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MMD > Archives > September 1999 > 1999.09.23 > 04Prev  Next


Duo-Art Cross Valves
By Craig Brougher

I was amazed at the lack of comment at the bottom of Brian Thornton's
letter regarding the inefficacy of the Duo-Art cross valve replacement.
Usually, when a subject like this one has been totally exhausted and
now resides in vast detail in the archives, the editor will refer the
reader to the archives.

We have hashed and re-hashed this subject for months, and I have
personally written many articles about cross valves, as has also Bob
Taylor and others.  Such information should not just be dismissed as
though we have a brand new subject, here. (I'm getting after you, Jody).
I don't mind broaching the subject again, but I think that a mention
should be made of what we have on file, already.

 [ Robbie has a great deal more time to do the research, and he
 [ seems to have a much better memory for what topics have been
 [ repeatedly discussed.  It seems that I'm often doing the
 [ editing at 2am (or worse) while Robbie's out of town, so I
 [ do what I can.  There's so much in the MMD Archives under
 [ "valves":
 [     http://mmd.foxtail.com/Archives/KWIC/V/valves.html  (135 hits)
 [ "valve":
 [     http://mmd.foxtail.com/Archives/KWIC/V/valve.html   (92 hits)
 [ Its clear that a real search engine is probably needed
 [ so that these hits can be qualified by valve type or
 [ procedure.  Maybe next week   ;-(

Brian Thornton wrote:

> First of all replacing the cross valves with round ones will not work
> unless you are prepared to add a set of primaries.   Aeolean wanted to
> save the expense of adding primaries.  The cross valve design creates
> an aerodynamic action that  enables a smaller pouch to power a larger
> valve, thus eliminating the need for a primary stack.  If you replace
> these with round ones you will have poor repetition and failing notes
> at the soft levels.

I have been replacing these bogus cross valves now for as long as round
valve replacements have been available, and I can guarantee you that if
a rebuilder cannot make any Duo-Art play with round valve replacements,
something else is wrong or missing, other than the valve replacement.

I have spoken with Bob Streicher who makes these plates, and who himself
had the same problem! So I cannot figure out what it is. Are they not
washing the plates good in lacquer thinner, first? Is it the leather
they are using?  It is very difficult to get an experienced rebuilder
to admit that he has done anything wrong. This is why it's so hard to
put a finger on the problem. Nobody wants to 'fess up.

The oldest versions of these had 1" diameter pouch wells, which is a
small pouch, but still plenty of power. That's what my tester used. I
can't figure it,  unless the new valve faces they are punching are
either too large in diameter or too thick and soft a leather.

If the rebuilder will notice the leather used in the original poppets,
he will see that it is not a soft hand, but a very solid, hard suede.
It's really heavy boot leather in solidity, but with a silky-smooth
suede surface. There's a reason for that!  Rebuilders today who try to
buy that same thickness of leather WILL have problems with those valves
since their leather will be soft garment leather and not the original
industrial prestretched, compressed leather (which was an entirely
different product altogether), and by not being very concerned with the
basic principles of this valve, they will have bobby-trapped themselves
by trying to use it.

I use a .025-.035 thick suede-- half as thick as the original leather--
never larger than the poppet diameter, and actually can be just a nip
smaller if you want, and then add the thickness difference to the top
punching with an extra leather on the top face of the poppet. The
result is a better-- not worse-- valve.

The original leather, being hard, did not conform and wrap itself
around the sealing face of the valve plate like soft, thick modern
garment leather is inclined to do, that's for sure. That kept the
contact area small. But to this day, I have never decided for sure what
a person could do to prevent good repetition with round valve
replacements. They're the best! And in later years, Aeolian was doing
all their pianos with round valves.

In the archives, you will find a great deal of information on cross
valves versus round, including thorough test results made from a
precision tester which uses bird shot to measure the pouch force
required for either valve face, the lifter disk sizes were varied from
the largest ever used to NO lifter disk and the pouch still easily
operated the valve at any and all pressures.

Sometimes I feel that all this effort has just gone down the drain, and
that the time some of us spend to document our findings are not really
appreciated. I dedicated an entire day to that project, just so the
MMD could have the facts and figures. I also described how the tester
was built, so the results could be duplicated if anybody was of a mind
to do so.

Craig Brougher

 [ Craig,  I hope that we have the time in the next year to make
 [ the Archives more easily searchable.  To be sure, many of our
 [ readers do not browse before asking and might learn a lot
 [ by doing so.  When I have time, I enjoy following an old topic
 [ and seeing what's been added recently.  The knowledge base is
 [ growing.
 [
 [ I would hazard that we still need a "Frequently Asked Questions"
 [ section on the Website.  We have enough material online that this
 [ FAQ could take the form of an outline with pointers (URLs) to the
 [ relevant discussions.  What's needed to accomplish this is one
 [ or more volunteer editors that would each be responsible for a
 [ section of the FAQ.  Those wishing to provide input to such
 [ project, either as an editor or as someone providing suggestions
 [ for the editor(s), should write to:  editor@foxtail.com
 [ Please include the letters FAQ in your subject line.
 [ Thanks!    --Jody


(Message sent Thu 23 Sep 1999, 12:59:00 GMT, from time zone GMT-0500.)

Key Words in Subject:  Cross, Duo-Art, Valves

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