Arthur De Wint Foote

“ The actual transmission of power by air from the compressor to the motor is simple and effective. The air admits of a velocity of 15 to 20 ft. per second through pipes, with very slight loss by friction, and consequently there is no necessity for an expensive pipe system in proportion to the power transmitted. It is found in practice that, allowing a velocity as given above, there is no noticeable difference in pressure between the compressor and the motor several miles away. ”

“ Such “ isothermal compression ” is never reached in practice, the best work yet done lacking 10% of it. It follows that the most inefficient compressing machine is one which takes away no heat during compression-that is, works by “ adiabatic compression, ” which in practice has been much more nearly approached than the ideal. It also follows that the ideal motor for using compressed air is one which will supply heat to the air as required when it is expanding. Such “ isothermal " expansion is often attained, and sometimes exceeded, in practice by supplying heat artificially. ”

“ Many stone quarries have a central plant for compressing air, which is transmitted through pipes extending to all working points, and operates derricks, hoists, drills, stone cutters, &c., by means of motors. Every considerable ironworks, railroad shop or foundry has its pneumatic transmission plant. Also in the erection of the larger steel bridges or buildings a pneumatic transmission system is part of the contractor's outfit, and many railways have a portable compressing plant on a car ready to be moved to any point as needed. ”

“ The reason for this is, the heat supplied to the air is used nearly five times as efficiently as an equal amount of heat employed in generating steam.” Practically there is a hotair engine, using a medium much more effective than common air, in addition to a compressed-air engine, making the efficiency of the whole system extremely high. ”

“ It is used Very successfully, however, both in Europe and in America., in underground mine haulage, being especially adapted to coal mines, where electricity would be dangerous from its sparks. The copper smelting Works at Anaconda, Montana., U.S.A., uses twelve large pneumatic locomotives for charging the furnaces, removing slag, &c. ”