The postings on rebuilding the Aeolian grand player organ pneumatics
have brought up the thought that I should address the variety of
pneumatic styles and why some fold in while others fold out.

The standard player piano pneumatic folds in.  It is open to the
atmosphere and the suction from the player system pulls the air out
of them.  They fold in and it is best for us to fold them this way
by hand after we recover them so that the folds will be uniform,
presenting the same resistance to the suction on all notes.

If you see pneumatics in a pipe organ instrument player system, say
a Chrysoglott or a Xylophone, you will notice that most of the ones
that are leather covered have the sides and open end that fold out
and the corners only fold in.  The pneumatic fills with air pressure
from the pipe organ which blows the sides out.  When you recover
these you fold them this way.

Those same pneumatics in some company's instruments will look like
giant player piano pneumatics covered in motor cloth or even leather
and they will fold in.  However, in the case of a pipe organ, these
pneumatics will have a complete set of stiffeners similar to those in
player feeders.  These are there to prevent the sides from blowing out.
If the pneumatic opens far enough they will blow out anyway so
regulation to limit travel is important.

This is also why some of the early player pianos have these stiffeners
glued on the outside of the pneumatics that fold in.  They were so used
to applying them in their organ work, they thought they needed them in
the piano player system as well.  Later players were made without the
stiffeners all around.

In smaller suction actions, like the early Melville Clark Apollo
players and player reed organs, you will find very small pneumatics,
some with and some without hinges, that are totally encased inside the
suction chamber.  These in the Apollo Grand look like two Popsicle
sticks about 3/8" apart with pouch leather on all four sides.  These
serve the same function as pouches being surrounded by suction and they
will have outward folds.

They are surrounded by suction and when the tracker bar hole opens the
two Popsicle sticks try to fly apart as atmosphere floods the inside
of the pneumatic.  This powerful force operates the valves that control
striker pneumatics in the Apollo Grand and often operate the reed
valves in a player reed organ or monkey organ.

Many pipe organ chests have a primary pneumatic similar to this which
is inside the wind chamber.  It is two 1"x1" boards separated by about
1/2" or more of leather on all sides.  These pneumatically operate the
big valves that open the wind up to the pipe feet, and when they are
opened by the solenoid or tubular pneumatic system these two boards try
to slam together pulling the valve open, exactly opposite of a suction
player piano system.  They usually operate a larger pneumatic or pouch
to do this.

So if you have an occasion where you don't really know how the
pneumatics should be folded, determine what the pneumatic operates on:
suction or pressure.  Then determine whether it is outside and open to
the air or inside and surrounded by suction or pressure.  Some of these
pneumatics do not move far enough to worry about folding them at all,
but you now understand the differences here.

D.L. Bullock    St. Louis
www.thepianoworld.com