In article , Ned Simmons
says...

Additionally, without the regulator the process is
reversible ...

But the example I used, of simply connecting two
tanks and allowing the pressure to equilibrate between
the two of them, is not. Regulator or not, you cannot
put the gas back into the first, smaller tank, without
doing work on it. The entropy of the system goes up
when you connect the two tanks.

Jim

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