Figure 8-17.--Variable displacement axial piston pump.
filtration is referred to as the filter element. Figure 8-18
shows some typical filter elements.
When small bits of metal, rubber, paper, dust, and
Filters are absolutely necessary to ensure proper
dirt enter into a system, they contaminate the fluid.
operation of hydraulic systems and to achieve long
This may happen in a number of different ways. The
service from the pumps, valves, and other components
of the system. In hydraulic systems, filters may be
manufacturing of the components or during servicing
located within the reservoir, in the pressure line, in the
and maintenance of the system; they can be created in
return line, or in any other location where they are
the system by internal wear of the components, or
needed to safeguard the system against foreign
These impurities can become suspended in the fluid
and circulate throughout the system. Because of the
There are many types of filters, but most filter
in a system must be kept at an acceptable level;
assemblies used in aircraft and support equipment are
otherwise, the components are damaged, destroyed, or
of the T-type shown in figure 8-19. The T-type filter
become clogged and inoperative. For these reasons,
assembly is composed of three basic units: a head
filters are essential in hydraulic systems.
assembly, a bowl, and a filter element. The head
assembly is the part that is attached to the structure and
A filter is a device whose primary function is the
retention, by some porous medium, of insoluble
In most aircraft systems, you must have the
medium is the screening or filtering material that
hydraulic fluid flowing for in-flight hydraulic
allows fluid to flow through it but traps solid particles.
functions. In these systems, it would be better to have
The porous device that performs the actual process of
particle-contaminated fluid than to have no fluid at all.