Hi All,  Thought I'd pass along this piece of information that
I received.  I think it's rather genius in it's simplicity:

An inside valve, an outside valve, the top, the bottom -- all as
ambiguous as you can get.  It's like calling a lift an elevator.
Nobody could ever get back down, since they only go up.

That said, 3 or 4 decades ago I was calling primary valves
"non-inverting valves", and secondary valves "inverting valves."
Then I defined it: when the input (air) is the same as the output
(air) that's a non-inverting valve.  Air-in, vacuum out is an
"inverting valve."

All valves are outside valves.  All valves are inside valves.  When
an "inside valve" is "closed,"  half of it is on the outside.  It's in
the room atmosphere, right?  So that's "outside," too.  Outside valves?
Most of an "outside valve" is inside, not outside.  Right?

When we call them inverting and non-inverting valves, one valve isn't
being defined by the other one.  But when we call a non-inverting valve
an "outside valve" -- which is 90% inside anyway, then it is relative
to something else and not descriptive of itself.

A "primary valve" is relative to a secondary valve, but not only that,
it _requires_ the [presence of the] secondary valve in order to be
called "primary."  And when a secondary valve is used alone it's no
longer "secondary."  It's "primary."

Musically,
John A Tuttle
Player-Care.com
Brick, NJ, USA