I have been reading with interest the latest thread on the Duo-Art cross
valves, and I wanted to mention that in the MMD Archives of 2000.04.28,
I suggested a possible solution to the problem.  So if this subject
interests you, it might be worth your while to take a look at it.

As long as we are on the subject of valves, I would like to see if
anyone has any comments to make on this question about the Ampico B
ball bleed.  My understanding of ordinary valves is that, if the bleed
is very small, practically all the air coming from the tracker bar will
rush under the pouch and lift the valve as fast as possible. That in
itself is good, but there is a problem: because the bleed is so small,
it cannot reduce the pressure of the air in the tube leading to the
tracker bar fast enough to allow a rapid repetition of the note.

The "obvious" thing to correct this problem is to make the bleed larger,
so it can exhaust the air faster.  But now another problem arises: when
the note is played at very low volume, the large bleed "eats up" a lot
of the air-signal coming from the tracker bar, and there is not enough
air to make the pouch lift the valve poppet.  Clarence Hickman realized
that a very efficient valve would be one that had a small bleed as the
note was being struck, yet would have a large bleed when the note
stopped playing, so that it could reset itself as fast as possible.

I was looking at the schematic drawing in the Model B manual, and
trying to see if there was any way it could be adapted to existing
stacks not meant for a Model B.  It occurred to me that the ball bleed
is a simple one-way air flow controller; but a flap valve is also a
one-way air flow controller.  I imagined using little squares of tan
pouch leather perhaps 1/4" on a side, and gluing one edge of them near
a hole that leads down to the pouch chamber.  When the note first gets
the signal to play, a very tiny fixed bleed allows almost all the air
signal to push the pouch and valve poppet up.  As the air is being
exhausted from the note pneumatic, the pressure in this area is
obviously lower than atmospheric pressure.  This would cause the tiny
square of leather to rise up along its unglued side, and help exhaust
the air coming from the tracker bar.

In other words, I am wondering why Hickman designed the ball bleed
mechanism, when it appears that a very tiny flap valve in the right
place would have the same effect.  I first thought that perhaps dust
could get under this flap valve and make the note's repetition
unsatisfactory.  But then I realized that when the air is being sucked
up through the hole covered by this tiny flap valve, it would be self-
cleaning.  And when the pressure changes so that air wants to move down
this hole, the flap valve is sealed tight, and once again, dirt cannot
foul it up.  We all know that Clarence Hickman was a remarkably
intelligent and creative person, and it does not seem likely to me that
he simply failed to realize the ball bleed could be replaced by a very
tiny and inexpensive flap valve.  It seems more likely that he knew both
systems were good in theory, but for some reason unknown to me, he
chose the expensive ball bleed over the cheap flap valve.

Does anybody out there have any suggestions why the ball bleed is better
than the flap valve?  It seems to me that it is just the other way
around.

Randolph Herr