On p. 89 of my book, Player Piano Servicing and Rebuilding, I made
this statement: Most ordinary inside valves should have .040" travel,
measured at the stem, although various manufacturers made other
recommendations ranging from .028" (Simplex), to .047" or 3/64"
(Baldwin), to .062" or 1/16" (Autopiano secondary valves). This
statement was in reference to the individual note valves in the
In our shop, we adjust most stack valves to a travel of .035" to
.040". I realize that the valves in certain brands of pianos had .032"
or less travel, but if an increase in humidity causes the valves to
swell and the travel to decrease, repetition will suffer.
As an extreme example of this, I've seen Hupfeld Phonoliszt-Violinas
in which the valves for the three pneumatics that push the three
violins against the strings swelled so much that the violins barely
moved when trying to play staccato notes. If you start with a few
thousandths more gap, the valves might produce just a little more air
noise (or spitting), but I'd rather have that than to take a chance on
humidity-induced swelling and consequent poor repetition.
No sustaining pedal pneumatic has the power and speed of the human
foot, but certain player piano and reproducing piano rolls call for
repetition of this large pneumatic as if it did. If the valves have
too little travel, you'll be able to hear the sluggish repetition of the
pneumatic in the performance of the music. If they have too much, you
might be able to hear the valves spitting, but the pneumatic will work
faster. Of course, you don't want so much travel that there's a loud
pop or thump as the valves slam against the seats and the pneumatic
Vent or bleed size is another important factor. The speed of the valve
and pneumatic depend on the proportion of atmospheric pressure admitted
under the pouch from the hole in the roll vs. the amount of vacuum
admitted under the pouch through the vent. In general, a valve with
a little more travel is happy to have a little more vent, and valve
with a little less valve travel can get by with a little less vent.
One would assume that the Aeolian Company got the vent size just right,
so unless an old mechanism has been altered, you should be able to
maximize the response by adjusting valve travel without changing the
The more adventurous restorer might be tempted to install adjustable
vents in a pedal pneumatic, since they seemingly give you precise
control -- and it can be educational to experiment with vent size vs.
valve travel. However, adjustable vents have two problems: dirt
collects faster in them than in bleed cups; and the wood surrounding
the point on the adjustable vent screw contracts and expands enough
with long-lasting humidity changes to affect repetition. These are
two reasons that most companies used non-adjustable vents once the
engineers figured out the correct size.
In short, if the Aeolian (or other) pedal pneumatic had a lot more than
.040" travel, leave it the way it was and see how it works. Its easy
enough to adjust the travel to see what happens, and then put it back
the way it was if that was better. It's better to err on the side of
a little too much travel than not enough.