Re: PVC vs CPVC (fwd)
---------- Forwarded message ----------
Date: Sat, 29 Jun 1996 11:48:52
From: Douglas C. Skokna <dougcs at gnn_com>
To: aquatic-plants-owner at actwin_com
Subject: Re: PVC vs CPVC
Wright Huntley wrote:
>The infrequent mention of the use of PVC, here, tends to make me
>nervous. There is a special formulation of PVC called "CPVC" that is
>always required for "potable water" applications. IMO, that's the only
>kind we should consider for any extended contact with our tank water.
In a previous life, I managed the operation of a PVC plant and a PVC
compound plant. PVC is safe for drinking water provided that you buy (IN
the USA) pipe and fittings marked, "NSF-pw." This is pipe that is made
from a compound that has passed tests of the National Sanitary Foundation
that show it is safe for drinking water and presumably for aquatic critters
too. This is usually the white pipe. The grey pipe is usually not
considered suitable for drinking water and should be avoided in the
aquarium as well.
The pipe compounds (the compound gets extruded to make pipe or injection
molded to make the fittings) we made contained: PVC resin, CaCO3, TiO2,
waxes, and a tin based stabilizer. The tin stabilizer is the most toxic
substance and does not migrate from the pipe to the water. One NSF test is
to test the pipe with acidic water and analyze the water for excessive
levels of tin.
As a precaution, you should always rinse the pipe and fittings before use
as there are small residues of tin chlorides which form during the
extrusion process and waxes on the surface of the pipe/fittings. These
rinse off easily.
CPVC is a co-polymer made from vinyl chloride and vinylidene monomers and
is stronger than PVC and uses similar compounding agents.
Doug Skokna in warm, humid, rainy Houston, TX