Air shaft

“ If they are deep, it becomes necessary to commence ventilation of the mere shafts themselves in the course of sinking. This is done344 by driving an air-way—a horizontal tunnel from one to the other, and then establishing an “upcast” in one of them by simply lighting a fire there. This destroys the balance between the two communicating columns of air; the cooler column in the shaft without a fire, being heavier, falls against the lighter column, and pushes it up just as the air is pushed up one leg of an U tube when we pour water down the other. ”

“ It is apparent that if any of the cross-headings nearer to the shaft than the last one should be left open, the air current would take a short course through it up to the airway, and so back to the shaft, without going to the extremity of the gangway at all. ”

“ Sometimes to afford better ventilation shafts 8 or 12 in. in diameter are sunk exclusively for the purpose of changing the air. When the inside temperature is equal to that outside, as often happens during the spring and autumn, there are no drafts, and consequently the air in the excavation is not renewed and becomes foul; then fires are lighted under the shaft and a draft is artificially produced. The hot air going out through the shaft, as through a chimney, allows the fresh air to come in as in ordinary ventilation. ”

“ To establish a proper air current, the usual method is to keep a large fire continually burning at the bottom of one of the two shafts of the pit, or of one of the two compartments of the single shaft, and the difference of temperature thus caused between the column of air of the upcast shaft and the downcast becomes the motive power which impels or drags the air current in obedience to it. ”

“ The higher the Shaft of the Chimney is, the Fire draws the Air the better. And this Invention may be made use of in the Pits or Shafts, that are Perpendicular, or any wise inclining towards it, when there is want of fresh Air at the bottom thereof ”

“ It is almost invariably found that where plain open pipes are used, or have merely a cap on the top to exclude rain, they are stopped up on account of the downdraught experienced.
" Gusts of wind will sometimes cause a reverse action in the tube. In hot weather if the shaft is colder than the outer air a down current may ensue.
" In consequence of the numerous causes of disturbance enumerated above, this method of extraction, when applied to a house, could not be relied on to act on all occasions with certainty as an extraction shaft."—Sir Douglas Galton, F.R.S.
Revolving Ventilators. ”

“ The hot air in the shaft, being lighter than the cold air outside it, tends to rise, and as it does so air flows in at the bottom to take its place. An ascending current is thus established in the chimney, its velocity, other things being equal, varying as the square root of the height of the shaft above the grate. The velocity also increases with increase of temperature in the gas column, but since the weight of each cubic foot grows less as the gases expand, the amount of smoke discharged by a chimney does not increase indefinitely with the temperature ”

“ The general plan of distributing the air, in all cases, is to send the first of the current that descends in the downcast shaft among the horses in the stables, next among the workmen in the foreheads, after which the air, loaded with whatever mixtures it may have received, is made to traverse the old wastes. It then passes through the furnace with all the inflammable gas it has collected, ascends the upcast shaft, and is dispersed into the atmosphere. ”

“ When the temperature of outside and inside air becomes equal or nearly so natural ventilation ceases or becomes insignificant. In a mine with two shafts a ventilating current may result from other conditions creating a difference in the temperature of the air in either shaft—for example, the cooling effect of dropping water or the heating effect of steam pipes. Natural ventilation is impracticable in flat deposits worked by drifts and without shafts. ”

“ The aereomotori continue their motion, another revolution of the main shaft shuts the exhaust and opens the equilibrium or admission valve; the column of water is again permitted to act, and the same action is repeated, more air being forced into the recipient at each round or pulsation of the machine. ”

“ If the gas should flow in too great a quantity, the pressure increases on the posterior face of the piston N, the spring is overcome, and the movable system advances a little toward the left; but then the orifices are partly covered and the flow diminishes. If the pressure then becomes too weak at the exit, the spring in its turn prevails, pushes the sheath toward the right, uncovers the orifices, and consequently a greater quantity of air may enter. ”

“ When the sides of the bellows are squeezed together the air molecules within are crowded closer together and the air is compressed. The greater the compression the greater, of course, is the pressure with which the enclosed air seeks to escape. That it can do only by lifting up, that is by blowing out, the two elastic strips which close the end of the pipe. ”

“ Engine-driving columns of air through a building is not ventilating it. . . . It is wholly misleading to take the registered volumes of air forced into or out of a building at certain points as in any way indicating how often in a given time the whole of the air is changed."—Building News.
Note.—When a volume of air is forced in under pressure a certain portion is deflected and descends, as with the downward system, returning the respired air to be reinhaled, also the products of combustion.'
Air Analysis and Defective Ventilation. ”

“ It presses with a weight of about fifteen pounds per square inch of surface, and its pressure is exerted in all directions, upward as well as downward. An ordinary man sustains a pressure of over one ton on each square foot of his surface, but as the air penetrates all portions of his body and exercises a pressure outward as well as inward he feels no inconvenience. If his body could be so tightly sealed that no air could enter and if then the air of the interior should be removed with a pump, his body instantly would be crushed to a shapeless pulp. ”

“ Most air lift propositions are deep-well cases—that is, the water is lifted a distance greater than 25 feet; and just in proportion as the lift is increased do we get away from the aerated form idea, and so when the air pressure is greater than the head of water, a certain volume of compressed air is received into the eduction-pipe, the water in this pipe is at that time moving rapidly upward; that is, its momentum has been established. Hence the air takes up this velocity and goes upward with the water from the energy received from the elasticity of the air due to its compressor. ”

