Special Valve in the Ampico B Drawer, Part 1 of 4

The drawer associated with the Ampico B reproducing piano is a
sophisticated example of engineering excellence. Some of the components
in the drawer reflect significant advances in the understanding and
implementation of devices to improve the playback capabilities of Ampico
piano rolls, both A and B type. One of those components is the Ampico B
unit valve, 83 of which are typically found in the piano's pneumatic
stack, and two of which are in the drawer. One other is also used
elsewhere (soft pedal) in the piano.

The Ampico B unit valve is renowned for its ability to be turned on
and off rapidly and quietly under demanding vacuum conditions in Ampico
reproducing pianos. In large part, this exceptional capability is due
to the presence of a specially designed ball-bleed device within the
note-activating Ampico B unit valve. Functionally, the ball-bleed is
a tiny 'check valve' that is judiciously placed within the body of the
Ampico B unit valve block.

The ball-bleed device incorporates a tiny ball bearing of about 3/32"
diameter. The ball is constrained to move up and down only about 1/32"
within a short hollow brass cylinder with mechanical limits at each end.
There is a centrally located circular air passage opening (constriction
of .040" diameter) in the blocked lower end.

The other end is just crimped slightly, which prevents the ball from
being ejected from the short channel. Its opening has an effective
diameter greater than .040", but less than 0.104" (#37 wire gauge drill
size). That is, the hollow circular channel within which the ball
travels has a diameter of about 0.104".

The .040" constriction diameter in the ball-bleed device is larger
than that of the circular opening of the one other 'fixed bleed' device
(constriction of .028" diameter) in the Ampico B unit valve. A fixed
bleed means that the airflow constriction in the hollow cylindrical
structure of the bleed cup (resembles a miniature thimble) is always
open. There is no ball bearing associated with the fixed bleed.

The ball-bleed device functions as a pneumatic switch. Its 'off' status
corresponds to a blocked passageway, and the 'on' status corresponds
to an open passageway (through the associated circular constriction of
.040" dia.). The ball stays in the downward rest position (blocked)
for the off condition and is displaced upward about 1/32" for the on
condition.

The ball-bleed can block or allow airflow from one location to another
within the B unit valve block, even if it is only for a short time. Its
'check valve' function (open vs. closed) is automatically triggered by
certain air pressure differences (between one end and the other) which
occur during utilization (activation and shut off) of the Ampico B unit
valve per se.

As previously mentioned, the Ampico B unit valve also contains one
conventional bleed cup device (fixed bleed). The bleed cup itself is
a tiny hollow brass cylindrical cup (about 3/32" in diameter and 7/32"
long) with a small circular hole located in the center of the surface
at the 'bottom' end. It is often referred to as a "bullet-bleed" because
its overall shape closely resembles (in miniature) the brass cartridge
of a spent rifle bullet.

(The modern technology term "bullet-bleed" has been used by Ampico A
and B rebuilders for many years, at least in the New England area. Its
use probably arose as a convenient way to distinguish the Ampico B
"ball-bleed device" from the conventional "bleed device that looks like
a miniature thimble with a small hole drilled in the closed end". The
bullet-bleed is the bleed _without_ the ball-bearing check valve. I have
never seen the term "bullet-bleed" used in any extant Ampico iterature.)

The "bullet-bleed" cup is located within a separate short internal air
passageway (about 3/32" diameter). The circular constriction opening
of this bleed cup is much smaller than 3/32" and fixed in its dimension.
The bullet-bleed does not function as a pneumatic switch or check valve
because its airflow passage (with appropriately sized constriction) is
always open.

Inspection of existing original ball-bleed devices from different
note-activating Ampico B unit valves reveals identical construction
geometry and dimensions. However, with certain specialized B unit valve
blocks, examination of the accompanying conventional bleed cup shows a
small, but noticeable difference in the diameter of the circular airflow
constriction (at the center of the bottom of the bullet-bleed). What is
the significance, if any, of the dimensional differences for the small
hole at the bottom of those bullet-bleed cups?

Typically, for the note-activating Ampico B stack unit valves, the
corresponding fixed-opening bullet-bleeds have a #70 circular opening
(wire gauge .028" diameter) present in the center of the bottom of
the brass cup. Each of the note-activating Ampico B unit valves also
contains a ball-bleed device (pneumatic switch) whose constricted
airflow passageway has a #60 opening (wire gauge .040" diameter).

The operation of the note-activating Ampico B stack unit valves is
described in detail on pages 34 and 35 of the 1929 Ampico Service Manual.

Bill Koenigsberg
Concord, Massachusetts

 [ To be continued ]

 [ Ref. https://www.mmdigest.com/Gallery/Tech/Ampico/amp34.htm 
 [ and https://www.mmdigest.com/Gallery/Tech/Ampico/amp34c.gif