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THE MUSIC TRADE REVIEW
The Meaning and Significance of Spring Pressure in the Player-Piano Is
Often Too Little Understood, Even by Those Who Are Intimately Connected
With the Player Industry—The Functions of the Exhauster Spring.
It is unfortunate that the generality of those
who make their living in connection with the
player business should be so appallingly ignorant
of the fundamental principles upon which the ac-
tion of the mechanism depends. Not only do the
prevalent professional ignorance and confusion
of thought tend toward a general and parallel con-
fusion in the public mind with reference to every-
thing that has to do with the player-piano, but
they affect also the practical ideas of those who
have to deal with the instrument as its repairers
and so-called "experts." Indeed, the advertising,
the literature and the conversation of almost every-
body who is interested, as a layman or otherwise,
ir. the development of the player in its promotion
or in its use. are vitiated by the perpetuation of
fallacies which it should be the first object of the
pneumatic engineer to remove.
One of these fallacies has to do with the matter
of spring expansion. As everybody knows, or
ought to know, the various bellows of the player
concerned with the production or regulation of
power, as opposed to those which consume or use
up the power, such as the speaking pneumatics, all
require for their functioning the use of properly
adjusted springs, either for purposes of compres-
sion or of expansion. It has for years been cus-
tomary to speak of the lightness or stiffness of
these springs, relatively to each other and to those
of individual players which happen to be under
discussion, as if in some mysterious way the pull
exerted by them promotes or hinders ease of ac-
tion, power, reserve, or responsiveness. In con-
sequence, much falsehood is innocently uttered by
salesmen and much error committed by repairers,
not to mention such bewilderment caused to users
of the player-piano who would like to adapt their
instruments to what they find to be their individ-
ual requirements. It is the purpose of the present
article to point out the truth of these matters and
thus assist in puncturing some of the grosser fal-
lacies which cluster around the subject; all in
the hope that the light thus thrown will illuminate
some dark realms of error.
pounds per square inch of surface upon which it
presses. Hence the thinning or dilatation of air
described as happening when the bellows are
opened is accompanied by a fall in pressure; or, in
other words, as the 'contained air is stretched or
thinned, any given cubic inch of it, to take a con-
crete example, will be lighter than it was when in
a normal condition. But since the opening of the
bellows brings about a marked dilatation of the air
contained in it, and since there is a flap both out-
side and inside, it follows (1) that the outside air
pressing against the outside flap prevents itself
from entering, while (2) the air contained in the
chambers and galleries of the player action, being
by hypothesis of normal pressure before the bel-
lows work is begun, must press against and open
up the inner flap and rush into the bellows space
until the pressure therein is equal to the pressure
throughhout the rest of the player. But since
this involves an expansion or dilatation in the
volume proportion of the bellows to the rest of
the player action, it follows that after the expan-
sion and the equalization of pressure, the pressure
throughout the player will be considerably lower
than normal.
All this happens while the bellows is pushed
open. When, now, the foot pressure on the treadle
is released, a spring behind the moving wall
thrusts the same back until the bellows is again
closed. This operation of closing squeezes the air
which has expanded in the open bellows until its
pressure rises above that of the atmosphere, when
it forces its way out against that pressure through
the outer flap. Thus at each complete stroke back
and forth of the foot on the treadles a definite
proportion of the air contained in the player is
expelled into the atmosphere.
The
Exhauster Spring and Its Work.
Now what part does the spring of the exhauster
play in this operation? It is plain that this spring
may be light or heavy, relatively speaking, but it
must be heavy enough to close the bellows against
the air pressure within, having the assistance of
the higher normal pressure without. It is likewise
plain that this function of closing the bellows is
The Operation of the Bellows System.
