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MMD > Archives > November 1997 > 1997.11.13 > 16Prev  Next


Duo-Art Cross Valve Replacement Mystery Solved
By Craig Brougher

I was talking to a fellow rebuilder the other day who told me that the
round valve plates designed to replace the old cross valve design have a
problem: They are slow to repeat.  I scratched my head for awhile over
that one.  I'd never had the problem.  They always went like trip-hammers
for me.  But he was so insistent that I started examining what it was
that I did differently.

I've been using them for probably about 20 years or so.  Finally, it
occurred to me that when replacing the inside valve seat, I always used
a thin, hard-surface, finely napped calfskin about .025-.035 thick.  He
was using a thicker, cushier organ leather about .050 thick.  What was
happening then, was that the valve leather had a wider footprint on the
seat, and because the pouch diameters of the old Duo-Arts in relation to
their valve size was marginal, it required a bit longer to unseat a valve
whose footprint area was larger.

The other thing about it was, the leather being very soft tended to
stretch some as the stem of the valve lifted, not allowing the valve to
instantly pop off the inside seat.  So you had two things that prevented
those pianos from responding well.  Hmmm.  No wonder  so many rebuilders
have been saying that cross valves are better.  They aren't.  They're
worse.  But when you put them back together with thick, cushy, inside
seat organ leather, you've made a problem for yourself.

Now, when your leathers are thinner than the original stock, you will
probably have to use two leather punchings on top instead of just one,
then fill in with papers.  That's not original with me, since you will
often find thick pouch leather punchings up there with the paper spacers,
anyway.

Maybe one day, a newly designed seat will be forthcoming that will end up
being a bit more conical and offer less footprint area to begin with, but
until that day, the round valve replacements are superior to cross
valves-- providing you know how to use them!  Once the clamping area
problem of the valve has been solved, the round valve is better because
it is symmetrical and will allow the valve to seat better.

It also allows the valve to "squirm" a little sideways because it is much
smoother, without sharp edged corners, which have always prevented sure
seating in a hurry.  Also, the round valve is about 20% more efficient,
given the same valve travel, and finally, it is much _much_ quieter.

I studied these valves out about 20 years ago, making tests and such, and
believe that cross valves were used solely because Duo-Art didn't want to
use any larger pouch well than about 1," because they probably felt that
in the red gum pouch boards, 1/2" spacing was "necessary" to prevent
internal checking from leaking between wells.  They were a very
conservative bunch.

Those pouches then would work well with a cross valve having a bit less
area, but not with an appropriately sized round valve, given the same
valve diameter, leather, etc.

At least now, in my own mind, the mystery has been solved.

Craig Brougher


(Message sent Thu 13 Nov 1997, 18:28:10 GMT, from time zone GMT.)

Key Words in Subject:  Cross, Duo-Art, Mystery, Replacement, Solved, Valve

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