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Air, What It Is and What It Does
By Wilberton Gould, Member N. A. of P. T., New York City
The following article is the first of a series describing the principles of the player and reproducing mechanisms. As the first installment indicates, Mr. Gould’s treatment will be simple and direct. He is starting at the very beginning, and of necessity must cover ground which many, perhaps most, of our readers have gone over. However, a review of the primary principles of the player and reproducing actions will have the effect of more firmly and definitely fixing them in the minds of the more experienced technicians and of materially helping those tuners who have not taken up player work seriously.
Service, as defined by Webster: "An act of one who serves."
It is one of God's greatest gifts to mankind, for who is happy who does not serve? Hence it follows that service requires sacrifice, it is the foundation stone of every enterprise. Whatever it may be, its success or failure depends upon whole-hearted co-operation.
And may service and sacrifice continue to be the keynote of our progressive Association.—The Author.
In order to service the pneumatic action intelligently, it is necessary to know the action of the atmospheric pressure both within and on the exterior of the pneumatic action.
A great many player mechanics do not give the least thought to what actually takes place when the pneumatic strikes the blow upon the piano action. Until they do they are only groping in the dark. It is needless to say that player mechanics do not know what causes the pneumatic to collapse, because they do. Unfortunately, however, there are many who cannot express themselves as they would like to, and I will endeavor to give a brief resume of the active agents which perform that function.
We know that the agent which actuates the pneumatic is free air, but what is air and what is its function in relation to the player piano? Strange as it may seem, air is an elastic gas, and according to Boyle's law, "at constant temperature the absolute pressure of a gas varies inversely to its volume." Also, according to Charles's law, "at constant pressure the volume of a gas is proportional to its absolute temperature." Thus it is shown that free air has weight and volume.
Atmosphere is known to extend for at least 45 miles above the earth, and its aggregate weight has been calculated at upward of 77,000.000,000 tons, or equivalent to the weight of a solid globe of metal 80 miles in diameter. This enormous weight reposes constantly upon the earth's surface, and upon every object, animate or inanimate, solid, liquid or aeriform. One hundred cubic inches of air at the surface of the earth, when the barometer stands at 34 inches, and the temperature is (10 degrees Fahr., weigh about 31 grains, and are thus about 815 times lighter than water and 11,065 times lighter than mercury.
Since air has weight, it is evident that a cubic foot of air at the earth's surface has to support the weight of air directly above it. The higher we ascend in the atmosphere the lighter the cubic foot of air becomes. In other words, the farther from the surface of the earth the less will be the density of the air. Air is composed chiefly of nitrogen and oxygen, or to express it more correctly, air consists of, by weight, 21 parts of nitrogen to 79 parts of oxygen. There is also a small mixture of carbon dioxide, argon and varying quantities of several other chemical substances too small to need mention here.
Thus we see that die atmosphere, like fluids, presses against any body with which it comes in contact, because fluids exert pressure in all directions—upward, downward, sidewise and obliquely. Also, its particles are so inconceivably minute that they enter all substances, even liquids, and penetrate to the innermost recesses of porous bodies. They even commingle with and circulate in the blood of men and animals, for by the pressure of the superincumbent strata air is urged into and through almost every substance. It is this circulation through the interior of the bodies of men and animals which counterbalances the outer pressure. If this weight were not neutralized it would be so great that neither man nor beast could withstand its pressure but would be as mute as a statue of metal.
The weight of a column of air whose base is one square foot, and whose altitude is the height of the atmosphere, has been found to be 2,156 pounds or 14.7+ pounds to a square inch at sea level, which for all practical purposes is the accepted standard in pneumatic engineering.
It should now be clear just what air has been doing when a player piano does not have the "pep" it used to have. As previously mentioned, Boyle's and Charles's laws state that air will always seek to equalize itself in space, no matter to what condition it is subjected. This being true, let us take, for example, a hollow vessel or chamber that is constructed strongly enough to withstand the pressure of the outside air. Let this vessel or chamber have an inside area of one square inch, in which the pressure is, say, ten pounds to the square inch. So long as the pressure remains the same we find that we have a working pressure of 4.7 pounds a square inch on the exterior of the chamber, but if we take another vessel or chamber of a similar size from which all air has been withdrawn and connect it with a suitable tube to the vessel or chamber which contains the ten pounds, the air in this vessel will at once enter the empty vessel and equalize itself, and in place of ten pounds a square inch we have only five pounds a square inch.
Let us now suppose that we have a valve in the connecting tube between these two chambers which when open will admit outside air to the amount of 14.7 pounds a square inch. If we now open tin's valve outside air will immediately enter through the valve and into the two chambers and equalize itself. The pressure in both chambers will immediately become the same, and will also be the same on the outside as on the inside. This proves that air is elastic and will equalize itself in space.
To service efficiently any player piano it is absolutely necessary that the player mechanic know the principle on which every unit operates. If these facts are kept in mind it is a very simple matter to trace any trouble and correct it immediately.
In my next article I shall treat the subject, "How and Why a Valve Actuates the Striking Pneumatic"
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