during SE-powered operation. A makeup reservoir is
a configuration in which all of the system return line
fluid does not pass through the reservoir. Fluid
exchange in the reservoir is limited, and results only
from the changes in fluid volume that occur elsewhere
in the system.
You should be able to use the sampling point after
an aircraft flight, without requiring the use of external
SE. Taking a sample with the aircraft engines turning
is satisfactory, provided no personnel hazards are
involved. You should be able to use the sampling
point when the system is being powered by external
SE, or immediately after such an operation.
The sampling point should be next, or reasonably
close, to the main body or stream of fluid being
A minimum amount of static fluid is
acceptable; however, purge it when you start the
sample flow. Do not take a sample from a point
located in an area of high sedimentation. If you
cannot avoid doing this, make sure sedimentation
effects are minimized by discarding an initial quantity
of the sample fluid drawn.
Ideally, sample fluid
should be obtained from turbulent high-flow areas.
When you take a sample at the sampling point, do
not introduce significant external contaminants into
the fluid collected. If you preclean the external parts
of the valve or fitting and self-flush the valve or
fitting before the sample is taken, the background
level attributable to the sample point itself should not
exceed 10 percent of the normally observed
particulate level. The internal porting of the sampling
point should not impede the passage of hard
particulate matter up to 500 microns in diameter. The
sampling point should be accessible and convenient.
There must be sufficient clearance beneath the valve
or fitting to position the sample collection bottle.
Under normal system operating pressure, the sample
fluid flow rate should be between 100 and 1,000
milliliters per minute (approximately 3 to 30 fluid
ounces). The flow rate should be manageable, and the
time required to collect the required sample should
not be excessive. The mechanical integrity of the
sampling valve or fitting should not degrade because
of repeated use. When not in use, it is mechanically
secured in the closed position.
Learning Objective: Recognize the analysis
methods used to identify and measure
Contamination analysis is used to determine the
particulate level of a hydraulic system and the
presence of free water or other foreign substances.
The methods used to identify and measure
contamination are patch testing, electronic particle
count analysis, and halogen testing.
NOTE: The President of the United States
has decreed that all production of
ozone-depleting substances will cease by
31 December 1995. NAVAIRSYSCOM is
striving to eliminate MIL-C-81302 (FREON)
much sooner. MIL-C-81302 has already been
eliminated in some of the geographical areas
that the Navy presently operates within.
MIL-T-81533 (TRIC) is also on the
hazardous material (HAZMAT) reduction list.
In the event these materials have been
eliminated in your command or geographical
areas, P-D-680 is the recommended solvent
for performing patch tests using the tans
standard. Before performing a patch test, it is
imperative that you check the NAVAIR
01-1A-17, Navy directives, and the Federal
and local HAZMAT regulations for the proper
material to use in your command and
This note should be
applied to all references to the use of these
materials throughout this chapter.
Patch testing is the primary contamination
measurement method used at all levels of maintenance.
The P/N57L414 contamination analysis kit (fig. 4-3) is
used to perform patch testing. In the patch test method,
a fluid sample of known volume is filtered through a
filter membrane of known porosity. When the fluid
passes through the filter, all particulate matter in excess
of a size determined by the filter characteristics is
retained on the surface of the membrane. The retention
of particulate matter causes the membrane to discolor
proportionally to the particulate level of the fluid
sample. Free water will appear either as droplets during
the fluid sample processing or as a stain on the test filter.
The typical color of contamination in any given
system is usually uniform. The degree of filter
membrane discoloration correlates to a level of
particulate contamination. By visually comparing the
test filter with contamination standards that represent
known contamination levels, the contaminant level of
the system can be determined.