Ned Simmons wrote:

Richard J Kinch wrote:
1. ANY EXPANSION OF COMPRESSED AIR NECESSARILY DOES WORK.

This is key to my misunderstanding. In everything I've read on the previous
(original) thread, this wasn't explained, only asserted. So, I have to ask:

Why does any expansion of compressed air necessarily do work?
Grant

Your intuition is right, expansion of a gas doesn't
necessarily do work, but the entropy of the gas increases
as it expands.

As I've said before, the "lossy" character of regulators is
easy to demonstrate without resorting to thermodynamics.
However, understanding the energy balance of the loss is
impossible without thermo, and entropy is central to the
explanation.

I'm not looking for a demonstration, Ned. A simple explanation would do.
If you find it "impossible" to explain then that's one thing, but could
you at least try? I'm very frustrated with people who simply assert complex
facts without trying to explain them. They do teach thermodynamics to college
freshmen, and I don't usually fail to understand concepts from freshman physics.
Grant