[ Pat DeWitt wrote in 111115 MMDigest:

> Can I make a one-way valve by using a small sealed wooden block with
> two tubes in, one out, and a pouch leather flap over one of the inlet
> tubes?  I have no "power" to open or close the pouch leather flap
> except the atmosphere level input from opening of the tracker bar
> hole or the key slip switch hole.

That is the way it's done on tubular pneumatic pipe organs which work
on very low pressure, e.g., 2" to 3" water column.  However, you will
need two flaps, one for each of the two "in's" or "out's", as the case
may be.

The flaps work just like one-way doors do.  You can go in either door
but you must leave by the third, or only go in one door and out the
other two, etc.  That way the wind cannot flow backwards into the other
"in/out tube", rendering the action useless.  Of course in player piano
actions you're working with vacuum instead of pressure so you do it
backwards.

In the organs where I've seen it done, a small lead weight is often
added to the flap to keep it closed, and of course mount the device
such that the flaps hang right!  Others use a small "pitman" -- a disk
or top hat shaped valve with a guide peg that can slide vertically
over the hole and is light enough to pop up under the pressures needed.
The flap or pitman works best if the hole is kept as small as possible
and seals well.

A small thin-walled tube or grommet of the right size may make
a good seal as the back-pressure may be quite small and the flap may
not always seal under it's own weight.  The flap/disk can often be
something as light as a sheet of paper or very thin leather.  It
depends on the pressures involved, etc.  Of course, don't glue the
whole thing together as you may need to open it to regulate it <LOL>.

To work things out like this draw a diagram or a flow chart on what
you want to do on paper.  Then draw people going in and out in the way
you want the air to go and add one way doors as needed.  It makes
simple ideas look really simple instead of mind-boggling.  Look up
"Logic Gate" on Wiki for the math on how these simple valves work.
All computers, organs and player actions work the same way -- we just
use hundreds or tens of thousands or more of them all together in
fancy ways.

Nelson Denton - Pipe Organ Builder