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Thoughts About How the Piano Lodeon Works
By John A Tuttle

Hi All,

My quest to figure out exactly how the Piano-Lodeon works
continues. I finished a graphic that accurately shows the
placement of the two 'vanes' in the plenum. 

Today, I tried to measure the vacuum level inside the
plenum without any success. Naturally, my immediate thought
was 'this isn't possible'. Closing off all of the ports on
the trackerbar with tape, I disconnected one of the tubes
and hooked up my vacuum gauge. The pointer didn't move at
all. Not even slightly. So, I tested it using my tongue,
which I believe is pretty sensitive to vacuum. Indeed, I
felt something, but it was an extremely small amount.

All of this made me stop and think. While the system most
definitely utilizes vacuum to do the work, it must be more
about 'air flow' than 'vacuum level'. I know that might
sound a little odd since the unit definitely uses vacuum,
but I believe it got me thinking in the right direction.
The next thing that came to mind was the flue in my forced
hot air furnace. (You say, "What?") Then I thought about a
carburetor and the 'venturi effect'. Air passing over an
orifice will create a partial vacuum -and 'lift'. Now I was
getting someplace. (huh?)

So I checked Google to find out how fast wind would have to
be moving over a closed-end pipe to create any vacuum in the
pipe. As I discovered, the term 'flow rate' comes into the
picture. And, if I read the charts correctly, about 1/2" of
vacuum (in H2O) is created by a 20 mph wind. So, I started
thinking about the plastic vanes in the Piano-Lodeon and how
much 'wind' it would take to get them to move. Unfortunately,
I don't have an anemometer. But as I had demonstrated in my
YouTube video (below), it only took a whisper of air to
get the 'valve vane' to open. (I know... what's a whisper of

All of this thinking was making me tired, so I took a nap -no
just kidding.... I started thinking that perhaps the basic
operating principles used in this instrument weren't nearly as
similar to a pneumatic player as I originally thought. In fact,
maybe they were quite different altogether. The more I looked
at it, the more I felt the need to start over at square one.

While it's true that the mechanism utilizes vacuum to function
and it has a trackerbar, those are about the only two things it
has in common with a pneumatic player action. It doesn't have
pouches, bellows, or air-tight valves. So, how does it work?

About the easiest way to explain it is to say 'it's a balancing
act', and it functions by 'upsetting the balance'. Think of a
'balance beam scale'. When weight is put on one side, it causes the
beam to move. Naturally, depending on the sensitivity of the
scale, adding a certain amount of weight will cause the beam
to move to its furthest extreme. Adding more weight will cause
it to move to that extreme faster, and so forth.

Now, consider that 'moving air' exerts a certain amount of force
on a balanced 'vane'. You begin to get the picture, and understand
that it doesn't take a whole lot of moving air to cause the vane
to move. And, if you increase the air flow, the vane will move
even faster.

Also, we have to understand that the weight and mass of the vane
play a critical role in determining the 'rate' at which the vane
will accelerate over a given period of time and distance. This is
important because the goal of moving the vane is to develop enough
inertia (or power) to move another device, which will strike a

(Let me stop at this point and admit that I'm not a physicist. I
don't know the formulas that are needed to prove anything I'm
saying. This treatise is my way of looking at the device and trying
to make some sense of how and why it works. Hopefully there is
someone in the group who can actually explain the principles
of operation in scientific terms.)

So, putting this all together, let's see what happens in the
Piano Lodeon. Unlike a balance beam scale, that is stationary
between two extremes when balanced, the vanes in the Piano Lodeon
are heavier on one side of the fulcrum point than the other. In
both cases, the vanes are 'weighted' such that the 'atmosphere'
side (or the side that's not in the plenum) is in a 'down'
position when at rest. And, both of them stay in that position
even when vacuum is applied to the plenum, as long as trackerbar
hole is closed.

Once the trackerbar hole is opened by a perforation in the music
roll, atmosphere rushes down a tube and blows on the 'valve vane',
which causes it to open. That action opens a much larger orifice,
which allows a large amount of atmosphere to enter the plenum, and
that air blows the 'striker vane' through its entire range of
motion. Now here's where it gets a little more interesting, and I
think I've finally figured it out.

After the perforation passes, both vanes return to their resting
point. But there's one more piece of the puzzle that had me a
little baffled. That was the hole in the striker vane. (You might
have seen it in the video. It's a 5/32" hole in the inside portion
of the vane.) Determined to know why it was there, I performed a
little experiment. I took a tiny piece of Scotch tape and covered
the hole. Then I tested two notes; the one with the taped hole and
one without the tape. Sure enough, the one with the tape returned
to its resting point (when the trackerbar hole was closed) more
slowly than the one without the tape. So, the function of the hole
is to allow the vacuum to equalize more quickly in the plenum. I
guess you could call it a 'bleed'.

One other point that has some relevance concerns the striker vane
and its associate chamber. The vane is 0.460" wide and the chamber
is 0.470" wide. Also, the length of the vane (inside the chamber)
is 0.005" shorter than the overall length of the chamber. Ergo,
there is 0.005" clearance on all three sides of the vane inside
the chamber. Considering that the vane is exactly 2-1/2" long, the
total area through which air can pass is 0.0273 sq. in. And, the
area of the 5/32" 'bleed' hole is 0.0192". So, it seems obvious
that the spacing around the vane, which also acts as a bleed when
the vane is returning to its resting point, was about 70% of what
the designer/manufacturer felt was needed to achieve a sufficient
repetition rate. Frankly, taping over the hole in the vane didn't
make much of a difference in the return speed. So, I don't know if
making the hole bigger would have made a noticeable improvement.

In closing, I'm more than open to any ideas and/or thoughts that
anyone has concerning this mechanism. Perhaps someone can explain
all of this in a much more succinct manner. If more details about
the parts are needed, I will do my best to provide them.

John A Tuttle
Brick, NJ, USA 

Other Pages about the PianoLodeon
Front Page
Page 1
Page 2
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This page was last revised July 1, 2017 by John A. Tuttle, who Assumes No Liability
For The Accuracy or Validity of the Statements and/or Opinions
Expressed within the Pages of the Player-Care Domain.
Cartoon Graphics by E7 Style Graphics (Eric Styles)

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