In MMD 19.10.09, Nevin Engle asks about regulating Standard Pneumatic
Action valves.  Perhaps a general review of valve design is in order.

There are probably a sizeable number of rebuilders and tinkerers
alike who may not realize or appreciate the need for what I refer to
as "wobble" in the design of pneumatic transfer valves of the type we
find in player pianos, pipe organs and similar applications.

Manufacturing techniques, tolerances and materials of the last
century almost guaranteed that various surfaces that need to seal
tightly against each other would not be (or stay) _exactly_ parallel
or perpendicular as the case might be.  So a _necessary_ element of a
well-designed valve is the ability of the poppet to move with several
degrees of freedom, not just in the axial direction of the stem.

The attached picture is taken from the 1983-85 catalog of the Player
Piano Company, a valuable reference document in its own right.  As
stated, some "wobble" is generally encountered in both inside and
outside seats; however, the outside, or lower seat is usually a bit
"looser" than the inside or upper seat.  No glue is used (or needed)
to keep it from falling off of the stem, and once the assembly is in
place, it is constrained by the surrounding structure.

As far as how "play" is affected, if the outside seat is loose enough
that it falls off of the stem by gravity, that is prima facie evidence
that there will be vacuum leakage around the stem at that point when
the valve is actuated, and needs to be corrected.  However, it needs to
be done so in a way that preserves the "wobble".

John Grant 

 [ http://www.mmdigest.com/Attachments/19/10/12/191012_203416_Standard_Valve.jpg