Paul Morris wrote, "I would not think leather, no matter how sealed,
would be tough enough for the job, and wonder what other people think."

Paul is relating this statement to a vacuum pump of a reproducing
player piano.  I agree with him that leather should not be used, but
for different reasons.  Leather has a tendency to stretch.  You need
a solid stiff surface area on the pneumatics to get the maximum vacuum
level from the pump.

If leather was used, you would select a grade that will fold well at
the corners as the pneumatic pump opened and closed.  This means using
a flexible type of leather.  When the pneumatic is closing, there is
a slight positive pressure during the exhaust cycle.  This tends to
push the soft leather outward and the pneumatic doesn't get totally
exhausted.  Now, when the pneumatic is opening, the leather will be
pulled in with a loud snapping sound.  You also loose some of the
vacuum since this energy is used to pull the leather tight again rather
than being directed to the player regulator and stack.   Adding gussets
to the leather will solve this problem.

About 10 years ago I heard talk on MMD about using leather but I have
questioned why.  I don't think it would be original.  Sealing the
leather can be overcome, and gussets can be added to stiffen the
leather, but why not use a good stiff pneumatic cloth in the first
place that doesn't have these problems?

How many player pianos used leather for the motorized pumps?  I haven't
seen any.  Of course, living in [arid] Arizona I haven't seen many
reproducers in original shape.

Pete Knobloch (Tempe Arizona, USA)