[TowerTalk] Pulling coax through PVC pipe
grants2 at pacbell.net
Wed Jan 31 15:40:41 EST 2018
A bit of terminology confusion. As shown with bell mouths and glued
joints is the way to go IMO. The wall thickness appears to be that of
SDR35 and not sch 40 and both are great choices. SDR35 is not stocked at
my HD store either. I purchased SDR35 at a construction supplier.
Here is the corrugated pipe also called "drain pipe" and think is a poor
On 1/31/2018 11:39 AM, john at kk9a.com wrote:
> FWIW, when I suggested drain pipe I was referring to this:
> There are no leaky fittings in my installation.
> John KK9A
> From: Grant Saviers <grants2 at pacbell.net>
> Date: Wed, 31 Jan 2018 10:49:21 -0800
> I agree, "different strokes" but to understand the principles, the Carrier
> Psychometric Chart was pretty helpful to me as it sorts out Rh from dew
> point and shows "lbs of moisture per pound of dry air". It was developed
> for HVAC uses.
> The variables for conduit are its (ground) temperature and air flow water
> content. I think that occupied buildings almost always have lower Rh than
> outside - heated in winter, AC in summer. That doesn't mean the inside air
> dew point is lower than that inside the conduit, which determines if there
> will be condensation. If temps inside the conduit are higher than dew
> point, no condensation and evaporation of water that is present. When
> reversed there is condensation, eg frozen ground and warm outside temps.
> Venting to outside is another set of differential temperatures and water
> content circumstances.
> So IMO, with varying seasons, lagging ground temps and variable inside (or
> vented) temps and moisture levels, it seems almost certain to get
> condensation at times in the conduit (extreme desert climates excepted).
> Sealing may help if done at the right time, but hermetic seals that
> prevent in/out air flow are really hard. Broadcast stations sometimes
> purge air dielectric coax with calibrated dry gases, bottled N2 or dry air
> from a refrigerated dryer or desiccant system or both. Then dew points are
> known to be in well into negative F temps (eg -40). Possible, but a bit
> over the top for hams.
> So my approach, since in conduit condensation is highly likely, is to
> always use direct burial cables in conduit with no connectors or breaks in
> cables. The polyethylene (PE) covered RG's or Heliax are my choice as are
> PE sheathed control cables and UF rated power cables (which go in the
> trench for AC, not inside the conduit for me). And water tight conduits
> with glued joints. Generally schedule 40 PVC but SDR35 is a good and
> cheaper choice for large diameters. Drain pipe IMO doesn't make water
> tight seals with the gaskets. Why let in ground water and dirt? I've seen
> the water flowing out of conduit (and out of coax!) as you had when there
> is a hole in the conduit.
> This is an interesting topic, maybe a few hundred threads about it on TT,
> but probably 97% of water in coax is due to poor connector sealing.
> Grant KZ1W
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