Hello MMD.  I am starting this submission with some hesitation,
suspecting that I may just be being dumb.  But I don't understand
the comments of Spencer Chase (090306) and Paul Manganaro (090307),
and I have looked at Paul's web site, as he suggests.  Forgive me
for stating the obvious, but here is my concept of the operation of
a pouch, valve and pneumatic of a single valve player action :

- The tracker bar port closed by the music roll.  The valve pouch is
collapsed, the valve is in the 'off' state, sitting on the lower valve
seat, the pneumatic is vented to the atmosphere and is open.

- The tracker bar port is open to atmosphere.  The valve pouch is
inflated, the valve is in the 'on' state, pushed up against upper valve
seat, the pneumatic is connected to vacuum supply and is collapsed.

During the brief transition between 'off' and 'on' states, the vacuum
chamber is connected to the atmosphere and there is a rush of air
through the gap between the top valve plate and the rapidly closing
upper valve face.  At the same time there is a rush of air into the
vacuum chamber from the closing pneumatic.  This air current continues
until the pneumatic is fully collapsed.

Once the 'on' state is fully established, the only air flowing within
the valve will be leakage between the upper valve face and the upper
valve seat, and air flow via the tracker bar port through the bleed
hole.  In the 'off' state there will be leakage between the lower valve
face and the lower seat.

My understanding, such as it is, is the that valve travel should not be
too small else the air flow to and from the pneumatic will be restricted
and it will be slow to open and close.  Conversely, the travel should not
be too large, or too much air will flow in through the top valve plate,
depleting the vacuum supply and causing unnecessary noise.  I hope all
the grandmothers out there are sucking happily on their eggs.

Spencer and Paul: what air flow are you talking about?  If it's the air
flow during the transition period (20 milliseconds?), surely one would
need a data logger with a very high sampling rate.  And how would one
cope with the air flow from the pneumatic?

I suspect that it's actually the leakage through the top valve plate in
the fully 'on' state that you are discussing.  If that's so, will leakage
through a particular valve seat seriously affect the operation of that
particular pneumatic?  Of course, leakage degrades the performance of
the whole system and is to be avoided.

I await a response to this submission with some trepidation.

John Phillips in Hobart, Tasmania

 [ In my understanding of the single-valve pneumatic action, the
 [ designer has established a compromise of the bleed orifice size
 [ (which affects the repetition rate), port area and valve core
 [ excursion distance (affecting air flow) in order to achieve a
 [ satisfactory balance of pneumatic force and repetition rate versus
 [ valve noise _at all suction levels._  That's why valve travel
 [ adjustment is especially critical in a single-valve reproducing
 [ piano action.  -- Robbie