In MMD 15.03.04, John Tuttle shows two stainless steel valve plates
with round openings made as replacements for troublesome aluminum
valve plates having cross-shaped openings.  See
http://www.player-care.com/valve_plates.html 

Unfortunately, the blotter paper gasket is shown with the wrong
one of the two.  In practice, it is the valve plate with the larger
opening that takes the blotter paper gasket, being the top one wherever
plates of two different sizes are used.  This allows freer movement of
air into the pneumatic after the note has played, for faster repetition,
because a pneumatic always generates less suction when opening than is
required to close it.

The lower plate with the smaller opening is sealed directly to the wood
without a gasket, for maximum airtightness, while the very slightly
porous blotter paper above allows easy accessibility to the valve
without breaking anything apart.

Jeffrey Wood