My Duo-Art (and I assume that it's true of all Duo-Arts that have
the graduated pneumatics) has shorter pneumatics for the treble, mid
sized pneumatics in the tenor range and longer pneumatics in the bass.
All pneumatics had identical spans (and my machine was untouched when
I started to restore it).

If the reason for the length were to compensate for the pushrods, then
the longer pneumatics would be on the lower deck where the pushrods are
longest, mid sized pneumatics in the center deck and shorter pneumatics
on the higher.

It would have to be that they wanted to strengthen the pneumatics for
the bass and weaken them in the treble (on the assumption that the
force from a longer pneumatic is greater).

Any mechanical engineers want to comment on the length of pneumatic
vs. force that it delivers?

Eli Shahar

 [ The force developed varies in direct proportion with the length
 [ of the pneumatic.  -- Robbie