With all those stop-gap halfway things going on, of course the Duo-Art
plays poorly.  You should understand the Duo-Art system is the fussiest
system there is.  If you have even a pinhole leak anywhere in the
system, it will not play.

Your four-bellows rotary pump in a Duo-Art is not intended to put out
50 inches suction.  That indicates the thing needs total rebuild.  They
often put out 120 inches in top condition.  When the bellows is totally
closed off and motor is turned on, the big pulley should turn about
one-half turn and then stop dead.  It should not continue turning
slowly as it likely does right now.

The foot bellows system should be tested by closing it off with tape,
pumping it up and checking how long for the reservoir to open.  It
should ideally take several minutes but few will do that.  If you can
get it to take a minute or close to a minute, then it is airtight enough
for Duo-Art.  I take it your motor is not a Duo-Art motor, so check that
the speed and the pulley size are correct.

As far as the expression box, it is the least of your problem.  Until
you make sure the complete system is totally airtight you would never
be able to know the condition of the expression box.  I suspect it is
fine.

To check the action stack, take a suction source and measure the
pressure coming directly out of it.  Connect the suction to the stack
alone and then measure the pressure coming from under any pouch (tube
to the trackerbar).  Compare the two measurements.  If you are losing
one inch suction or less then your stack is acceptably airtight for
a Duo-Art.  If you are losing three inches it is acceptably tight for
a regular 88-note player.  Any more than that and it may be difficult
pedaling rolls and the Duo-Art will not function optimally.

Get back to us when you get the leaks dealt with.

D.L. Bullock
www.dougbullock.ws