of the personnel who service and maintain the
equipment. During installation, maintenance, and
repair of hydraulic equipment, the retention of
cleanliness of the system is of paramount
importance for subsequent satisfactory per-
formance.
The following maintenance and servicing
procedures should be adhered to at all times to
provide proper contamination control:
1. All tools and the work area (workbenches
and test equipment) should be kept in a clean,
dirt-free condition.
2. A suitable container should always be
provided to receive the hydraulic liquid that is
spilled during component removal or disassembly.
NOTE: The reuse of drained hydraulic
liquid is prohibited in most hydraulic systems. In
some large-capacity systems the reuse of fluid is
permitted. When liquid is drained from these
systems for reuse, it must be stored in a clean and
suitable container. The liquid must be strained
and/or filtered when it is returned to the system
reservoir.
3. Before hydraulic lines or fittings are
disconnected, the affected area should be cleaned
with an approved dry-cleaning solvent.
4. All hydraulic lines and fittings should be
capped or plugged immediately after discon-
nection.
5. Before any hydraulic components are
assembled, their parts should be washed with an
approved dry-cleaning solvent.
6. After the parts have been cleaned in
dry-cleaning solvent,
they should be dried
thoroughly with clean, low-lint cloths and
lubricated with the recommended preservative or
hydraulic liquid before assembly.
NOTE: Only clean, low lint type I or II
cloths as appropriate should be used to wipe or
dry component parts.
7. All packings and gaskets should be replaced
during the assembly procedures.
8. All parts should be connected with care to
avoid stripping metal slivers from threaded areas.
All fittings and lines should be installed and
torqued according to applicable technical
instructions.
9. All hydraulic servicing equipment should
be kept clean and in good operating condition.
Some hydraulic fluid specifications, such as
MIL-H-6083, MIL-H-46170, and MIL-H-83282,
contain particle contamination limits that are so
low that the products are packaged under clean
room conditions. Very slight amounts of dirt,
rust, and metal particles will cause them to
fail the specification limit for contamination.
Since these fluids are usually all packaged in
hermetically sealed containers, the act of opening
a container may allow more contaminants into the
fluid than the specification allows. Therefore,
extreme care should be taken in the handling of
these fluids. In opening the container for use,
observation, or tests, it is extremely important that
the can be opened and handled in a clean
environment. The area of the container to be
opened should be flushed with filtered solvent
(petroleum ether or isopropyl alcohol), and the
device used for opening the container should be
thoroughly rinsed with filtered solvent. After the
container is opened, a small amount of the
material should be poured from the container and
disposed of prior to pouring the sample for
analysis. Once a container is opened, if the
contents are not totally used, the unused portion
should be discarded. Since the level of con-
tamination of a system containing these fluids
must be kept low, maintenance on the system’s
components must be performed in a clean
environment commonly known as a controlled
environment work center. Specific information
about the controlled environment work center can
be found in the Aviation Hydraulics Manual,
NAVAIR 01-1A-17.
HYDRAULIC FLUID SAMPLING
The condition of a hydraulic system, as well
as its probable future performance, can best be
determined by analyzing the operating fluid. Of
particular interest are any changes in the physical
and chemical properties of the fluid and excessive
particulate or water contamination, either of
which indicates impending trouble.
Excessive particulate contamination of the
fluid indicates that the filters are not keeping the
system clean. This can result from improper filter
maintenance, inadequate filters, or excessive
ongoing corrosion and wear.
Operating equipment should be sampled
according to instructions given in the operating
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