In response to Mr. Tuttle's submission about Neoprene valve facings
collecting dust; valve theory suggests some insights.

In any valve where the open-valve gap is small compared with the
passages leading to or from it, there is a great increase in air
velocity at the point where the restriction is greatest.  In the case
of a player valve, this is the ring shaped (or German cross shaped)
line where the valve facing is opposite the edge of the seat hole.
This reduction in pressure persists, and in fact increases slightly,
for a short distance beyond this 'edge' in the direction of flow (the
Vena Contracta) due to inertia; probably about 1/32" away from the
'edge'.

Because the energy contained in the air stream can not change along the
line of flow, energy stored in the flowing air in the form of pressure
is 'robbed' to create the acceleration required to produce this
increased velocity (Bernoulli's Principle).  This is what creates the
temporary drop in pressure at the seat.

Another phenomenon comes into play here.  Any abrupt change in
velocity, flow direction, and pressure in a fluid , all of which occur
near the valve edge, tend to make particles suspended in the fluid fall
out of suspension.  This is made use of deliberately in the 'Cyclone
Separator', where fluids are caused to swirl around in a vessel to make
the dirt suspended in the fluid fall to the bottom, and the fluid to
thereby be cleaned.

This accounts for the black rings around valves, the black lines near
any leak, and the black dots seen on the wood opposite the bleeds, in
old players.  The suspended gummy smoke particles in the air are
'cycloned out' and stick near such points where abrupt changes in flow
direction or velocity occur.

It would be impossible to make a functional player valve with a gap
large enough to preclude these temporary flow changes, and such a valve
would not 'control' anything anyway if it could be made.  Any change in
the valve gapping would not prevent suspended dust from being
precipitated out in the region near the seat.

Air flow is perfectly able to create a static charge.  Industrial
piping and ductwork handling non-conductive fluids has to be carefully
grounded to prevent fire or explosion.

Therefore if the valve disk material is a good insulator such as
Neoprene, it will become charged, and dirt precipitated out of the air
stream by the valve's action will stick to it.  Nothing much can be
done about it if the valve seats are wood or plastic, or otherwise
unable do discharge the valve facing.

Natural materials such as wood, leather, shellac and real [animal] glue
(still another reason for your list of its advantages, Craig), are
complex hydroscopic substances which contain enough moisture that
static electricity is usually not a problem in players.  (Except for
rubber-mounted reproducer pumps, which if not grounded to the motor,
will throw harmless but noisy sparks!)

Richard Vance