Sewer pipe engineering?

[Jeff Miller]

The tanks were connected around '79 or '80. It has always been a
rigid connection, one run of ABS. The tanks are not that tightly
mounted either, often can be moved a little when empty. I don't see a
concern with the original setup. The 3/8" means that each end has to
flex 3/16" maximum over that temp. range, doesn't sound like a
problem for ABS. If you replaced the solid-body (DuPree) valves with
a 4-bolt type like the Valterra I would expect that the strain could
cause a leak, but solid-body valves and ABS should be fine with the
original setup IMO.

Putting flexible couplings on both ends as you're suggestion could
allow the main pipe to droop. Putting a flexible coupling in the
middle shouldn't cause it to droop in the same way, but would in
theory increase the stress on the tank fittings and valves.

- Jeff Miller
http://www.wanderlodge.net


--- In WanderlodgeForum@yahoogroups.com, "surfer46us"
wrote:
>
> I have been doing some extensive research about ABS sewer pipe.
> (I know...I need to get a life!). What I learned is that ABS pipe
> contracts/expands 5 inches per 100 feet for each 10 degrees F.
> change in temperature. Applying this to the approximately 6.5 feet
> of pipe connecting the black and gray tanks, there is nearly 3/8 ths
> inch of expansion with 100 degrees change of temperature. It
appears
> to me that this puts excessive strain on the tanks that could cause
> cracking. I am going to saw the pipes in too on each side between
> the dump valves and the 90 degree bend and reconnect them with
> flexible
> hose clamp type unions. I would appreciate some opinions pro and
con
> if this idea is sensible? Also did all Wanderlodges come with the
> tanks plumbed together with no provision for pipe expansion or does
> mine have a non standard repair? Thanks
>
> Jim Keefauver/Jonesborough, Tn./1985 PT36