On the continuing thread about Duo-Art Regulation, I have taken all the
advice and attempted to re-regulate my 1925 Weber.  I wish to thank all
of you MMDers who unselfishly share your knowledge on this (and other)
subject(s).

I reported earlier that the vacuum ramped up too rapidly (causing me
to fail the play/no play tests on the test roll).  To pass the play/no
play test I had to reduce the travel of the accordion pneumatics, and
was only getting about 20" WG vacuum at level 15 (without crash
valve).   Per Pete Knobloch's suggestion I put in weaker springs, and
reset the accordion pneumatics to the prescribed 1/16" increments and
15/16" total travel.  Now it does very well on the play/no play test,
but my maximum vacuum at level 15 is 17" WG.

Bottom line is I get good expression at low volumes, but I lack the
power I should have.   The expression box has been rebuilt.  The knife
valves are good.  The spill valve is working, and the muffler felt
seems correct, giving about 33" WG vacuum with the spill valve open.
I get about 60" vacuum with the spill valve closed.

Mike Kitner's pamphlet, "Rebuilding the Duo-Art," says to adjust the
expression control arms for 1/16" regulator motion, and then adjust
for 5" vacuum with the regulator springs.  This does not work for me.
If I adjust for 1/16" collapse, I cannot get any vacuum whatsoever by
pulling the regulator wide open, which takes a lot more spring force
than my springs give me.  Therefore, I set the springs to zero
clearance at regulator wide open (off) and set the control arms for 5"
(accompaniment) and 6" (theme).  I get about a half inch collapse on
the regulator.

If I graph the chart of vacuum vs. expression level, I get a very nice
straight line, from 5" to 17".  If I use the spring that came with the
piano (probably not original), I go from 5" to 30", but I don't pass
the play/no play test, and I'm way too loud at low intensities.  It
appears to me that I need a variable rate spring.

The only thing I can figure is to run with my weak springs as presently
installed, and add "secondary" springs to each regulator, with a
mechanism that doesn't allow them to start stretching until I hit level
4 or level 8.  That way I will get a shallow vacuum curve until the
secondary spring kicks in, at which point the curve should get steeper.
I'll pass the play/no play test, and then ramp up to higher vacuum
levels for the louder passages.

Have any of you experienced the type of problem that I am having?  If
so, what was your fix?  Any comments on my proposal to add a second
spring?  It doesn't seem like I should have to resort to this type of
shenanigan.  What am I missing?

Any comments would be appreciated.

Ray Fairfield
misterfixit@ix.netcom.com.geentroep [delete ".geentroep" to reply]