In MMD 2013.05.01.02, Paul Rumph opines about the use of thin
aluminium sheet from the offset lithography industry as flap valve
backing material.  I have a large supply of this material and have
used it with success as he describes.  I also agree that it is
difficult to cut precisely and maintain straight, flat edges.

In my machine shop I have an industrial sheet metal shear that is the
perfect tool for this application.  For anyone who would like to try
this technique, let me know the length and width of the pieces you
need and how many and I will send them to you for the price of mailing.
Unless you need hundreds, then we'll talk.  They are not limited to
Ampico (or Simplex) pumps of course, as any flap valve design or
application can benefit from preventing the leather from curling at
the edges, which this does very well.

John Grant