Dave,  There were several designs for Duo-Art rotary pumps, but in
general they are usually disassembled by removing the large pulley from
its threaded shaft in order to gain easy access to the screws holding
the metal front plate to the square assembly of pump bellows.  Usually
there is at least one screw and sometimes as many as three screws along
each side of the plate under the pulley.

Typically the pulley and shaft threads are left handed (the reverse of
normal) so that the normal counter-clockwise drive direction of the
belt pulls things tight rather than risking unscrewing the pulley.

It can be tricky to get the pulley loose, since it is often very tight
on the shaft, or the threads may be a bit rusted.  And unless you know
the shaft is threaded, it may not be obvious from visual inspection,
as it can resemble a pressed fitting.

A large wrench bracing the bent part of the shaft inside the pump can
help loosen it, but be careful not to damage threads on the eccentric
shaft or the shaft bearings pressed into the plate.  Once loose, the
pulley should twist off the shaft easily by hand.

Some pumps have a round hole in the pulley rim that might allow
a screwdriver to reach the screws without removing the pulley, but
usually the hole doesn't line up well with the screws even if it is
there.

And I've also seen some people work the screws out slowly and evenly
working from the side in the little bit of clearance that may be there
under the pulley.  Reversing that process is very difficult, and it is
much easier to simply remove the pulley.

Best Regards,
Ralph Nielsen
http://www.historicpianos.com/