amounts of water, hydrolyze to form hydrochloric
Air Contamination
acids. These acids attack internal metallic surfaces in
Hydraulic fluids are adversely affected by
the system, particularly those that are ferrous, and
dissolved, entrained, or free air. Air may be introduced
produce a severe rust like corrosion that is virtually
through improper maintenance or as a result of system
impossible to arrest. Extensive component overhaul
design. Air is sometimes introduced when changing
and system decontamination are generally required to
filters. You can minimize this kind of contamination by
restore the system to an operational status.
putting hydraulic fluid into the filter holder before
Foreign Fluids Contamination
reassembling the filter. By doing this, you have
introduced less air into the hydraulic system. The
Contamination of hydraulic fluid occurs when the
presence of air in a hydraulic system causes spongy
wrong fluids get into the system, such as oil, engine
response during system operation. Air causes
fuel, or incorrect hydraulic fluids. Hydraulic oil
cavitation and erodes hydraulic components. Air also
coolers, which are used in some aircraft, leak and cause
contributes to the corrosion of hydraulic components.
contamination of hydraulic fluids. If you think that
contamination has occurred, the system must be
Water Contamination
checked by chemically analyzing fluid samples. This
Water is a serious contaminant of hydraulic
analysis is conducted by the cognizant engineering
systems. Corrective maintenance actions must be taken
activity, which verifies and identifies the contaminant
to remove all free or emulsified water from hydraulic
and directs decontamination procedures.
systems. Hydraulic fluids and hydraulic system
The effects of foreign fluid contamination depend
components are adversely affected by dissolved,
upon the nature of the contaminant. The compatibility
emulsified, or free water. Water may be induced
of the construction materials and the system hydraulic
through the failure of a component, seal, line or fitting,
fluid with the foreign fluid must be considered when
poor or improper maintenance practices, and servicing.
dealing with contamination. Other effects of this type
Water may also be condensed from air entering vented
of contamination are hydraulic fluid reaction with
systems.
water and changes in flammability and viscosity
The presence of water in hydraulic systems can
characteristics. The effects of contamination may be
result in the formation of undesired oxidation products,
mild or severe, depending upon the contaminant, how
and corrosion of metallic surfaces will occur. These
much is in the system, and how long it has been in the
oxidation products will also cause hydraulic seals to
system.
deteriorate and fail, resulting in leaks. If the water in the
Q8-7. What type of contamination is most often
system results in the formation of ice, it will reduce
found in aircraft hydraulic systems?
fluid flow and impede the operation of valves,
Q8-8. What unit of measurement is used for
actuators, or other moving parts within the system. This
particulate matter?
is particularly true of water located in static circuits or
system extremities and subject to high-altitude,
Q8-9. Oxidation of hydraulic fluid can produce
low-temperature conditions. Microorganisms will grow
what type of contaminants?
and spread in hydraulic fluid contaminated with water.
Q8-10.
Most metallic contamination in a hydraulic
These microorganisms will clog filters and reduce
system is produced by what component?
system performance.
Q8-11.
The presence of air in a hydraulic system has
Solvent Contamination
what effect?
Solvent contamination is a special form of
SAMPLING POINTS
foreign-fluid contamination. The original con-
taminating substance is a chlorinated solvent
LEARNING OBJECTIVES: Identify the
introduced by improper maintenance practices. It is
procedures for sampling hydraulic fluid.
extremely difficult to stop this kind of contamination
Identify the sampling point requirements.
once it occurs. This type of contamination can be
A fluid sampling point is a physical point in a
prevented by using the right cleaning agents when
hydraulic system from which small amounts of
performing hydraulic system maintenance. Chlorinated
hydraulic fluid are drawn to analyze it for con-
solvents, when allowed to combine with minute
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