BLOWING Machines, in the arts and manufactures, and in domestic economy, are instruments for producing a continued current of air, principally for the purpose of facilitating the combustion of fuel. The first idea of such a machine was doubtless derived from the lungs, which we are constantly in the habit of using for the purpose of blowing, but more especially in the simple and useful application of the blow-pipe.

Of these different machines, the common bellows bears the greatest resemblance to the lungs, and was in all probability the first contrivance for artificial blowing. In the first instance, this instrument might be a simple bag, capable of distension by a mechanical force, the air being drawn in and pressed out of the same aperture in the manner of breathing. The first improvement upon this simple form would be to admit the air by a valve opening inwards when the bellows were distended, the blast outwards being from another aperture. This improvement consists in the air being admitted at a wider aperture, which fills the bellows in less time than would be required by the small pipe through which the air is allowed to escape. The blast, in this state of the machine, is not continuous, but in puffs, at intervals of time required for the air to enter the bellows through the valve; the blowing interval being to the filling interval as the areas of the apertures. This irregular blast was for some time remedied by employing two bellows which blew alternately, the blowing on one taking place while the other was filling. The inconvenience, however, was but partially remedied by this contrivance. The invention of what are called double bellows must have been considered a valuable acquisition in the art of blowing. But previous to describing these, it will be necessary to give a description of single bellows above mentioned.

It will be needless, however, to say more than refer the reader to common domestic bellows, which are in every respect the same as the single bellows first used. The leather nailed to the upper and lower boards is prevented from collapsing, when the boards are separated, by a hoop of wood contained within, performing the office of the ribs in the sternum of animals, without which the breathing would not be performed. The lower board contains the valve which admits the air. When the two boards are separated, the air lifts the valve in entering the cavity. Men full of air, the closing of the boards causes the air within to close the valve, thus preventing its return in that direction, and compels it to escape at the pipe, the mouth of which is called the nozle or nose-pipe.

In order to conceive the construction of the double bellows, we have only to take a third board of exactly the same shape as the other two, and connect it with the lower board by a piece of leather similar to that of the single bellows, making two cavities exactly similar, and separated by the lower board of the single bellows, which now becomes the middle board of the double bellows. The third board we shall now call the lower board. This latter has a valve in it exactly similar to the first, which still retains its place in the new construction.

The middle board is now fixed in a horizontal position, the pipe being placed to the fire to be blown. The lower board is held down by a weight, which keeps the lower cavity constantly full of air. The top board has a weight laid upon it, which presses all the air out of the upper cavity through the pipe.

The machinal action by which the blowing is performed is, first, to lift up the lower board. This forces the air from the lower into the upper cavity, the valve in the middle board preventing its return. The weight on the upper board now presses the air with a uniform blast through the pipe. During this time the lower board descends, which fills the lower cavity with air from the atmosphere; and this again rises and gives its contents to the upper cavity, and thence passes through the nose-pipe. Hence we see that that irregular puffing blast which belongs to the single bellows is here confined to the lower board, which supplies air to the upper cavity, while the upper board is constantly pressing uniformly upon the air in it. Although this is a considerable improvement upon the single bellows, it does not completely obviate the irregularity of the blast. So long as the lower board is not in action, the pressure on the upper board being uniform, the blast is the same. Every time, however, the bottom board rises to force the air into the upper cavity, an extra pressure is given to the air in the upper cavity, and a temporary puff is produced. In the application of bellows to the smith’s forge, the continued blast was of less importance than in the blast-furnaces applied to the smelting or refining of ores. The single bellows are at present almost exclusively employed by anchor-smiths and cutlers; while the blacksmith and most others use double bellows, which are doubtless better for all purposes.

In France and other parts of the Continent, bellows have been formed entirely of wood, instead of the flexible sides of leather, which serves to increase and diminish the capacity. The wooden bellows consist of two boxes, each open on one side, the one being just capable of containing the other; the outer box being placed with the mouth upwards, the other is made to descend into it with the mouth downwards, the latter being capable of moving up and down, while the other remains fixed. In the bottom of the fixed box is a valve like the common bellows, and a pipe on the same level to let out the blast. The change of capacity, by the motion of this box, causes the blast, and with less waste of power than that occasioned by the bending of the leather in the common bellows. This advantage is, however, probably more than compensated by the loss of air from the box not fitting on the sides. See a description of this and some other blowing-machines under Pneumatics.

The common smith’s bellows have lately been construct-1 ed of a circular form. The boards of these bellows arel round, and the movable boards parallel to the horizon and to each other. We have given a view of this construction in Plate CX, figures 4 and 5. A is the blast-pipe, B the movable lower board, C the fixed board, into which the pipe is inserted, and D the upper movable board, on which is placed a weight to regulate the strength of the blast. Motion is given to the lower board by the lever L, and the chain H working on the roller R.