“ By pulling out one of the buttons of the wind chest, we admit the air through eleven holes at a time, having an angular distance of 30° and directing it against the corresponding circle of holes on the turning disk. If the arrangement of holes is not repeated identically twelve times on the same circle, we cannot, of course, make use of the above arrangements of holes of the wind tube, and we must then employ one of the movable brass tubes, which communicate with the interior of the wind chest by means of rubber tubes and stopcocks. ”

“ It uses the force of the wind, whenever there is a current passing over the top of the building, for sucking the air out of the ward, because the air in passing across the top of the building is deflected from the straight line by the angle of the roof-board, which creates a partial vacuum in the space below, which, with the friction of the passing current with that coming out of the ward, makes an outward draught, varying in proportion to the velocity of the external current. ”

“ Besides merely forcing the steam and water through the radiators and piping, it is necessary to force out the air which accumulates, and to do this the system must carry a pressure somewhat above that of the atmosphere, unless a vacuum system, which will be described later, be used. ”

“ Now, the property I am going to tell you about this evening is this—that, if the man lets go of the piston rod, the air that is condensed into the bottom of the cylinder, will spring up, and force the piston up again. This property is called elasticity. It is sometimes called the expansive force of the air. For it is a force tending to expand the air, that is, to swell it out into its original dimensions. ”

“ Of the more usual mechanical aids at the disposal of the glass-blower, we have already mentioned hand-tools, blocks, and moulds of various kinds. Next in importance to these is the use of compressed air91 for blowing large or heavy articles; the pressure available by the human breath is very limited, and the volume of air that can be thus delivered is not very large, while the constant use of the lungs for such a purpose is trying for the workman. ”

“ By the action of the ram at each stroke, a partial vacuum is formed below the air chamber, and the air rushing through the small hole in the inlet pipe, passes into the air chamber, making good that which the water absorbs. ”

“ A bag full of air, such as a common air-cushion, can be squeezed till the air in its interior occupies a much smaller volume; and, if you treat a syringe full of air in the same way as the syringe full of water was treated, you will find, if the piston fits well, that it can be driven down some distance and then springs back again. Air in fact is not only a compressible, but it is an elastic fluid or gas. Heat expands air just as it expands water, but the expansion of air for the same degree of heat is much greater.
36. Steam is an Elastic Fluid or Gas. ”

“ Five minutes later, he was back in the airshaft, wielding his broom energetically. He forged on to the front of the group, heading further and further along in the airshaft, until finally he came to the place he was looking for—the tube that led to the heart of the air supply. ”

“ I would shut off the air-escape valve on my helmet, so that the air being pumped in would inflate my india-rubber dress like a bladder. Then I would cut my air-pipe and communication cord, stuffing the pipe and tying it as best I might, take off my leaden shoes and rise to the surface triumphantly, like an air-cushion, or, say, an oil barrel. Specific gravity having taken a rise—all the rise—out of me, I would proceed to take a rise out of specific gravity; a great, glorious, and effective rise to the upper world. ”

“ If an independent chest be employed, its closeness to the ground renders it possible for dust easily to pass through the air-holes in the walls at the moment of suction, and even to enter the cylinder, where its presence is particularly harmful, leading, as it does, to the rapid wear of the rubbing surfaces. ”

“ This apparatus consists of two hollow brass hemispheres of 420 to 41⁄2 inches diameter, the edges of which are made to fit tightly, and are well greased. One of the hemispheres is provided with a stop-cock, by which it can be screwed on to the air-pump, and on the other there is a handle. As long as the hemispheres contain air they can be separated without any difficulty, for the external pressure of the atmosphere is counterbalanced by the elastic force of the air in the interior. ”

“ The low pressure (partial vacuum) draws blood to the part. Cupping is used in congestion of internal organs, e.g. lungs, kidneys.
The artificial application of air to lungs at varying pressure is carried out by inspiring rarefied air or compressed air and expiring into rarefied air or into compressed air. Only inspiring compressed air, or expiring into rarefied air, can be practically applied. There are many kinds of apparatus for this. The best is the compressed-air bath (seen at Brompton Hospital, London) , consisting of three parts—the engine, receiver, and air-chamber. ”

“ The air in the tube is an elastic substance, and it resists compression. At constant temperature the volume into which the air is squeezed is inversely as the pressure applied.
The air, therefore, possesses elasticity of bulk, as it is called, and it resists being made to occupy a smaller volume. Again, the air possesses inertia, and when it is set in motion it continues to move like any other heavy body, after the moving force is withdrawn. We have, therefore, present in it the two essential qualities for the production of a wave-motion, as explained in the first lecture. ”

“ The suction nozzle through which the material enters the system, together with the “free air” which is to act as the conveying medium.
Pumps and Exhausters. The type of apparatus used for creating the flow of air varies according to the ideas of the numerous makers of the plants. It must be remembered that for a pump working under the conditions required for pneumatic plants it is not a high vacuum that is required; the most [Pg 11] important function is to handle very large quantities of air at a comparatively low vacuum. ”

“ The region in the rear of the plane is occupied by the turbulent “dead-water” at a pressure below that of the undisturbed fluid. When a hole is made in the plane, the air flows through from the front to the rear under the influence of the difference of pressure between its two faces. The stream of air finding its way through the perforation carries with it an amount of momentum per second, equal to the force of which the plane is relieved. ”

“ Any pressure brought to bear on the column of liquid contained in the porous duct of a plant, must quickly cause the expulsion of a contained air-bubble through the minute openings in the coats of the duct. The greater molecular mobility of gases than liquids, implies that air will pass out far more readily than sap. Whilst, therefore, a slight tension on the column of sap will cause it to part and the air to enter, a slight pressure upon it will force out the air and reunite the divided parts of the column. ”