Learning Objective: Identify the procedures for sampling hydraulic fluid and the sampling point requirements.

A fluid sampling point is a physical point in a hydraulic system from which small amounts of hydraulic fluid are drawn to analyze it for con-tamination. Sampling points include air bleed valves, reservoir drain valves, quick-disconnect fittings, removable line connections, and special valves installed for this specific purpose.

Hydraulic fluid sampling points for most naval aircraft are designated in the applicable MIM. Two major factors determine if a sampling point is adequateits mechanical feature and its location in the system. To determine the contamination level, a single fluid sample is required. This sample must be representative of the working fluid in the system, and it should be a worst case indication of the system particulate level. The worst case requirement is necessary because the particulate level in an operating
system is not constant throughout the system. Instead, particulate levels differ because of the effects of components (such as filters) on circulating particulate.

The mechanical features of a prospective sampling point are evaluated on the basis of accessibility and ease of operation. The sampling point should not distort the particulate level of the sampled fluid either by acting as a filter or by introducing external or self-generated contaminants. The latter point is particularly critical. You can minimize the introduction of external or self-generated contaminants before collecting a sample by cleaning the external parts of the valve or fitting and by dumping a small amount of the initial fluid flow.

Consideration must also be given to removal of any static fluid normally entrapped between the actual sampling point and the main body of the fluid to be sampled. To do this, you dump an initial quantity of the sampled fluid. Problems may be encountered where a long line is involved, as in certain reservoir drain lines. You should take the fluid sample from a main system return line, pump suction line, or system reservoir. Also, take the sample upstream of any return or suction line filters that may be present. Do not take reservoir samples in a system that has a makeup reservoir, or if the reservoir is bypassedduring 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 sampled. 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.

ANALYSIS METHODS

Learning Objective: Recognize the analysis methods used to identify and measure contamination. 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 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 geographical area. This note should be applied to all References to the use of these materials throughout this chapter.