The form of these bellows being cylindrical, the weight required to produce a certain pressure and strength of blast will be easily determined. If the diameter be one foot, the area will be 113∙19 inches. The most convenient and proper[7:4:718] blast for smiths’ bellows is about į lb. upon the inch, or from that to ∣ lb. The upper board, in this case, would require a weight of 56∙5 to give a blast equal to half a pound upon an inch. This pressure would give a velocity equal to about 207 feet in a second. If the diameter of the nose-pipe be changed, the number or length of the strokes, or both, must be changed, in order that the pressure and the corresponding density of the blast may remain the same. If the number and length of the strokes be kept up, and the aperture diminished, at the same time that the capacity of the bellows admits not of enlargement, the pressure and density of blast will be increased, although no additional weight be laid on. This frequently happens in the smith’s bellows when he makes an increased effort to blow after the upper cavity is full. It is much better, however, not to exert the bellows in this way when a stronger blast is required, but to produce the effect by an additional weight. A very strong blast is found to be injurious to the iron when welding heats are required, and still more so in working steel. It is much better that an increase of air, which is frequently wanted, should be furnished by increasing the aperture, supposing the power to be at the time adequate to keep up the increased supply. Bellows should therefore be so constructed that the pressure may be uniform, and not immediately under the control of the workman. When he wishes to quicken his heat, he should have the means of increasing the aperture by a circular plate turning on an axis at right angles to the length of the pipe, as seen in fig. 9. When in the position ab, the whole area is filled; when in that of cd, the air passes in its full quantity. The index being placed at any intermediate points er, will let in any proportionate quantity required.

The aperture might be made to change, by the increase of power upon the machine, and thus caused to regulate itself. Several simple contrivances of this kind may be applied by any one skilled in machinery.

These improvements would render the common leather bellows, of the form above given, very useful for smiths. The irregular blast occasioned by their present construction is found to be very injurious to the iron, both as to its quality and economy. This is abundantly shown in the use of some blowing machines lately invented, which have the advantage of a blast that is uniform, and at the same time much softer, being produced by a small pressure.

These blowing machines are also found to answer very well for melting cast iron, the soft blast having less tendency to destroy the carbon, and the quantity of air being compensated by increasing the aperture.

One of these machines is the invention of Mr Street, for which he took out a patent. It consists of a barrelshaped vessel, from four to five feet in diameter, and of a length more or less proportionate to the work it has to perform.

This cylinder is supported on two bearers by the two ends of its axis, like a barrel churn. The cylinder is divided into two equal parts by a plane in the direction of its length, fitting .the two ends and the upper side, watertight, and extending downward to a small distance from the opposite side. This septum is in a perpendicular position when the cylinder is at rest. When this vessel is partly filled with water, and is made to pass through a certain space on its axis, the air which occupies the upper part of the vessel will be compressed on one side by the water, which flows from one side of the septum to the other, and will become in the same degree rarefied on the other, from a contrary cause. If, however, in this situation, a valve be made to open inwards from the atmo-spheιe on the rarefied side, and another to open outwards on the condensed side, two equal and contrary currents will be established, one inwards and the other outwards. On the returning stroke both these valves will shut, and the other two sides will be put in the same situation with the first cavities. If, now, two similar valves to the last be introduced, two similar currents will be produced. If the two valves at which the air escapes from the machine, one on each side of the septum, be made to communicate with one cavity from which a nose-pipe proceeds, while the other two valves communicate with the atmosphere, every stroke will discharge a quantity of air through the nose-pipe from one cavity, and introduce the same volume of air from the atmosphere into the other cavity. These strokes are produced by the oscillating motion of the machine, the limit of its vibrations being about a quarter of the circle, or 90°.

These alternate puffs of air are first propelled into a vessel containing water to regulate the blast. This vessel is divided into two portions by a septum, which passes from the close cover at the top nearly to the bottom. When the air is forced into the cavity, which is close at the top, it expels the water under the septum at the bottom into the open cavity, so as to keep a constant head in the latter, compressing the air in the former. From this airchest a nose-pipe proceeds to the fire, and the air escapes from it with a uniform velocity so long as the same column of water in the chest is preserved. This description answers to the first machine of the inventor; he has since taken out a second patent, the specification of which is given in the Repository of Arts, vol. xxviii. p. 193. We shall here give a description of this machine, with the patentee’s improvements. See Plate CX. figs. 1, 2, and 3.

Fig. 1 is a longitudinal section of this machine. AB is the cylinder resting upon the axis ab and cd, which are supported on the uprights gg. The oscillating motion is given to it by a rod working upon the pivot p, the other end of which is connected with a crank of such a length as to cause the cylinder to move through an arch of 90 degrees. The vessel is filled with water to the height ws.

