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THE MUSIC TRADE REVIEW
NOVEMBER 26, 1921
9
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The Following Article on the Use of Pressure Gauges Will Prove of Value
to Practical Designers and Engineers Who Are Seriously Endeavoring to
Perfect the Player-piano So Far as Its Pneumatic Equipment Is Concerned
It- is a rather unfortunate fact that the en-
gineers who are responsible for most of the de-
signing now standard in the field of pneumatic
playing mechanisms have been so willing to
do their work on the basis of rough and in-
exact experience. One seldom finds a playei
action shop equipped for precision work. There
are exceptions, but the statement holds true
for the greater number of such shops in this
country.
Now, the use of instruments of precision for
measurement involves two different purposes.
The first relates to the discovery of true dimen
sions, proportions and relations in the various
parts. The second relates to the production of
those parts strictly according to pattern. This
second branch of the subject is already to some
extent recognized as essential, so that we find
our best shops equipped with micrometer gauges
for the accurate measurement of thicknesses
of leather and cloth, and with automatic ma-
chinery for assuring that measurements once
determined may be duplicated indefinitely with-
out change.
The Place of Calculation
But in respect of the first branch of the sub-
ject very little has been done. Yet it must
be obvious that careful calculation of the dimen-
sions of parts is an absolute essential to the at-
tainment of precise results. To take one exam-
ple, we ought to know exactly what weight a
valve has to lift, in the shape of atmospheric
pressure, at the maximum of possible attainable
vacuum, and then from this data we ought to
be able to calculate the precise diameter of the
valve openings and of the discs and pouch. To
use at such a place as this precise measurement
means to get the best possible results without
uncertainty. Not to do so means that perhaps
good results will be had, but that perhaps they
will not be had; probably not.
The power which we utilize for operating the
player mechanism is derived as the result of
allowing the atmosphere to act against the mov-
ing parts of closed boxes, within which the air
pressure has been artificially reduced. The work-
ing pressure thus produced depends, of course,
upon the difference between the pressure of the
atmosphere and that of the internally con-
tained, partially exhausted air. In practice it
is found that many advantages are derivable
from allowing the difference mentioned (which
measures the working pressure) to fluctuate
under the control of the player-pianist or of a
set of automatic governors, as the case may be.
In other words, seeing that the power of the
sound from moment to moment emitted from
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ACCOMPLISHMENT
the elements of the musical instrument being
played by the playing mechanism must never,
for artistic reasons, remain fixed, the mechanism
must always be designed to work at any pres-
sure attainable above the minimum at which the
resistance of the moving parts can be overcome.
The Case of the Reproducer
Now, so long as all player-pianos were built
to be operated by foot-power, and therefore
their expressive qualities were at the command
of the human performer, it really did not so
much matter whether there were or were not
any precise knowledge as to the exact working
pressures used or available. But during the
last few years there have been developed vari-
ous players designed to reproduce the play of
individual artists. In all these instruments the
principle of the expressive control is identical.
That is to say, the action is provided with gov-
ernors, adapted to control the area of the open-
ing or openings through which the air passes
between pneumatic stack and bellows. The
level of the internal air-pressure at any moment
depends upon the size of the opening through
which the exhausted air passes, as well as upon
the quantity of air brought into the stack
through the bleed-holes from the tracker-bar at
any moment. Spring-control of a moving wall
of a bellows is usually introduced in order that
the opening which corresponds to each governor
may be enlarged or diminished slightly in size
from moment to moment as the quantity of air
drawn in through the bleed-holes is greater or
smaller.
until the air in the tube above the water has been
compressed to a point where its weight, with
that of the water in the tube, balances the atmos-
pheric pressure. Obviously, the water will rise
higher and higher in the tube as the internal
pressure in the player action sinks. The higher
the partial vacuum, in other words, the higher
the water will rise. If, now, a scale of inches
is placed alongside the tube, then the height to
which the water column rises can be measured
(assuming the tube to be transparent) in inches
and read off.
It is thus possible to obtain a standard of
pressure measurement. We may speak of a
pressure of "ten inches" or "twenty inches" or
whatever it may be, meaning in each case that
the difference between outside (atmospheric)
and inside (exhaust) pressure at the moment is
sufficient to drive up the water column ten inches
or twenty inches, or whatever it may be.
The Ounce Scale
A more rational scale would be founded on
ounces of pressure and would measure the pres-
sure upon the outside of the moving parts per
square inch of area. If the water column be
of one square inch cross-sectional area, then
408 inches of water column balance 236 ounces
of atmospheric weight (14.75 pounds). An
ounce of weight, therefore, is equivalent to 408-
236 inches of rise of water, which is almost 1$4
inches (more nearly 1.72 inches). A scale can
be made on this basis reading in ounces.
The "U" Tube
For practical purposes the pressure gauge is
When we are dealing with arrangements like best made in U shape. The tube is bent into
this it is obviously important that the exact an U, with each leg the same length, preferably
measure of the working pressure assigned to four feet. One end of the U is left open and
each governor should be known, for otherwise the other is connected to the player action.
the mechanism would not give uniform results Water is poured in at the open end till the bot-
nor would it be possible to duplicate those re- tom of the scale is reached. It must be re-
sults from piano to piano.
membered that in the U tube when the Water
The same may be said of the roll-driving rises one inch in one leg it falls one inch in
motor of any player-piano, the dimensions of
the other, so that it is best to mark off the
which and the measure of its efficiency can scale on the suction side in half-inches and
only certainly be obtained by measurement of
mark each as if it were a whole inch. The
the pressure at which it works and by realization same is true of the ounces, of course.
through such measurement of the ideal combina-
tion of pressure dimension and gear proportion.
The Water Column
THE WONDERFUL!*
Now, the most valuable and simple of all
pressure gauges is the water column. To make
this instrument is so easy and the work it does
so excellent that no engineer should fail to have
one by his side in the experimental and inspec-
tion rooms.
r Piano
The water-column pressure gauge depends
her Bar Cleaner
upon the fact that a column of water one inch
in diameter and thirty-four feet in height bal-
EVERY NOTE PLAYING
ances the pressure of a column of air of the
HELPS TO DPIN6 OUT THE FULL
same cross-sectional area and the height of the
TONE BEAUTY OF PLAYER
atmosphere. Suppose that a tube open at each
end is plunged into a tank containing water and
EQUIPPED WITH SPECIAL
cpen to the air. If, now, the upper end of this
VALVE £/CREEN FEATURES
THAT COLLECT THE DIRT
tube be connected with any part of a player
^PREVENT DEVICE FROM
action from which air is being drawn by the
GETTING OUT OF ORDER
operation of a bellows system the atmospheric
ton f*umcuiAnr,MHCtETc mm
air which has been filling the tube down to the
AMERICAN PENCE mrcxa
point where it touches the water in the tank
rT.LOUIf.UTA.
will also be partially exhausted. The atmos-
Export Department:
pheric pressure against the surface of the water
130 W. 42nd St., New York City, U. 8. A.
in the tank will immediately, of course, come
Canadian Distributor:
into operation and force water up the tube
Jno. A. Morris, Toronto. Canada.
LEERNOTE
^AUTO-PLAYER ~
fhe WERNER INDUSTRIES CO.
P I A N O S
AND
P LAY E R S