BLOWING MACHINES. Machines employed for producing a rapid com bustion of fuel, by furnishing a more copious supply of our than can be obtained by the mere draft of the ordinary chimneys. Although the common bellows is undoubtedly a blowing machine, yet the term is generally restricted in its appli cation to those machines which are employed at large furnaces, as in foundries, forges, &c. Blowing machines are constructed of various forms, the great object in all being, that the blast should be as continuous and uniform as possible. The method of producing such blast by a centrifugal force has long been known, but the first blowing machine on this principle, of which we have a distinct account, is that invented by Mr. Teral, in 1729. It consists of a number of vanes or fanners, radiating from a horizontal shaft, and enclosed within a cylin drical box, having two apertures at opposite sides of the cylinder, to one of which is fitted a conical pipe leading to the furnace, whilst the air enters by the other aperture, and the shaft being turned with great rapidity, a copious and uniform current of air may be impelled through the conical pipe to the furnace. From the great simplicity and cheapness of these machines they have recently been coming into more general notice.
Another kind of blowing machine, and which is very extensively used for smiths' forges, is the double bellows. This machine in form resembles an ordi nary single bellows, but is divided into two parts by a middle board, similar to the bottom board, and like it furnished with a valve opening upwards. The upper and under boards are each loaded with weights, which compress the upper and distend the lower compartments, and the middle board is supported in a horizontal position upon a frame. The pipe or nozzle of the bellows commu nicates with the upper compartment of the bellows only whilst the air is admitted by the valve in the lower compartment. The action of the machine is as follows : The lower board being raised by the brake or handle, the air contained in the lower compartment is driven through the valve in the middle board into the upper compartment, and not escaping from it through the nozzle, as fast as it is forced into it, it elevates the upper board, and thus distends the upper com partment. Upon the descent of the lower board, the valve in the middle board closes, and the upper board descending by the pressure of the weights upon it, the air beneath it is urged through the nozzle in a continuous current. During
the descent of the lower board, the air enters by the valve in the board, and fills the lower chamber of the bellows ; and upon the rise of the board it is forced into the upper chamber as before, and thus a continuous blast is maintained. But although continuous, it is not quite equal, or of a uniform force; for during the up-stroke the air is compressed by a force exceeding that of the weights on the upper board, since it causes the upper board to ascend; but upon the descent of the lower board, the air is expelled by the pressure of the weights alone, which, being at all times the same, the current is then nearly uniform.
Another species of blowing machine is the water bellows, invented by Hornblower, several of which machines have been erected in various parts of the country. The nature of these machines will be readily understood by tbe the following diaeram side figure is vertical section of the machine. a is the fulcrum of the lever or beam, with two inverted vessels b and c suspended from its ex tremities ; these vessels are open underneath, but air-tight above. d and e are two larger vessels, filled with water to the same level in which the vessels b and c rise and fall alternately. g h i is a tube or pipe, which passes through the vessels d and . .
e, and reaches above the surface of the water ; at the extremities are two valves, (omitted by mistake) which respectively open outwards into the inverted vessels, with a pipe at h open to the atmosphere. k and 1 are pipes passing through the bottom of d and e, and extending a little above the surface of the water; they are open at top, and have valves at bottom opening into the trunk o, to which the pipe is fitted which con ducts the blast to the furnace. An alternating motion being imparted to the beam by a steam engine or other first mover, the air passes up the tubes g h i and fills each inverted vessel as they are successively drawn up out of the water; the descent of the inverted vessel closes the valves at g and i, and opens those at the bottom of the tubes k and 1, through which the air is driven forward by the trunk o, and thus, by the reciprocation of the beam, a continual blast is maintained through the trunk o and the tuyere of the furnace.