The pouch "addition" to the spring of an Ampico air motor governor
is a simple leather pouch with a fiber disk (or what you are calling
a thick leather valve) glued to the center of the leather (from the
inside) Through the center of the disk, a small bolt goes through a
hole in the spring, and is fastened by a nut on the reverse side.

_After_ this is done, the pouch outer edge is glued to the bottom of
the governor pneumatic.  Test for tightness, and rubberize the leather
and dust with talc.  The pouch is indeed, exposed to view.  I would not
use heavy leather on this, tan pneumatic leather .016 thickness should
be about right.

Bruce Clark