SMALLEST PARTICLE THAT
0.001 INCH
CAN BE SEEN BY UNAIDED
EYE (APPROX. 40 MICRONS)
LARGEST PARTICLE PASSED
BY OLDER TYPE WIRE MESH
FILTERS
LARGEST PARTICLE PASSED
BY PRESENT TYPE WIRE
MESH FILTERS
LARGEST PARTICLE PASSED
BY MODERN SE FILTER
1 MICRON = 1 MILLIONTH OF A METER (1 METER x 10-6 )
1 MICRON = 39 MILLIONTHS OF AN INCH
1 INCH = 25,400 MICRONS
APPROX. CLEARANCE
FOR SLEEVE / SLIDER
SERVO VALVES
0
3
10
20
30
40
ASf08020
Figure 8-20.--Graphic comparison of particle sizes.
A typical micronic filter is shown in figure 8-21.
support equipment. This type filter is still in use but is
not specified in newer equipment.
This type of filter is designed to remove 99 percent of
all particles 10 microns (0.00394 inch) in diameter and
The micronic filter assembly contains an integral
larger. The following discussion will help you to define
bypass valve to prevent possible element collapse or
this capability in meaningful terms: If 100 particles
system starvation. If the micronic filter element
measuring 0.000394 inch in cross section were
becomes loaded, the bypass valve will open when a
dropped into pure hydraulic fluid, a 10-micron filter
predetermined pressure differential exists, allowing
hydraulic fluid to bypass the filter element.
will intercept 99 percent of these in one pass. A
40-micron particle is regarded to be the smallest that
The replacement element is made of specially
can be seen without magnification. A micronic filter
treated cellulose paper, formed in vertical convolutions
assembly contains a replaceable micronic filter
(wrinkles). Generally, the micronic filter element
element and, in some cases, an integral pressure
slides onto the head and is held secure by the filter
differential bypass valve. The micronic filter was first
bowl, which has external threads machined on the
outside and top. A groove machined around the base of
procured in the 1950's and widely used in aircraft and
8-16
