All atmospheric air contains some water vaporwhich will begin to condense into liquid water inthe compressed air or gas system when the air orgas cools past the saturation point, i.e., the pointwhere it can hold no more water vapor.*The temperature at which this happens is knownas the dew point.** This dew point becomesall-important in determining how much dryingis needed.Condensation in the compressed air system wouldoccur at the inlet air saturation temperature if temperatureremained constant as air was compressed.However, since there is a rise in temperature duringactual compression, condensation generally isavoided within the compressor. Later, as compressedair is discharged and cooled in an aftercooler,condensation begins to occur. The condensedmoisture must be removed by a separator and trap.The air leaving the aftercooler normally is saturatedat the aftercooler discharge temperature.For many years, problems from moisture in airlines were tolerated. To prevent freezing, alcoholswere injected into the lines and electric heaterswere used during cold periods. Filters were used toseparate moisture and other contaminants but didnot completely solve the problem.The increased use of compressed air and the developmentof many new and more sophisticateddevices and controls have accelerated the need forclean dry air. Hence, drying technology advanced,and dryers came into general use