A STAINLESS STEEL
Figure 8-18.--Different types of hydraulic filter elements.
Some filter heads contain a differential pressure
indicator, which gives a visual indication of when the
element should be changed. The bowl or filter case is
the housing that holds the element to the filter head,
and it is removed when the filter element requires
The size of particulate matter in hydraulic fluid is
measured in microns, (millionths of a meter). A micron
is equivalent to 0.0000394 inch, and 25,400 microns
equal 1 inch. The largest dimension of the particle is
TO CHECK FOR
measured when determining its size. For comparison
value, consider that the normal lower level of visibility
CUT AS INDI-
to the naked eye is about 40 microns. (A grain of table
salt measures about 100 microns; the thickness of a
human hair is about 70 microns; and a grain of talcum
powder is about 10 microns.) A graphic representation
of the relative size of particles measured in microns is
shown in figure 8-20.
MICRONIC-TYPE FILTER ELEMENTS.--
Micronic, a term derived from the word micron, can be
used to describe any filter element. Through usage,
Figure 8-19.--T-type micronic filter assembly.
micronic has become associated with a specific filter
with a filtering element made of a specially treated
The bypass filter assembly is used in this type system.
cellulose paper. The paper is formed in vertical
In aircraft hydraulic servicing equipment, the
convolutions (wrinkles) and is made in a cylindrical
non-bypass filter assembly is used because you would
pattern. A spring in the hollow core of the element
not want to service an aircraft system with
holds the element in shape (view B of fig. 8-18).