AIR COMPRES'SOR, or AIR PUMP. A machine for air. Compressed air is used for a multitude of purposes in the arts and in manufacturing, and to catalogue all of its uses would require a great amount of space. The simplest form of air pump is the little appara tus for inflating bicycle tires, with which nearly every one is familiar. These bicycle pumps are made both single and double acting, the single acting pump being the simplest form of air com pressor. Compared with the enormous air com pressing machines used in shops and mines, this little device seems almost, too trivial to merit notice, but by carefully observing its actions and their effects we have brought to our attention several phenomena which are important facts in air compressing on a large scale. (Inc of these phenomena is the power required to pump against the resistance of the compressed air in the nearly inflated tire; the second and more important is the fact that a very perceptible development of heat results as the pumping Pro ceeds. The bearing of both these observations will appear as we primeed. For the present it need only be observed that hand air pumps j)f the simple form indicated are used for a variety of purposes where only a small amount of com pressed air is required. Where a somewhat larger volume of air is required, hand pumps provided with tly-wheels and operated by one or more men by means of a crank, are employed.
With these large hand pumps we arrive at power air compressors.
The air pump was invented by Otto von fluericke of Magdeburg, (termany. about 11154. In 1753 hull used an air engine for raising water, and in 1788 Stneaton invented a pump for use with diving apparatus. In 1851 c0111 pm:sed air was used by William Cubitt for bridge work, and a little later it was used by Brunel for the same purpose. 10 18•2 Colladon patented the application of compressed air for driving machine drills in tunnel construction. Sommeiller developed Colladon's idea, and eon structed an air compressing plant for the Mont Celli,: Tunnel work. ( See Tux N ELS. ) The SOM" mei] kr compressor was operated as a ram, util izing a natural head of water to force air at 80 pounds pressure into a receiver. The eolumn
of water contained in a long pipe on the side of the hill started and stopped automatically by valves eontrolled by engines. The weight and momentum of the water forced a volume of air with such a shook against a discharge valve that it was opened. and the air was discharged into the tank. The valve was then closed and the water checked, and a portion of it was al lowed to discharge and the space to fill with air, which was in turn forced into the tank. The, injection of water in the form of a spray into the compressor eylinder was first introduced on the St. 1:othard 'num.] work in 1872. The first compressor used in America was developed by Mr. Thomas Doane, the chief engineer of the Iloosac Tunnel, and was employed on that work. This compressor had four single acting cylinders, and was pooled by the injection of water through the inlet valves into the cylinders. These early compressors are of historical interest only at the present time. As the necessity for com pressed air power grew, inventors turned their attention to the design and construction of com pressors which would combine efficiency with light weight and economy of space and cost. As the result of this work, the modern air compres sor has been developed.
The simplest form of power air compressor is the air brake pump. with which practically every American locomotive is equipped. In this pump, it will be readily understood, the main considera tions are economy of space, light weight, and absolute reliability of action; economy of steam consumption being quite a secondary matter. A inch air brake pump, for example. will give 1.85 cubic feet of at 90 pounds pressure, with a consumption of 1 pound of steam at 140 pounds pressure, while a two-stage Corliss air compres sor will give 13.7 eubic feet of air at 90 pounds pressure with the same steam consumption. The standard air brake has a steam cylinder and an air cylinder of the same size, viz., diameter and 10 inch stroke, set vertically I me above t he other. with a CO111111011 piston rod. see Ain BaAky.