I'd like to offer some comments about Duo-Art cross valves.

In my opinion, arbitrary replacement of Duo-Art cross valve seats with
after market replacements of alleged equivalency is not a good idea.
Such replacement should only be done perhaps as a last resort if the
original valve plates are no longer usable, i.e., corroded or
physically damaged.

For one thing, such a procedure forever destroys originality by
implementing irreversible design changes never intended by the
manufacturer.  As Bob Taylor accurately pointed out, the currently
available replacement valve seats have different operating parameters
than the originals, meaning that valve performance is certain to suffer
some amount of degradation.  Not all ears may hear it, but it's there.

Duo-Art cross valves represent one of the most efficient designs ever
conceived for reproducing piano use.  They were by their nature
expensive and difficult to manufacture, but the Aeolian people kept
them for many years, wanting the best they could put into their top
instruments at the time.  When in good operating condition, these
valves exhibit superior performance in virtually every way.  They are
very sensitive, have excellent repetition at all suction levels, and
operate quietly.  They are perhaps more susceptible to leakage problems
than some other valve types, but this can be effectively dealt with by
a competent technician.

Valve design is a very complex subject.  I labored at some length in
the late 1970s to design and manufacture an experimental set of valves
for my own personal use and evaluation.  They're described in a 1979
AMICA bulletin article.  These were built in Ampico-type detachable
blocks so as to keep originality easy to preserve.  I got them to work
quite well, but they underwent several design changes (including
changing pouch dimensions three times) before I was happy with them.
Years later, I sold them with the piano they were in, with the full
knowledge and appreciation of the buyer.  They are still in service
today, although they could easily be replaced by standard Ampico valve
blocks if the current owner desired.

Although I'm happy at present  to be using original valves in my
present pianos, I learned a great deal from that experience.  For one
thing, bench tests of valve action, although helpful, can never take
the place of the ultimate test of listening to a large number of rolls
containing many different kinds of musical passages.  A sensitive
musical ear is the ultimate test instrument.

The engineering of reproducing pianos was generally well suited to the
musical goals to be achieved; any irrevocable change to a reproducing
piano is ultimately counterproductive.

Dave Saul