MAINTENANCE PRACTICES
NOTE: Do not use chlorinated solvents to clean
connectors. Use dry-cleaning solvent MIL-PRF-680 or
Good housekeeping and maintenance practices
filtered hydraulic fluid.
help eliminate problems caused by contamination. Be
Store O-rings, tubing hoses, fittings, and com-
careful if you work on a hydraulic system in the open,
ponents in clean packaging. Do not open or puncture
especially under adverse weather conditions. Use cau-
individual packages of O-rings or backup rings until
tion if you work on hydraulic equipment near grinding,
just before you use them. Do not use used or
blasting, machining, or other contaminant-generating
unidentifiable O-rings. Replace seals or backup rings
operations. Often, you cannot see harmful grit. Do not
with new items when they have been disturbed. Use the
break into hydraulic sys tems unless absolutely
correct O-ring installation tool when you install
necessary (this includes cannibalization). Use the
O-rings over threaded fittings to prevent threads from
proper tools for the job. Use only authorized hydraulic
damaging the O-ring.
fluid, O-rings, lubricants, or filter elements. When
dispensing hydraulic fluid, make sure you use an
If packages of tubing, hoses, fittings, or compo-
authorized fluid service unit. Check to make sure that
nents are opened when received or found opened, de-
the hydraulic fluid can is clean before it is installed.
contaminate their contents. Decontaminate the system
After use, dispose of all empty hydraulic fluid cans and
if you suspect it is contaminated (including water).
used hydraulic fluid in accordance with Navy and local
Keep the working area where hydraulic components are
hazardous material (HAZMAT) instructions. Keep
repaired, serviced, or stored clean and free from
hydraulic fluid in a closed container at all times.
moisture, metal chips, and other contaminants. Perform
required periodic checks on equipment you use to
Keep portable hydraulic test stand reservoirs above
service hydraulic systems. Use hydraulic fluid
three-quarters full. Seal all hydraulic lines, tubing,
MIL-H-46170 in stationary hydraulic test stands.
hoses, fittings, and components with approved metal
closures. You should not use plastic plugs or caps
Q8-4. What is the maximum acceptable Navy
because they are possible contamination sources.
Standard Class hydraulic fluid particulate for
Install quick-disconnect dust covers. Store unused caps
naval aircraft?
and plugs in a clean container.
Q8-5. What manuals specify how aircraft hydraulic
Remove exterior contaminants by using approved
fluid sampling is conducted?
wiping cloths. Lint-free wiping cloths should be used
Q8-6. What are the four approved lubricants to be
on surfaces along the fluid path. If possible, have the
used on O-ring seals?
replacement component on hand for immediate
installation upon removal of defective component.
TYPES OF CONTAMINATION
Replace filters immediately after removal. If possible,
fill the filter bowl with proper hydraulic fluid before
LEARNING OBJECTIVE: Identify the
you install it to minimize the induction of air into the
types and sources of hydraulic contamination
system. Do not reset differential pressure indicators if
found in naval aircraft.
the associated filter element is loaded and in need of
There are many different forms of contamination,
replacement. When cleanable filter elements are
including liquids, gasses, and solid matter of various
removed from hydraulic systems, put them in
composition, size, and shape. Normally, contamination
individual polyethylene bags and forward them to the
in an operating hydraulic system originates at several
intermediate- or depot-level maintenance activity for
different sources. The rate of its introduction depends
cleaning. Do not clean cleanable filter elements by
upon many factors directly related to wear and
washing them in a container and blowing them out with
chemical reaction. Contamination removal can reverse
shop air. Cleanable filter elements must be cleaned and
this trend. Production of contaminants in the hydraulic
tested according to applicable procedures before they
system increases with the number of system
are reused. Clean all connections, interconnect the
components. The rate of contamination from external
pressure and return lines of the stand, and circulate the
sources is not readily predictable. A hydraulic system
hydraulic fluid through the test stand filters before
can be seriously contaminated by poor maintenance
connecting portable hydraulic test stands to aircraft.
practices that lead to introducing large amounts of
external contaminants. Poorly maintained SE is another
source of contamination.
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