The part CBD (fig. 2) is cut off from the rest of the cylinder by two planes meeting at c, and continuing down to the axis x, so as to work upon its convex surface. These planes extend the whole length of the cylinder, and are then divided transversely into three cavities GHI, as seen in fig. 1. The cavity G is for the reception of the external air, and is called by the patentee a receiving box. The cavity H is open to the atmosphere, the periphery of the cylinder being removed in that part. The cavity I is appropriated to the air which is driven out of the machine, through the valves tt and qq (fig. 3), which open alternately on each side. The cavity G is divided longitudinally in the middle, forming two cavities, m and n, fig. 2; two valves, e and f, fig. 1, open into each, one from the end of the cylinder, and the other from the cavity II. Each of the cavities m and n communicate with the body of the cylinder by the holes hh in the dividing planes. The cavity I has no division, as it receives the air from both sets of exit valves, which escapes at the pipe P.

The axis av works within the axis ab and cd, and is rendered air-tight by a stuffing-box within the latter. This axis will have the effect of remaining at rest while the cylinder is in motion, there being no other force exerted to turn it than the friction of the stuffing-box. The use of this axis is to support and turn a swing valve MV, which is made of rolled iron, strengthened by ribs connected with the axis. This valve is a plane, which would exactly sweep the interior surface of the cylinder without touching it. If the axis vx be held fast, the valve will retain its perpendicular position, while the cylinder performs its vibrating motion. The water would also remain at [7:4:719]rest, with the exception of the motion which its friction and the compression of the air occasions. When the machine moves from D (fig. 3) till the plane DC comes very near to the surface of the water ws, the valves qq open, and a volume of air equal to the space DCS will be expelled through the cavity I (fig. 1), along the pipe P, during the time the valves in the cavity m (fig. 2) have opened to admit the same volume of atmospheric air on the returning stroke. The point B is carried the contrary way, by which another portion of air opens the valves tt to pass through the pipe P, while the same volume of air from the atmosphere enters the cavity n, which in its turn is forced through the exit valves tt.

The use of the swing valve MV will now be obvious. If it did not exist, every time the air was compressed on one side the water would be depressed on that side, and the compression of the air would be limited by the increased column of water on the other side. This valve, however, prevents the water from immediately changing its situation, no more escaping from one side of the valve to the other than what can pass between the edges of the valve and the cylinder, which,-in the short space of one stroke, can be only a very small quantity. This may be considered as a great improvement upon the first machine, which we have before described. The patentee further intends occasionally to give to this swing valve a contrary motion to that of the cylinder, and thus still more to increase the blast. Or, in the use of a very small blast, the valve may be left at liberty, and used merely to prevent the too great agitation of the water, which in the original machine was considered as an objection. Two of those machines are frequently used together, and worked by cranks, forming an angle of 45° with each other, to make the strong part of the blast of the one to concur with the weak part of the blast of the other.

The part I of the exit pipe PL, must be precisely to the centre of motion. The part L works in a stuffing part, or a ground socket connected with the pipe LN. The latter should communicate with a regulator, which the patentee does not describe, but recommends one of water. This may be a vessel at least of the capacity of the cylinder, inverted in a reservoir of water, and may stand near to the bottom. The pipe N is inserted into the bottom, which is now uppermost. The height of the water in the reservoir must be such as to give the required pressure to the air.

When the air is forced into the inverted vessel by the machinery, the water descends in this, and rises in the reservoir, which now gives a pressure to the contained air equal to the difference of the height of the water in the inverted vessel and the reservoir. The surface of the reservoir should be the greatest possible, in order that it may be raised in the least degree by the water coming from the inverted vessel, which will have the effect of keeping the blast more uniform.

The water regulator is certainly the best for smiths’ bellows, for refineries, forges, and perhaps the common melting furnace, but they have been found very objectionable in the blowing of large blast-furnaces. The air m the common blowing engine undergoes a great increase of temperature during its passage through the machine, often as much as 40 or 50 degrees. The heated air has the effect of carrying a greater quantity of water along with it into the furnace, which destroys a larger quantity of carbon than the same bulk of common air, without producing an adequate portion of heat. A great part of the heat of the air is doubtless produced by the friction of the piston of the blowing cylinder, which, in this construction, has a very tight wading. In the blow- ιn g machine above described, the water would doubtless be an objection in blast-furnaces, but, as its little friction would not heat the air like the common blowing cylinder used in blast furnaces, the objection would be less formidable. Air must doubtless give out some heat by its decrease of volume, just as it will absorb the heat by rarefaction, as is experienced in exhausting the receiver of an air-pump. The converse of this is equally shown in the little instrument employed to kindle tinder by condensing the air within it.

