as adsorption There is a difference between absorption
and adsorption.
Absorption takes place in the telltale oil filter when
it removes oil by soaking it up as a liquid (the same way
that a sponge absorbs liquid water into its interior pores).
Adsorption is a surface and a molecular
phenomenon. Mobile gaseous and liquid atoms or
molecules are attracted to the surface of any solid
because of unbalanced forces existing at the surface.
Good absorbents are those that present large surfaces
per unit and have high attractive forces. One cubic inch
of the adsorbent material used in this dryer has an
adsorbent area greater than the area of two football
fields.
The wet air passes through chambers filled with a
molecular sieve type of desiccant, or adsorbing material.
Vapor molecules are left behind on the desiccant and the
air emerges clean and dry.
The dehydrator has two such chambers through
which the air passes alternately. While one chamber is
removing vapor from the air, a small portion of the dried
air is routed through the second chamber to purge it of
all collected vapors and to prepare it to do the drying
during the next half cycle.
The reactivation of the desiccant is completely
automatic, and unless slugs of entrained water or oil are
permitted to enter the desiccant chambers, the material
should not be replaced except at major overhaul. The
fluid separator and the telltale oil filter, located
upstream, prevent slugs of liquid from reaching the
desiccant if they are kept in good operating condition.
The dust filter, located downstream from the
dehydrator, removes any desiccant or other dust
particles that might otherwise be carried along in the dry
airstream. At the outlet of the drier unit, a flow limiter
is used to prevent the electronic equipment from
exceeding the capacity of the dryer. In normal
operation, the flowmeter has no effect. However,
should an air line or waveguide downstream from the
dryer be opened, the flow limiter would prevent an
excessive airflow beyond the capability of the dryer.
DRYER COMPONENTS
In figure 2-1, the placement of the individual
components is shown for a typical dryer. This is the
order that you should expect to see them. The air dryer
is a very reliable piece of equipment and with proper
PM can give you years of service.
The operation of the dryer can be bypassed by
changing the selector valve. With the selector valve in
the position as shown, all air is routed through the dryer.
Starting at the inlet, the individual operation of each
major component will be discussed in depth. Let’s
begin with the fluid separator and its dump trap.
Fluid Separator and Dump Trap
The fluid separator and dump trap consist of two
interconnected assemblies, the separator and the
automatic trap, connected together as shown in figure
2-2. The separator itself is a welded metal tank within
Figure 2-2.—Fluid separator.
2-4
