Single Post

JIMMIE · October 23rd 08, 09:41 PM posted to rec.radio.amateur.antenna

On Oct 23, 12:02*am, "Jerry" wrote:
"JIMMIE" wrote in message

...
On Oct 15, 1:17 am, Ed wrote:

I know this is slightly off topic, but since I am intending to run
some RF cable in the conduit, and since there are a lot of intelligent
hams on this group, I will proceed anyway:

Last year at the beginning of construction of a new house I buried
about 50 feet of 3/4" Sched. 40 PVD between the house and a location on
the property perimeter. Now that I am ready to use it, I can not
locate the perimeter end.... it is somewhere in about a 10' area, and the
end curves up to probably about a foot underground.

The ground is nearly pure sand, and is well landscaped now to the
point that I do not want to randomly dig it up.

The end terminated in an elbow curving up and is well duct taped
shut.

Can anyone suggest a method or equipment I might use to locate that
far end?

Tnx.

Ed K7AAT

I have some pipe that I had run for an outdoor spigot that I never
finished installing. *To test a method of finding it I shot some air
into it the other end was pretty easy to find by listening. I could
hear the rush of air and a lot of gurgling. My dog actually found it
in the roses bushes before I did.

Jimmie

* Hi Jimmie

* That "air" idea wont work, Jeff told me so

* Quote Jeff --

"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 95060http://802.11junk.com
Skype: JeffLiebermann * * AE6KS * *831-336-2558"

* * * * *Jerry * KD6JDJ- Hide quoted text -

- Show quoted text -

Obviously you're an engineer. LOL

Jimmie