The contact bounce is easily filtered with a simple resistor and capacitor
(RC) filter before the signal goes into the CMOS commutator circuit.  The
signal level preceding the filter network must be limited to twice the
threshold voltage of the CMOS device.  In this way no timing distortion
will be introduced.  Since the fall-time of the pouch and bleed
combination is around 20 milliseconds, the RC time constant can be
about the same without affecting the data.

Richard Tonnesen is the expert on these matters -- his pneumatic reader
has been in use almost 15 years!

-- Robbie Rhodes