To begin at the beginning, let us briefly state the only function of the spring. Now, the heavier
the purpose of the bellows system and its opera- the spring may be the more quickly will it close
tion. The two pumper bellows, or exhausters, as the bellows, and therefore the more rapidly can
they should better be called, are worked alternate- the bellows be operated, since the quicker closing
ly open and shut by the action of the performer's means that the foot may open the bellows more
often in any given time. But it is also plain that
feet moving on suitable treadles. Each of these
the heavier the spring the more work will be re-
exhausters is simply a leaf bellows of relatively
large size, having a flap valve on the inside wall quired, in the sense of physical effort, to open
nearest to the air trunks of the action and an out- the bellows against its resistance. So that it is
side flap on the moving, or outer wall opening, to plain that the heavier spring simply means that the
the atmosphere. Now, the atmosphere is a com- foot, by icorkitifi harder, is enabled to produce a
given vacuum in less time or to produce a higher
plex of gaseous matter, and it is a property of all
gases to expand indefinitely. That is to say, if a vacuum in a given time.
bellows when closed contains (as, of course, it
Evidently, then, since the converse is true of
does) a minute quantity of air in the shut up the lighter spring, one can only say that the
spaces between its leaves, then when this bellows weight of the spring of itself has no effect, and
is opened the contained air, if no more can enter that indirectly it has the effect of permitting
from the outside, will expand to fill the enlarged
slower, lighter work, or faster, heavier work, as
space. The atmosphere has weight, and this weight the case may be. Therefore it may be said in
corresponds to a pressure at sea level of 14%
general terms that the heavier spring is better for
those who can put the effort behind it, and vice
versa.
The function of the spring in the equalizers, or
so-called "reservoirs" (the term is incorrect), is
exactly the reverse. In this latter case the equal-
izer is held open by the spring, and its function is
tc impose resistance to the closing of the equalizer
under the atmospheric push from the outside, which
is realized when the interior air is dilated. As
soon as a "partial vacuum" is created in the equal-
izer by means of the exhausters, as described
above, the atmospheric push from the outside will
close the equalizer, provided the spring resistance
is not too great. Thus the heavier the spring the
greater the resistance to the work of the equalizer
and the more slowly will the equalizer close. But
the equalizer does no work till it has closed, at
least party, and is ready to open again. When it
begins to open it becomes an auxiliary exhauster
and steadies the work of the regular exhausters.
Xow it is easy to see that the more resistance im-
posed by the spring the less chance there is for
the equalizer to close and remain closed. If the
equalizer under hard pumping remains closed it
cannot do any work as an auxiliary exhauster, and
so its extra additional force is lost and the possible
vacuum level remains lower than it otherwise
would. iHence the heavier the spring pressure the
higher will be the vacuum level and the louder one
can play. Yet, at the same time, higher spring
pressure means more physical effort required to
close the equalizer even partly, and since it must
be first partly closed in order to begin to open,
and thus to do work, it follows that heavier spring
pressure gives more power only by giving oppor-
tunity to harder physical effort. In fact, once more
we perceive that increase in spring pressure simply
means that by working harder we are able to gain
effects which otherwise we cannot gain, no matter
how hard we work.
The
Motor and Expression Governors.
Similar reasoning applies to the motor and ex-
pression governors. Increase the spring expansion
of the motor governor and the motor runs faster
on any given position of the ttmpo lever. Why ?
Simply because for any given force of pumping
and consequent level of vacuum the governor
closes less in proportion to the strength of the
spring. But this simply means that, as the lesser
closing implies a greater size of passageway
through which the displaced air flows, more air
must be displaced in a given time and therefore
the drag on the bellows is greater. Hence, again,
the spring merely gives the opportunity, by working
harder, to gain results not otherwise attainable.
The same applies exactly to the expression gov-
ernor. In consequence we are compelled to the
conclusion that the player obeys the laws of nature
just as any other machine does, that something can-
not be had from nothing and that energy is never
created, only transformed.
Chas W. Norton, of Farmington, Me., is mak-
ing extensive repairs to his piano and player store
in that city.
WRIGHT METAL PLAYER ACTION
ADDRESS
ALL
CORRESPONDENCE:
TO
George H. Beverly
Sole Distributor
Easily 100% in advance of any action ever offered. Simple—Responsive—Durable
—Beautiful. Contains the Wright "Ideal" bellows.
Being made of metal (the logical material for player actions) it cannot be affected
by dampness or any climatic conditions. Its exclusive features save many dollars
in repair work and make many sales in competition.
KNABE BUILDING
437 FIFTH AVENUE, NEW YORK
M
s WRIGHT CO.
WORCESTER, MASS.