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MMD > Archives > January 2000 > 2000.01.24 > 14Prev  Next


Duo-Art Valve Leakage
By Craig Brougher

Just a quick note in regard to valve leaks, particularly in the Duo-Art.
Robbie commented [in 000123 MMD, Sponge Neoprene in Reproducing 
Piano Valves]:

>[ Craig correctly noted that the Duo-Art expression system is dependent
>[ upon a small amount of air flow at all times, but I don't agree that
>[ it must come from leaking valves.  A small flow through a bleed at
>[ each end of the Duo-Art action stack serves the need just as well,
>[ and it is easily adjusted or replaced if the valves begin to leak
>[ after many years of service.

I realize that it would "seem" so, Robbie, but you are wrong.  Of
course, you've not worked on the problem, so it would seem very logical
that a simple bleed would take care of an over-tight Duo-Art stack.
Well, let me tell everybody an interesting story about that.

About 18 years ago, I was asked to come to Ohio to see if I could
regulate a certain Steinway AR, which everybody and his brother who had
ever regulated a Duo-Art had also been asked to "fix," too.  The
musician/owner knew something wasn't right, but didn't know really what
it was.  I finally asked who did the initial work on the action and was
told that it had been done right there, in their own garage and on the
kitchen table by a traveling rebuilder who put patent leather valves
throughout the action, not realizing the problem he was to cause.
There was no regulating it!

 So I did what I could.  After three hours on my backside, realizing
I wasn't getting anywhere, I figured I could surreptitiously at least
get the "low end" of the dynamic scale correct, and it worked.  (It
still wasn't right throughout, because it screwed up the top end, but
it was better).  The instrument had the early stack with cloth patches
over the screw access holes in the supply manifold blocks for bass and
treble.  I peeled two off and punched a neat little hole in each one,
then inserted a brass bleed, and glued them back on.  Over that, I
glued a 1" diam. muffler felt "cover."  After that, I could somewhat
regulate it.

The customer was satisfied.  She loved it -- for a few years.  And then
I got a call from the client demanding to know why I had drilled holes
in that piano stack!  The owner still wasn't satisfied (as I wasn't,
either) but had been told by the next rebuilder about 6-7 years later
that the last guy (me) had "put holes" in their Duo-Art stack --
knowing full well how they would take that, and what effect that
information, presented that way would have, of course.

His solution was to "gray-scale" the accordions and upset the expres-
sion balance all across the dynamic spectrum of the piano.  This
customer has passed away, and as far as I know, to this day that piano
has never played right, and will never play right, because some
rebuilder decided to "improve" the valves by making them perfectly
airtight!

The Duo-Art relies on valves which progress in tightness as the vacuum
pressure increases.  No fixed bleed is able to do that, or we could
have very easily fixed it with a fixed bleed.  However, if you doubt
this, I suggest that you prove me wrong by replacing your suede
leather Duo-Art valves with patent leather ones, and adding the
requisite fixed bleed in each end of the stack.

But I hope you will only do it to your own instrument.  Then you will
live with it long enough to realize that perhaps you should change it
back again to the way it was designed to be played.  You will at first
think it's just great.  But after a few months or years, depending on
your personal musical sensitivities, you will hear the "flat spot" just
above MF and extending through FF, and you will then realize that you
got rid of all the sparkle.

Craig Brougher

 [ Well, Craig, you've made a good point, and I'm actually glad that
 [ I questioned your statement, 'cause now I've learned a lot more.
 [ Thanks for your continuing patience with novices like me!  ;)
 [ -- Robbie


(Message sent Mon 24 Jan 2000, 17:34:39 GMT, from time zone GMT-0600.)

Key Words in Subject:  Duo-Art, Leakage, Valve

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