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@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-----
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|