On Mon, 29 Dec 2003 18:33:09 -0500, Ned Simmons
wrote:

The weight on the piston at the end of the expansion is
zero. As the graph shows, the force that is exerted varies
over the two paths.

It declines linearly from 30 to 0 in the unregulated case
(red line).

The weight changes. Ooo-kay!