The use of the swing valve MV will now be ob. vious. If it did net exist, every time the air was . compressed on one side, the water would be pressed on that side, and the compression of the air would be limited by the increased column of water en 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 pais between the edges of the valve and the cylinder, which, in the short apace 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 cy linder, and thus still more increase the blast. Or, in the use of a very small blast, the valve may be left at liberty, and merely prevent the too great agita tion of the water, which, in the original machine, was considered as an objection. Two of these machines are frequently tised together, and worked by cranks, which make an angle of with each other, to make the strong part of the blast of the one to oc sur with the weak part of the other.
The part I of the exit pipe PL, must be precise ly in 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' io reservoir of water, and 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 equal to giving the required pressure to air.
When the air is forced into the inverted vessel by the macbiner, the water descends in this, and rises in the reservoir, which now gives a pressure to the continued 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 which comes 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 melting common :elting furnace, but they have been found very objectionable in the blowing of line blast-furnaces. The air in the common engine, which has been already described under PNEUMATICS in the Encyclopedia, 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 carry. ing 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, out producing an adequate portion of heat. A part of the heat of the air is doubtless pro great duce by the friction of the piston of the blowing cylinder, which, in this construction, has a very tight wadding. In the blowing-machine above described, the water would doubtless be en 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 lest formidable. Air must doubtless give out some heat by its de crease of volume, just as it will absorb the beat by rarification, 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 the air within it.
The heat by the friction of this piston, is probably mur.h 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 blowy. ing cylinder, but in practice it is found superior.