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THE MUSIC TRADE REVIEW
11
The Theory and Construction of the Governor and the Importance of
That Adjunct to the Player Mechanism—What it is Designed to
Accomplish—Makes Player Control Possible—Some Interesting Details.
The player-piano mechanism is afflicted with one
peculiarity that colors its entire construction. It
depends upon a source of power which is variable
by nature and yet, in some of the work which it
has to do, is required to be steady. The foot-
driven bellows system of the player is admirably
adapted to the purpose of giving that varying touch
which is of the essence of good piano playing. But
it is by no means so admirably adapted to the pro-
duction of power for operating the motor which
drives the music roll. For, although the speed of
the motor must be frequently and quickly varied,
these variations do not correspond with the varia-
tions in power which the fluctuating requirements
of touch induce us to produce through the bellows.
We must cause the bellows to produce a constantly
fluctuating power for the actual operation of the
notes; while we need a steady form of power, con-
trolled quite independently of any other circum-
stances, for the use of the motor.
Tt is, therefore, necessary to provide some form
of auxiliary governor for the motor which will
enable us to assure steadiness of power under all
conditions of pumping.
Theory of the Governor.
If we turn back for a moment to earlier articles
in the present series, we shall find a discussion of
the process which is commonly called "producing
a vacuum." This process depends on the fact that
the atmosphere has weight and at the same time
consists of what is called gaseous matter. Now a
property of any gas is its unlimited powers of ex-
pansion. If some of the air contained in a closed
vessel be withdrawn, without permitting the en-
trance of more from the outside, the remainder
inside will expand to fill the entire space again;
and this process may continue indefinitely, result-
ing in an ever-decreasing internal and ever-increas-
ing external pressure.
When we have a non-static condition, such as
that which exists in the player mechanism during
use, where the process of reducing pressure and
the contrary process of air inflowing to restore
normal pressure are simultaneously going on, it is
clear that there must be a continual flow of air
from the interior of the player outward to the
atmosphere. If this outflow displaces from the
interior more air than can flow in within the same
time, the internal pressure will be reduced con-
stantly and progressively, resulting in a higher and
higher partial vacuum. In fact, and this is the im-
portant point, the height of the vacuum is in pro-
portion to the rapidity of the outflow; which, in
turn, is proportionate to the rapidity of displace'
ment; which, lastly, is proportionate to the rapidity
of operation of the exhausting bellows. We con-
clude, therefore, that fluctuation in the rate of
pumping means fluctuation in the state of the
vacuum. It will, of course, be remembered that
in the actual playing of the player mechanism the
inflow of air through the tracker is continuous
and prevents the constant maintenance of any even
vacuum level.
But the height of a vacuum in these dynamic
conditions is proportionate also to the size of the
orifices on the channels through which the outflow
takes place. It is, therefore, plain that if an in-
crease in the pumping speed can be balanced by a
proportionate decrease in the size of any orifice
through which the outflow must pass, the fluctuation
due to increase of pumping speed may be neutral-
ized ; while, conversely, if the process be capable
of reverse action, decrease in the speed of the
pumping may be balanced by increase in the size
of any orifice through which the outflow must
pass.
It is plain then that, given the essential of a con-
nection between rapidity of pumping and the di-
mensions of an orifice, the problem of providing
steady power for a motor from a fluctuating source
is solved.
Construction of the Governor.
The connection is found by utilizing the collapsi-
bility of a bellows in which a partial vacuum has
been produced. If we examine the equalizer of a
player mechanism, we shall find that it is a small
bellows held open by a spring, and connected with
the bellows system of the mechanism. If we be-
gin to operate the bellows and thus produce a par-
tial vacuum within, the air inside the equalizer
flows out, and as soon as the difference between
the air pressure inside it and that of the external
atmosphere is greater than the pressure exerted by
the expansion spring, the moving wall of the equal-
izer moves inward under the stress of the external
pressure. Conversely, when the internal pressure
again rises, due to decrease in speed of pumping
and consequent slacking of the outflow of dis-
placed air, the moving wall, which has been closed
in, moves outward again and the equalizer is said
to "open."
Now if we construct a small equalizer and place
it in such a position that the air withdrawn from
the motor while the latter is running must pass
through an orifice into this equalizer, through the
equalizer and out through another orifice to the
main bellows, and if further we so arrange mat-
ters that the moving wall of the equalizer, in the
course of its travel, opens and closes a valve over
the orifice of outflow to bellows, then we shall
have in essence a true motor governor, capable of
maintaining the effective working pressure at a
constant level, no matter what the condition of
the bellows or what the rapidity or otherwise of
the pumping.
In practice the construction is as follows: A
small form of equalizing bellows, having a moving
wall of area, say thirty-five square inches, is ex-
panded by means of a spring, the pressure exerted
by which may be varied at will through some form
of tensioning screw or by similar methods. This
small bellows, which is called a governor, is placed
in the wind-way between motor and main bellows
system. The air displaced from the motor enters
an orifice in the fixed wall of the governor and
finds its way out through another orifice in the
same wall. This latter, however, is covered by
some form of sliding valve which in turn is con-
nected with the moving wall. When the partial
vacuum rises high enough, due to increase of
pumping speed, to cause the external pressure to
force in the moving wall against the pressure oi
its expansion spring, the valve partially closes up
the outgoing orifice, the amount of closure depend-
ing upon the proportionate closing of the governor
and hence upon the speed of pumping. When the
speed of pumping decreases, the reverse action
takes place and the valve opens up, increasing the
effective size of the orifice accordingly.
Low Pressure for Operating Motor.
Now if the spring be capable of exerting a pull
of, say, four and one-quarter pounds and the area
of the moving wall of the governor be, say, thirty-
five inches, then the spring exerts a pressure of
about two ounces per square inch. If the partial
vacuum induced by the action of pumping be
greater than this, the governor will tend to shut
and the orifice of outflow be closed down until
the rate of flow is adjusted to balance the equiva-
lent of a two-ounce pressure. If, however, the
partial vacuum falls below the equivalent of a two-
ounce pressure, the governor will open and the
orifice of outflow be enlarged to a point where it
permits a rate of displacement flow equivalent to
the two-ounce pressure. In this manner the motor
will continue to operate, under all conditions, on
a vacuum equivalent to two-ounce pressure; or,
roughly, of .0085 of an absolute vacuum. Such a
pressure, of course, is low, but a motor rightly made
(Continued on page 14.)
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