Hello Bill and MMD,  Ref. 061129 MMDigest.  Restricting the atmosphere
port on an "inside" (secondary) valve serves to increase the valve's
sensitivity on turn on, but slows the turn off response in direct
proportion to the amount of restriction.  For any valve situation,
there is an optimum combination of port size, (suction and atmosphere),
valve travel, and pouch diameter.  For single valves, the bleed size,
pouch porosity, and tubing length also enter into the mix.

It is extremely unlikely that your 1926 Mason and Hamlin was originally
built with the restrictions you described.  Rather, that they were added
at some later date to compensate for some perceived valve malfunction,
or to improve the valve reaction time (turn on) on extremely low suction
at the expense of slower turn off and reduced repetition capability.

If the valve poppet travel is too long, the transition losses on soft
playing will weaken the suction to the point that the poppet will not
lift to close off the atmosphere port with normal dimensions.  Adding
the 1/8" restriction will "fix" the problem.  This may be okay for
the automatic shutoff valve, but not for note valves as this also
significantly slows the valve's ability to re-inflate the pneumatic
on turn-off.

Ampico (Amphion) valve parts have been available in the past from
Robert Streicher of Pond Eddy, New York.

Bob Hunt
Hunt Piano Company
Kennebunk, Maine

 [ Streicher lives in Shohola, Pennsylvania, but he receives mail
 [ at this New York address:
 [
 [ Robert Streicher
 [ P. O. Box 36
 [ Pond Eddy, New York 12770-0039
 [
 [ -- Robbie