Blower
The name now applied to designate almost all descriptions of machines for creating an artificial current of air by pressure. It is claimed for the positive pressure-blowers, now in constant use, that they measure and force forward at each revolution a fixed quantity of air, whether the pressure be high or low or the speed fast or slow; and the amount of air delivered can be accurately determined and controlled, and the exact quantity necessary to effect the perfect combustion of a given amount of fuel at a given time supplied with perfect certainty.
The blowing-engine or piston-blower also gives a forced blast, but it is not so good for the cupola as the positive blower, because the blast produced is irregular and comes in puffs with every motion of the piston, making it necessary to provide a large receiver to equalize the blast. This is, of course, both expensive and bulky. This class are sometimes called cylinder-blowers.
The common fan-blower, a rotative blowing-machine, consisting of vanes turning upon an axis, has nothing positive in its operation. The wings merely beat the air, imparting a momentum corresponding with the velocity, but, as resistance is opposed to the blast, the volume is diminished in the ration of the resistance till a point is reached where the momentum and the resistance are equal, when no air whatever is discharged; but the fan-wheel continues to revolve in the case with great rapidity, absorbing a large amount of power, but doing no work at all. See CUPOLA; BLAST; COMBUSTION.