Pete and others changing Duo-Art cross valves to round valves should be
aware that this change upsets the "pouch vs valve area" geometry.  The
working area of the cross valve is .1468 sq. in. while the newer round
valve has working area (opening) of .1962 sq. in.  This is a 33% change
in working area which must be compensated for by one of several ways.

  1.  The weight of the entire valve must be reduced, or

  2.  The valve button area (point of contact with pouch) increased, or

  3.  Increase the pouch size (which is the same a two),

  4.  Any combination of the above to compensate for the 33% area
      increase.

The point where notes "miss" should always occur when the pneumatic is
too weak to lift the weight of the piano action.  When cross valve
plates are replaced with round valve plates, (and no other
modifications are made) the valve will fail at vacuum levels still high
enough to otherwise lift the piano action. Failure to compensate as in
the steps above will result in extremely poor low vacuum
response-notably the inability to obtain soft, even playing.

I presented a paper and slide discussion at the 1983 AMICA Chicago
Convention which gave the supporting evidence, both theory and
empirical, which fully explains the problems of upgrading to round
valve plates.  While I may sound like I support the use of cross
valves, make no mistake--I hate'em and change them every time.

Footnote:  In valve calculations it is the size of the valve plate
opening that determines the working area--NOT the valve face.

Bob