I have just begun the stack for a mid-'Twenties art case Ampico with
upside down wooden top valves.  It has two odd valve blocks among the
normal ones.  They are positioned where there is no pneumatic for them
to control and the top case has been carved away so that when the valve
activates, it opens to the air instead of a pneumatic.  I guess these
are to bleed off residual pressure in the stack on rewind, but I have
never seen this in any stacks before.  Why did they put these here and
have any of you seen this before.  What do you tube these to since all
the tubing was crispy and gone by the time I got it.

D.L. Bullock    St. Louis
http://www.thepianoworld.com/

 [ This description is on page 36 of Ampico Service Manual 1929:
 [
 [   The Wind-Chest Spill Units
 [
 [   Spill units such as are shown in Fig. 18 are placed on each
 [   side of the wind chest. They normally spill atmosphere into
 [   the chest.
 [
 [   This spill is used to maintain a flow of air through the
 [   expression regulators so that the regulator pouches are kept
 [   in active operation whether few or many notes are being played.
 [
 [   When the No. 6 intensity valves are sprung, atmosphere raises
 [   these spill pouches and cuts off the leak of atmosphere to the
 [   chest.
 [
 [   The tubes leading to the pouches of these units contain No. 60
 [   constrictions -- the purpose of which is to control the amount
 [   of air "robbed" from the No. 6 intensify valves.
 [
 [   To give a flow of air through the regulator even when the spill
 [   valves are closed, there are two No. 52 permanent leaks to
 [   atmosphere, one in the bass and the other in the treble wind-
 [   chests.  They are located near the ends of the regulators.
 [
 [ -- Robbie