when the system is being powered by external SE, or
tamination. Sampling points include air bleed valves,
immediately after such an operation.
reservoir drain valves, quick-disconnect fittings,
removable line connections, and special valves
The sampling point should be next, or reasonably
installed for this specific purpose.
close, to the main body or stream of fluid being
sampled. A minimum amount of static fluid is
Hydraulic fluid sampling points for most naval
acceptable; however, purge it when you start the sample
aircraft are designated in the applicable MIM. Two
flow. Do not take a sample from a point located in an
major factors determine if a sampling point is
area of high sedimentation. If you cannot avoid doing
adequate--its mechanical feature and its location in the
this, make sure sedimentation effects are minimized by
system. To determine the contamination level, a single
discarding an initial quantity of the sample fluid drawn.
fluid sample is required. This sample must be
Ideally, sample fluid should be obtained from turbulent
representative of the working fluid in the system, and it
high-flow areas.
should be a "worst case" indication of the system
particulate level. The worst case requirement is
When you take a sample at the sampling point, do
necessary because the particulate level in an
not introduce significant external contaminants into the
operating system is not constant throughout the sys-
fluid collected. If you preclean the external parts of the
tem. Instead, particulate levels differ because of the
valve or fitting and self-flush the valve or fitting before
effects of components (such as filters) on circulating
the sample is taken, the background level attributable to
particulates.
the sample point itself should not exceed 10 percent of
the normally observed particulate level. The internal
The mechanical features of a prospective sampling
porting of the sampling point should not impede the
point are evaluated on the basis of accessibility and ease
passage of hard particulate matter up to 500 microns in
of operation. The sampling point should not distort the
diameter. The sampling point should be accessible and
particulate level of the sampled fluid either by acting as
convenient. There must be sufficient clearance beneath
a filter or by introducing external or self-generated
the valve or fitting to position the sample collection
contaminants. The latter point is particularly critical.
bottle. Under normal system operating pressure, the
You can minimize the introduction of external or
sample fluid flow rate should be between 100 and 1,000
self-generated contaminants before collecting a sample
milliliters per minute (approximately 3 to 30 fluid
by cleaning the external parts of the valve or fitting and
ounces). The flow rate should be manageable, and the
by dumping a small amount of the initial fluid flow.
time required to collect the required sample should not
Consideration must also be given to removal of any
be excessive. The mechanical integrity of the sampling
static fluid normally entrapped between the actual
valve or fitting should not degrade because of repeated
sampling point and the main body of the fluid to be
use. When not in use, it is mechanically secured in the
sampled. To do this, you dump an initial quantity of the
closed position.
sampled fluid. Problems may be encountered where a
Q8-12.
What two factors determine if a sampling
long line is involved, as in certain reservoir drain lines.
point is adequate?
You should take the fluid sample from a main system
return line, pump suction line, or system reservoir.
Q8-13.
The internal porting of the sample point
Also, take the sample upstream of any return or suction
should not impede the passage of particulate
line filters that may be present. Do not take reservoir
matter up to what size?
samples in a system that has a makeup reservoir, or if
the reservoir is bypassed during SE-powered operation.
ANALYSIS METHODS
A makeup reservoir is a configuration in which all of
the system return line fluid does not pass through the
LEARNING OBJECTIVE: Recognize the
reservoir. Fluid exchange in the reservoir is limited, and
analysis methods used to identify and measure
results only from the changes in fluid volume that occur
fluid contamination.
elsewhere in the system.
Contamination analysis is used to determine the
You should be able to use the sampling point after
particulate level of a hydraulic system and the presence
an aircraft flight, without requiring the use of external
of free water or other foreign substances. The methods
SE. Taking a sample with the aircraft engines turning is
used to identify and measure contamination are patch
satisfactory, provided no personnel hazards are
testing, electronic particle count analysis, and halogen
involved. You should be able to use the sampling point
testing.
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