After reading about pressure and organ reeds I felt prompted to add my two
cents worth.  I believe the original question was about converting a reed
organ so that it could play rolls.  I have an Aeolian player reed organ
which I rebuilt about 5 years ago.  It is a model 1500 which was the
forerunner of the Aeolian Grand and was manufactured in 1895.  I tried to
measure the suction with a dial type gauge.  The suction is actually too low
for an accurate measurement, plus I don't really trust the gauge at low
readings.  To get a more accurate measurement one would have to use a water
type gauge.  The needle barely moved, so it seems that the organ operates on
a suction of 2 or 3 inches of water at the most.  The player mechanism is
designed to operate on this low suction.  BTW, the player section is
actually separate from the manual.  The only thing they have in common is
the bellows and reservoir.  Each has it own banks of reeds and valves.  When
a hole in the (wooden) tracker bar is uncovered, it inflates a tiny "pillow"
pouch pneumatic.  This pneumatic is 3/8" wide by 1 11/16" long with a span
of 1/2", and uses pouch leather as a covering.  Everything is designed to be
narrow, so that it takes up no more width than an ordinary key on the
keyboard.  When that pouch expands it presses open a pallet valve which is
designed exactly as are most reed organ pallet valves.  The pallet valve is
inside the suction chamber.  When it is pushed open it pulls a small outside
valve closed to close off the atmospheric pressure going to the "action"
pneumatic.  The valve clearance is .030".  The action pneumatic is 9/16" by
6" with a span of 7/8".  The original covering was something like a thin
chrome pneumatic leather making them very flexible.  Even though the span is
7/8", these pneumatics do not need to close in order to sound a note.  As
the pneumatic closes it pushes a pitman rod which goes through into the
suction chamber and pushes open the pallet valve which allows air to pass
through the reed.  Remember that the force of the pneumatic does not have to
move the mass that it would have to in a piano action.  It only needs to
open a pallet valve enough to permit air flow.  That pallet valve is inside
the suction chamber and therefore the atmospheric pressure is already trying
to push it open.  The only thing that is holding it closed is a spring.  It
is important that these springs be just strong enough to hold the valve
closed with the most vigorous pumping.  Therefore, it does not take very
much force for the "action" pneumatic to push the pitman which opens the
pallet valve.

It does take more vigorous pumping to play a roll than it does to play the
organ manually but this is probably because of the extra air required to
turn the wind motor.

Howard Wyman   (hwyman@digital.net)