Fellow List Members:
I've followed the thread on using PVC pipe in compressed air service and
feel that I need to add my two cents worth.
Let me state now that PVC and compressed air are a deadly combination.
PVC has a high "rubber to glass" transition temperature. This means that at
higher temperatures (>45 degrees F, approx.) PVC exhibits rubber like
characteristics; it's somewhat flexible. At lower temperatures, PVC goes
through a "glass" transition which (as the term would imply) means that it
exhibits glass like characteristics; it's extremely brittle.
It is this brittleness that causes PVC to be deadly in compressed gas
service. When it fails it is catastrophic, hurling sharp pieces of shrapnel
at high speed into anything and anyone in the way. Failure can be caused by
simply plugging in to a compressed air line or even starting or stopping a
compressor.
Additionally, the quality of the system can be compromised by the installer
in that, by using too much primer and cement, a weak spot can be caused from
puddling of the cement in the fitting.
I've seen these failures and they're quite frightening.
Don't be confused by pressure ratings on the pipe. The pipe is perfectly
capable of containing the pressure but under NON SHOCK conditions.
There are two companies that manufacture an ABS compressed pipe system that
can be solvent joined like PVC. One is Chemtrol (their product is called
ChemAir) and the other is Duraplus (Durapipe in the UK) the product name is
Airline.
We can't afford to lose any LBC entusiasts. Please, keep your shops as safe
as your cars.
Rodney McDonald
Spanish Fort, AL
'76'B 393703
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