[VAC] Re: pipe sizes and PEX

[jon fitz <fitzjo1@xxxxxxxxx>]

Although Gary already spelled out the details, let me
put this another way.  The topic of pipe and tubing
sizes is often confusing.

Pipe is sized according to inside diameter.  So, in
theory, a nominal 3/8" pipe will have an ID of 3/8". 
Pretty simple so far, right?

The trouble is that pipe is available in a variety of
wall thicknesses.  Some applications require really
thick walls, while others don't need the added
material expense.  But, folks would like to be able to
use the same fittings for all 3/8" pipes, regardless
of the wall thickness.  SO, in order to do this, all
pipe is made to a standardized OD which will result in
the NOMINAL ID if the standard wall thickness is
selected.  Got it?! :)

Tubing is more straightforward.  It is sized by OD. 
You can pick a variety of ID's for the same OD based
on wall thickness.  Copper is a good example of this,
with at least three wall thicknesses I know of, two of
which are available at most hardware stores.

I think the issue with PEX tubing size will have a lot
more to do with the ID and number of fittings.  When
you do piping loss calcs, you'll find fittings create
much more loss than the pipe they work with.  I
suspect the 1/2" PEX is fine--IF the fittings have a
large ID.  (My entire household is supplied from the
main by a single 1/2" copper line.  But, of course,
that's at city water pressure.)

Let me second the opinion of Joy about valves and
other fittings.  It's worth the money to buy them with
bigger ID's when you are using precious battery power
to push water through them.  So, unless you plan to
use full hookups, I'd look carefully at the fittings. 
This may require the larger diameter pipe, but not for
the pipe's sake.

Jon in SC
68 Overlander