[Ref. John Phillips in 120921 MMDigest]

Hello John and MMD, Regarding the difference in behavior of one note
in the Half Duo-Art stack pneumatics, Aeolian uses a pressed-on ring to
hold the outer valve leather against the wooden poppet.  The purpose of
this ring was to prevent the outer leather punching from being pushed
against the outer seat by the air exhausting from the pneumatic when
it was being acted on by external forces.  These rings tend to stretch
or break easily, so it is not surprising that one or more is not
holding the leather in place as intended.

In normal operation, the leather will be held more or less in place by
the force of the atmosphere when the valve is returning to the closed
position, so the ring has little effect on normal operation.  Many
manufactures did not use outer valve leather retainers (Standard
Pneumatic Actions, for instance.)

Bob Hunt - Hunt Piano Company
Kennebunk, Maine