Those rectangular openings at the rear of each pneumatic _in no way_
are supposed to connect directly with the interior of the pneumatic.
If they are "totally unnecessary", simply plug one up, making certain
no air gets by via the screw slot, and see what happens.  The pneumatic
will have no way of opening after a note has played, except through
unintentional leakage.

There is, however, a distinct possibility that through pouch shrinkage,
maladjustment or wrong thickness(es) of gasket material and/or valve
facing(s), one or more pouches will inflate to capacity before the
secondary (main) valve is able to seat over the smaller of the two
round holes shown in the bottom of the lower pneumatic board.

When this situation occurs, air _will_ rush in around the valve as
it floats between its upper and lower seats, creating the pneumatic
equivalent of a short circuit (whew!).

Jeffrey R. Wood