The heat by the friction of this piston is probably much more than by the condensation of the air; the latter is obviated in the machine above described, and in another blowing machine lately introduced, of which we shall give a description.

This machine, in its general appearance, does not seem to have any advantage over the common blowing cylinder, but in practice it is found superior.

It resembles in some degree the common smith’s bellows of the Chinese, which consists of a square wooden trunk, in the form of a parallelopipedon. A board is made to fit pretty nearly its cross section, to which is attached a long rod, by which the board is pushed backwards and forwards like a pistbn. At one end of the trunk is a valve opening inwards to admit air, and at the same end is a pipe with a valve opening outwards.

The machine above alluded to as having some resemblance to this, is the invention of a Mr Vaughan, who has fitted up several of them for founderies, and they are much approved. The writer of this article took a drawing from one of these machines employed to melt cast-iron at the Phoenix Foundery in Sheffield.

Figs. 6 and 7 are two views of the machine. ABCD is a square box formed of pieces of cast-metal, screwed together by hinges. Two of these are placed side by side, as may be seen in the end view, fig. 7. MQ is a piston fitting the square box, which is drawn backward and forward by the rod EF, which works horizontally on the wheels wx by the spear G, which communicates with the crank of a wheel at a distance.

The piston MQ, which is the most ingenious part of this machine, is enlarged in fig. 8, to render it clearer. The body of the piston is a cast-iron plate about half an inch thick, with a socket in the middle to receive the rod. The diameter of this plate is about one fourth of an inch less than that of the box. Two pieces of wood, v n, are cut diagonally, in order to place the pieces of leather, l l, between them. These leathers, with the wood, are firmly fastened to the plate by bolts, such as gh.

The leathers extend about two inches beyond the wood; and their slight elasticity keeps them in contact with the metallic surface, which is not required to be very smooth. When the piston moves towards the end of the box, to which the leather projects, the leather claps close to the surface, rendering it air-tight, while the leather on the other side of the piston becomes loose, and has no friction. These leathers will be contrarily acted upon when the piston acts the contrary way. The projecting curved pipes HI form a communication between the box where the piston works and the air-chest N. When the piston moves from B to D, the valves F and V open, while L and S are shut. The air contained in the box is now forced through the valve R into the chest N, and from thence along the blast-pipe P.

In the returning stroke, which is the whole length of the box, the valves R, V, and K, are shut, while L and S open. The air is forced through H to N, and then through P.

Two of these work at the same time by two cranks, which cause one to be in full blast at the time the other is returning the stroke; so that, with due management, [7:4:720]the four puffs produced by two double strokes may be made to succeed each other at equal intervals, which almost amounts to a steady blast. The inventor recommends four of these boxes all to work together, which would produce eight puffs in the time of one double stroke, which, if divided into equal intervals, would produce a sufficiently uniform blast for any purpose.

When the leathers of the piston are rubbed with black lead, the friction almost amounts to nothing. The leather acts so easy to the surface, and is so flexible, that it may be very easily raised with the fingers. This could not be the case if it were applied in the same way in a cylinder; and this is a sufficient reason for using the square box instead of the cylinder.

This machine makes 70 strokes in one minute; the nosepipe, where the blast enters the furnace, is 2∣ inches in diameter. When the length of stroke is the greatest, at the above speed, it furnishes about 1200 cubic feet per minute.

This machine steers clear of the objection of the water, and, from its small friction, will have less tendency to heat the air. Its original cost is also less than any other machine yet constructed. In the situations where it has been adopted it gives the highest satisfaction. The first construction of Street’s bellows, above described, was only fitted for some smiths’ fires, where a very soft blast was required. In their improved state they may be employed for most purposes.

• All the calculations relative to bellows will be easily made, by the following rules and formula:

First, get the space or capacity formed by one stroke of the machine; call this c, cubic feet.

Then get the number of strokes per minute, which call n.

The area of the nose-pipe, in feet, call a.

The pressure on the air to be discharged, whether by a column of water or by a weight, call p. v — the velocity with which the air escapes.

r = the resistance, in pounds, which the blast will give.

Then en — q, the quantity discharged in one minute;

CTí ∙ . CTb and v =—-—in one minute, or = —— for one second. a 60 «

Then, since the resistance is equal to a column of the fluid of the area a, and twice the height to give the velocity, g g ×∖⅛ ~ P ’ ’ hθ weight of 14 cubic feet of air being equal to one pound.

The energy of air in blowing fires is as the quantity, and inversely as the space it occupies. For if the same quantity of air be consumed in half the space, the intensity of the heat, or the temperature of that particular place, will be double. Hence it is found that the same quantity of air, by weight, in winter will produce a greater effect on a blast-furnace than in summer, merely from the difference of density. The great difference in produce of iron in the cold and hot seasons of the year is a fact notorious to iron masters.