Several MMD'ers have recently mentioned the tiny pouch spring that
holds the pouch in the "at rest" position, and wondered why it is
installed.  There is one main reason for this spring, and that reason
is not founded within the crescendo mechanism itself, but rather the
manner in which the crescendo is activated.

First, one must realize that the crescendo has no standard mounting
position.  There is no top and bottom.  Depending on the space
available, crescendos may be mounted with the valves on top, or on the
bottom.  Consequently, gravity is not depended upon the operate these
valves.

Second, and most important, the tracker bar source of input to the slow
crescendo is at the outer edge of the paper.  On Ampico A coded rolls,
it is the "1 Treble" or "1 Bass" tracker position.  A slight amount of
leakage at the edge of the paper, into the first perforation channel,
is to be expected.  The crescendo could conceivably be activated by
this leakage.  Keeping in mind, that the leakage may only be momentary,
but multiple pulses to the mechanism are cumulative, it is possible for
the crescendo to have considerable "position error" as time passes.
Poor tracking and feathered edges exacerbate the problem.  The slotted
hole in the tracker bar, for reading long chain, crescendo
perforations, is also a factor.

The pouch spring is present to prevent spurious, unwanted crescendo
movement.

This brings up a second issue, that could be debated.  A pouch always
has some natural porosity.  The bleed size designed for the pouch
is in balance with that porosity.  Making the pouch 100% airtight,
essentially makes the bleed size incorrect.  The resulting valve action
is similar to a clogged bleed which is manifest by an overly sensitive,
too fast, "on event" and a sluggish "off event".  The use of silicone
sealer _may_ create this situation.

Silicone sealer has long been used within the pipe organ trade.
Typically, in pipe organs, there is no delicate bleed size balance as
in the vacuum operated player piano.  Research within the pipe organ
trade has found the silicone sealer has no bearing on pouch life.
Tighter pouches within a pipe organ aid significantly in the
preservation of wind power.  There is no parallel situation in the
player piano trade.

Those of you who have worked on the Ampico B will notice that the
valves activated by the extreme edge holes, are heavily weighted with
large brass top valve buttons.  These "sub intensity" and "trigger"
valves depend upon the weight of the valve, rather than pouch springs,
to eliminate spurious inputs from leaks at the paper's edge.

So back to the original issue of missing springs in the slow crescendo
pouches, be aware that the crescendo _may_ be in an active position,
resulting in louder playing, when indeed, the crescendo is supposed to
be a rest.  Very little movement of the crescendo can destroy the soft
playing that really shows off a good Ampico.

Bob Taylor