.0055 IN.
MICRONIC
CROSS-SECTION OF
FILTER
A STAINLESS STEEL
ELEMENT
HYDRAULIC FILTER
B
ELEMENT
D
WIRE
SINTERED
MESH
BRONZE
A
ASf08018
C
Figure 8-18.--Different types of hydraulic filter elements.
Some filter heads contain a differential pressure
LOCKWIRE
HEAD
indicator, which gives a visual indication of when the
HOLE
element should be changed. The bowl or filter case is
the housing that holds the element to the filter head,
BACKUP
O-RING
and it is removed when the filter element requires
RINGS
replacement.
RETAINING
RING
Filter Elements
O-RING
The size of particulate matter in hydraulic fluid is
(INSTALLED
IN ELEMENT)
measured in microns, (millionths of a meter). A micron
is equivalent to 0.0000394 inch, and 25,400 microns
ELEMENT
equal 1 inch. The largest dimension of the particle is
TO CHECK FOR
HYDRAULIC,
measured when determining its size. For comparison
SYSTEM CON-
value, consider that the normal lower level of visibility
TAMINATION,
CUT AS INDI-
RETAINING
to the naked eye is about 40 microns. (A grain of table
CATED BY
RING
DOTTED LINES
salt measures about 100 microns; the thickness of a
GROOVE
AND INSPECT
INTERIOR OF
human hair is about 70 microns; and a grain of talcum
ELEMENT.
powder is about 10 microns.) A graphic representation
LOCKWIRE
of the relative size of particles measured in microns is
HOLE
shown in figure 8-20.
BOWL
OR
MICRONIC-TYPE FILTER ELEMENTS.--
CASE
Micronic, a term derived from the word micron, can be
ASf08019
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).
contaminated fluid.
8-15
