to the naked eye may be contaminated to the point that
it is unfit for use.
Practice proper O-ring installation techniques.
Large particles of impurities in a hydraulic system
indicate that one or more components in the system are
Ensure that hydraulic fluid containers are clean
being subjected to excessive wear. Isolating the
defective components requires a systematic process of
Always dispose of unused hydraulic fluid
elimination. Fluid returning to the reservoir may
remaining in an opened container.
contain impurities from any part of the system. In order
to determine which component is defective, take fluid
Use the proper tools for the job.
samples from the reservoir and various other locations
Before assembling hydraulic components, wash
in the system, including filter bowls.
all parts in an approved dry-cleaning solution.
Take fluid samples in accordance with the
After cleaning parts in dry-cleaning solution, dry
instructions contained in the applicable technical
the parts thoroughly and lubricate with the
publication for the particular hydraulic system, and in
accordance with chapter 7 of the Aviation Hydraulics
Manual. Some hydraulic systems are provided with
permanently installed bleed valves for sampling ports;
NOTE: Use only clean, lint-free cloths to wipe
and dry component parts.
on other systems, lines must be disconnected to
Replace all seals and gaskets during the
provide a place to collect a sample. In either case, while
the sample is being collected, apply a small amount of
pressure to the system. This ensures that the fluid flows
Connect all parts with care to avoid stripping
out of the sampling point, preventing dirt from entering
metal slivers from threaded areas. Install and
torque all fittings and lines in accordance with
applicable technical instructions.
Keep all hydraulic servicing equipment clean, in
Various test procedures are recommended to
good operating condition, and protected from
determine the contamination level in hydraulic fluids.
Analysis Kit 57L414 (fig. 8-48) provides a reasonable
idea of the condition of the fluid. This test consists
If a hydraulic system is known to have been
basically of filtration of a sample of hydraulic system
contaminated by an external source and there is no
fluid through a special filter paper. The darker the filter
damage to the system, simply flush the system to take
care of the problem. Often, however, the problem is
sample tested. It is compared to a series of standardized
more complex and may require checks to determine
filter discs that, by degrees of darkening, indicate the
exactly what the problem is or to locate a component
various contamination levels.
that is contaminating the system.
Fluid sampling points and procedures will vary
with the support equipment type and model. Employ
specific procedures applicable to the particular
Whenever you suspect that a hydraulic system is
equipments and consistent with the general
excessively contaminated, or when the system
operates at temperatures in excess of the specified
maximum, you must make a check of the system. The
filters in most hydraulic systems are designed to
NOTE: Ensure waste oils and fluids are properly
remove most foreign particles that are visible to the
disposed of in accordance with applicable
naked eye. However, visual inspection of hydraulic
environmental instructions and Navy pollution control
fluid may not suffice to determine the level of
contamination, and hydraulic fluid that appears clean