On Duo-Art accordion pneumatics, regulating the space between the felt
and the adjustment screws does not always move the system precisely.
That is the first step, however.  Regulate the space using front or
center rail paper punchings stacked to precisely the desired spaces.
(1/16, 1/8, 1/4, 1/2)

I find regulation of the Duo-Art expression box can be mostly trouble
free from that point.  Remove the unit to the workbench and set up a
ruler fixed above the accordions.  Find the threaded wire with the
leather nut on it, that goes through the wooden arm connected to the
box linkage.  It is about one inch above the top board of the stack of
accordions in the center of the board.    Align ruler and wire so that
the end of the threaded wire points at a line on the fixed ruler.  By
mouth or using the valve box, suck each accordion closed one at a time.
Regulate the screws so that the number of the accordion moves exactly
to that number of 1/16" marks on the ruler.  Make sure that the three
screws are evenly adjusted.  You don't want one side deeper than the
other two screws.

I usually tube and wind the expression box to the 8-valve box so that
I can open #8 and #2 and I can regulate the spill valve.  With a
stethoscope, there should be absolutely no spill when 8 and 2 are
activated.  There should be some spill when 8 and 1 are activated,
however.  This adjustment is to be made on both sides.

Most important is the stack and how airtight it is.  There should be
0 inches of pressure lost when you attach one side of the stack to your
suction box.  Make sure you know how much pressure your suction box is
putting out using a fan speed dimmer or a Dremel "Moto Tool" speed
control if yours does not already have one of Durrell's speed controls
on it.  One or two inches lost is acceptable.  If you put 30" of water
lift into the stack with all tracker bar holes closed, you should not
find 10" or 20" of suction at one of the tracker bar tubes.  No piano
will work right with the stack that leaky.

You may visit my page on rebuilding this system with pictures at
http://www.thepianoworld.com/technical_tips/duo_art_expression_box.htm

D.L. Bullock    St. Louis
http://www.thepianoworld.com/