DIYbanter - View Single Post

wrote:

The OD for 3/4" schedule 10 pipe is 1.050".
The OD for 3/4" schedule 40 pipe is 1.050".
The OD for 3/4" schedule 80 pipe is 1.050".

The ID's are different for each.

Why did you not say that the OD for *1.050* schedule 10 (or 40 or 80)
pipe is 1.050" ? Because to most of the plumbing world (and yourself),
it's known as 3/4" nominal ID pipe, not 1.050 OD. Are we arguing over
how a pipe is "measured" or "sized" vs. how it is "named" or "called"?
How are we to reconcile that 3/4" pipe is named for its nominal ID, yet
it is hardly ever called 1.050" pipe, unless it is called by something
for which it is "measured"?

Because the ID was the most important characteristic in terms of
determining the pipe's resistance to flow, water pipe was named for its
ID. The 3/4" pipe size was thus established by some 'primordial 3/4" ID
pipe' whose OD turned out to be 1.050". When they made pipe with other
wall thickneses, for the sake of compatibility with existing fittings
(and dies) which thread onto the OD, they varied the ID slightly to be
able to keep the OD constant. Nevertheless, they persisted in calling
it by its nominal ID.

However, some types of tubing were always named for their OD, thereby
avoiding this whole mess.

%mod%