[ Ref. Joseph Osborne in 140120 MMDigest ]

The typical Duo-Art steamboat pump contains 84 felt-backed flap valves
covering narrow slits.  This design causes each bellows to generate
appreciable pressure upon closing, making stiffeners a necessity.
The stiffeners are stapled to the cloth using a type of staple I've
never seen anywhere else.  I would caution against using just ordinary
heavy-duty staples.

However, there is an uncommon later style of steamboat pump with a
different type of flap valve, fewer in quantity, presumably covering
round holes, thus generating less pressure and making stiffeners
possibly unnecessary.  Does any MMD reader have access to one of these
later pumps still having its original cloth with no stiffeners in
evidence?  Once the existence of such a pump can be confirmed, the
improved design can be copied for incorporation into the earlier units
during rebuilding.  For identification, it has been noted that the
later pumps often have pulleys made of unstable pot-metal.

Another possible solution would be to widen the slits a bit and use
unbacked leather, gluing the felt to the wooden cross strips instead.
Originally the felt backing was secured to the leather using a flexible
adhesive which shrank with age, warping the leather and causing the
pump to move a lot of air around within itself while not drawing very
much in from the outside.

Jeffrey Wood

 [ MMDigest articles about the Duo-Art steamboat pump are indexed at
 [ http://www.mmdigest.com/archives/KWIC/S/steamboat.html  -- Robbie