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
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