Compressed-air Motors

Compressed-air Motors. One mode of employing air as a motive power has been described under AIR-ENGINE (q.v.). Another obvious way is to compress the air and then apply it in the manner of high-pressure steam. But the great loss of power, due principally to the dissipation of the heat which results from the high compression of the air, will always render the employment of such a motive power very wasteful. There are, however, many conditions under which the use of compressed air is convenient and advantageous. The air-gun, although more a toy than a useful weapon, is one of the oldest examples of a compressed-air motor. Partly by compression and partly by exhaustion of air, pneumatic tubes are worked in connection with central post-offices for the transmission of letters and messages to and from various districts in large cities. In boring in mines, and in blasting and tunnelling operations, compressed air is an exceedingly useful agent, the power being easily carried by tubes into confined areas where the air when liberated, after it performs its primary duty, is of great value for aiding the ventilation of the spaces (see BORING). In the application of automatic brakes to passenger trains, compressed air has also been found to be the most convenient power (see BRAKE). Air compressed and stored in a reservoir under the vehicle has also been proposed as a motive power for tramway cars. In a different direction the agency of compressed air is important in the artificial production of cold for chilling-houses for meat-preservation on land, and for frozen-meat chambers for preserving fresh meat on board vessels (see REFRIGERATION).