In article , Jack Stein wrote:
Lew Hodgett wrote:
Somebody wrote:

I don't see any need for tape or dope on compression fittings.

Compression fittings require a metal to metal fit to work properly,
thus tape or dope defeats the purpose except on the threaded portion
of the fitting.

But, on the brass threaded portion the tape/dope is not needed, and
probably should be avoided.

That said, compression fittings are a poor choice where high flow
rates may be required.

I never heard this before, and not sure I understand why? Not saying
it's incorrect, just that I don't get it? They don't appear to restrict
flow at all?

Actually, they do. Take apart a compression joint in copper tube and take a
look.

Compression fittings are used in high pressure conditions, which I guess
would infer high flow rates?

Pressure and flow rate are completely different. Pressure is the force moving
a fluid (air, in this case) from one place to another; flow rate is the amount
of fluid moving per unit time. Most easily illustrated by example:
Low pressure, low flow rate -- the water in your rain gutters.
High pressure, low flow rate -- a mountain stream.
Low pressure, high flow rate -- the Mississippi.
High pressure, high flow rate -- Niagara Falls.

Now that I think about it, for Doug, the disconnects at the end of your
air hose are compression fittings. Not particularly the type we are
discussing but thought I'd throw that in.

Obviously a very different type from what we're discussing.