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Duo-Art Operating Pressure
By Alan Turner

Hi MMDers.  I am fairly new to the group (and mechanical music
machines), though I am jumping in with both feet: two upright
Themodist players, WW1 vintage, both Mission Arts & Crafts Style,
and a 1933 Mason & Risch 6-foot grand with the Duo-Art system.

My query today is with regard to the operating pressure for the
Duo-Art system.  Most all of the literature I've read (AMICA Technical
Bulletin #5 and other papers and MMD articles) indicate that the
pressure at the outlet of the primary regulator should be in the range
of 50 inches water column, yet when reading one of the testimonials
on the Gerety-Chase web page (by Tim Baxter), mention is made that
for his restored Duo-Art he was running about 80 inches water column.
My question is: what should this vacuum pressure be?

When I first got this piano the vacuum at the outlet of the primary
regulator was well in excess of 90 inches water column.  The expression
unit was essentially bypassed (through a botched up rebuild) allowing
the full 90+ inches of vacuum through to the stack.  As you can imagine,
when played the energy of the pneumatics nearly made the piano "take
off".

Since this was (at least to me) totally undesirable I adjusted the
primary regulator to give an output of about 45 inches water column.
This seems to work very nicely and, although at full crash the piano
is not nearly as loud as it had been, its quite acceptable.  (I have
totally redone the expression unit and its working flawlessly now.)
The piano will now play from a soft "kissing of the strings" to a
respectable forte, with a very smooth crescendo and decrescendo from
level zero to full crash and back.

I will be tapping the knowledge base of MMD to try to figure out the
age and design of the Duo-Art system on this piano.  As near as I can
tell its quite a mixed bag: internal roll tracking ears, through the
keybed tubing, all on a 1933 Mason & Risch piano (Canadian maker).

I suspect the Duo-Art system on this piano was cobbled together from
parts available, perhaps as a custom build?  I am trying, unsuccessfully
so far, to determine more of this piano's provenance.  I bought it from
Southern Ontario, Port Hope area; however, it passed through a few
hands from its original owner on its way to me.

Thanks in advance,
Alan Turner


(Message sent Sun 6 Feb 2005, 05:43:42 GMT, from time zone GMT-0600.)

Key Words in Subject:  Duo-Art, Operating, Pressure

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