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MMD > Archives > February 2000 > 2000.02.27 > 14Prev  Next


Boyd Pistonola Player Action
By Craig Brougher

Keith Pritchett was kind enough to recopy the Pistonola description
from an original manual pertaining to it.  It said:

"The Pistonola.  This instrument is manufactured by Boyd Ltd., London.
The action is all metal and works with a tension twenty-five times
greater than that usually employed in pneumatic players.  The action
can be installed into a piano of ordinary dimensions"

Just so everybody understands what is meant by this statement and
where it leads, I would like to take the Boyd Ltd. brochure to task.
(Something's goofy here).

The lowest pressure commonly used in foot-pumped players at the MF
music level (that I know of) is around 10" of water column (old
Melville Clark with forward-facing pneumatics).  25 times 10" is, of
course, 250" H2O.  That is 20.8 ft.  Quite a feat for a single piston
foot pump 3.5" in diameter.  That equates to about 2/3rds of the way to
a perfect vacuum!  You seldom achieve that with a single stage foot-
treadled piston, even in a glass bell jar.  Just think -- the pianolist
was able to do it while sitting on a wooden bench without any other
support.  I suppose a hugely muscular 350 lb. athlete might knock out
a few bars before he collapsed.

Why is this ridiculous?  Because a 3.5" piston would require 86.5 pounds
pumping pressure by each foot to maintain 250 inches of vacuum as long
as no notes were playing at the time (think what kind of spring you'd
require in the reservoir!).  That's like squatting 180 pounds as quickly
as one would pump a player piano.  The bench would have to be bolted to
the floor or attached to the player somehow, and you would have to
train hard first, just to be able to play this thing.  It would be much
easier just to learn how to play the piano, I'd think.

But on the other hand, most players' average pressure was a bit over
10." So if the average MF playing required about 15", then we would
have to pump 25 times that, or 375" of a working water column vacuum,
unattainable by all but the largest high vacuum systems.

I would agree with David Evans that the downfall of the Pistonola would
be its vulnerability to dirt.  It would take practically nothing to
stop up a valve or a bleed that small, and the tiniest little flake
of paper resting on the valve seat would cause its pneumatic pistons
to be actuated all the time.  Its perfect air-tightness would have,
by necessity, been legendary (or else).

So I suggest to anyone rebuilding this player to make a bit of a change
in its design by adding a perfectly airtight well-machined clamp-in
dust filter system (caution: because of the tiny bleeds required, the
volume of the filters may have to be very minimal to maintain valve
response time).

Another consideration is that the tremendous amount of pressure
required to play it would also be present at the trackerbar, possibly
making lots of noise, and clamping the roll paper so strongly that
I wonder how the air motor could even pull the roll?  Forget tracking.
Even the porosity of the paper in this instrument might be a factor
in the bleed sizing, I would think.  And the wear experienced by the
trackerbar under such static trapped pressure should have all but
removed it from the piano by just wear and tear.  The trackerbar hole
edges would be scraping paper dust by sanding the rolls bare.

(Just think: 86 pounds of force required by each foot to create 25 times
normal pianola pressures.  Here is a player for Hulk Hogan!  And this
is only equivalent to 10" on the regular player, not even mezzo-forte.
Are we sure this thing wasn't really an early exercise machine?)

Then comes the idea of "expression."  The excursions of expression
usually amount to a minimal factor of 3-5 times.  Well, we could go
into the arithmetic for that and it would really get comical.  I think
I'll just leave it up to the imagination.

The only advantage had to be in piston velocity, which can be
considerably faster if it is friction-free.  And since the piston is
glassy graphite in precision cylinders so that friction is nil, the
losses are going to be the high pressure air leaking around the walls
of the cylinder, the valve seats, and especially the bleeds.

Despite it all, I am amazed that this mechanism was ever chosen to play
a piano.  I too have known engineers who jump on an idea before ever
considering all the ramifications they are going to encounter, simply
because their initial idea is so "way-cool!"

I sure hope that David Evans is able to successfully clean up this unit
and give it a try.  Surely, it can't be this bad.  The manufacturing
problems seem horrendous to get even 100 of them working without some
real return headaches, I'd think.

"I can see it now -- The players were actually built in a small 2 room
flat.  The factory was needed only for rework, quality control, and
testing."

Craig Brougher


(Message sent Sun 27 Feb 2000, 16:04:39 GMT, from time zone GMT-0600.)

Key Words in Subject:  Action, Boyd, Pistonola, Player

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