[TowerTalk] TowerTalk Digest, Vol 122, Issue 58

[Roger]

On 2/26/2013 5:33 PM, Patrick Greenlee wrote:
> Would someone please explain to me why you can seal a water pipe made of
> PVC and withstand over 100 PSI but not be able to seal a PVC pipe
> against 0.0 PSI because it has wires in it?

You are are not sealing against 0 psi, but against several inches of 
sustained water pressure.

Yes it is very difficult to "seal" cable entry into conduit.

Sure some regions of the USA
> have high humidity so a little moisture will get into the pipe before it
> is sealed but not huge amounts.

The conduit breathes as it's almost impossible to really seal it in a 
practical environment.

The relative humidity may be low on a hot day, but it goes up 
substantially ay night or with the cooler temps in conduit

If you have 100% relative humidity and
> want to have a dry interior of your pipe, drilling holes in it won't dry
> it out but will admit moisture.  Purge the pipe with CO2 from an
> extinguisher, or dehumidified shop air, or a bottle of dry nitrogen, a
> SCUBA tank,  or ... and then seal it.  Really, water doesn't penetrate
> PVC pipe very well if the joints have been properly assembled. This
> leaves just plugging the ends and sealing them with an appropriate
> adhesive sealant such as GE II silicone rubber or Excell (silicone
> alternative.)
>
> The above assumes you seal all terminations of all the wires so that
> there is NO path for water ingress. I assert that if the above is
> accomplished in a workman like manner there will not be water intruding
> into the conduit. Come on, this isn't rocket surgery..... or brain
> science.... ;) ;)

Or even necessary.

I live in central Michigan where the conduit is in, warn, dry sand 
during the summer and froze solid in the winter. Part of it is below the 
water table in the spring and both ends (which are open) are about 2 to 
3 feet above the main run.  I've never had a water problem, but even 
were the conduit to be filled with water I'd still not have a 
problem...unless I tried to add or remove a cable this time of year.
They are kinda difficult to get through solid ice.
>

Actually it is very difficult to really seal conduit with wires running 
through it in a practical environment.  I've had coax braid ruined from 
moisture and could find no hole in the jacket. Turns out the jacket had 
microscopic pores that developed from UV exposure..

BTW if you check the material specs, the Silicone RTVs are water proof, 
not moisture proof.  As they use water vapor to cure they tend to be 
rather porous to it.

As Larry said, you can purge like the telcoes do and they are likely to 
choose the most practical and cheapest method in the long run, but most 
times it's not worth the effort.

Oh!... I don't even bother sealing/bonding the conduit joints.  I just 
grease them with DC-4 compound  so I can fully seat the joints (and get 
them apart if necessary.

73

Roger (K8RI)

>
> Patrick AF5CK
>
>
> -----Original Message----- From: Larry stowell
> Sent: Tuesday, February 26, 2013 1:06 PM
> To: towertalk at contesting.com
> Subject: Re: [TowerTalk] TowerTalk Digest, Vol 122, Issue 58
>
> I live in NC and its gets humid here. Sometimes in the morning it looks
> like it rained overnight.
> You would have to seal and purge the air out with a gas as the tele
> companies do to keep the water
> out. It's going to get water in it plain and simple.
>
> 73 Larry K1ZW
>
> -----Original Message-----
>
>
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