The compressor may be driven by a steam engine or in any other convenient manner.
The compressed air, leaving the compressor at the temperature T2, passes through the cooler, where it is cooled by means of water, and is then admitted to the expansion cylinder, where it is expanded to atmospheric pressure, performing work on the piston.
Another, perhaps the principal, feature was the interchanger, an apparatus whereby the compressed air was further cooled before expansion by means of the comparatively cold air from the room in its passage to the compressor, the same air being used over and over again.
Further, though the interchanger is still used by some makers, it has been found by experience that, with properly constructed valves and passages in the expansion cylinder, there is no trouble from the formation of snow, when, as is the general practice, the same air is used over and over again, the compressor taking its supply from the insulated room.
With dry compression, vapour alone is drawn into the compressor, and the temperature rises to as much as 180 or 200 degrees.
This is known as the membranous urethra, and is very narrow, being gripped by the compressor urethrae muscle.
Compressed-air Machines.-A compressed-air refrigerating machine consists in its simplest form of three essential parts -a compressor, a compressed-air cooler, and an expansion cylinder.
The compressor draws in air from the room and compresses it, the work expended in compression being almost entirely converted into heat.
The refrigerator, which, Refrigerator Condenser T, Compressor consists of a coil or series of coils, is connected to the suction side of the pump, and the delivery from the pump is connected to the condenser, which is generally of somewhat similar construction to the refrigerator.
Mitted to the coils through an adjustable regulating valve, and by taking heat from the substance outside is evaporated, the vapour being continually drawn off by the compressor and discharged under increased pressure into the condenser.
This liquid enters the compressor with the vapour, and is evaporated there, the heat taken up preventing the rise in temperature during compression which would otherwise take place.
Wet compression theoretically is not quite so efficient as dry compression, but it possesses practical advantages in keeping the working parts of the compressor cool, and it also greatly facilitates the regulation of the liquid, and ensures the full duty of the machine being continuously performed.