In my last posting under this topic heading I omitted information
that I had planned to include [121021 MMDigest].  No harm done.

Since my posting I have heard publicly and privately from several
other collectors.  As this discussion proceeds, it is important to
note that the intended function of a valve is to turn something on
and off.  It is presumed that the valve should do that efficiently
and not leak when in either position.   Also, the material of the
valve should have good longevity.

The longevity part is well-known for the original materials used
during the heyday of player pianos.  Leather was that material, and
we know now that it probably will last at least fifty years -- maybe
seventy-five years, if the leather surface is on the inside of the
valve.  We should be satisfied with that performance.   Does anyone
have a cell phone (car, clothes washer, television, air conditioner,
etc.) that works that is fifty years old and unrestored?

But, if we change the valve material to something more airtight than
leather, do we adversely affect the mechanism?  No, but we might
improve the overall efficiency and performance of the machine.

Take the Ampico, for example.  Most of us know that the Ampico 'A' was
(is) deficient in pump capacity.  That is, if many notes are being
played, it cannot sustain high stack vacuum.  The larger 17" Duo-Art
pump does much better in that regard.  So if a more airtight valve is
used in an Ampico system, the conservation of pump power by non-leaking
valves is a good thing.

If we think that all things airtight are good, think again.  The
leather pouches within the valves also leak.  But if we make them
airtight, it upsets the bleed balance that was designed into the
system.  The size of the bleed is based on a certain amount of pouch
leakage.

If we replace the leather pouch with something absolutely airtight,
then we must increase the bleed size to insure quick return to the
off position of the valve.  What this means is we get a net zero on
conserving pump power.  In other words, don't mess with the pouch
because it will just not change performance for the better.   We know
pouches have longevity of about 75 years.  That is hard to fault.

Why, then, did the movement to Perflex pouches back in the 1970s
have any traction?   The need to try to improve longevity was obviously
not a consideration.  Making the pouch more airtight shouldn't have
been desired nor needed.

The Perflex movement was a knee jerk and not well reasoned.  Had it
been properly analyzed in terms of need and improvement, the gamble
would have never been made.

The same is not true in new valve facings.  Something tighter than
leather is not bad; if it lasts just as long as leather and has
no adverse operating characteristics, it has no down side.  That is
why I experimented with closed cell sponge neoprene.   There are
many grades of sponge neoprene and some do not hold up.

If I were in my thirties again, I now would experiment with sponge
silicon.  That material will probably last for hundreds of years
without change.  It is airtight, it is supple -- it is the perfect
valve facing.  That is what I omitted in my last posting.

Has anyone experimented with silicon sponge?

Bob Taylor
Missouri