Figure 2-1.-Desiccant air dryer

Figure 2-1.-Desiccant air dryer. After the fluid separator, the air is passed through a telltale oil filter, which removes oil through a combination of mechanical means and absorption. The oil that is removed mechanically drains into a dump trap and is discharged into a waste line as in the fluid separator. The oil that is absorbed causes the absorbing material to change color from pink to deep red, starting at the bottom, as it becomes saturated. Since the absorbing column is in a transparent plastic tube, the color change is visible. Before the color change reaches the red line on the column, the absorbing material is discarded and new material is installed. At this point, liquid oil, liquid water, and some oil vapor have been removed from the air. The air is, in most cases, still saturated with water vapor and still contaminated with oil vapor. After passing through a pressure regulator, which reduces the air pressure and holds it constant, the wet air passes through the most important unit of the system—the purifier-dehydrator. The purifier- dehydrator performs a cleaning step by a process known 2-3