Figure 12-29.--Fin tubing assembly installation.
integral check valves to direct the flow of fluid through
filtration rating is the measurement of the average size
the manifold, filters to clean the fluid prior to its entry
of the openings in the filter element. The nominal
into the main system, and quick-disconnect fittings for
filtration rating is usually interpreted to mean the size
the connection of ground test hydraulic equipment.
of the smallest particles of which 90 percent will be
trapped in the filter at each pass through the filter.
FILTERS
Figure 12-31 shows a typical filter arrangement in a
hydraulic system.
Hydraulic fluid will hold in suspension tiny
particles generated during normal wear of selector
Filters may be located within the reservoir, the
valves, pumps, and other system components. These
pressure line, the return line, or any other location
minute particles may damage or impair the function of
where they are needed to safeguard the hydraulic
the units and parts through which they pass if they are
system against contaminants. Their location in the
not removed by a filter. Because close tolerances exist
system and other design criteria determine their shape
within a hydraulic system, the performance and
and size.
reliability of the entire system depend upon adequate
filtration.
Basic Units
Continuous filtration of hydraulic fluid during
The filter assembly is composed of three basic
system operation is necessary to maintain system
cleanliness. You should use filters that have fine pores
units. The units are a head assembly, a bowl, and a
or openings to allow hydraulic fluid to pass but that are
filter element. See figure 12-32.
small enough to trap contaminant particles. Hydraulic
HEAD ASSEMBLY.--The head assembly is
filter elements are rated in several ways. The absolute
secured to the aircraft structure and connecting lines.
filtration rating is the diameter in microns of the largest
The head assembly of some filters have a
spherical particle that will pass through the filter under
pressure-operated bypass valve, which will route the
a certain test condition. This rating is an indication of
hydraulic fluid directly from the inlet to the outlet port
the largest opening in the filter element. The mean
12-29
